Some ideas for RX noise reduction and a Mains Filter for your Radio Shack…

Got Noise? -Then this might get you back on HF if you’ve switched off because the “S” meter is S9 or S9+ when you turn on your rig, especially on the lower 160-80-40-30 Meter Bands…

If you live in suburbia, or even semi-suburbia, you might have, or are currently dealing with, high levels of noise in your Receiver when operating your radio. This is usually the worst when you’re trying to work that rare DX, a weak digital signal or even just your club HF net or Society news broadcast. Noise can be wearing. I have heard of many an Amateur that has switched off due to excessive noise and placed their hobby in the “too hard basket”. I even personally know of two radio friends who sold up and “moved to the country” in search of that holy grail of noise levels…S0.

I don’t claim I’m going to fix your noise issue but hopefully I can offer some guidance and experience in dealing with radio noise in the HF spectrum in your environment.

Firstly, If you can, set up your radio to run of of a battery and plug in your main antenna. Cut the power to your WHOLE HOUSE, (yes go out to your meter box and throw the main switch!), so that nothing is energised on your property. (Also cut your Solar if you have it and are able) Now see what your noise level changes to. Chances are, the noise level will drop, sometimes significantly. This is actually a good thing, because it means that it is highly likely that the noise source is at your place, and you can do something about it. More later.

If your noise doesn’t change significantly, then the likely scenario is that that your antenna is picking up a noise source from a neighbor, or a utility such as a nearby power line or other service.

***My first piece of advice is to make sure that your antenna feed line has a common mode choke.***

This will need to go at the feed point if it is a coax fed dipole or variant, or right at at the radio if it your antenna is an End Fed Half Wave or similar. If you are unsure what a common mode choke is, then grab a coffee, and  have a look at this from Steve, G3TXQ (SK).

Now have a read of this from Jeff, K6JCA. Both links are extensive and extremely informative.

If you’re still not convinced that you need some kind of common mode choke on the feedline of your antenna, please have a look at this video.  You can clearly see the effect on both Receive and Transmit.

Now back to our main objective, let’s look at another known source of noise, the very common Switch Mode Power Supply. These. things. SUCK!!! They are known generators of RF noise and interference. Generally, their cost is inversely proportional to the amount of RF they generate! The cheaper units leave off a few cents worth of EMI suppressing components to make them as nasty as can be. Most modern households these days have many gadgets and low cost Asian electronics, and they often come with one of these Switchmode power supplies. Phone and Tablet chargers, computer and laptop power supplies, garden and Christmas lighting, toys, decorations and fixtures containing electronics, LED light fittings and bulbs…Just about everything these days has an SMPS. Some are clean, but many can be excellent generators of broadband RF hash. Indeed, some can completely wipe out radio reception up into the UHF range, (like the charger our boys portable DVD player!!!)  The best way to find them is by a process of elimination, simply by going around the house and turning stuff off at the wall. This will soon expose the culprit , but don’t forget you need to cut the power to the particular device completely, not with just switching of with a remote or the front panel power switch, as this usually just turns off the displays, (think home electronics, Audio Visual gear etc. etc.) and the unit is still effectively powered up, and still drawing current from the power supply.

I had a particular problem with the power supply for my shack laptop, which is a Dell Lattitude E6410. Even though Dell is a reputable brand, used by business and governments around the Globe, the power supply generated a bad hash causing up to an S7-8 noise level, from 80-20 metres.


Simply wrapping the power connector lead through a FT240-43 Toroid core as pictured above, went a long way to eliminate this noise. The difference was remarkable. A point to note was that the power supply itself had just about every compliance tick and UL listing .



They mean nothing!



***My second piece of advice – hunt down, find and eliminate any cheap Switchmode Power supplies***

Replace them if you can, or alternatively get some ferrite rings and wrap the output leads through the cores as many times as you can.

Other sources of noise can be from the cables coming from your shack computer to peripherals such as printers, keyboards and mice, displays and USB leads and hubs etc.etc. Give these the toroid treatment as well, everything helps. (As an example, here is the USB lead from my laptop to the USB mixing desk I use to route microphone and other audio to my main HF radio directly into the balanced modulator), and to the little Raspberri Pi I use for digi modes. These all help in the scheme of things to drop your RX noise closer to S0. If possible switch to a bluetooth mouse and keyboard if you’re running a PC . This eliminates 2 leads from radiating computer hash in your shack.


Sometimes, noise can come from the 230V mains supply to your shack from many different sources. Perhaps from an appliance located at your or a neighbours house, such as a dishwasher, washing machine, deep freeze, hot water heater, solar hot water booster, microwave etc.etc if they are on the same supply phase. The noise this equipment can generate could radiate to your station via your power supply.

This is where this mains filter comes into play. Just like a common mode choke on our feed line (you have installed one, haven’t you?) the best way to eliminate or greatly reduce supply noise is to have a mains filter that incorporates a 2 stage EMI Filter with some hefty, multi frequency common mode choking of the 230V supply, before it powers the equipment of your shack.

After doing a bit of reading and on the advice of others, I was directed to this most excellent presentation describing a holistic approach to finding and eliminating such noise and the construction of such a filter by Ian White, GM3SEK, and the update here.

Here I’m describing my version of the filter that I built. Anyone should be able to reproduce this filter, using parts that were easily obtainable here in Australia. My parts came from Jaycar, RS components, Bunnings and Cheap as Chips.

***Disclaimer – this project describes working with Mains Voltage!!! ***

***If you are not experienced with working with the 230V mains wiring, find someone with expertise to assist and check your work!***

Parts List:

  • 1 x Sealed Polycarbonate Enclosure 171 x 121 x 80 Jaycar Cat No. HB6224
  • 1 x EMI Filter  – I had mine laying around, see Note 1 – RS Components
  • 1 x Fair -Rite Large Ferrite core (clamp type) RS Components Stock No. 466-9164
  • 4 Small Ferrite cores, Jaycar L15 Cat No. LO1238
  • 1 x 10 amp 12 way Terminal strip (chocolate block) Jaycar Cat No. HM3196
  • 1 x length 10 amp extension lead – Cheap as Chips
  • 1 x 6 outlet power board overload protected – Cheap as Chips
  • 2 x 16mm Cable Glands – Bunnings

Note 1: Delta Electronics 10 DRC5W 250Volt 10A 2 Stage EMI Filter or equivalent. I used one I had kept from an old Photocopier, hence the surface rust ! Just about any EMI filter with a 10 amp rating should do, RS Components lists many single and double stage filters that would be suitable.

