antennas

A/B antenna testing is always plagued with the “propagation constantly changes” remark that suggests the tests at different times are never equivalent. The technique I use here compares 2 antennas over the SAME timeframe, not two separate timeframes. I do this by switching the antennas back and forth for multiple 2 minute WSPR cycles as shown in part 1. That closes the gap on the changing propagation argument. THANKS to Lord Callum McCormick, M0MCX, for showing this technique.

Then, I Take the results from those runs and use AI (Grok is my AI choice) to do the grunt work of separating the 2 minute runs and analyzing the results. See part 2 for how that is done.

This post describes how the antennas are setup and points to complete results for tests run on 3 bands: 20M, 15M, and 10M.

EFHW

This EFHW is my everyday multi-band choice here at the Casa Easton Antenna Test Range. It consists of a wire approximately 62 feet long poised in an inverted vee form with the apex at about 20 feet, supported by a carbon fiber mast. There is a small coil (about 1uH) 7 feet from the feed end to balance the resonant nulls to where I expect them, the CW portions of the bands. It is fed by a home-built 49:1 autotransformer and that is preceded by a home-built Common Mode Choke.

I use it nearly everyday because it is easy to deploy (my antennas are all daytime-only) and band switching is done from my rig without any physical antenna manipulation. Simple, it works acceptably well for my favorite activity, POTA chasing. It can’t always reach the West Coast from central Florida, but covers a good part of the USA.

POTA PERFormer

Before anyone asks about the power lines in the distance, about 100 yards away, they are operated by Duke Energy and are completely free of any HF RF interference. Now, those plants in the raised bed are a different story. They are victims of an unusual hard frost here in central Florida.

Results: Each of the links below includes the prompt I used for Grok and Grok’s full response to those prompts. Quick bottom line: the PERFormer outperforms the EFHW on 20m and 15m, while the EFHW performs better on 10m. Caveat: 10m is always a crap shoot from here.

• Complete A/B results for EFHW vs POTA PERFormer 20 meters
• Complete A/B results for EFHW vs POTA PERFormer 15 meters
• Complete A/B results for EFHW vs POTA PERFormer 10 meters

There are other A/B comparisons I might run. The physical constraint is both antennas should be different shapes. Running 2 verticals against each other in the confined space of the Casa Easton Antenna Test Range will interfere with each other. Yet, the EFHW vs a Marauder or a Marauder vs a TW2010 might work. Perhaps…

There’s a new technology in town. Let’s persuade ChatGPT or GROK to do the grunge work. That’s what robots are for. Right?!

Lord Callum McCormick demonstrated how he uses AI to do the tedious work and to produce wonderful comparison charts. Basically, he asked ChatGPT to separate results stored in a spreadsheet and do various calculations on the two sets of results. Callum was seeking which antenna is “better.” But, better at what? Well, that’s why we want various calculations; number of stations that heard us, number of times they heard us, distance, and signal strength, etc.

Callum used ChatGPT. I stole his prompt and did the same with Grok. It’s fascinating watching the AI machine, collect the information, learn about how WSPR works, build a program to separate various data and do calculations. It tells you what it is doing as it goes along, and then shows the results you asked for. Be aware: one has to be precise in what we ask for. Some report that AI can sometimes give you more than you expect. Adherents of the AI industry describe these adventures into uncharted, unspecified, territory as “hallucinations.” My antennas are mysterious enough without hallucinations. Just give me only what I asked for. Thank you.

Callum specifies the prompt he used in his video. I copied it and modified it a bit for my own interests, omitting his RX analysis. I simplified the process to need only 2 log file uploads. We arrive at very similar results. Since I use most of my antennas enough to have a feel for them, these tests confirm and solidify what I know about them. They also give me a quick way to compare a newly built antenna with one of my long time favorites. It quickly eliminates the “Is it the antenna, or today’s propagation?” question.

Process:

• Set up both antennas
• Connect them to an A/B switch
• Set up the WSPR transmitter and use a PC to control the transmitter. Set the callsign, grid square, and band for the test.
• Start running.

• Watch the WSPR Transmitter control screen and every time the little red light shuts off, switch the A/B switch. Missing this will spoil the results.
• Continue for as long as you please. I like to go through 6-8 cycles for each antenna
• Collect the results from wsprnet.org. My preference is to sweep the data into a spreadsheet. Name that spreadsheet Transmit log.xlsx
• Create another spreadsheet named Time slots.xlst

• Fetch the prompt from the bottom of this post. NOTE WELL: Edit at least the line which specifies the label for the report.
• Upload the A/B prompt and the two spreadsheets to Grok.
• Sit back and watch it work.

