6m EME & HF trials for the A35JT Expedition – the aftermath

6m EME & HF trials for the A35JT Expedition – the aftermath

What can I say, it has been an eventful month! After all the preparatory work to date, we took most of the antennas bound for Tonga out to a remote location SE of Adelaide to run shake down trials. It was good that we did, for we learned a few thing that are best learned back home rather than out in the Pacific.

What worked – 6m EME!

One of the key things we wanted to do was repeat the trial of the 6m EME station with the final antenna array with it’s elevation mount on the final Spiderbeam 10m aluminium mast using the M&P Hyperflex-13 feedline we obtained from RF Solutions. This was the first time we were looking to test the entire system end to end. We achieved success 5 deg above moon rise with contact to W7JW. We also heard 2 other stations but were unable to complete with them this time.


What didnt work – 6m EME

6m Beam on it’s elevation bracket

Things were going well until about 2 hours in. Then chaos broke out when the SPE 1.5K-FA amplifier failed catastrophically. This caught us by surprise as we were only driving it to 2/3rds of its output power (running 1kW) with the PA temperature remaining under 65deg Celsius (the documentation said that the amplifier wouldn’t take steps to protect itself until it reached 75deg C). Knowing that JT65 is a demanding mode, we had actively sought to treat the amplifier with care (even ensuring that the K3S was unable to generate more than 12W input to avoid any risk of over-driving it). Unfortunately it turns out it wasn’t carefully enough, although we believed it should have raised alarms etc first.

The fallout of this has been very expensive for the team. While the suppliers have been good with regards to honoring warranty repairs, it has become clear this week that we face the very real chance of the SPE not making it back from repairs in time to be included on our customs import/export documentation. This has thrown several aspects of the operation into re-planning to see what we can do (including back up amplifier purchases).

6m EME – Back on Track

On the 6m EME side, we have already started recovering the situation. We were very lucky that an alternate 1kW solid state amplifier came onto the second hand market just after the failure. The replacement, an M2 Systems M6-1K2 amplifier (the same type Lance W7GJ uses for his expeditions), is now enroute to Australia. We will conduct a followup systems integration test at the QTH of EME operator Peter VK5PJ as soon as it arrives. This will put the 6m EME part of the project back on track. We must thank Bjorn SM7SJR for his help with the replacement amplifier and Peter VK5PJ for the power supply to run it.

What did work – HF Antennas

Also over the test weekend we erected the final configuration of the 30m and 40m 4-square arrays. 30m was the first to air and the tests showed excellent directivity and performance. Steve VK5SFA who had led the 30m 4-square array development project was very happy with the results. 40m was next.

Oly VK5XDX and Steve VK5SFA assembling the 40m 4-square
40m 4-square at Nanda Farm

40m was an array we were watching closely. We had prior to the test weekend seen problems with it when trying to measure it’s radiation pattern in a park in suburban Adelaide. We had been thinking, at the time, that perhaps there were interactions with the local power poles or perhaps even the 30m array, as the directivity was nothing like what was expected.

Unfortunately, once testing began, it became clear that the 40m array did have a problem that we hadn’t seen on the first test earlier in the year. Oly, VK5XDX, then started investigating, aided by the team. Once back in Adelaide, he found a broken joint hiding in one of the 1/4 wave phasing feeders that drove the array. This was causing severe pattern distortion. Oly also made some changes to the ground radial design too. These two issues combined were responsible for severely degrading the 40m performance.

To prove it once and for all, Oly then set the array up again (a time consuming task when undertaken solo), this time on a farm north of Adelaide. Grant then went out to help test it with Oly the following weekend. The results were excellent, and we were met with fantastic reports. Front to back ratios in excess of 20dB (in fact we estimate closer to 25-26dB) were observed and excellent reports were received with stations both in Europe as well as domestically. The 40m 4-square project was finally finished ready for packing.

Progress in other areas

We also did some more testing on the 80/160m antenna at the farmstead and debugged a few more issues. That antenna will receive it’s final shake down testing during the Remembrance Day contest to be held on the weekend of August 16-17th but is now looking very promising. We also hope to test the beverage antenna for the first time during that contest.

Progress has also been made both on the tune and test weekend and over the following weeks, with most of the PC network and Logging / digital modes software integration completed. We are also considering what the 3rd back up transceiver will be and are in fact preparing to potentially have up to 3 stations on air at times (although it should be noted at least one will only be 100W at the time). All up our preparations are on track. For such a small team this has been a huge amount of work, but the testing and construction work we feel will be invaluable in bringing Tonga to the world in September.

HF Challenges still to be faced

Unfortunately we have one remaining challenge to overcome. The loss of the SPE amplifier is a serious blow and our resources wont stretch to any further amplifier purchases at this late stage. We are still following up on sources of a 2nd amplifier for HF as we have reservations that the SPE will not return home before we leave. If these alternate plans come to fruition, we will hopefully be back to our original planned strength before long. We will let you know more as things unfold.


While we have had our setbacks in July, the team is still in great spirits and is keen to get everything out to Tonga and get started. We are now under 60 days to go before we leave Australia and are looking forward to bringing you the best signals we can from the Kingdom of Tonga in only 2 months time! If you would like to support our efforts, donations are most welcome. See our donations pages for details.

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