A picture tells a thousand words, so here is how my filter came together…

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The completed unit with the lid off…


The end result is shown here. The filter simply installs between your wall socket and your equipment. The Cable glands grip the cable to prevent it from being pulled out. Cord grip grommets like Jaycar CAT No. HP0718 would probably be better, but I had the glands, so I used them.

So how does the filter perform? I have been using the filter for a little over a month. My location is quite good for HF and I am blessed with a quite low noise level on most bands, it was reasonably high on both 80 and 30M. I am unsure of the sources (it’s not my place) and my nearest neighbor is 250 metres away. The filter has dropped my 80M noise from S8-9 back to S3-4. this is a significant improvement on that band and I have been able to make contacts I probably would have struggled with previously. My noise on 30M did seem to come and go, noticeably with the operation of our dishwasher and washing machine. There can also be a bit of a noise hash on this band that was sometimes up to S7. I’m pleased to report that the hash has been significantly reduced and my 30M noise level sits at around S1, and I can no longer tell when the dishwasher is on! I like to take a holistic approach to noise and this filter has made a difference.

This is a simple project that might significantly reduce your noise level in the shack – build one and let me know if it works for you!

73 – Andy, VK5LA




An update to the 40M Half Square antenna

I thought I’d give an update on this antenna since I’ve had several emails and messages enquiring about it. The antenna has been up for 3 weeks, and I’ve had over 500 QSO’s and worked some great DX, mainly using FT8 mode on 17, 20, 30 and 40M.

I ended up with a broken support after some strong winds so I had to buy a new squidpole for the fed end support. This new 9M pole ended up being about 1 metre shorter than the existing pole when added to the extensions. This has bought the feed point about a metre closer to the ground, and I’ve added a 200cm piece of fibreglass rod to the tuning cap shaft, to make it easier to adjust. I didn’t bother with adjusting the other vertical support leg lower to match, the antenna still works!


The angle of radiation is also low on 20 Metres and I’m using a 49:1 broadband matching transformer to put power into the antenna and touching up the match via my Radio’s internal antenna Tuner. It’s a reasonable performer on 20, but not as good as it is on 40

Another surprise is the 30M band. Although the modeling suggests the radiating pattern is quite potato shaped, I’ve been able to work pretty much everything I hear when the band is open. I do better into Europe on this band than 40 and 20 Metres

Best DX on 40M looking West (Africa) to date would definitely be Charles, 5H3DX in Tanzania…Al time new country!


and looking East to the Central America and the Carribean, Dev, 9Y4DG in Trinidad on 30M…(Then Frank, HB9EUW in Switzerland called me!)


I have been delighted so far with the performance of the antenna, especially since we are at the bottom of the cycle with no sunspots. I am at 199 DXCC countries worked. Who knows what will happen when ‘ol Sol wakes up!

I have also experimented with a 20M version of this antenna for portable operation. It fits in a plastic sandwich bag, takes minutes to set up, as it is only 2×5 metre lengths and 1×10 Metre length of wire that’s suspended between 2 squidpoles on stands. For the 20, however, I fed this at the 50 Ohm point with some coax at the top of a vertical section. The bottom of the vertical legs were about 1.5M  above ground, to get them away from the stands. This was very promising, as after adjusting the antenna to be resonant at around 14.1 Mhz, I was easily hearing stations from South Africa on the litte FT817. I didn’t bother to reply to them with my 5 watts, but they were good copy. I did have a good contact with Gerard, VK2IO, on 40 Metres, just before I packed up the antenna after my experiments. Gerard was operating from the Yellowmundie Regional Park, VKFF-0558. He gave me a 57, not bad for 5 watts.

The next outing for the antenna will be to use it on an activation in a VKFF park. On 40 and 30 Metres as an end fed, this antenna is looking promising as a decent NVIS radiator, ideal for this king of operating. Stay Tuned!

A Half Square Antenna for the 40 metre band…

Now that there are social distancing rules that have us mostly at home for the near future, I realised that this is an excellent time to do some upgrades to the VK5LA antenna farm.  I have wanted a low angle, dedicated and resonant radiator for 40M for some time, and recent reading had me thinking about trying a Half Square antenna for that band. The full size dimension would fit easily across my my back yard, and I had available the supports required to get it to the correct height.

An added bonus is that I would be utilising Mmana Gal antenna modeling software and my new nanoVNA to observe and adjust the antenna once erected.

Like many other VK hams, I really enjoy watching VK3YE’s You Tube videos, particularly when he heads to the beach and operates portable…it was this video that started me on the journey for this antenna…if Peter’s antenna worked ok on 20M why not try one one of these on 40M at my place?

For those unfamiliar with a Half Square, the easiest way to describe it, is to think of a single staple, like you would find holding a couple of sheets of paper together.

That hasn’t been used yet!

Now orientate it so the pointy points, point at the ground!


So as you can see in the above screen shot from the Mmana Gal software, here is a diagram of the  antenna. It is simply 2 1/4 wave verticals on 40M joined by a 1/2 wavelength wire at the top. This diagram show it being fed at the top corner (the small red circle) this is a 50 ohm direct feed point, great electrically, but it’s not very convenient to feed it here as *ideally* you have to get heavy coax to this point and lead it away at 90 degrees for a 1/4 wavelength…not very practical…Other more obscure feed methods are feasible, and you can find them on the internet or in good antenna books if you look hard enough. Perhaps the best way to feed it is at the bottom of one of the vertical wires, far more practical, but tricky electrically!  Nothings easy is it? Using the software, we can see in theory how the antenna will perform when fed with RF at our chosen frequency, at the place we want to feed it…

So let’s run model of the antenna in the software. I’ve told Mmana Gal to feed it in a top corner…


This image above shows the antenna radiation pattern. The diagram on the left shows the antenna, looking down directly on top of it. You can see that the long halfwave section going from left to right, the feedpoint (red dot) is shown for reference. The diagram on the right shows the results of the modeling and the elevation pattern. We can see here, that at our design frequency of 7.074 Mhz (for FT8), the Gain is 4.31dB over an isotropic radiator, there is a 0dB front to back ratio as it’s radiating equally well in 2 directions, the  impedance at the feedpoint is very close to 50 ohms and that the reactance is very nearly 0 Ohms. I made the lowest point of each the 2 vertical radiators 250 mm from the ground, as I wanted there to be sufficient room without having the feed point in the dirt.

