Today the noise floor and the propagation was very bad so even though Ive got a 35ft long wire antenna I went do to 80meters as I saw some JT65 activity there.
My new T match based tuner, MFJ 971, couldn’t get the antenna (35.5ft + 9:1 and 15m coax) to tune better that 2.8-2.9:1.
I remember that at some point I had some fun on 80m with my ZM-2, Z match based, tuner so I tried to tune it with that and I got 1.5-1.6:1…
Is there a technical reason that helps Z type configuration to match it?
As far as I remember from the schematics, MFZ has more inductance range and more capacitance variation.
Remove the 9:1 balun, toss in bin… Now feed the wire 6 feet or 2 m from the end with 12 feet of balanced feeder, TV 300 ohm or ac power figure of 8 flex - it’s really 80 ohm elcheapo feeder but that’s a secret. Add a 4:1 current balun and run coax to the ATU. You will be pleased with how many bands it works on and how efficient it is.
There should be many configurations that will help tune a wire but its not that easy for me to change my setup at the moment.
80meter tuning seems to be possible with MFJ 971 (based on specs) and I remember cutting the wire in a non resonant length (35.5feet) so together with the 9:1 unun I could see any it coming.
The Z-match is an amazingly versatile tuner.
The T match will also match just about anything if it uses a roller inductor. The tapped coil versions are a compromise but do pretty well. Changing the tap point would probably give a good match in your case.
35 ft is close to a quarter wave on 40 m and a half wave for 20 m. It would not be my first choice of length for an 80 wire antenna. However sometimes we must use a wire that is long enough to fit between two supports and it will present a challenge to resonate.
As you will have gathered I certainly don’t like the idea of using a 9:1 balun to match a short wire. It is meant for high resistance feeds - many kohms. The 35 ft wire will have a low radiation resistance and a lot of capacitive reactance on 80 m.
A loading coil would change the electrical properties to a more optimum value but the issue of the other half of the antenna remains - earth, counterpoise or more wire with another loading coil?
Is your 9:1 voltage transformer designed for 80 m? Most seem to be for 40 to 10 m.
Can you run a single wire feeder from your 35 foot wire to the ATU and use a metal water pipe as a ground? Or the same single wire feed but with a short tuned counterpoise?
As indicated my preference would be to use some tuned feeder, offset from the end, to change the reactance values and try to match that. Running twin feed line all the way to the ATU is a simple option but you need to use the Z-match or a 4:1 current balun with the T-match. It is often inconvenient to bring twin feeder inside so putting the balun outside (in a rain proof box) and using coax to the ATU is often done.