Doug, the preamp does not discriminate between signal and noise. It does not bring the signal "out of the noise". It will raise the level of the signal and the noise if the noise level is very low such as happens frequently on VHF, sometimes on ten meters and occasionally on 15 meters. Preamps seldom help on the lower bands.
The ten meter contest this weekend was a time where a preamp helped. I used the one in my K3. For me, most of the time the noise level was low enough that the preamp was of benefit. It raised the signal about an S unit which was enough. Part of the time the local power line noise was enough that I turned the preamp off because the noise level was moving the S meter. The best place for a preamp is at the antenna before the coax. Needless to say, this presents a lot of complications for transmitting antennas so hams usually use a preamp at the receiver. Preamps are great for receive only antennas that are far away from the shack, particularly if they are not very sensitive (such as a Beverage on 160 meters) As you observed, preamps are not very smart. They are just a transistor or two and some filtering. They are useful sometimes, harmful at others. I hope this helps. Willis 'Cookie' Cooke K5EWJ --- On Mon, 12/15/08, DOUGLAS ZWIEBEL <doug...@gmail.com> wrote: > From: DOUGLAS ZWIEBEL <doug...@gmail.com> > Subject: [Elecraft] K3 sensitivity + preamp: looking for wisdom > To: "Elecraft Reflector" <elecraft@mailman.qth.net> > Date: Monday, December 15, 2008, 8:14 AM > Hi... > > The following request for information is not specific to > the K3 (or > even to Elecraft). Please craft your response to be > generic. > > Despite being an active ham/contester for over 40 > continuous years > (but not being an ee), I just do not understand how a > "preamp" works. > It is not a "smart" device, so how does it > "know" to amplify the > signal and not the noise? I first used a preamp way back > when > (1960's) when I was a teenager...it was an Ameco job. > It was more > "fun" than useful, because I could give out > "big" S meter reports. > > Later, when listening in the noise became more important to > my style > of operation, I never could notice a difference between > putting the > preamp "on" and just turning up the volume (many > rigs with built-in > preamps too). Sometimes, turning up the AF gain worked > better. > > So...HOW does a preamp help to "bring a signal out of > the noise" > without the use of some fancy computer algorithms backed by > lots of > computing power? Further, does a preamp really > "improve" sensitivity? > I have yet to find a signal that I could not copy (or > hear) with any > preamp "on" vs increasing the AF gain. PS...I am > talking about HF. I > know that lots of guys use a preamp on 160m with their > beverages, so > the effect must be real...right? HOW does a > "dumb" device do it? > > de Doug KR2Q > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