Let look and see what happens if we feed the antenna at the bottom of one of the vertical radiators…this is far more convenient…


We can see here that comparing the 2 diagrams, the only real change at our 7.074 Mhz design frequency is the resistance at the feedpoint is now at 3250 Ohms with LOTS of reactance. Other important parameters like elevation angle, gain and vertical radiation remains virtually the same.

So there we have it, here are the plots of the radiation patterns, first, horizontal polarisation and then Vertical polarisation…this indicates that at least some of our vertically polarised radiated power should head towards the horizon at around 23.3 degrees. There seems to be very little Horizontally polarised radiation, and what little there is, is going straight up to warm clouds. Vertically polarised radiation, at a low angle towards the horizon, is what we want.

OK so now we have to put power into the antenna. How can we do this so that the maximum power is transmitted by the antenna?

What we have here is basically an End Fed antenna, in this case on our design frequency of 7.074Mhz, it’s a full wave (1/4,+1/2,+1/4 =1) End Fed. Steve, AA5TB explains all about the End Fed antenna in this link way better than I can…Another way to describe the antenna is an 80 Metre End Fed Half Wave.

So we need to transform the high impedance, in this case 3520 ohms (at the base of one of our 1/4 wave legs) to 50 ohms so our Transmitter is happy to deliver full power.

We could use a matching Transformer, like the popular 1:49 or 1:64 transformers that many hams are using with end fed antenna these days. See here for the lowdown on the transformer construction. A 3 turn Primary and 24 turn secondary version (roughly 1:64) works well with this antenna on the bands that are multiples of a half wave. In this case, 80 – 10M. This is convenient if you just want to push the tuner button on the rig when you change bands, but you sacrifice efficiency and the radiation pattern has many more sharp lobes and deep nulls, with increasing Horizontal radiation at high angles away from the design frequency. That’s not good for DX.

I chose to feed the Half Square as a single band antenna on 40M with a parallel resonant circuit. This is quite efficient and ensures the maximum power is transferred to the radiating element rather than heating a ferrite core in a broadband matching transformer.

John, M0UKD, has an excellent website on how he made a matching unit for his 15M 1/2 wave vertical antenna. I used the information from that site and the calculations to come up with my own matching unit, shown below. I used an old capacitor and coil section I had in my junk box and finished up with this unit. Not as pretty as his, but it certainly does the job…(hot melt glue for the win!)


Ok, so now we have a design, we have a way of matching it and we have plenty of time on our hands in self isolation to put it up…

I positioned the antenna in the back yard, the height of the two vertical supports are around 11 metres each. It fits nicely in between the two side boundaries of my average size block. Here is one of the vertical radiators,  both supports are lash ups of broken squid pole sections and ally/steel tube sections I had kept/salvaged for projects just like this…never throw anything out!

Here you can clearly see the 90 degree transition to the 1/2 wave phasing wire…


…to the other Vertical radiator at the other end of the antenna.


Here is the feed point, here I’ve temporarily strapped the matching unit and a 1:64 Transformer to the stake for testing until I come up with a more permanent setup. The capacitor in the matchbox can be adjusted so that X=0 on an Aerial Analyser or vector network Analyser.


So how do you adjust something like this? how do you know it’s doing its thing?

Ok, lets go with what we know. We want the antenna to be resonant at 7.074 (in this case for FT8 mode on 40M) so we want a low SWR reading on this frequency and we also want the resistance as close to 50 Ohms as possible with a reactance close to 0 as well, to make our transceiver sing, and develop full power to the antenna.

I was actually quite gobsmacked at what I was seeing on the VNA. This is one of the first readings I took,  I set it to have a centre frequency of 7.075 Mhz with a 1 Mhz span. (this was straight after adjusting the capacitor in the matching box to peak the noise on RX with my FT817 Transceiver). This is what the VNA showed first up. The SWR is 1 to 1.16, the Resistance is 58 ohms with 24.nF of reactance. The frequency is shown as 7.005 Mhz. Moving the marker (the little triangles on the VNA screen) so the reactance is very close to 0, (resonance) showed a frequency of around 7.050 Mhz. So if we’re splitting hairs, the antenna is a fraction too long. The Mmana Gal model prediction seemed pretty spot on. I would only need to make minor adjustments to the lengths of the vertical radiators to shorten the antenna to raise the resonant frequency to 7.074 Mhz


These numbers makes our Transmitter very happy to deliver full power to the antenna, no tuner (internal or external) needed…


OK so the $64.000 question, does it work? Well yes, it certainly seems to!

I have the antenna orientated north/south, so it is radiating pretty much east west.

The antenna went up on the 2nd of May 2020 at around 5:00pm local time here in South Australia, here are the first few contacts on the antenna after calling CQ on 7.075 Mhz. 1st up is VK3FAC, who was receiving me at +10dB

Then followed by the USA,  Robert, K9U0 in Portland Oregon with a -13 report…nice, looks promising…

Then the friggen DOMINICAN REPUBLIC answers my CQ call!!! Migue HI3MPC with a -22 report…very nice!

Next? CUBA! Eduardo C07EPP answers at -17…Then I think I had to go have a lie down!! Here is a snippet from my log…LOG

The contact circled in green, with Slovenia is actually on 20M when I was testing the antenna with a 1:49 transformer to see if my radio would tune it on all bands from 80 to 10M with the rigs internal tuner, via the broadband 1:49 transformer…th 30, 17 and 12 Metre bands won’t match which isn’t surprising as they aren’t a multiple of 80, 40, 20 or 10…

So yes, it certainly seems to get out, and in the direction the modelling said it would.

