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G8MNY > TECH 08.10.24 07:50l 65 Lines 2965 Bytes #999 (0) @ WW
BID : 17553_GB7CIP
Read: GUEST
Subj: High Gain 70cm Preamp
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 241008/0644Z @:GB7CIP.#32.GBR.EURO #:17553 [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
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄ<+12V
2K2 680R === u1
1n ÚÄÄÄÅÄÄÄÄ¿ 1nÚÄÄÄÅÄÄÄÄ¿ _³_
___ === ³ | ) ___ === ³ | ) ___
Û ³ _³_ 220K| )L Û ³ _³_ 68K | )L Û ³
Û ³ ³ | ) n68 Û ³ ³ | ) n68 Û ³
Û ³ ³ |_ÃÄÄ´ÃÄÛ ³ ³ |_ÃÄÄ´ÃÄÛ ³
BNC Û ³ ³ ³/ Û ³ ³ ³/ Û ³ BNC
o)ÄÄÄÛÄÄ)ÄÄÄ´ÃÄÄÄÁÄ´BFR34A ÛÄÄ)ÄÄÄ´ÃÄÄÄÁÄ´BFR34A ÛÄÄ)ÄÄÄÄÄ(o Output
³ Û ³_ n68 ³\e Û ³_ n68 ³\e Û ³_ ³
³ Û ³/| |³ Û ³/| |³ Û ³/| ³
³ Û === |³ Û === |³ Û === ³
³ Û /³2-10p |³ Û /³2-10p |³ Û ³2-10p³
ÀÄÄÄßÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÁÄÄÄÄÄÄßÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÁÄÄÄÄÄÄßÄÄÁÄÄÄÄÄÁÄ
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
cÄÂÄÄÄÄÄÂÄÄÄÄ+12V The PCB box is built around the BNC
ÉÍ _ÍÏËR _ÍÍËR _ÍÍ» sockets that fill in the lower 2 corners.
º / \ÚÄ´/ \ÚÄ´/ \ º Start with bottom side & input corner,
º \ø/³Çc\ø/³Çc\ø/ º then solder in the strip.
Inputº Þ ³º³ Þ ³º³ Þ ºOutput Middle partitions have 2 holes, 1 for the
BNC º Þ ³ºLÚÞ ³ºLÚÞ º BNC transistor & 2nd for the bias wire.
ÚÄÄÄÝ Þ Rº³cÞ Rº³cÞ ÞÄÄÄ¿ With all the outer walls in place & all the
³ ÝÄÄÞcÁTÁÙÞcÁTÁÙÞÄÄÞ ³ components fitted it can be powered up.
ÀÄÄÄÝ Þ º Þ º Þ ÞÄÄÄÙ Check the currents are about right if not
ÈÍÍÊÍÍÊÍÍÊÍÍÊÍÍÊÍͼ change the bias Rs to suite your Transistor.
ÍÍÍ =Double sided PCB box & dividers Ý = brass/copper strips 3cm long
/ \ = a 10pf Trimmer. c = capacitor. L = Choke. T = Transistor.
\ø/
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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