-----Original Message-----
From: ZR
Sent: Tuesday, May 22, 2012 4:28 PM
To: g3pqa@onetel.com ; TopBand List
Subject: Re: Topband: Two wire Beverage Question
>
>
> I recently measured Gary's 2-way boxes and they are good (virtually flat
> freq response) to over 21 MHz..
> Unfortunately my 200m 2-way is down on 3.5MHz in reverse direction, and
> also
> deaf on 7MHz probably because total transmission line losses are over 20dB
> on that band. Plus earth and transformer losses another few dB.
> (I was thinking of trying a remote preamp).
> 73
> John G3PQA
>
> How was that measured John? On the bench can miss a lot and flat to me
outside usually means excessive loss.
Im using WD-1A, WF-16/U, and 2 wire rural telephone cable which is
copperweld.
Listening on 40 a few minutes ago shows no particular loss but very sharp
directivity. The directivity really knocks local crud right into the noise
floor and the band sounds dead but signals are loud with fantastic SNR..
RG-6 up to about 150' feeds the switching box and then 750' of 1/2" CATV
hardline back to the house. A preamp is available but hasnt been needed
since the rebuild started 2 years ago.
>Transformer cores are all BN73-202 with primaries and secondaries isolated
>in individual Teflon tubing for minimal C coupling.
>Carl
>KM1H
Carl,
Thanks. The 75 ohm feeder loss measured with a home-made dBm meter. I should
have said, I use 75 ohm twin for the beverage, and I measured the loss of a
spare drum in the shack on a VNA as just under 4dB per 100m. on 7MHz.
Adding, say 3 dB loss, for plugs, transformers and small mismatch, plus 2 dB
for earth loss, the total loss in reverse direction comes to approximately
23dB, perhaps not surprising it does not work.
As my system is 75 ohms, I use home made transformers , feed type 43 binoc,
refl BN73-202.
I will re-measure over the summer to double check all this, your results are
encouraging.
Unfortunately it would be a huge job over other property (some of it stealth
work!) to replace, so the preamp route may be the best in my case.
73's
John
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|