From: John Woodgate
Subject: Re: Help needed with my A-level project - RF link
Date: Fri, 1 Nov 2002 23:27:39 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Fri, 1 Nov 2002 23:30:59 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Sanjeevan
wrote (in ) about 'Help needed with my A-level project - RF link', on Fri, 1 Nov
>As an A-Level project, it does not have to work properly, or work at all.
BAD! Not your fault, but you don't get ANY grade in the real world for
something that doesn't work, no matter how much 'coursework' you support
it with. Besides, if you get it to work, YOU will feel on Cloud 9.
You seem to have most of the system worked out, but it's unusual to use
a dual-gate FET as a modulator, and I don't think you need to do that.
You can easily key a bipolar or FET oscillator on and off with a digital
signal (just use the signal as the base or gate supply voltage).
If you keep the oscillator output low (or attenuate it), you could use a
TV aerial booster as your amplifier; if so, you really need to go up to
90 MHz to get within the amplifier pass-band (they amplify FM radio
signals as well as TV), or you could stay at 50 MHz and learn how to
take out the high-pass filter in the amplifier, if necessary. You
wouldn't find it at all easy to design and build the amplifier itself,
but you can find the data sheet for the active device the TV amplifier
uses and see how that ties up with the actual amplifier components and
layout. That way, you stand a chance of getting something to work.
For the receiver, you also have a VHF design task. Certainly, to make a
superhet receiver is too much to ask. You should do a web search for
'super-regenerative receiver', and if you can get to see copies of the
'RSGB Handbook' (British) and 'ARRL Handbook' (USA) you will find a huge
amount of information in there. Find your local amateur radio club (ask
at the public library). Someone will be sure to want to help you, not
only with the books but with practical advice.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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