[amsat-bb] Re: (no subject)

Edward Cole kl7uw at acsalaska.net
Tue Mar 16 13:36:13 PDT 2010

At 11:45 AM 3/16/2010, Jack Barbera wrote:

>Bob,with the AG25 preamp on I see s5/6. I do get the audio at a 
>higher level ,it seems to me,.
>Just added to AO-51 the L/u to my doppler for satpac32 FM/FM to add 
>for cross mode do I have to add a separate line or add to the info 
>on the FM/FM string.
>If anyone can figure out what my ? is pls let me know what has to be done.
>ThanksJack WA1ZDV
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Sorry if this was covered, but do you have an internal preamp in the 
radio?  If you do, turn it off.  Even if there is not one, maybe you 
have an attenuator on the input ( a lot of the newer radios do 
nowdays).  Try turning on the attenuator (probably 10dB) and see if 
that sounds better.  If you have SSB see what S-meter rise you see in 
SSB.  My preamps push my S-meter in FM a lot higher than when in SSB 
(typ S-5 vs S-2/3).  I am running a 22-sB gain 432 preamp on my new 
Lindy antenna into a FT-847.  The NF is probably approx 0.5 dB (Mgf-1302).

The others gave you methods for testing it with local signals 
(measure S-meter rise on/off with a local rptr; compare S-meter with 
preamp connected with just the radio connected; moving antenna so 
that a local signal becomes near noise level and see if preamp pulls 
it up out of the noise (by ear)).  Usually a rise in background noise 
is the sign of a healthy preamp - but not always.  If signals are 
heard better without the preamp, then it probably is "broken" (always 
check dc power connections in this case).  the AG25 is probably 
powered thru the coax by your radio (check that the radio is putting 
out voltage on the center pin).  Since you are seeing noise rise 
these latter ideas are applicable (just covering the field for others 
that may be having preamp problems).


73, Ed - KL7UW, WD2XSH/45
  BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
DUBUS Magazine USA Rep dubususa at hotmail.com

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