Składamy wzbudnicę SSB G4CLF

[bolanren]

Mietku,

Wygląda na to, że lada moment usłyszymy Ciebie w eterze pracującego na naszej płytce. To dobra wiadomość. Piotrek już nie może się doczekać kiedy będzie mógł nawiązać łączność z drugim "Plesseyowcem".

Dzisiaj otrzymałem e-mail od James`a. Poprosiłem go o krótkie naświetlenie dyskutowanego zagadnienia dotyczącego dopasowania mieszacza do kwarcowego filtru. Poniżej jest jego odpowiedź.

"Dear Jerzey

Thirty five years ago when this transceiver was designed the J310,
operating with zero gate bias, was the best affordable choice for
a low noise, low distortion amplifier at 9 MHz. Its input impedance
is 4 pF shunted by the 22k gate bias resistor which does not have a
significant effect on the termination of the mixer or the filter.
It is still a good choice, except for its rather high drain current.

The attached diagrams show the transmit and receive paths of the
G4CLF Transceiver. T1 has a turns ratio of 1:3 so for correct mixer
termination the transformer should be loaded with 450 ohms. During
reception the load is actually R1, R2 and R3 in parallel = 452
ohms, which is good, but during transmission the load is just R3
(= 560 ohms) which is over 20% high, and will slightly degrade the
IMD performance of the mixer - fortunately this is less important
during transmission than during reception.

The crystal filter should be terminated by 500 ohms and 25 pF.
During transmission it is terminated by R1, R2 and R4 in parallel
which, as we have already seen is 452 ohms - 10% low, and during
reception just by R4, 560 ohms - 10% high. This 10% mismatch does
not have much effect on the filter performance.

I cannot help at all with SL600/1600 circuits - all mine are long
gone. I do suggest that you consider redesigning with the same
mixer/filter/bidirectional amplifier and more modern IF and 9 MHz
mixer/modulator ICs. There is no modern equivalent of the SL621
but it should not be hard to build one with an RMS-DC converter
and a few op-amps.

73 de G4CLF - James"

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Komentarz James`a dotyczący rewersyjnego wzmacniacza na J310 potwierdza tylko to o czym wcześniej napisał Henryk SP2JQR i Piotrek SP9LVZ.