-----Mensaje original-----
De: Goeran Stigler <ghost@PE.CHALMERS.SE>
Para: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Fecha: jueves 7 de mayo de 1998 14:31
Asunto: Re: RC Transmitter


>Zoltan Perhacs wrote:
>
>>The hard part for me is the RF stage. Can someone help me in this (40MHz).
>
    Well, you can do it as complicated as you want... PLL for frequency
sintesys, FM modulation,  various mixers, etc, or you can just build a
quartz controlled oscillator and a single amplifier stage using an VMOS will
provide as much power as 0,5W, which in 40 Mhz makes a pretty long path (a
couple of kilometres, if the receiver is stable and well designed).

    For the receiver you can use a FET input stage with either an NE602 or
SO42P mixer -quartz controlled, also-, along with a ZN414 for intermediate
frequency amplification and detection, along with a OP-AMP for audio
amplification. With these devices you can get 0,5 to 1 microvolt
sensibility, a good signal/noise (provided by the FET input stage), and also
a very little size and low power.


>Try buying a complete RF stage as a spare part. I had no problem buying one
>when I thought my Hitec transmitter was broken.
>

    Of course!


>Also, stay away from airplane frequencies unless you really know what

    Well, 40 Mhz is RC band, so there should be used. You could also use 27
MHz (very noisy, so you'll need much more transmitting power), or 72 Mhz
(pretty unstable regarding coils, and hence you'll need silver-mica
capacitors and a good RF shielding.

    Regards,

    Andres j. Ogayar