Topband: Help for Preamplifier

by way of Bill Tippett <> topband-bounces at
Thu Mar 23 06:04:47 EST 2006

Date: Wed, 22 Mar 2006 19:31:01 +0100 (CET)
From: =?iso-8859-2?Q?Petr=20Ou=F8edn=EDk?= <indians at>
Subject: Re: Topband: Help for Preamplifier


I am looking for solution of the same problem for long time too > 
even I am still not sure which pre-amp design would be best to use. I 
already tried the pre-amp with monolytic active amp from 
Mini-Circuits MAR-8, also BF981 tranzistor...but always dissapointed 
with results on band > the main problem was high noise figure, bad 
IMD/IP3. General problem could be in PCB layout mistakes in my case 
but I did not find any solution in magazines or on the web sites to 
make just copy of the construction.

Regarding the filters I already tried the elyptic filter by W3LPL, 
also Cauer BPF designed by me but dissapointed too. I think that main 
troubles I had with impedance matching or so cause when I tested on 
HP analyzer own filter seemed well but when I connected to pre-amps 
the response and figures been totaly damaged...

Finaly I am using only 10dB pre-amp with BF981 unipolar transistor 
w/o any filters only time to time cause in most of cases my rotable 
Delta receiving loop for 160m has better performance (even own sigs 
are weaker) then with pre-amps...noise figures etc.

So it will be interesting if somebody has any practicaly tested 
solution to make a copy...


Petr, OK1RP

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