Antonio Vernucci wrote:


Hi Randy,

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

Thanks for the advice, and you suggestion is just what I am going to do next.

As a matter of fact, 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.

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.

73

Tony, I0JX

Tony....

I think there is something wrong. The manual I downloaded from BAMA says
the oscillator frequency is ABOVE the signal frequency on ALL bands!

73, Roger


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