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Variactor diode for receive loop


Simon
 

Does variactor variable capaciance diode has high Q factor that is comparable to air cap?   

Can it be used for receive loop?  

Prelimary loop calculator shows signal at says -30 dBm will induce tens of mV and NOT significantly affecting the cap value.


Immo, DL5KB
 
Edited

hi Simon,
main issue will be to find a Varicap which gives up to 50pF. I did a little calculation: Loop consisting of thin wire, i.e. 1.5mm diameter and loop of 60cm with 3 close windings will have abt. 15µH. For tuning it to 7MHz you need 35pF.
The blocking inductivity should be abt. 10 times the loop inductivity. 

I don't believe, that there will be any issues, except if you transmit on similar frequences nearby. 

So, do a try and let us know your success or issues.
73
Immo


Gary W9TD
 

DC blocking capacitor required or else loop shorts out the varactor bias.
Gary
W9TD


Immo, DL5KB
 


at the first drawing I missed the blocking C. Thanks to Gary!
73