Thursday, September 14, 2017

Starting a new receiver with a Lamda Diode Oscillator

I'm starting a new project that will be to make a receiver around a Double Balanced Mixer (DBM). The set will require an Oscillator , DBM, and AF amp. The oscillator could be a signal generator, dip meter, or oscillator built for the set. My favorite oscillator for the is a Lamda Diode Oscillator(LDO). I like the little oscillator Andy presented to the group at TRB and may try one of them but for now I'll stick with the LDO because it has functioned well in the past.
To build the LDO I'll need a PJFET, a NJFET, a couple of pieces of wire for the leads and a means to make the connections.
 They could easily be soldered but I'll use the crimps because I have them.
The first step is to bend the leads out to each side.
Tie the two center leads to a piece of wire. As I said it could be soldered. Here I just insert and crimp. The onlt advantage here is the insulator on the connector. If you solder it you could use a sleeve or tape to insulate it.
This is the hard part of the whole procedure. If you connect a meter on diode function from the center leads to the outside leads it will buzz on one side and not the other. We need to spare the pairs that buzzes.
The final step is to attach the second lead to the remaining leads. I now have a Lamda Diode.
 I like to put the little buggers in a shell. You could skip this step. I put a little blob of clay on it.
Now how to use it to make an oscillator?
Put the plus lead on the bugs antenna (the center) and put the negative THROUGH a coil to the other lead. If you adjust the voltage it will oscillate with less than 3 volts and up to 7 or 8 volts.
2 volts produces 1.99Mhz.
3 volt gives 8.5Mhz . I am using a coil with a core. I removed to core to let it go up. What I wanted to show here is that it will oscillate at low voltage and the frequency will respond to the voltage level. In the build I will use a pot to supply the oscillator that is fed from a regulated supply. I use the pot as a fine tuning adjustment.
That's about it for now next the DBM.

No comments:

Post a Comment