|[AMRadio] new antenna and matchbox a bust.|
brett.gazdzinski at verizonbusiness.com
Mon Jan 29 21:04:03 EST 2007
> It sounds like you got through this OK, and the results
> are good for you.
> I have a couple of comments however:
> * The EF Johnson Matchbox's have in my experience limited
> tuning range when
> the load is reactive, and even if the load is resistive, they
> don't like
> anything under a few hundred ohms or so. Feeding a resonant
> antenna with 450
> ohm feedline, and a High Z antenna (like a folded dipole),
> and they work
I noticed the caps are really small...(in capacitance)
> * Others are all upset at you using dual coax feed. You and I
> realize that
> this is a compromise. One advantage here is there is no HOT
> wires coming in
> the shack this way, and you can have a balanced feed all the
> way to your
> tuner. This approach is more lightning friendly too. To keep
> losses down
> however, I'd keep the length at a minimum, and the SWR less
> than 10:1 on
> those lines. A Coax with Teflon insulation and lower capacity
> per foot might
> be lower loss. Your tuner will have to compensate for the ~
> 30pf / foot of
> the Rg-214.
I tried that, I am not doing that anymore.
The way things are, I am not sure I would gain
anything by keeping things balanced, since I only
have 20 feet (at most) of coax in line.
How much loss can 20 feet of good coax have at 80 and
> The W9INN balun is a commercial variation on this where you
> have coax from
> tuner to balun, and the balun is outside. The coax runs at
> high SWR like
> what you are doing. As a suggestion, I'd take a impedance
> bridge outside
> where your 450 ohm line comes down, and see what the line
> looks like on your
> favorite frequencies. If the SWR is high, add or subtract
> from the feedline
> a little at a time until the SWR is < say 3:1. This should
> cut the loss in
> the Rg-214 to negligible.
> Folks go berserk when they hear about high SWR with coax.
> They need to be
> reminded that this is 80 meters, and not 2 meters.
I know better then to try to run high power through a balun
that has high swr on it.
So I don't think I have a lot of loss in coax or a balun.
The antenna tunes up fine on 80 and 40 meters which is what
counts. I don't have any idea what the pattern looks like, but
on Sunday morning I worked:
3835, the AM carrier net..
Sunday night I worked:
Steve, WA1QIX seems to always be 60 over at my shack.
Matter of fact, I may have to do something with the
homebrew receivers, as many signals are at the top
of the S meter range.
Maybe build in an attenuator or something.
I have not made any contacts on 40 meters yet,
maybe this weekend. I would think more wire in the air
would give gain on 40 meters though.
As it is, I am VERY pleased with the antenna.
So pleased I replaced the phone wire
in my house with cat5 cable, and put a filter on the answering
machine that was freaking out at full power on 80, and now
I have NO rf/audio in the phones in the house.
I did not interfere with the TV or VCR, I was on when my wife
was using them, so things look very good for nighttime
operation, at least from time to time.
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