[Elecraft] K1 sideband question

[Mike]

MFoster wrote of the K1 receiver:

> may I choose which sideband I listen to as I tune CW?

No, not without re-designing the radio.

> I prefer, as I tune upward in frequency, to approach
> the received signal from the high-pitch side and tune
> toward its zero-beat frequency.

That is a classic way to show that receiver is fuctioning in the UPPER
sideband mode.

> Currently my K1 encounters the zero-beat frequency first, then the
> signal is heard.

That's because the K1 receives in LOWER sideband mode on all bands.

If I recall correctly, in the K1 the BFO injection frequency to the
product detector is on the low side of the IF, so the BFO frequency
would have to be shifted to the high side of the IF for USB operation.

It seems that many QRP rig receivers are designed for high-side BFO
injection (in contrast to the K1), with the claim that due to the
asymetrical shape of the crystal filter bandpass, high-side injection
results in improved opposite sideband rejection compared to low-side BFO
injection.  I think I have proved the theory of that to my own
satisfaction, which makes me wonder why low-side BFO injection was
chosen for the K1 product detection system.

73,
Mike / KK5F