Antenna transmatch

[KC2UGV]

What size attic?

If large enough, consider running a loop all the way around it, then build separate - switchable - matching networks for each band you wish to cover. Remotely activate each when you wish to change bands,

If I'd hazard a guess, I'd say 30x60ft...

[N8YX]

What size attic?

If large enough, consider running a loop all the way around it, then build separate - switchable - matching networks for each band you wish to cover. Remotely activate each when you wish to change bands,

If I'd hazard a guess, I'd say 30x60ft...

That would be great for such an antenna.

30ft x2 + 60ft x2 = 240ft; you can always switch in extra inductance for 75/80 if necessary. All other bands would be fairly easy to match.

[KC2UGV]

What size attic?

If large enough, consider running a loop all the way around it, then build separate - switchable - matching networks for each band you wish to cover. Remotely activate each when you wish to change bands,

If I'd hazard a guess, I'd say 30x60ft...

That would be great for such an antenna.

30ft x2 + 60ft x2 = 240ft; you can always switch in extra inductance for 75/80 if necessary. All other bands would be fairly easy to match.

Don't loops need those monster butterfly caps at the feedpoint? I'm not averse to that at all, but the one's I saw had these huge 5000V variable caps at the feed point.

[KC2UGV]

And I need to use ladder line for a loop right, or else it defeats the purpose of the loop?

[N8YX]

Don't loops need those monster butterfly caps at the feedpoint? I'm not averse to that at all, but the one's I saw had these huge 5000V variable caps at the feed point.

What you can do is to use some doorknobs (7.5kV) in parallel with smaller, "trimmer" style variables with large plate spacing. Switch in and out per band (as needed) via relay.

And I need to use ladder line for a loop right, or else it defeats the purpose of the loop?

Nope - you can use coax feed up to the matching network, which must transform an unbalanced low-impedance input to a higher impedance balanced output.

You can even build the balun out of coaxial cable if you wish. This way you'll not get into core-saturation issues.

[N8YX]

Food for thought - check the following:

http://www.eham.net/forums/Elmers/227332

I have a couple more references that I'll post later.

[KC2UGV]

Food for thought - check the following:

http://www.eham.net/forums/Elmers/227332

I have a couple more references that I'll post later.

Sweet! I think this is getting me on the right start. one of the posters (N3OX) talks about how to build the matching networks and the inductors :)

Thanks a bunch! And to think I tried to steer clear of eham...

[ka4dpo]

You can build an L network tuner for next to nothing. All you need is a coil of about 25 turns spaced one wire width and about 2 or three inches in diameter, and one 10 to 200 Uf variable capacitor. You can find these at a hamfest or on Ebay for very little money. The tuner can be built on a pice of wood and will load darn near anything. If you are an ARRL member here are two links that will help you build a dirt cheap all bander and tuner that really works.

http://www.arrl.org/members-only/qqnsea ... %5B%5D=QST

Look at the 1957 article by Lew McCoy. It shows how to build the tuner. You can substitute any length of wire for the whip, just make sure you have a counterpoise or, you can connect the coax from your dipole to the tuner and use it that way. Just some food for thought, the most expensive tuner Ten Tec makes is an L network. These have the lowest internal loss of any matching network and you can even connect a Balun to it and run ladder line or TV twin lead if your poor (that works fine by the way, I've done it). So, hope I helped you.

John..

[KC2UGV]

Ok, so I think I might venture into building a tuner. A T-network one (Seems easiest to build), and since my theory is a little weak, I need as few things that can go wrong as possible.

For building the air capacitors, what should I aim for on plate spacing? 1/16"? Is that too much, too little?

I saw a plan that uses metal venetian blinds as the stock material (I got lots of those :) , but they are laminated (Painted). Would this work as stock? I'd think so, but wondering if bare metal vs. painted metal is a big deal.

And, how many plates should I look at? 10? 20? 100?

[N8YX]

Once again...eHam to the rescue:

http://www.eham.net/articles/5217

A bevy of capacitor calculators:

http://www.csgnetwork.com/capacitorinfoconverters.html

In this application - and for 100w RF power input - I would use a plate spacing which yields at least 1kV breakdown in humid air. 2.5kV would be better.

The dielectric strength of air is as follows: 3 × 10e6 V/m

Using that figure, one may extrapolate the distance required between plates for a given breakdown voltage.