Switched Transformers (Great Input from Ed, AG6CX)

I met Ed at Pacificon this year, and he has built some very nice matching devices and also shares a love for Johnson Viking Matchboxes. Our discussions have really helped me learn, and more than just getting some validation on things that I am experimenting with – our discussions help push me forward in the learning space. I have also enjoyed such conversations with Andreas, N6NU and others – who understand the challenges of the low bands and trying to match where high power is used – especially on 160M.

Here are a couple of quotes from Ed that I really appreciate:

“Now sorting out the frequencies of the ham bands as you did in the few days since you posted the initial results, your conclusion is pretty much spot on: You could have a switching network to add the appropriate transforming balun in line. As for the 1:1 feedline isolation balun 1115dt, I would suggest running output of the 1:4  or 2:1 ununs and any other frequency on which you don’t need Rs transformation thru the 1115dt as it leaves the switching network for the shack. It adds the benefit of increased common mode impedance to the signals coming out of the 1:4 and 2:1,and should have no effect on anything else. I use several of Bob’s devices, 1:1, 2:1, 4:1. and 9:1 and they are just fine. He is knowledgeable and fair.”

I just happen to have the 1:1 version with SO-239’s at each end, so adding that is a done deal.

It really is great to get some validation for my approach. I have two antennas that are resonant and where I have nothing to do but use them – my DX Engineering DV-40-P and my home brewed 20M yagi – where I used a solenoid style coil as the hairpin – something Tom, N6BT taught me, and which he did on that fabulous N6BT DXU-32 that I used to have.

But one thing Ed said really has me thinking:

“Now, to specific frequencies, I had no way to expand your data around the ham bands, but note that even in the ham bands with steep resonance (Xs) curves,you encounter Rs not unlike those encountered in any shortened antenna, such as a mobile HF antenna where Rs typically runs in the range of a few ohms, despite a steep Xs curve, These installations use shunt-feed, relying on an inductor across the feed for inductance, and stray capacitance of the installation to translate the typical Zs = 2-6 ohms + jx.xx ohms to Zs = 50 +j0,0.”

I just happen to have this monster coil that Ed gave me – and what Ed is saying jives with what Andreas, N6NU has done with his Inverted L. I have tried a shunt feed before, but found that my coil stock was not exactly right. I have several Airdux coils – but I suspect that they were not wide enough. This monster coil that Ed gave me is something I am going to try before the UNUN’s get here.

Another thing Ed said:

“Nothing wrong with your network switching device, but you might find a length of coax addition that picks up 40 as well as 160 and 80. Who knows! That’s the great joy of out hobby.”

This is really fantastic, because I have to admit, I have never tried using coax stubs as transformers. I just happen to have two 75 ohm 1/4 w.l. coax lines that I was going to use to try to phase two 1/8 wl spaced shortened 160M verticals. That project was shelved, and it just happens that disconnecting the line that goes from the remote Ratpack antenna switch to the 160M Inverted L gives me a very easy little experiment. I have read countless pages in the ON4UN Lowband DX-ing book – where phasing lines, shunt coils and UNUN or other “impedance transformers” are all over that book.

In fact, I opened up the pages where Robye Lahlum, W1MK discusses his matching and phasing circuits. When I first purchased that book – his stuff seemed so advanced, I was overwhelmed.

Now that I have been experimenting “hands on” and because I have had such conversations with Ed and Andres, it is all starting to really make sense. Bob at Balun Designs has also been fantastic to work with. Not only are his products top shelf, he provides great support and is willing to discuss solutions and he also validated my ideas for this most recent set of little projects.

I posted the Smith Chart above because while Ed and I were looking at the Antscope plots where The R, X and Z intersect:

Embarassingly, I had never even looked at those charts, and maybe only ever looked at the Smith Chart much. The upshot is that just by having a discussion, I have learned these things:

  1. Resonant antennas are easy to match and deal with, non-resonant antennas are hard to match when you want a good match on multiple bands
  2. The “other” plots that you can look at on the Rig Experts Antscope are a must for such work
  3. When using coils and capacitors for a feed, you can’t have enough different components to try – and I will try that massive coil that Ed gave me soon
  4. Stub matching can have the same effect as using UNUN’s and other components – I will try this for sure now

SO, my learning continues and I feel like my discussions with friends who share the same interest really help me take that next step up the education ladder.

Thanks Ed!

Thanks Andreas!

Thanks Bob!

3 Comments on “Switched Transformers (Great Input from Ed, AG6CX)

  1. Any time Rich!

    If you send me another AntScope file for the HF spectrum plus type and length of coax to shack, ill look again!

    If you send AntScope files taken around 160, 80, 40, 20,17 meters in expanded scale I’ll ski down the steep Xs slopes and see what you’ve got.

    In the meantime, add and subtract coax lengths and enjoy the shifting sands of resonance.

    73,
    AG6CX

    Like

    • Ok, all good ideas, and I’ll do that. My feedline is in two segments. 70′ to the Ratpack and 40′ to the antenna.

      Like

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