I'd use an O'scope to look at the local osc. - see if the waveform is=20
"funky"... If it's not a nice sine-wave - that could be the source of =

your "sub-harmonic"... which might cause the image you're picking up. =
Be=20
careful when probing with a scope - you'll want to use some sort of =
weak=20
/ high impedance coupling - certainly not a direct connection with a =
1:1=20
probe, etc. If the local is producing some odd waveform - check the=20
power supplies / decoupling / tuning of the osc. Someone may have=20
cranked a slug or trimmer cap into some weird tuning that "sorta"=20
works... but not where it should be.
=20
best regards...
--=20
randy guttery

Hi Randy,

sorry for my late reply, but I have been out of town.

Thanks for the advice. By making some measurements, it was easy to =
determine what the problem is.

As expected, on 80 and 40 meters I measured the conversion oscillator =
frequency to be 1,650 kHz (i.e. the IF value) higher than the receive =
frequency, .

Conversely, on 10, 15 and 20 meters, the frequency meter indicated that =
the oscillator fundamental frequency runs at HALF the figure one would =
expect. For instance, when the receiver dial is at 14.000 kHz, the =
oscillator runs at 7,825 kHz and the converter tube then works on its =
second harmonic at 15,650 kHz (equal to 14,000 + 1,650). Measuring the =
oscillator waveform period with an oscilloscope, it was easy to confirm =
that the fundamental is at 7,825 kHz. The waveform is not sinusoidal and =
then has a rich harmonics content.

This is just the Hallicrafters design approach, not a problem of my =
receiver. Probably they found it easier to build a high-stability =
oscillator at a lower frequency and exploit the second harmonic.

But, with the oscillator fundamental at 7,825 kHz, the receiver will =
receive both 14,000 kHz and, even better, 9,475 kHz, unless the RF stage =
provides a sufficient block for the latter frequency. =20

Unfortunately, in Europe we have terrific BC signals in the 9.5-MHz =
range, that pass through the receiver RF stage tuned coils, =
independently of the frequency they are tuned at. Problem is that their =
ultimate rejection is too low, and peaking the preselector does not help =
at all.

The next step will be to try putting a 9.5-MHz band stop filter at =
receiver input.

73

Tony, I0JX