I’ve worked 158 qso’s 19 DXCC entities so far in the 9 days as of 11/5/20 since the antenna has been up. I certainly do ok in the direction of the USA, Canada, the Carribean and Africa. An added bonus is the antenna is very quiet noise wise on RX, and the lack of horizontally polarised high angle qrm signals from Indonesia is noticeable. Also, I don’t get many JA stations returning my CQ calls as well, when before they were in plague proportions…this further reinforced the radiation pattern is favoring east/west.

So there you have it, I have described my journey with the Half Square antenna. I’m very impressed, I’m working stations I could only hope to before! I intend to try a portable version for 20M fairly soon, either near some salt water or a lake, as soon as these bloody social distancing rules are relaxed.

Happy Hamming, Andy, VK5LA

A 3/8 wave vertical for 20m


Building this antenna came about after I wanted to put something up at home specifically targeting 20M FT8 on 14.074 Mhz.


The 3/8 wave vertical for 20m in my front yard…

I’m fairly time poor so I needed something quick, simple and cheap to get going with asap. Whilst doing a bit of research I came across the winners of the 2018 QST Antenna Design Competition, and interestingly, third place was a 3/8 wave vertical for 20M by Joe Reiart, W1JR. As I’m not an ARRL member, I asked if anyone in my HAM community  would be kind enough to let me have a copy of the article. Several people kindly sent it to me.

Surprisingly, there is virtually nothing on the internet about a practical example about this antenna. I did find an old reference to the antenna, but no solid build details.

In a nutshell, according to the article, the 3/8 wave vertical has the advantage of requiring less radials than your standard 1/4 wave, but is about 50% taller for the same band. A 1/4 wave vertical requires at least 16 1/4 wave radials for good performance due to the low feed point impedance of around 35 ohms, whilst the 3/8 wave requires just 4, having a feed impedance of around 200 ohms. It also sports a lower take off angle of radiation of 23°,  vs 26° for a 1/4 wave (better for DX), and as the radiating current maximum point is 1/8 wave up the vertical instead of at ground level, it is ideal for ground mounting in situations of nearby clutter. It is easy to match to 50 ohms Coax via a simple 4:1 Unun and a series capacitor.

The materials

I decided to go with a squid pole for the vertical radiator, as they are cheap and easy to keep in the air, so I purchased a 6M pole to which I added 2 base sections from older broken squid poles to bring me up to 7.5m in length. This size slides neatly over 38mm PVC pipe, which is the diameter of my portable stand mount that I use for field work. I also had to purchase the 2, FT240-61 Ferrite cores for the Unun and choke, ( I got mine from Minikits in Adelaide) and a box for the Unun (Jaycar) at the feed point. So for less than $100 I was ready to go.

The Unun


The 4:1 Unun…

This turned out to be very straight forward, and is explained in the article. There is quite a bit online about 4:1 Ununs, I’m sure you’ll have no drama constructing your own. I used Jaycar red and white power cable cat. No. WH3057, I stripped off the black outer PVC sheath and lightly twisted the wires in a drill, then wound on the FT240-61 ferrite core to get the result shown in the above pic…

The In-line choke

The article is fairly vague on this describing it as 10- 12 turns of RG-303 wound “W1JR style” A quick Google returned lots of hits for this, and you can see my resultant choke in the pic…I used RG-316, as it was what I had lying around.


The W1JR choke…

Mounting it

By now, I had gathered all the materials I needed so it was time to put the antenna together and see if it did what it was supposed to do.

I initially mounted the antenna on one of my ALDI bike stands as that’s what I normally use for testing and portable operating but my initial tests showed there was a LOT of interaction with the stands metal base/legs and support and the antenna. Readings on the antenna analyser were nothing like I was expecting and confirmed when I moved the Unun away from the base, the readings began to move towards something more like I was expecting.

So I then decided to shift the whole shebang to my PVC vertical antenna mount in my front yard…

This is simply a length of PVC pipe driven into the ground and about 600mm protruding out to mount antennas on, with a short extension that the squid pole just slips over…simple! The pictures below show how…


I set the whole thing up, with the vertical wire length calculated to 8.010 metres in length and the matching unit lying on the ground with the 4 radials connected. This showed the 50 ohm point to be around 13.8Mhz, so I shortened the antenna to raise the 50 ohm point to 14.075 MHz. I had a variable capacitor in between the unun and vertical, so I adjusted this capacitor to bring the X=12 reading on the analyser to zero. This measured at 7pf, close to the 10pf mentioned in the article…

Gotta be happy with that!







The squid pole ended up being about 7.5 m in length, so the vertical wire and match box at about 7.8m hung just nicely just above the ground on the mount. You can see the match box with its coax capacitor, how the choke ( to keep RF of the coax outer) connects to the match box and where the 4 radials attach…


I only had a brief opportunity to have a listen with the FT817 on the antenna, and the receive was very lively, especially on the frequency of interest. SWR was flat, with the radio developing full power on TX.

I’ll update this article when I’ve had a chance to evaluate the antenna on the air…

Andy, VK5LA


Reference: The 3/8-Wavelength Vertical – A Hidden Gem. Joe Reisert, W1JR P44 QST April 2019.


…And now for something completely different!

I was lucky enough to be thought of when a dear friend of mine, who runs an antique and curio business, came across this old piece of medical equipment. This set off her NERD meter and she messaged me asking if I was interested!


I immediately replied yes and she snapped it up for me for next to nothing…the reason being is this thing, the way those knobs are laid out and that big beautiful meter, just screams


But before I consider butchering it and using it for a project I decided to find out a bit more about it…

…and basically ran into a brick wall…

There is very little info on the Internet about the device and definitely no manual!

I actually had to read a couple of scientific papers to work out what the unit actually did, and how it works. This was the only source of information on the unit I could find.

So what is it? – It’s basically a medical radiation detector. specifically it detects radiation from medical isotopes that are injected/ingested/inhaled into the body, that accumulate in a specific area, like the restriction/blockage of blood flow, lymphatic system issues or uptake from tumors/cancer. The patient is probed locally at the site of interest with the large silver hand held scintillation detector that detects the radiation, which shows as a deflection on the meter. It dates from the early mid 70’s when, I guess, it was the early-ish days of nuclear medicine…


So how does it work? It is certainly an interesting device. It is battery powered, by a couple of PP9 9V batteries in series, to give an 18V supply. There is a battery check area on the meter, this is activated by turning the range switch to the “B” position, just up from the “OFF” position. The PP9 battery is still available from a few different places, I’ve ordered a pair to see if this thing still works. It will be interesting to see if the unit is capable of detecting background radiation. I hope it does.

