To: <topband@contesting.com>
> Date: Thu, 09 Apr 1998 19:00:48 +0300
> From: YO3CTK <yo3ctk@alltrom.ro>
> I'd say that one of the best solutions is to use a good old 2N5109 in
> non-dissipative negative feedback circuit (patented by Norton). About 25mA
> of collector current yields a +30dBm input IP3 with a very low noise and
> 50ohms input and output impedance. This arrangement has been used with great
> success by Rohde&Schwarz in their EK070 VLF/MF/HF communication receiver.
> The amplifier use a specially wound trifilar transformer, which is easy to
> do after careful study of the patent.
Hi Mike,
Ulric published the details in RF Design magazine back in the early
70's. VK5KL and myself mailed some preamps back and forth using that
design. I used LT-1001 gold metalized CATV bipolars, and obtained a
noise figure of about 2 dB with near 30 dB IP3 intercept.
However, this low noise figure is totally unnecessary with a Beverage
antenna... even in a very quiet rural location. On six meters, with
an array pointed away from noise sources, it may be a good idea. But
on 160 any noise figure less than 20 dB is generally enough at
night, so the extra work just isn't worth the effort.
They do make excellent loop pre-amps.
73, Tom W8JI
w8ji.tom@MCIONE.com
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