[AMRadio] new antenna and matchbox a bust.


Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Mon Jan 29 21:04:03 EST 2007


> 
> Brett,
> 
>    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
> great.

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
40 meters???


> 
> 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:
AB2EZ
K2FW,
N1VIV
KG2IR
KC2IFR
W2TDS
W1NZR
W1GHW
K0UL

3835, the AM carrier net..


Sunday night I worked:
WA1QIX
KF4EOM
W9AD
WB2EMF
KB1HYS
K1KBW

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.

Brett
N2DTS

> 
> Regards,
> Jim
> JKO
> 




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