Thanks Ray. And Pete +David.

A relay would would work, that's for sure. Hmm .. but mechanical
switching? Relays have a switch-on delay of around 20 msec, I think,
plus there's contact chatter to allow for. I wouldn't think it would
allow for a fast or smooth transition between Tx & Rx data flows?

PIN diodes sound encouraging but might be hard to get. Jaycar's
catalogue has fast recovery diodes on offer. I'm thinking of this as a
school science project for next year/this year(2001)? Needs to be
reasonably cheap as well, although I have PIC 84s & encoder/decoder
chips on hand.

Can't figure outbhow you'd connect the pin diodes anyhow!

Thanks - Ian.



Ray Gardiner wrote:
>
> A small relay with low series inductance is probably the easiest, next
> choice would be
> a pin diode.  Coaxial relays are expensive. (Depends on your application.)
>
> If you use a relay then the normally closed contact would be the receive side.
>
> Some extra hints, if you are connecting to an external antenna, put some
> thought
> into lightning protection. Transient suppression and a resistor to ground.
>
> >
> >Just casting about for ideas here ....
> >
> >I want to build an Rx/Tx master/slave system using a PIC, 16F84
> >probably, and a pair of RF Rx/Tx modules that are available these
> >days. But it seems grossly inelegant to use two aerials for separate
> >channels.
> >
> >One idea that occurred to me was :-
> >
> >
> >\|/ Aerial
> > |________________|Switch|_____|Rx    |_______|Decoder|____|   |
> >                  |      |     |module|       |145026?|    |   |
> >                  --------                                 |PIC|
> >                      |________|Tx    |_______|Encoder|____|   |
> >                               |module|       |145027?|    |   |
> >
> >OK, the switch would have to pass a VHF signal in either direction,
> >depending on whether the PIC was sending or receiving. You'd only get
> >half-duplex with this arrangement, but that's OK. You'd be
> >sending\receiving binary data, not analogue but that's also OK. You
> >MUST keep the Rx module's input isolated when the Tx module is Tx-ing.
> >Obviously. You'd control the switch with a PORTA pin, probably.
> >
> >So what about the RF switch? Any ideas for that come to mind?
> >
> >Many thanks for ideas!
> >
> >Regards - Ian Hynes
> >
> >PS: May I wish PICers everywhere all the best for the New Year?
> >
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> >
> >
> >
>
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