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Date: Fri, 01 Nov 2002 23:43:29 +0000
From: Steve Taylor
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
X-Accept-Language: en-us, en
Subject: Re: Help needed with my A-level project - RF link
Organization: Zen Internet
> 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 have
> a frequency
> around the 50MHz mark (Is this an approiate frequency? Tell me). The
> data is
> going to be
> amplitude modulated onto the carrier wave,as this is within my ability.
Don't bugger about - buy the RF modules from
http://www.rfsolutions.co.uk - or direct from Maplin. You won't get a
500Khz bandwidth though.
> 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
> te siganl will be fed into a schmitt trigger to clean up the signal.
You can have a lot of fun receiving the signal, and you don't have to
worry about emitting illegal signal levels into the spectrum
> 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
> 0", how can I
> prevent the reciever from picking up a mixture of BYTE A and BYTE B
> (e.g. "1
> 1 1 1 0 0 0
What reference books have you read ? What do you know about receiving
Serial data from an FSK transmitter. Hint: The usual method is not the
bald switching on and off of the transmitter.
> 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.
!!!!!!! And people wonder whether A levels have been devalued. For your
own sense of self worth MAKING IT WORK IS THE WHOLE BLOODY POINT. No
amount of theory or elegant maths makes up for the final product being
crap ! If you really think it doesn't matter, you should be doing A
> What I want is to get the theory behind the project correct, and have
> a basic schematic of all sub-systems which make up this project, e.g.
> mixer, filter, amplifier.
Read some books. One of the classic texts is by Terman.
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