Below is part of what Grok reported. I’ll explain this particular test in the next post. Or, you can go here to see all of what Grok prepared. Note that at the top of the Grok report you can see the actual prompt I used (feel free to steal for yourself) and the data files. Next post: more detail about this particular comparison.

72 de N4REE, Bob

===== Below is PART of the results from Grok =====

Overall Statistics

Metric	POTAPerformer (PERFormer)	EFHW
Total number of reports	384	236
Number of unique reporters	128	95
Median SNR	-17	-18
Median distance (km)	1551	1498
Maximum distance (km)	6599	3949

Distance Bucket Analysis

Bucket	POTAPerformer (PERFormer) Count / Median SNR	EFHW Count / Median SNR
Short haul (0–2000 km)	321 / -15	204 / -17
Medium haul (2000–4000 km)	62 / -18	32 / -19.5
Long haul (>4000 km)	1 / -26	0 / null

Observations on Antenna Behavior

Based strictly on the provided data, the POTAPerformer (PERFormer) generated 63% more total reports and engaged 35% more unique reporters than the EFHW, indicating broader overall reception during the test periods. It also achieved a slightly higher median SNR across all distances (-17 vs. -18) and a marginally higher median distance (1551 km vs. 1498 km), suggesting more consistent signal strength and reach under the tested conditions.

In short-haul distances, the POTAPerformer received…. (See more at the GROK report link)

---

Grok A/B Prompt

I have conducted a controlled A/B antenna comparison using WSPR only.
Both antennas were tested: at the same station on the same band at the same power within clearly defined time windows.
Nothing else was changed.
Find two files attached.
Both files are in Excel format.
1 The Timeslots Log in UTC notes which antenna was in use and exactly what time.
2 The Transmit log downloaded from WSPRnet in UTC.
The logs are accurate and in clear two-minute chunks – there is no need to be concerned about the times. 
My timeslot log includes the antenna label for every 2-minute WSPR slot. 

Your tasks: 
Label this report "A/B EFHW vs. POTAPerformer - 20m"
Identify which antenna was in use for each transmit period.
For each antenna, calculate:
- total number of reports
- number of unique reporters
- median SNR (not maximum)
- median distance
- maximum distance

Group TX results into distance buckets:
- short haul (0–2000 km)
- medium haul (2000–4000 km)
- long haul ([greater than] 4000 km)

For each bucket, show report count and median SNR. 
For each antenna, calculate:
- total decode count
- median distance (if available)
- maximum distance

Output requirements: Present results in clear tables.
Do not declare a single winner.
Explain what each antenna appears to be better suited for - based on the data.
Focus on differences in behavior, coverage, and application rather than preference or opinion.
Base conclusions strictly on the data provided, not on predicted behavior.
Explain how you calculated the results.

A common method of testing antennas uses weak signal propagation reporting (WSPR) to see how far a signal reaches.

OK. Let’s use WSPR to compare two antennas, A/B testing. Being a lifelong nerd, I really really like data driven results. We can run WSPR using one antenna and then the other, and compare results. Sounds simple.

Oh!!! Propagation varies by time of day, by band, and even from minute to minute. This leads many to think that an A/B comparison between 2 antennas using WSPR is not valid, because if I run 20 minutes on one antenna and then take time to switch, and maybe rearrange antennas, and run 20 minutes on the other, propagation will most likely have changed, especially if there is a notable amount of time between the two test periods.

Yes, there are those of you out there who will suggest using 2 different callsigns, one for each antenna. First, good if you have 2 available. Second, you have 8 seconds to pause the transmission, change the callsign, throw the switch, and restart transmission. See how well that works out. It’s a lot less error prone to let the transmitter run continuously and sort out the collected results.

Next, collect the results from wsprnet.org of from wspr.rocks, separate the reports into two buckets, one for each antenna, and analyze things such as number of spots, signal strengths, and distances. Yeah, sounds simple. … until you get this honking large spreadsheet downloaded and tediously try to separate every other line into two separate spreadsheets (one for each antenna). OH SNAP!

Doing this without any other tools is so tedious and error prone that I defy anyone not mix up results between the two antennas.

There is a better way. Lord Callum McCormick led the way recently and I’m stealing directly from him. I’ll show you the technique in the next post. …

72 de N4REE, Bob

Some very kind communication from “RF Guru,” Joeri, leads to more experimentation. Joeri offered an interesting analysis of my previous post and had a few good suggestions. Among those, I focused on one important aspect of this antenna and how that aspect is achieved. OCF. Off Center Fed, places the feed point at a certain point along the antenna’s wire. In this case, the short side of the antenna consists of using the braid of part of the feed coax … but only part. This antenna should have 16.8 meters of wire on one side of the feed point and 3.7 meters of coax sleeve on the other side.