The probes are also very interesting. They employ a Scintillation Crystal and a Photomultiplier Tube to detect radiation from the patient. It’s a 2 stage process. The 1st stage involves the Scintillation Crystal. This is located at the site where the probe contacts the patient, and detects the radio active particles that are emitted from the patient who has been administered a Radio Isotope. This crystal then emits a pulse of light (Scintillation), usually in the visible spectrum. This pulse of light is then detected by the photomultiplier tube and “multiplied”  – resulting in a pulse of current for each radiation particle detected, which is then passed to the instrument itself, where the result is processed and displayed.

The Photomultiplier tube is pushed hard up against the Scintillation Crystal via spring pressure. It is encased in an Aluminium tube, most likely for protection.

There are 2 probes with this unit, one marked “Probe type 235N”, which has a moveable shroud with what looks to be a ferrite or powdered iron inner ring touching the probe surface, with a long, curly connecting lead, and another marked “Probe 235”, which has a moveable, plain aluminium shroud. I haven’t been able to establish the difference between the two probes.

OK, so how does it ACTUALLY work? – much simplified, here is how i think it works…


The 18V battery supply is boosted by what looks to be a Cockcroft-Walton voltage multiplier, to a high voltage, most likely variable up to around 3Kv. This is all at very low current, judging by the size of the transformer drive circuit, probably in the uA range. The range switch looks like it selects a number of set voltages. The voltage multiplier board is located in the rear of the unit, seen here. The transformer and drive circuitry are hidden behind the panel with the 3 connectors on it.

This high voltage is fed to the photomultiplier tube via the front panel BNC connector and any detected radiation from the probe results in a current pulse that is measured across an anode load resistor by the metering circuit. This pulse looks to then be fed to an integrator circuit, whose role it is to change the pulses received from the probe to a proportional, steady voltage, (i.e. more pulses more voltage) which is then displayed on the meter. I imagine the fast/slow push buttons would relate to the speed of integration. As an example, if the probe detects little or no radiation, (low or no meter deflection) from an area on the patients body and then more radiation (meter deflection increases) when moved to another part of the body, then that increase for that area would be a concern. A practical example of this (now old!) technology was to use this device after injecting the patient with radio isotope Iodine i-133, to detect blood clots in the legs of patients suspected of suffering with deep vein thrombosis. A meter deflection on a particular area of the leg indicated the clot site.

My limited knowledge of nuclear medicine hasn’t helped in deciphering the Isotope control. I’ve learnt that differing Isotopes are used for differing areas on the body, for example, the Isotope Xe133 (Xenon Gas) position is used when checking the lung and brain. How this transpires to readings from a probe that only has 2 connections for +ve and Gnd  is a mystery. More research showed that other Isotopes on the dial are used for checking other areas like kidneys and heart. I’m sure there’s a perfectly clear explanation out there somewhere. Maybe the different voltages are used with the different isotopes…i.e. 1000V range for Chromium51? Who knows? If anyone can add any insight as to how these units operate I would be forever greatful.

The unit is beautifully made. It has a number of quality circuit boards and the wiring is super neat, and has been laced up. it has a number of gold plated edge connectors. It’s all analog, it’s full of IC operational amplifiers operating on a split rail +/- 9V supply. There is a very nice precision 50uA meter movement that would be a bit better quality than your average. The case is a work of art, I have a number of ex scientific instrument cases from England and all are wonderful!!! Should I turn it into an Antenna tuner?

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We have certainly come a long way from using this type of instrument for medical diagnostics. The clarity and resolution of todays 3D medical imaging machines is mind-boggling!!!

On that note I’d like to take this opportunity to wish all BRL blog readers a happy,  healthy and prosperous 2019.


Andy, VK5LA

Summer Fun – A Moxon Antenna for 6 metres

Six Meters is a great Amateur Radio band, and there are quite a few active operators,  but just about everyone I’ve talked to recently says something along the lines of “ Six Meters sounds great I’d love to be on it”,  or “I’d love to get on Six Meters but I don’t have an antenna” It seems it’s seen as more of a “summer only”  band in times of slow solar activity. Indeed, ‘ol Sol isn’t going to let you talk to England via the F2 layer with the current number of sunspots.

Even without big sunspot numbers,  Six meters is a lot of fun via Summer Sporadic “E” layer propagation. VK wide and VK-ZL paths are often a daily occurrence, and VK-Pacific regions, VK-Hawaii, VK-West Coast NA/SA are all a possibility. 

The fact that just about all modern Transceivers now include Six Meters as standard, and the demise of channel 0 and the accompanying TVI issues that went along with that, ( thanks digital TV!) means that “6” is now more useable than ever. 

Another plus with 6 metres is that getting a decent antenna up for the band isn’t difficult. For Sporadic E contacts, although a simple vertical or even a dipole will get you on the band, having a bit of gain and direction will often turn what would be a marginal contact on a vertical into a solid contact. This gain and direction is even more important when using weak signal modes like WSPR, FT8 and JT.

i have been on 6 metres off and on over the years with various antenna I’ve put together, from verticals to beams. This year I decided to put up something better than the 40M dipole tuned up on 6.

I’ve  always been aware of the Moxon antenna . I have often contemplated constructing one to use portable for the 20 metre band vertically polarised near salt water. It’s smaller size, small footprint 2 element design seemed ideal to sit on top of one my push-up masts at home.

One of the good things about building a Moxon is that at 50 MHz, it’s not a very big antenna at all and, is easily managed by one person. Lightweight construction methods and wire elements will work a treat.

Fortunately, there is a good deal of info on the internet about the antenna. There was a very good page called “ The Moxon Antenna Project” , but unfortunately it appears to be down at the moment. There was good information, and many build examples on that page, I hope it gets put back up soon. If working with aluminium tubing is your thing,  then DK7ZB has a dedicated section for the Moxon on his website.

Step one is to find a Moxon program, either a stand alone downloadable app or one of several online calculators…I went with this one


It really is as simple as putting in the frequency you want to build the antenna for, and letting the program do the work. you’ll be presented with a nice table with all the dimensions. Stick to them to the millimetre if you can, and I”ll bet you’ll be rewarded with a working antenna first pop. Pay special attention to the gap between the two sets of folded elements (measurement “C” in the table above), this dimension is critical to the correct operation of this antenna.

