The old saying goes, “The proof of the pudding is in the eating.” Of course, the same goes for amateur radio. We can argue about theory all day long, but it’s on-air performance that really matters.
Last Saturday, I finally got a taste of some pudding. Last week, I put the latest version of the 9:1 unun that I’ve been experimenting with into a box (see below) and took it to the park to make some contacts.
I first had to decide on a length of wire for the radiator. I chose 30-ft. because that’s the length that Thom, W8TAM, had such good success with a couple of weeks ago. I also cut a 13-ft. counterpoise. I’m not sure exactly why I chose that length, but in the end, it seemed to work.
I shot the radiator up into a tree, connected the antenna and counterpoise to the unun, and connected the unun to an antenna analyzer to make a few measurements. On both 40m and 20m, the SWR that I measured was about 4:1, well within the range of the antenna tuner in my KX3. One amusing thing that I noted is that this measurement didn’t seem to change at all on 20m when I disconnected the counterpoise. It made a definite difference, though, on 40m.
Just for kicks, I also tried to measure the SWR without the unun. In both cases, the SWR was greater than 10:1.
I could have made more measurements, but I wanted to make some contacts. I tuned up on 40m and found AA3EJ calling CQ. He heard me right away, and we had a short QSO. By the way, I decided on working 40m as Rich, KA8BMA, had also come to the park today to try out his end-fed antenna, and he was on 20m.
Next, since the band sounded like it was in decent shape, I thought I’d give SSB a try. Tuning around 7200 kHz, I found an NPOTA station in Kentucky callling CQ. After a couple of tries, he finally heard me. That was actually my first SSB contact with the KX3.
I don’t think I can draw any real conclusions from this operation, except to say that the unun does indeed transform a high impedance to a lower one, and that I was radiating some RF with the antenna. More experimentation is definitely in order. I want to try a longer radiator and maybe different lengths of counterpoise. I also want to try building a 64:1 unun and see how the SWR measurements compare to the SWR measurements made with a 9:1 unun.
In addition, I want to get some smaller gauge antenna wire. I was using some 18 AWG wire that I had on the shelf. While that wire is great for stationary dipoles, I think more flexible, smaller gauge wire is more appropriate for field application.
I’m also going to be modify the 9:1 unun assembly. Rick noted in watching WG0AT videos that his unun used a panel-mount male BNC connector. That allows him to plug the unun directly into the radio, so there’s no need for a jumper cable. Rick bought a bunch and gave me one on Saturday. Thanks, Rick!
Great fun experimenting and operating on weekends.
My antenna was a low sloper,58′ and the counterpoise was 13′, per Elecraft recommendations. I had read somewhere that the counterpoise should lie underneath an inline with the radiator. I saw a major drop in SWR when I rotated it 90 degrees.
Dan, in case you’re worried, I have no intentions of integrating goats into our AAPOTA activations.
Dan,
For antenna wire try the 26 or 28 ga wire from either RF Davis or Wireman. I’m using the Wireman product and it works great.
FYI, I am using a length of 60′, no counterpoise. I’m also using RG-174 cable. I bought the LNR winder and it all cobbles together like a charm. Transports and winds up neat as can be.
Thanks for the tips. I have some 26-ga. wire on order.
Well said Dan, glad your 9:1 triumphed!!
I started operating /P this year, motivated by ARRL’s NPOTA. QRP has been a ton of fun. I have put together a pretty nice fit-in-a-bag antenna to get me out and about.
Your antenna journey parallels mine. Uncanny. Above is a picture of what I put together. I’m getting really good at winding those 9:1’s. Here is what I’ve got:
Here is a picture of the unun with the cover off:
I didn’t analyze the antenna, but I’m glad you did. Very interesting. I was making no attempt to achieve a 1:1 match. Doing antenna setups in the wild can leave you with extremely variable setups. As such, a tuner is always part of my gear.
FWIW, last year I pulled off a portable operation in the Wisconsin QSO Party using my YouKits HB-1B with a 9:1 antenna. Manged to activate 6 counties logging 150 QSO’s doing QRP CW. I’d say the antenna works.
If I pull a repeat this year, I’m going to change to a doublet, though. It will be easier to set up, plus 80 meters was not a good performer with the end fed.