Many thanks to Keith (KY4KK) who shares the following report:
Extreme QRP – Testing the AX1 with WSPR and 20mW
by Keith (KY4KK)
Thomas, thanks for all of your activation videos related to the Elecraft AX1 antenna. I ordered one the day you announced the package deal, and it arrived in less than a week. I’ve activated a few parks with it already (20m SSB). Like you and many others, I’m impressed.
I was very interested in Thomas Barris’ (DM1TBE) March 12 QRPer post using WSPR to test his POTA antennas in Germany. Then I saw Bob’s (K7ZB) post about his ZachTek Flea with 300 milliwatts in CW mode. To me, extreme QRP represents some of the magic of HAM radio. I’d like to share one of my most recent WSPR experiments related to the AX1.
About a year ago, a friend (NG4S) loaned me his pair of WSPR transmitters and suggested that I explore building and comparing antennas. I’ve been hooked on antennas of all kinds and WSPR since then.
I began doing WSPR tests on the AX1 the day after it arrived. With two transmitters set to the same frequency and power output, you can do direct comparisons between two antennas under identical propagation conditions.
I’ve already done a couple of comparisons between the AX1 and other commercial antennas. But I think the test I just completed might be of particular interest because it pits the AX1 against an antenna I’ve seen you use many times – a 28.5’ end fed with a 28.5’ counterpoise. I used 24 AWG silicone insulated wire. The end of the radiator was placed on a 19’5” telescoping fishing pole. This is my preferred POTA mast when I can’t use a tall tree.
I spent some time trying to control other variables so that the only significant difference during the test would be the antennas themselves.
For example, the SOTA Beam WSPRLite Classic transmitters don’t have an ATU. So, I had to make the antennas resonant on the 20-meter WSPR frequency of 14.097 MHz. For the AX1, Thomas’ videos helped a lot. I used a clip-on capacitance hat and adjusted the counterpoise to 15’ 2”. This gave me an SWR of 1.17:1. For the end fed, I tried the two UNUN’s I had available and settled on the 49:1, which got me the closest (2.2:1). I then used a manual tuner to achieve an SWR of 1.29:1.
I also wanted to deal with the difference in power output between the two transmitters. Although they’re identical, and both set to 20 milliwatts, there is no way to ensure both are actually producing that output level. Based on tests by NG4S, one of the transmitters runs at 19 milliwatts. The other actually outputs 27 milliwatts. So, my plan was to run the test for 48 hours. At the end of 24 hours, I would switch the transmitters (and callsigns) so that both antennas would benefit (relatively equally) from one of the transmitters being stronger.
At the end of Day 1, I reviewed the data from the two transmitters on dxplorer.net/wspr. The end fed averaged a 5.7 dB gain over the AX1 based on reports from receiving stations that spotted both transmitters in the same 10-minute block (simultaneous spots).
On Day 1, the stronger transmitter was on the end fed. The maps below are from WSPR.rocks.
AX1 – Day 1
End Fed – Day 1
I was pretty impressed that the AX1 got into Europe and Africa on only .019 Watt! I always have good luck with end feds, so was not too surprised to see this one perform well.
At the start of Day 2, I switched the transmitters and changed the callsigns so that the stronger beacon would now be assigned to the AX1.
At the end of Day 2, the simultaneous spots data showed that the end fed still had a 3.4 dB gain over the AX1. This excludes all spots from the first 24 hours.
AX1 – Day 2
End Fed – Day 2
These maps represent only a portion of the data collected and compiled by the WSPR network. For example, the graphs below show an hourly comparison of the average distance of the receiving stations for each transmitter for each day [click images to enlarge].
The red line is the AX1 and the end fed is blue. Note that on Day 2, the AX1 was using the stronger transmitter. I think it’s interesting to see how each antenna and transmitter combination handled the period over night when 20-meters is less reliable on the east coast.
I’m not nearly qualified to draw any scientific conclusions from this experiment, but I will offer a few humble observations:
- The 40% difference in output power between the two transmitters didn’t seem to result in a similarly significant variation in the performance of either antenna. Day 1 and Day 2 contact coverage was almost identical. While the graphs and maps tell a general story, the proof exists in the raw data. A deep dive showed that the variation in the received signal strength between the two transmitters was LESS THAN 1dB. Interestingly, NG4S assured me that the 40% variation in output would be immaterial. But he also knew I wouldn’t really believe it till I proved it for myself. From now on, I will run comparisons for 1 day and flip a coin to determine which antenna gets which transmitter.
- Not all WSPR receiving stations run all the time, and this can skew results if you’re looking at averages. I analyzed the raw data for each antenna, comparing the received signal strength from only stations that picked them up both days. From this, I once again found only about 1dB variation in received signal strength from Day 1 to Day 2.
- For the 2-day period, the end fed had 1487 spots compared to 616 for the AX1. This is obviously statistically significant, but I’m not sure how to interpret it. Again, looking at the raw data from stations that received signals from both antennas on both days, it looks like the end fed had a 3dB gain over the AX1.
- Domestically, where the vast majority of my POTA contacts are made, the antennas had roughly the same reach. The end fed clearly had an advantage for DX.
- I didn’t pay much attention to the direction of the end fed slope or the direction of either counterpoise. I just put everything in the least likely position to be tripped over for two days. Both configurations appeared to be fairly omnidirectional.
- I really like the AX1. It’s a well-engineered purpose-built antenna, and I plan to use it very frequently when in populated areas. As mentioned on QRPer, the AX1’s super power is its speed of deployment. It was perfect for my recent activation at Santee National Wildlife Refuge (K-0521), where the ranger invited me to set up on his deck overlooking the lake. He even let me use his rocking chair! My POTA partners were off in the grass with the bugs.
- I picked the 28.5’ x 28.5’ end fed for this test knowing that it was an apples to oranges comparison to the AX1. When I’m in a wildlife management area with 100’ pines and plenty of time, my long wires will continue to be my preference. They may take longer to set up and tear down, but I get multiple bands, and that makes hunting P2P contacts a lot easier.
But Wait – One last thing:
The day after I completed this test, my friends and I activated Woods Bay State Park (K-2915). I set up the AX1 and 28.5’ end fed in the same configuration as before. I connected them to an antenna switch feeding into my KX2 set to 10 Watts SSB. I switched antennas every 10 contacts for a little over an hour and stopped at 40. Actually, I had 1 duplicate and 1 bad callsign due to my sloppy penmanship – both on the AX1. This was in South Carolina early in the morning, so half of the country wasn’t awake yet.
The results are effectively the same, and prove that with an antenna switch, you don’t need WSPR transmitters and careful management of variables to do meaningful field comparisons of antennas. The WSPR data just makes it more fun for me.
I’ve been a HAM for about 18 months. I’m fortunate to have two very experienced HAM friends who activate parks with me nearly every week. We’re all antenna experimenters and get a lot of enjoyment in reveling in our successes and laughing about our epic failures (mostly mine). We’re all QRPers too, and always look forward to your daily posts. Thomas, thanks for all you do to promote the hobby.
Cheers to all,