Ok, so on paper, we have all the information on the dimensions of the antenna, now we have to translate those lengths into an actual antenna. I found the best place to start was just googling “Moxon Antenna” and looking at a lot of the images and videos available on line. Everything you thought of (or didn’t), will come up and you’ll soon be inspired. Aluminium, wire, wood, steel, nylon, plastic, fiberglass and PVC are just some of the materials people have used in the construction of this antenna.


I decided to go with a Nylon chopping board from BigW for the baseplate. This is only going to be in the air for the summer, so longevity isn’t a priority. I used smaller short squidpole tubing from Haverfords as my spreaders. The spreaders had a 150mm length of wooden dowel inserted for strength, and were clamped to the chopping board with conduit clamps from the local plumbing supply house. The right angle bracket is a pergola fixing from Bunnings, drilled to accomodate the U bolts I used to suit my mounting mast. Simple!


I mounted a BNC socket through the chopping board and bought out the cable and sealed it with liquid electrical tape. I put a balun at this point also (yeah you should use one). I used an FT140-43 Toroid and wrapped 8 turns through it. I ended up hot gluing the balun assy to the nylon surface, seemed to be quite sturdy.

At this stage, I temporarily mounted the antenna after fitting the wire elements. Click on the pictures to enlarge them, you’ll see the pink brickies cord I used as element spacers. the second picture shows the short piece of 16mm PVC water pipe I used to guide the coax to the feed point. I used a two terminal piece of chocolate block electrical connector, hidden inside the far end of the pvc pipe to transition the coax to the elements feed point. I sealed up the ends with bluetack to keep any water or creepy crawlies out. Unfortunately I forgot to get a photo of this arrangement.

The wires were stretched out and attached with cable ties slipped over the end of the squid pole spreaders and secured with PVC electrical tape.

I used a super strong PVC jacketed, 7 strand copper clad steel, kevlar reinforced antenna wire that I had left over spare from a previous project, but you could use just about anything that can take a bit of tension. 1mm enamelled copper wire for the elements would work well and would be more than strong enough. Just tension everything so that its sits nice and taut across the spreaders.

The Moxon calculator must have got it right the first time, as I couldn’t measure any VSWR on my FT-817 at the design frequency of 50.110 Mhz . The antenna seemed to be working, a quick test with some local operators, Adrian VK5AW,  Rob VK5TRM, and Mal VK5MJ showed it was both getting out and had directivity. Conveniently, I was able to hear a couple of Six metre beacons from QLD as well. Turning the antenna to test the front to back ratio demonstrated a deep null in the pattern with the antenna driven element 180 degrees to the source, exactly as expected.


I decided to mount the antenna above my 8 ele 2/70 Quad, so it is about 13 metres above ground level. I’s rotated with an armstrong rotator, the mast for both antenna is strapped to the palm tree!

The antenna seems to be performing well, It’s only been up for around 10 days and I’ve already had several solid SSB and FT8 Sporadic E contacts so far this summer, exactly the reason I built it in the first place. I leave it on the 6M WSPR frequency all day and have spotted stations as far out as 3D2 Fiji and FK1 Vanuatu. So it hears great as well. It’s also small and light enough to pack it in the car and see if you can get some contacts from a park or summit on Six too.

So if you’re sick of hearing about Six metres and wish you could get on the band, then this simple antenna should be on your to-do list this weekend!

See you on Six


Andy, VK5LA

The ALDI Bike Repair stand – A park activators/Satellite Op/Microwavers best friend…

Several Hams have asked me what on earth is , and where did I get, the stand supporting my Antenna?


The answer will be revealed in these pages! There’s not much to reveal actually, around every 6-9 months or so, the ALDI supermarket stores sell a 5 legged “Bicycle Repair Stand” for $39.99.

It’s a sturdy stand for elevating your push bike to waist level or better to effect repairs and or maintenance to said bike. However, they also double as a brilliant stand for various Ham Radio activities, as I’ll demonstrate here.

In detail, it features a large footprint so that it’s difficult to tip over, either accidentally or by other means, is made of steel, and boasts a height adjustment and a quick release Antenn…I mean “bike” mount,  that allows stuff to be held horizontally…other bells and whistles include a chintzy tool tray and handlebar stay bar.


So what’s in the box?

You get the stand itself, the centre support with the T adapter, the horizontal clamp bar, the chintzy tool tray, and the handle bar stay. The two straps are for use with the handle bar stay, and the plastic bag contains the bolts and allen key for attaching said chintz. The allen key fits all bolts on the stand.

It comes with a set of instructions and a 1 year warranty. For something ALDI, it actually is quite well made!

Assembly is very straightforward 

just clamp it up tight or as loose as you like…

But for a park activation with a squid pole, I remove the T head and just use the pole out the top to slip the squid pole over…

For a Satellite pass, I attach the Bike head and use the clamp to hold the X-Yagi. It’s easy to turn the Yagi to adjust the AZ EL to suit the pass…The clamp is plastic and I can’t measure any increase in SWR or pattern distortion in use…

For Microwave Field Day work, the Bike Stand is a cheap way of getting a sturdy stand for Ex Sat. dishes and Gridpacks.

The stand would also do well as a sturdy portable Satellite dish mount for Caravan users and RVers.


A nice touch is the holes in the feet, ready for tent pegs as tie-downs…

So there you have it. These bike stands are a cheap way to get a sturdy stand for Amateur radio related activities, use your imagination! Keep an eye out in your local ALDI catalogue for the next sale date, and grab yourself a bargain!

*Disclaimer* – I have no affiliation with ALDI stores whatsoever!

Swan Reach Conservation Park VKFF-0832

On Friday, 16/11/18 I planned to activate the Swan Reach Conservation Park VKFF-0832 for the Murray River Parks Award that is administered under the umbrella of the World Wide Flora & Fauna in Amateur Radio (WWFF) Program,  so popular with Amateur Radio operators world wide now days.

