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ATV 23cm PreAmplifier


From the Electron of July 1990 I once rebuild the preamplifier for 23cm.
When I started testing the preamplifier, by attaching it to my satellite receiver and tuning to the local ATV transponder at Soest I was confronted with all kinds of rubbish, much oscillation tendencies and a lot of noise amplification.
At my QTH (JO22MG) I received the ATV transponder of Soest (PI6ATS 1280Mhz) with signal strength of 8 but with a lot of noise (B1).
Soon it appeared to me that the MF-signal was far too big, caused by the consecutive MSA0685's (MAR8). Most wideband satellite receivers get overmodulated due to this and all starts mixing in the receiver casing.

23cmvvschema.jpg (87668 bytes)

In this schematic I replaced both MSA0685's with the BF65 that is easily obtainable at local stores. I also added two rings so the amplifier has a smaller bandwidth resulting in less mobile phone interferences.

The result was satisfying, very low noise and enough gain to receive weak signals. (over 29dB between 1240Mhz and 1300Mhz within 2.5dB)

23cmvvmeetrpt.jpg (127543 bytes)

I now receive Soest with signal strength 1 on the S-meter but without noise (B5) !
This preamplifier is tested, and has a maximum gain of 29.66dB on 23cm, and the 900Mhz (GSM) signal is reduced by 10dB.

I have made a new layout and schematic. Notice that you should place and solder the last SMD condensator C12 straigt up from print to BNC connector. The print is double-sided, the bottom-side is ground so the components should be placed on the top-side. Dimensions of the print is 3,5 x 11 cm (WxH) exactly.

23cmlayo.gif (56163 bytes)

Parts list:
R1 = 100 Ohm resonator
R2 = 270 Ohm resonator
R3, R4 = 56 Ohm resonators
R5, R6 = 330 Ohm resonators
1 X MGF1302 fet
1 x 78L08 regulator
2 x BFG65
FK = Ferritekrale 3mm
C2,C3,C5,C8,C11 = Sky trimmers SPF green (or equal ones 0.8 till 5pf)
C1,C6,C7,C9,C10,C12 = 10pf SMD
C4 = 1,8pf SMD
C13,C14 = 47Pf keramic
C15 t/m C20 = 1nf keramic
C21,C22 = 1nf trapezium condensator
L1,L2 = 1 coil of 0,5mm zilverwire, inside diameter 3mm
L3 = 10µh coil
D1 = 1n4003

Good luck with building this preamplifier.

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