Started a new project. It is taken from the the Lo-Key magazine, number 121, March 2014. It is published by the VK QRP Club from down under, and the article is by Peter Parker, VK3YE. Actually it started out wanting to play with a ceramic resonator oscillator and this receiver had one. So I built the oscillator first…it worked first time and I am quite happy with the results thus far. It was to be for 40 meters…but found that it will oscillate on both 40 and 80 meters, so thinking I may end up with a dual-band binaural receiver. Will have to build a second LPF for the input…and I need to look into the RF Shifting network to see if it is frequency sensitive.
Here is the schematic:
The range of tuning is from 6.978 MHz to 7.295 MHz. I am only interested in 7.0 to 7.18 MHz…primarily the CW portion of the 40 meter band. The tuning capacitor needed turned out to be only 250 to 30 pf (7.0 to 7.18 MHz respectively). The LO signal level is 3.3 dbm at 7 MHz and drops only to 2.5 dBm at 7.18 MHz.
I found out that the oscillator will also put out a signal from 3.47 MHz to 3.627 MHz…and the LO signal level is 4.5 to 3.7 dBm. Considering the capacitance swing needed, I can use a simple polyvaricon (Nine Volt Transistor Radio variable capacitor type) for the tuning capacitor.
We are getting our RV ready for our annual trek to Dayton for FDIM/Hamvention in a couple of weeks, so not sure how much of this project will get done till we get back… but it has been fun so far. I want to play with the oscillator a bit before I move on with the rest of the receiver. I used molded inductors to make the 3.3 uh tuning inductor and want to try a roid and then try the whole circuit with the small variable capacitor.
Enjoying the bench time and snuffing solder fumes. It was so cold this winter and the shack/workbench are in the unheated basement…so needless to say, I spent less time this winter down here than I had hoped too. Either I have to move the shack/workbench upstairs or come up with some sort of heating that is affordable when the outside temps tend to stay below 32 degrees (if not below zero) for days and weeks at a time!