My Chauffeur (my affable 16yo son Riley) and I left our home location at approximately 8:15 am for the journey to Swan Reach. We followed the conventional route from home via the Sturt Highway, and stopped to stretch our legs at the look-out above the town, just before you ascend into the town  itself from the Blanchetown Rd cliffs. It was then the chauffeur’s first go at navigating us across the Ferry, over the mighty River Murray, and onwards to the park,


The Parks is located about 15km from Swan Reach heading west on the Stott Highway towards Sedan and Adelaide. We accessed the park after turning off the the Stott Hwy onto the Old Punyelroo Rd and into the Park entrance itself. It is all clearly signposted. The blue dot on the satellite image was our operating spot, in a nice clearing, a short drive into the Park under some trees.


It was a beautiful day, wall to wall blue sky and a slight, cool southerly breeze, the temperature about 22 deg C. The Chauffeur expertly parked our Millennium Falcon under the nearest shade shrub, and I wasted no time in setting up the portable antenna. For drive-in activations I have settled on my trusty ALDI bike stand tripod, 8M squid pole and 40-30-20 M inked dipole. It goes up in minutes, and radiates my signal very well. I have opted for the tripod instead of tying to a tree or support, as I have usually found that the available centre antenna supports like posts and tress don’t suit where I want to set up. The tripod takes that unknown out of the equation, and allows me to have my  squid pole supporting the antenna, right next to the operating position. I have a couple of heavy sandbags to stop the lot tipping in strong winds, but its not often needed. certainly not today in the perfect weather! Coupled with my Icom IC-7300 Transceiver, this setup is a pleasure to use on the air.


I was soon on the air and calling CQ Parks on 7.144Mhz, the 40 Meter band. First in the Log was Gerard, VK2IO with a lovely 55 signal into Swan Reach, followed by numerous stations in VK2 and 3, including Peter VK3TKK/M and Brad VK2BY/M who were both very readable from the mobile, Paul, VK5PAS/3 and his wife Marija VK5FMAZ/3who were enroute to Bendigo, also called in. They were easily worked 56 and It was nice to get them both in the log. After about an hour I decided to change bands by removing the 1st link on either side of the dipole (quick and easy when the antenna is supported by the bike stand) and started calling CQ again, but now on 14.244, the 20 Meter band. This only resulted in 3 contacts, including Geoff, VK3SQ, who had a massive 59++ signal into my location. I was equally strong at Geoff’s end. There weren’t any other takers so I headed back to 7.144 on 40 Meters after about 10 minutes to finish up my activation. This time John, VK4TJ, was obliging along with Marija and Paul, who had found a park to operate from and popped up for a park to park from the Barrett Flora & Fauna Reserve VKFF-2264. Thanks Guys!

By this time, my Chauffeur was starting to eye off the Falcon’s upholstery he was that hungry! Likewise, I was also keen for a feed as well. We packed up, left nothing but footprints, and headed straight for the Swan Reach Hotel.



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Swan Reach Hotel – a bit of history

The Swan Reach Hotel wasn’t actually purpose built to be a hotel , but morphed from original Swan Reach Station homestead built circa 1865.

Beginning 1861 the original Swan Reach Station was just of a couple of huts, workers’ and shearers’ quarters, some shedding and ramps. You can still see the remnants  of some of the buildings located in the beer garden. On the other side of the fence are the remains of the loading ramp, where wool bales from the shearing shed were loaded on to the small tramway that sent the bales down to the river’s edge via wooden slides, and on to the waiting barges that made their way to Goolwa.

In 1896, a Mr Paul Hasse from Lobethal purchased 520 acres of land which included the Homestead. His wife, Emma, applied and was given a licence on the 12th September, 1899. Unfortunately Emma passed away the following year, then Paul continued to run the hotel until 1909.

There have been many major additions to the Swan Reach Hotel over the years of its operation. The stone, single room public front bar was built after 1907,  and the second storey added in 1912. Around in 1940s the block form of the hotel evolved with its rendered finish. The grand dining room was added in 1996. The hotel boasts a spectacular view overlooking the Ferry as it completes its never ending to and fro crossing across a lazy river.

Most importantly , the food, drinks, service and view were first class, and my chauffeur pronounced his Chicken Parmy ( we’re from South Australia, so deal with it) one of the better ones he’s had. My rump steak was delightful, and cooked to perfection! We bid Swan Reach farewell, we’ll be back!


BRL Gathering 2019

* Announcing *

The Riverland Radio Club Inc.

BRL Gathering 2019

To be held at the Overland Corner Hotel Goyder Highway, Overland Corner, South Australia

Saturday, 6th of April, 2019

Ok Folks, come one come all, it’s on again, the BRL Gathering for 2019 is on Saturday, the 6th of April, at the same sensational location, famous for its picturesque setting, Fantastic Hospitality, Great Food and Cold Beer.


(Registration isn’t compulsory, but it really helps out with catering, and you’ll go in the draw to win lunch for two on the house courtesy of the Overland Corner Hotel. It also helps us make sure your visit is the best it can be…)

Breakfast – Bacon and egg Sandwich and coffee will be available from 7:30am on Saturday and Sunday mornings.

Lunch –  Lunch at the Hotel is a must! Check Printout the menu and get your taste buds excited for April. The Hotel’s food is renowned for its quality and value!

*Dogs are welcome at the Overland corner Hotel*


Dinner – Will be at the award-winning Mallee Fowl Restaurant for those wishing to catch up with friends old and new! Please let us know if you wish to attend. Check out their Menu here.

* Getting There *

The Gathering is in the Beautiful Riverland in South Australia.We have more sunshine than the Sunshine Coast!

BRL map

* Accommodation *

Accommodation – The Riverland has many accommodation options catering for all budgets. See here for some ideas. Got an RV, Motor Home or Van? The Overland Corner Hotel has an RV staging area “out back” that is a stones throw close to the Gathering action. There are 4 powered sites. (Bring your power leads) and room for many self sufficient vehicles. Many BRL-ites stay here, and enjoy the added camaraderie!

VK5BRL has planned a fun day of Activities, Awards and guest Speakers. There’s also a

* Home Brew Award *

Have you made something for your shack? Then enter it in the BRL Home Brew competition. There will be two prizes awarded, a “People’s Choice” award, judged by the BRL gathering attendees, and the prestigious BRL “Constructors Award” for the best piece of Ham Radio related gear presented for Judging by our panel. It can be anything radio related, from something simple like a Balun, to a complex microwave transverter!

