[HBR] HBR Receiver BFO Question

[Walt Hutchens]

Whitebear1122 said:

> What is the BFO output wave shape supposed to look like? Is it
> supposed to be a sine wave?

Probably not.

Most bfos -- most ham-purpose oscillators -- operate class C. The
current suppling the power -- plate current -- flows in pulses. Unless
the oscillator is designed so that current drives the tank circuit at
a capacitor -- a Colpitts circuit for example -- the VOLTAGE there and
often at some other places in the circuit will be a distorted
sine wave at best.

This isn't a problem for the BFO as such -- only its fundamental
matters to that function. However a non-sineusoidal voltage waveform
will increase the difficulty of eliminating BFO harmonics from the
front end of the receiver.

100 kcs BFO? Or 85 kcs? Far enough off that the problem should be
minor. Follow the HBR-13C design closely and I'd guess you should be
okay, though receiving SSB calls for more BFO output than was needed
for the original designs so the harmonic levels will be higher.

Just one footnote to that: Since the CURRENT is always a pulse (lots
of harmonics) if it flows in very much chassis it can be coupled to
other signals that flow in that chassis. As a rule of thumb return all
the grounds for an oscillator to the same lug, including bypasses,
etc.

Many words to say 'not a problem to worry about now.'

Walt Hutchens
ex-KJ4KV