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Re: Topband: Where to place a preamp? Switching Beverages?

Subject: Re: Topband: Where to place a preamp? Switching Beverages?
From: Bill Cromwell <>
Date: Fri, 20 Jan 2012 10:57:23 -0500
List-post: <">>
On Fri, 2012-01-20 at 10:53 -0500, Pete Smith N4ZR wrote:
> Having totally struck out raising this topic on Towertalk, I'm bringing 
> it here in the hopes of getting some solid advice.
> I have a 20 dB ARR preamp of the type praised by ON4UN in his book.  I 
> want to use it with a variety of RX antennas - loops, BOGs, etc. - that 
> have very low output levels.  My choice is whether to put it at the 
> antenna end, incurring the added complexity of sending 12V DC to it via 
> the coax, or to put it in the shack.
> I realize that if this was 2 GHz, there'd be no question where it should 
> go.  But for 160-meter purposes, I don't know.  I am wondering if 
> putting it at the antenna end might enhance directivity, by amplifying 
> the signals from the directive antenna relative to any pickup on the 
> 350-foot feedline.  I will be trying to choke as much common mode 
> current as possible, at both ends, but am not sure how effective I can be.
> On another topic, I am building a hub for BOGs.  Rather than switch at 
> 75 ohms and putting a matching transformer on each BOG, I wonder if it 
> would be feasible/desirable to switch at the high-impedance side and use 
> a single transformer.  It would certainly simplify the hub.
> Any advice would be much appreciated.

Hi Pete,

I'm thinking if your 350 foot feedline is coax and your antenna output
is very low it will be even lower at the shack end before it meets the
preamp. I think I would put mine at the antenna end of the feedline and
for the same reasons as you would at microwave frequencies. Once the
received signal is 'lost' no amplifier is going to get it back.


Bill  KU8H

UR RST IS ... ... ..9 QSB QSB - hw? BK

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