* Contact us *

If you need any help with any aspect of getting to the venue, accommodation, special dietary requirements or other issues, feel free to Phone the Secretary Andy, VK5LA on 0488778154 or email him.

The 2019 Riverland Radio Club BRL Gathering – The Friendly Gathering!!!

Setting up a modern APRS mobile station…

This is a post about my journey in getting a compact portable APRS station going for portable and emergency use…it will be over a few posts as I try a few different methods of implementing my system…enjoy!

APRS stands for “Amateur Packet Reporting System” – APRS has been developed since the late 1980s by Bob Bruninga, (call sign WB4APR), He still maintains the main APRS Web site. The initialism “APRS” was derived from his call sign.

First a brief history of my packet and APRS setups…

I have run packet Radio, off and on since 1995, when I was first licensed as VK5XAW. My first Packet Rig consisted of an Apple Mac Plus, a VK7TM (Sadly, long now a Silent Key) “Pocket Packet” modem I built from a kit, and my first 2m Radio, an Icom IC2GXAT 7watt handheld radio,  plugged into a pole mounted vertical up at about 10m high.21DA2C36-D048-4DEB-A013-974BD1EBE7A0

Everyone said it wouldn’t work, but work it did. As far as I knew I was the only one in SA using a Mac for Packet.

D0B662F1-8C16-485B-A430-D062F18D7BBBThe VK7TM kit modem worked
well and the software for the Mac impressed. I had a lot of fun on the VK5TTY bulletin board, and many direct contacts with Stef, VK5HSX.

I went to my first PC, a 486DX100, (!) and then a PK232 – a 424A8507-D7A7-4CE8-95B3-B45B0F806CD6real proper modem. The 232 soon got relegated to RTTY duties in contests, so I graduated to the PK88 and the MFJ TNC2 clones. I’m sorry to say I can’t even remember the name of the terminal software everyone used to use, written by a French ham? It was a long time ago.

Packet usage began to decline and started to go the way of the Dodo, When it was well and truely elbowed by the newly emerging all singing all dancing APRS.

I believed my first system, from (fuzzy) memory was a MFJ TNC2 clone with a custom ROM, not even a GPS, just  home lat/long entered in to the software as a home station. Quite boring really!

I then moved on to a couple of mobile setups, including a BD5C7FD5-A29C-4063-B62D-F3DCC85FDB52Byonics Tiny Trak3 with a Garmin GPS and Yaesu VX6R 5 Watt handheld, then neat system with an Alnico DR135 Mk111 2M Rig with an Argent Data Systems T2-135 internal modem fitted, with data display and FFD3BA14-A8D5-4189-9EC0-2EA0962494BEmapping/messaging from a dash mounted Garmin c510 StreetPilot in-car GPS/navigation unit. Luxury!!! The argent data setup used the proprietary Garmin sentences to do the overlays on the Streetpilot.

That system served me well despite its warts. It tended to D5C72EFE-8F88-44B7-B238-C16CD45AFCE8be erratic with keeping my own path on the GPS map, but did quite a good job of updating other stations. I found the Alnico Radio to be a good performer with bomb proof front end.

I hadn’t run packet for a number of years until recently. My needs with APRS have now changed, and as I’m quite often out doing Park Activations for the WWFF program, so I like the ability to map for two reasons.

A) As proof that I was where I said I was…and

B) Safety. If I’m lost, it should be easy to find me!

After doing a bit of trawling on the ‘net, it seems that there is quite a few options for APRS these days.

Kenwood and Yaesu both seem to have full function units, both high power mobile and Handheld, that are ready to go out of the box – just put your callsign and SSID in and you’re  away. These are a few generations in now, and have matured into 1 box solutions. Both have limitations with the information that can be displayed

As tech has moved on, so has software and by far the best 3571B18B-5DAF-4681-908F-A37F5C756F6Away to display yours and others APRS data is on, a web based app that uses google maps to plot positions and  track stations world wide in a web page.

Tablets have revolutionised mobile computing and this is the way I have chosen to go as a display for my vehicle APRS system that I’m currently putting together.

I have recently acquired a Samsung Galaxy Tab A, as the dash mounted Display for my APRS set up. It is simply Velcro’d to the dash surface, when in use, and removed when not required to reduce the risk of sun/heat damage or theft. It seems to work extremely well. The tablet doesn’t have to be flash, as long as it has an inbuilt GPS, most reasonably recent ones do, it should be suitable. not that you can even use an Android phone at a pinch. 20180706_163906

It is a perfect size for this application, and is a bigger, brighter and clearer display than any currently available out of the box APRS Radio, and can be used as an Android tablet when not pressed in to APRS duty.

The software that makes this all modern day APRS happen is an Android app called APRSDroid. It is a free download from the Google Play store. There is no equivalent iOS app, as iOS lacks support for Bluetooth Serial Port Protocol (SPP). The software supports the following connections…

1.via TCP/IP ( needs an internet connection), 2. via AFSK ( audio in and out using the headphone socket to a Radio, 3. via a Bluetooth to a TNC (like the Mobilinkd TNC) and finally, 4. Kenwood (NMEA waypoint)

At the moment, to get my position on the APRS network, my setup is operational with the2018-07-06 22.14.00 Samsung tablet > an ASFK connection via a simple interface> Yaesu FT7800R mobile radio.  APRS RX displays the incoming packets from the 2M Radio, and everything is displayed on the Galaxy tablet in the APRSDroid app. The only disadvantage is that it is not a wireless solution from the Tablet at present, but it’s cheap and it works. The goal is to have say a Pelican style case, with a 2M mobile radio and a Bluetooth capable TNC and all connections ready to go. Just plug it in to some power and an antenna and you’re on APRS, using the Bluetooth connected Tablet as a remote display. A picture tells a thousand words… I have started on the case for the setup, adding an auxilliary USB charging port shown here being tested on the way to help out on a Horus ballon launch with the club…

Until the next instalment on this build, here are a few links to the software and hardware I’m using…

Mobilinkd –

APRS.FI –!lat=-33.86670&lng=151.20000

APRSDroid –

Samsung Galaxy Tab A6 –