So, how to use only 3.7 meters of coax sleeve? The suggested answer is to use a clamp-on ferrite bead at that point on the coax. That is exactly what I did with the first tests.

After Joeri’s response about my previous post, and thoughts about what mattered, I responded to him that my suspicion rests with those clamp-on ferrites. Are they effective enough to do the blocking we expect?

Now, let’s try again with variations. This time I’ll use two masts with the transformer and coax raised off the ground as follows. The old, broken, fiberglass mast raises the transformer and dangling feed line to 5.1 meters. A “Pota20” carbon fiber mast raises the other end of the 16.8 meter wire to 6 meters above ground. The remaining portion of the dangling coax (ABR 400) enters the shack (actually my lanai) through a bulkhead connector and is immediately met with a homebuilt* common mode choke (CMC).

It’s very clear now that choking this part of the coax sleeve is critical, and I’m uncertain of what is “good enough.” Perhaps stopping at 5 beads is enough. OK. Let’s stop at 5 and then see what individual bands look like. Each of these shows my preferred CW part of the band near the markers. The QMX rigs will be OK with 20m, 15m, 10m.

BTW… Where’s the 40m resonance point? It doesn’t show up at all on the nanoVNA. The QMX+ reports 3.6 for 40m, beyond its internal tolerance. Instead, we have a contender for 80m, a band I rarely try. At some point, I’ll try both 80m and 40m with the TR-45L’s internal tuner.

UPDATE: further fiddling … further unsatisfactory results. Wasted time. I’m placing “RF Guru” Joeri in the same category as The Music Man’s Harold Hill; Charming, persuasive and a salesman. Some might buy his unproveable promises, but there’s no happy ending at the Casa Easton Antenna Test Range. i.e. My name is not Marion Paroo.

Mark, the Ham Florida Man has been running a series of YouTube videos scorning the ever popular EFHW antenna. See his latest here. The basis of his concern is that the 49:1 transformer is inefficient, robbing power before it gets to the antenna. Probably true, no matter how much research Colin, MM0OPX, has put into making them more efficient.

Mark’s answer is a collaboration with an RF engineer in Belgium, Joeri Van Dooren, ON6URE, who writes about all sort of antennas that he sells through his own store. In particular, Mark suggests replacing EFHW antennas with End Fed Off Center Fed, EFOCF, antennas which use a 4:1 voltage balun, one with much lower losses than the 49:1. Mark is a very good spokesperson for Joeri, making all the right points. Interesting ideas that sound reasonable. Maybe I should try one?

My deployment options here in the HOA controlled Casa Easton Antenna Test Range are few. There are no tall trees on this property, and no tall vertical structures. The best I can, unobtrusively do is a telescopic mast about 20 ft (6 meters) tall. That’s one of the reasons I use an EFHW much of the time, in an inverted vee deployment. Using a 3 ft plastic fence post at each end and the mast in the middle and about 66 ft of wire, I can easily reach anything East of the Rocky mountains from Central Florida, and sometimes well beyond, with the 5w TR-45L, QMX or QMX+ (actually 3.8w out).

I like this antenna because I can effortlessly switch between 40m, 20m 15m and 10m with NO need for a tuner.

Can I get the same convenience and improved efficiency with an EFOCF?

Of the EFOCF antennas at Joeri’s store, the EFOC17 appears the best fit for my property. “Why the EFOC17 is the Better Choice for 40M to 10M Operation” makes all the sales points. Length of 17 meters fits. Band coverage 40m – 10m fits. Sounds great. Let’s build one. Yes, as you know, I prefer to build when I can. The sales page for the EFOC17 has enough details for construction. I already had a good 4:1 voltage balun and plenty of wire. A group of clamp-on ferrite bead chokes arrived after a few days. It didn’t take long to assemble and deploy.

I deployed just as I do my EFHW, this time with the 3.7m coax counterpoise laying on the ground.

I captured VNA charts for individual bands, but will save the bandwidth of posting them here. A summary of the 4 bands I really want show the following SWR levels and only 2 will work with my radios without needing a tuner. Definitely not a useable antenna for my needs.
40m, 7.040 Mhz, 6.715:1
20m, 14.060 Mhz, 3.504:1
15m, 21.060 Mhz, 1.937:1
10m, 28.060 Mhz, 1.585:1

Unresolved question:

I can’t really expect Joeri to answer this question since I’m not using an antenna I purchased from him, only one that I think is similar to his.

Does this antenna really need to be 10m high (impossible here), or did I make some other blunder building it?