[AMRadio] Receive Preamp question


Bob Macklin macklinbob at msn.com
Sun Nov 4 11:24:47 EST 2007


Steve WD8DAS comments:

"One way you can know if you have enough gain is to note the background
noise your receiver picks up with the antenna connected, versus not
connected.  If the background hiss (not lightning crashes or the various
buzzes from local noise sources, but just the steady even
background hiss) is louder with the antenna connected, then you already have
enough RF gain.  If it doesn't jump up with the antenna connected, then you
need more gain, either thru repair of the receiver or an extra stage."

Or you need to make a better antenna!

What are "ACTIVE ANTENNAS"? I just see them as WIDEBAND amplfiers the raise
everything. That's sure not waht I want.

But many old receivers are poor perfomers from 20M and up. These receivers
would benifit more from a frontend converter than they would from a
preselctor.

BTW:
Thare are designs in the older ARRL hanbooks for both preselctors and
converters.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"


----- Original Message ----- 
From: <sbjohnston at aol.com>
To: <amradio at mailman.qth.net>
Sent: Sunday, November 04, 2007 8:07 AM
Subject: Re: [AMRadio] Receive Preamp question


>
> >Does anyone have a good recommendation for a preamp to
> >help my radio receive better.
>
> It depends to some degree on what receiver you're using, and the bands
> of interest.  On the lower shortwave frequencies, almost all receivers
> already have enough gain (if they are working OK), but as you go higher
> in frequency, say 14 MHz on up, many receivers can benefit from another
> stage of RF amplification.
>
> For example, I built an extra preamp into my Heath HR-1680 receiver and
> rigged it to be in-line when the bandswitch was on the 21 and 28 MHz
> band positions.  Let's see if I can recall what preamp board that
> was... hmmmm... OK I had to get my notes on that project... it was a
> Hamtronics LNY preamp.
>
> See  http://www.hamtronics.com/pdf/Manuals/LNY-WB.pdf
>
> One way you can know if you have enough gain is to note the background
> noise your receiver picks up with the antenna connected, versus not
> connected.  If the background hiss (not lightning crashes or the
> various buzzes from local noise sources, but just the steady even
> background hiss) is louder with the antenna connected, then you already
> have enough RF gain.  If it doesn't jump up with the antenna connected,
> then you need more gain, either thru repair of the receiver or an extra
> stage.
>
> Steve WD8DAS
>
> sbjohnston at aol.com
> http://www.wd8das.net/
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