From: "gert baars"
Subject: Re: Help needed with my A-level project - RF link
X-Newsreader: Microsoft Outlook Express 5.00.2919.6600
Date: Sat, 02 Nov 2002 07:50:18 GMT
NNTP-Posting-Date: Sat, 02 Nov 2002 08:50:18 MET
Organization: Chello Broadband
I think your approach could be succesfull. I often use DG-mosfets like the
BF9xx series as low level mixers.
You can actually make the transmitter as simple as an oscillator that is AM
modulated with a square wave.
In the receiver you need a good IF amplifier for reasonable sensitivity, but
for short distances you could keep it simple.
If you want to send data it's easiest to use the comports of 2 PC's (or 1).
These provide you with RS232 standard
data that includes start and stopbits to determine a 'frame' 8 data bits (10
"Sanjeevan" schreef in bericht
> I'm an A-Level student who is currently contructing my end of year
> I intend to
> build a simple RF transmitter, and reciever to send digital data. The
> digital data is going
> to have a maxmium frequeny of about 500KHz, and the carrier is going to
> a frequency
> around the 50MHz mark (Is this an approiate frequency? Tell me). The data
> going to be
> amplitude modulated onto the carrier wave,as this is within my ability.
> Currently I intend to use a dual gate JFET ( the only FET with two gates
> our school) to
> mix the LO with the digital signal. After this I'm going to put a bandpass
> filter which will
> reject unwanted frequencies created by the mixer. Then the signal is going
> into the input of
> an amp, then to an antenna. This is hopefully the end of the transmitter
> section of the
> project, tell me otherwise.
> The reciever is going to consist of a tuned circuit, to only accept the
> frequency my data is
> on, then it is going into a mixer. The mixer will be a dual gate FET, and
> will have an input
> from a LO and the RF signal, so that the output after it has been filtered
> will have a lower
> intermediate freqency. This intermediate frequency will then be fed into a
> diode to
> demodulate the AM signal into a digtal one. Then the siganl will be fed
> a schmitt
> trigger to clean up the signal.
> I want to know if the approach I going to use is approiate for this
> and if not i
> want to know where I am going wrong.
> The data I'm going to be sending is going to be in the form of 8 bits at a
> time. So for
> example if I send BYTE A:"1 1 1 1 1 1 1 1", then send BYTE B:"0 0 0 0 0 0
> 0", how can I
> prevent the reciever from picking up a mixture of BYTE A and BYTE B (e.g.
> 1 1 1 0 0 0
> 0")? Will i need to synchronise the digital clocks on the transmitter and
> As an A-Level project, it does not have to work properly, or work at all.
> What I want is to
> get the theory behind the project correct, and have a basic schematic of
> which make up this project, e.g. mixer, filter, amplifier.
> I would appreciate any comments on how to improve this design, or any help
> in general.