I have a fair number of 2N5179s (metal can package, with can grounding
lead)kicking around--they're rated for up to 1GHz--I think they'll make a
suitable transistor for the job, might even make it up into the unliscenced
band, and therefore not have to worry about FCC people in their white vans
comming to find me if I try for slightly higher power.

I'm afraid that I'm fairly new to RF, and I have virtually no experience
with transciever circuits.  Though I've wanted to play with R/C for years,
I've never actually buckled down and figured out what I need to do it.

Is the 500nH coil is the actual tranmission element?  Is there any way of
amplifying the ouput to get a longer range capability?  If so, is there any
way of amplifying the input as well?

Am I looking at the wrong kind of circuitry to do what I want to do? (i.e.
R/C via a PIC)

I think I'll go hunt through the PICList archives for a while.  There's
probably been many discussions on this subject before.


----- Original Message -----
From: "Richard Prosser" <Richard.Prosser@ENERGY.INVENSYS.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, June 24, 2002 2:58 PM
Subject: Re: [OT]: RF Transmitter, Receiver


>
>
> OK - Here's the circuit so far - Setup for about 22MHz as the transistor
is
> only a 2N2222
>
> L2 and C4 basically determine the frequency, with some help from C1 & C2.
>
> In RX mode an approx 20kHz pulse train appears at the output with about
> 2.1V to 3.0 V range.  The actual pulse frequency depends on the received
> feild strength in a roughly logrithmic relationship.
> So, the PIC has only to count the number of pulses in a given interval -
or
> measure the time for a number of pulses and it should be able to figure
out
> if there is a signal being received (i.e. it maintains a record of the
> timing under idle condition and looks for a change).
>
> Under TX, the PIC pin changes to output and pulls low. This changes the
> bias conditions and removes the super-regen effect, turning the circuit
> into an oscillator.
> For short ranges, this can be sufficient (I hope) to be regarded as a
> transmitter.
> Modulation by manchester coding should be OK to pass data at a few
> kbits/sec - depending on range etc. required.
>
> A small aerial connected to Q1 Collector appears to assist reception.
>
> Note: this circuit is copied from a working PSpice simulation. I have used
> the same basic circuit but with component values altered & a better
> transistor at about 70MHz but have not yet tried making 2 of them &
> connecting to PICs for communication.
>
> One area of possible difficulty is that according to the simulation, the
RX
> frequency is centred at about 22MHz, while the TX frequency is about 1MHz
> higher. Possibly a better transistor would reduce this effect.
>
> As with most minimal component circuits, there is a fair amount of
> interaction between components and frequency, sensitivity etc. but it may
> serve as a starting point for someone.
> If anyone does play with it I'd be interested to hear of the results.
>
> Enjoy
>
> Richard P
>
> (See attached file: superregen.jpg)
>
> (See attached file: superregen.jpg)

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body