Although I had little time today, I experimented with adding varicap tuning to the Tenbox AM transceiver's RX section. Only problem was I had no varicaps, so tried using a few different diodes and a transistor as a varicap. 1N4148 and a Germanium diode reverse biased hardly produced any change in capacitance going from 2-12V. I know a 1N4007 works quite well but could not find one. Then I used a 2N3904's base-collector junction and got a few pF of change. In the end I just did as I did in the Sixbox and used a fixed capacitor in series with a 365pF polyvaricon tuning capacitor. This moves the RX frequency as much as I need at around 2MHz maximum.
Red LEDs make good varicaps, Roger.
ReplyDeleteThanks for that tip Julian. I'll try it.
ReplyDeleteHere is the link to LED's as varicaps:
ReplyDeletehttp://www.hanssummers.com/varicap/varicapled.html
Martin, OE5HYM