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G8MNY  > TECH     12.12.25 17:07l 66 Lines 2966 Bytes #8 (0) @ WW
BID : 47042_GB7CIP
Read: GUEST
Subj: High Gain 70cm Preamp
Path: JH4XSY<IW0QNL<HB9ON<DK0WUE<ZL2BAU<GB7BED<GB7YEW<W9GM<W9LCF<N9LYA<
      VK7AX<GB7CIP
Sent: 251212/0802Z @:GB7CIP.#32.GBR.EURO #:47042 [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
                  ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ<+12V
                 2K2                    680R     === u1
           1n ﾚﾄﾄﾄﾅﾄﾄﾄﾄｿ           1nﾚﾄﾄﾄﾅﾄﾄﾄﾄｿ  _ｳ_
      ___    ===  ｳ  | )     ___    ===  ｳ  | )     ___
      ﾛ  ｳ   _ｳ_ 220K| )L    ﾛ  ｳ   _ｳ_ 68K | )L    ﾛ  ｳ
      ﾛ  ｳ        ｳ  | ) n68 ﾛ  ｳ        ｳ  | ) n68 ﾛ  ｳ
      ﾛ  ｳ        ｳ  |_ﾃﾄﾄｴﾃﾄﾛ  ｳ        ｳ  |_ﾃﾄﾄｴﾃﾄﾛ  ｳ
BNC   ﾛ  ｳ        ｳ ｳ/       ﾛ  ｳ        ｳ ｳ/       ﾛ  ｳ     BNC
 o)ﾄﾄﾄﾛﾄﾄ)ﾄﾄﾄｴﾃﾄﾄﾄﾁﾄｴBFR34A  ﾛﾄﾄ)ﾄﾄﾄｴﾃﾄﾄﾄﾁﾄｴBFR34A  ﾛﾄﾄ)ﾄﾄﾄﾄﾄ(o Output
  ｳ   ﾛ  ｳ_  n68    ｳ\e      ﾛ  ｳ_   n68   ｳ\e      ﾛ  ｳ_    ｳ
  ｳ   ﾛ  ｳ/|         |ｳ      ﾛ  ｳ/|         |ｳ      ﾛ  ｳ/|   ｳ
  ｳ   ﾛ ===          |ｳ      ﾛ ===          |ｳ      ﾛ ===    ｳ
  ｳ   ﾛ /ｳ2-10p      |ｳ      ﾛ /ｳ2-10p      |ｳ      ﾛ  ｳ2-10pｳ
  ﾀﾄﾄﾄﾟﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾁﾄﾄﾄﾄﾄﾄﾟﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾁﾄﾄﾄﾄﾄﾄﾟﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄ

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
          cﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ+12V        The PCB box is built around the BNC
     ﾉﾍ _ﾍﾏﾋR _ﾍﾍﾋR _ﾍﾍｻ           sockets that fill in the lower 2 corners.
     ｺ / \ﾚﾄｴ/ \ﾚﾄｴ/ \ ｺ           Start with bottom side & input corner,
     ｺ \�/ｳﾇc\�/ｳﾇc\�/ ｺ           then solder in the strip.
Inputｺ  ﾞ ｳｺｳ ﾞ ｳｺｳ ﾞ  ｺOutput     Middle partitions have 2 holes, 1 for the
 BNC ｺ  ﾞ ｳｺLﾚﾞ ｳｺLﾚﾞ  ｺ BNC       transistor & 2nd for the bias wire.
 ﾚﾄﾄﾄﾝ  ﾞ Rｺｳcﾞ Rｺｳcﾞ  ﾞﾄﾄﾄｿ       With all the outer walls in place & all the
 ｳ   ﾝﾄﾄﾞcﾁTﾁﾙﾞcﾁTﾁﾙﾞﾄﾄﾞ   ｳ       components fitted it can be powered up.
 ﾀﾄﾄﾄﾝ  ﾞ  ｺ  ﾞ  ｺ  ﾞ  ﾞﾄﾄﾄﾙ       Check the currents are about right if not
     ﾈﾍﾍﾊﾍﾍﾊﾍﾍﾊﾍﾍﾊﾍﾍﾊﾍﾍｼ           change the bias Rs to suite your Transistor.

 ﾍﾍﾍ =Double sided PCB box & dividers      ﾝ = brass/copper strips 3cm long
/ \ = 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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