Topband: Where to place a preamp? Switching Beverages?

[ZR]

----- Original Message ----- 
From: "Don Kirk" <wd8dsb at aol.com>
To: <n4zr at contesting.com>; <Topband at contesting.com>
Sent: Friday, January 20, 2012 12:08 PM
Subject: Re: Topband: Where to place a preamp? Switching Beverages?


>
> --------------------
> N4ZR said : I have a 20 dB ARR preamp", "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."
> --------------------
>
> Per the ON4UN book, "In most cases you can put the preamplifier in the 
> shack.  The signal loss in the feed line is a loss that affects both the 
> signal and external noise.  That means that the loss in the feedline does 
> not affect the S/N ratio."
>

That is a very misleading statement typical of all revisions and corrections 
to that book.

Any loss before the first active device will degrade the MDS, noise figure, 
SNR, or whatever else you wish to call it.

A low NF preamp with sufficient gain will overcome the feedline loss as well 
as the radios front end noise resulting in a better SYSTEM noise figure, 
MDS, SNR, etc.

While the 350' feed of the OP should have a minimal loss of about .8dB at 2 
MHz and an in shack preamp would be sufficient 99.9% of the time others with 
more loss should do the calculations to determine the cost/benefit of both 
settings.

Carl
KM1H