Antenna Length importance?

Thread Starter

Shelton

Joined Mar 13, 2008
19
Hi All

I have built the circuit on this website


http://braincambre500.freeservers.com/rss(1)(1)(1).htm


and the circuit diagram is here:


http://braincambre500.freeservers.com/rss schematic.gif


My question is this:


When I increase the antenna length to say 30cms, from the recommeded
6inchs or 15cms, the circuit does not work. Why is this? I know the
antenna captures RF signals and this current is fed into the circuit,
but I dont know why the circuit stops working - is it something to do
with overloading the circuit ?


Thanks for your time
Shelton.
 

Thread Starter

Shelton

Joined Mar 13, 2008
19
Hi

Thanks for your answer.

But If i increase the antenna to half wave length - the circuit should still operate correctly right ?
 

thingmaker3

Joined May 16, 2005
5,073
Since the specified antenna is less than half wave length, we can deduce the designer has added inductance in series. You might experiment with L1 turns and tap.
 

Audioguru

Joined Dec 20, 2007
11,251
The radio circuit is a super-regen.
If the antenna is too efficient then stong signals overload the super-regen.
If the antenna is not the short length in the design then the FET might oscillate too much.
 

Thread Starter

Shelton

Joined Mar 13, 2008
19
Ok thanks Audioguru and the others - yes i think audioguru is quite right as it is a super regen circuit and the antenna if too long can overload the oscillation.

Thanks all!
 
Top