[HBR] Another Receiver Project -- HBR-4, Part 9

[waltah at earthlink.net]

Jim, N2EY wrote:

> refresh my memory...
> 
> why a Butler oscillator, rather than a conventional triode overtone?

Laziness or perhaps sheer poor judgement?   A Butler circuit 
(which is just a cathode coupled multivibrator with a series mode 
crystal between the cathodes) will *always* work right off.   The 
others seem generally to take some tinkering to get working.   

This is particularly true when the oscillator must work with the 
same coil and preset capacitor adjustements with various crystals 
over a wide range -- here, 16 Mcs (for 160M) to 43.5 Mcs (10D).   
But I did make a single triode work in the HBR2K with an even 
slightly wider range, so it can be done.

The Butler gives better stability for variations in tube and tank 
parameters because there's greater total gain available but that's 
rarely an issue in ham practice.   

The Butler is also a very simple circuit.   

But for equal crystal current it has less output voltage because the 
plate voltage swing is limited by the grid to ground voltage swing.   
In other circuits there's some sort of voltage divider there and the 
plate swing is greater.

I expect that with the rearranged circuit -- push-pull VFO and single-
end output from the Butler crystal oscillator -- I'll be able to reduce 
the input and get satisfactory stability even from the new 18 Mcs 
crystal.    We'll see ...

Walt
KJ4KV