Tony....
=20
I think there is something wrong. The manual I downloaded from BAMA =
says
the oscillator frequency is ABOVE the signal frequency on ALL bands!
=20
73, Roger

Hi Roger,

what you say is interesting.

I have an original SX-101A manual, which I presume should be the same as =
the BAMA copy. Could you please tell me at which page you read that? In =
my manual I was unable to find any mention of the oscillator frequency.

I am pretty sure of the oscillator frequencies, as I measured them both =
with a frequency meter and with an oscilloscope (the oscillator waveform =
period on 20 meters is somewhat longer than on 40 meters, no question =
about that). And the strong 9.5 MHz phantoms frequencies are exactly =
what they should be with an halved oscillator frequency.

On the other hand my receiver was owned by a person who never put his =
hands in it, but even hypothesizing that someone did something in it, =
what could he have done to make the oscillator frequency exactly half of =
what one would expect to be, and on 10, 15 and 20 meters only? Halving =
the oscillator frequency would cause the dial scale to be no longer =
correct; matching is instead fairly good (with normal tolerances for a =
receiver of that kind).

73

Tony I0JX / K0JX

Antonio Vernucci wrote:
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


Hi Roger,

what you say is interesting.

I have an original SX-101A manual, which I presume should be the same as the BAMA copy. Could you please tell me at which page you read that? In my manual I was unable to find any mention of the oscillator frequency.

I am pretty sure of the oscillator frequencies, as I measured them both with a frequency meter and with an oscilloscope (the oscillator waveform period on 20 meters is somewhat longer than on 40 meters, no question about that). And the strong 9.5 MHz phantoms frequencies are exactly what they should be with an halved oscillator frequency.

On the other hand my receiver was owned by a person who never put his hands in it, but even hypothesizing that someone did something in it, what could he have done to make the oscillator frequency exactly half of what one would expect to be, and on 10, 15 and 20 meters only? Halving the oscillator frequency would cause the dial scale to be no longer correct; matching is instead fairly good (with normal tolerances for a receiver of that kind).

73

Tony I0JX / K0JX


Hi Tony....

It's on page 15 under RF ALIGNMENT. It's the last sentence before the
actual proceedure. I have no idea what could be wrong with your receiver
but to use the second harmonic for mixing is very unusual. The only time
I've seen it used is when a manufacturer was trying to add a "VHF" band
to an early receiver and couldn't get reliable oscillation at the
fundamental frequency.

73, Roger

--
Remove tilde (~) to reply

Remember the USS Liberty (AGTR-5)
http://ussliberty.org/

Roger,

I carefully re-checked the manual and I found the text you mentioned.

It literally reads: "The 1st conversion oscillator operates at a =
frequency higher than the incoming signal by an amount equal to the =
first intermediate frequency of 1650 kc/s"

That sentence clearly states that the beat frequency is higher than that =
of the incoming RF signal but, in my opinion, it does not absolutely =
also imply that the beat frequency corresponds to the fundamental =
oscillator frequency.

In other words, it is true that the beat frequency is always higher than =
the incoming RF signal, but the beat frequency could be obtained by =
taking the second harmonic of the oscillator frequency. And the sentence =
would still be meaningful.

I am taking that interpretation as I am 101% sure that, on 10, 15 and 20 =
meters, the beat frequency is twice the fundamental oscillator =
frequency.

73

Tony, I0JX=20

Antonio Vernucci wrote:
Roger,

I carefully re-checked the manual and I found the text you mentioned.

It literally reads: "The 1st conversion oscillator operates at a frequency higher than the incoming signal by an amount equal to the first intermediate frequency of 1650 kc/s"

That sentence clearly states that the beat frequency is higher than that of the incoming RF signal but, in my opinion, it does not absolutely also imply that the beat frequency corresponds to the fundamental oscillator frequency.

In other words, it is true that the beat frequency is always higher than the incoming RF signal, but the beat frequency could be obtained by taking the second harmonic of the oscillator frequency. And the sentence would still be meaningful.

I am taking that interpretation as I am 101% sure that, on 10, 15 and 20 meters, the beat frequency is twice the fundamental oscillator frequency.

73

Tony, I0JX


Hi Tony....

The "beat" frequency is generally the difference (IF) frequency. In a
receiver the "beat frequency oscillator (BFO) is used to generate a
"beat" frequency in the audio range for CW reception. My copy of the
manual clearly states that the OSCILLATOR frequency is HIGHER than
the signal frequency on ALL bands.

73, Roger

--
Remove tilde (~) to reply

Remember the USS Liberty (AGTR-5)
http://ussliberty.org/

If no other fix comes along ,do this ;connect a series resonant circuit
to ground in the if path .use a small coil form and a variable cap
,tune it with grid dipper before you install it.. This circuit should
be a sharp trap and can easily be tuned to the interfering frequency to
remove the culprit..This may not be top notch engineering,but, it
always works for me..We used to call it a suckout trap... GL W4PQW

If no other fix comes along ,do this ;connect a series resonant =
circuit
to ground in the if path .use a small coil form and a variable cap
,tune it with grid dipper before you install it.. This circuit should
be a sharp trap and can easily be tuned to the interfering frequency =
to
remove the culprit..This may not be top notch engineering,but, it
always works for me..We used to call it a suckout trap... GL W4PQW

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. =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.

73

Tony, I0JX