Message 21851 in TECH.WW
From: G8MNY
Date: Mon, 04 May 26 06:45:00 Z
Newsgroups: TECH.WW
Subject: High Gain 70cm Preamp
Message-ID: <58833_GB7CIP>
Path: N2MH4|GB7BED|GB7YEW|GB7CIP
R:260504/0652Z 30877@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260504/0651Z 10732@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260504/0651Z 17917@GB7YEW.#79.GBR.EURO LinBPQ6.0.24
R:260504/0645Z @:GB7CIP.#32.GBR.EURO #:58833 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Dec 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is a design I used for ATV Rx as well as a linear 400W SSB PA wrap around
RX path.
I used it in a 1 or 2 stage configuration giving 14 or 33dB gain, one of the
main advantages is it is a narrow highly tuned design keeping out strong out of
band signals.
CIRCUIT
2K2 680R === u1
HOW IT WORKS
The 1st transistor is lightly biased for 2-3mA to give the lowest noise figure,
the base Z is low, so it is fed at the 50ohm air spaced strip line point
opposite the input.
The collectors are all both tapped into 2-3x the length of the 50ohm point for
best match (200-500R).
The collector chokes Ls are 3cm of thin enamelled wire coiled up on a 2mm drill
former. The base C (n68) has next to no leads on it.
The 2nd stage is biased for 10mA for max gain & higher power handling. If only
a single stage is used just put in the BNC socket as on the 2nd stage.
LAYOUT
/ \ = a 10pf Trimmer. c = capacitor. L = Choke. T = Transistor.
When all is OK & the preamp all tunes & peaks the band, tack on a lid (you may
need to unsolder it!) & the gain & selectivity will improve.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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