No, what I mean is that the carrier insertion point, instead of being -25dB
down on the I.F. passband slope shifts to -35dB down on the slope. If you
play with a receiver that has passband tuning, the description becomes
apparent. I will describe the sound when the unit
malfunctions.....................the noise from the receiver becomes very
high pitched and voices become inaudible. The reason for this is that as the
BFO signal is moved out of the I.F. passband, the resultant audio is in the
supersonic region. Because of the low-pass filtering that is prevalent in
communications receiver designs, these high frequencies are bypassed to
ground, resulting in no apparent received audio.
Evidently, this failure mode is pretty rare, so it is pretty unlikely that
you will experience this condition with your receiver.
I hope this helps.

Pete

"Lucky" wrote in message
...

"Pete KE9OA" wrote in message
...
The folks at Lowe UK were nice enought to steer me in the right direction
with my carrier injection problem. Any of you Lowe folks, take note!
Apparently, Q4, the carrier generator (MC14569) is being run near its
design maximum. Out of 10,000 units, I was told that 12 of them have
failed because of this chip.
I let the receiver run for about 15 minutes and the carrier injection
problem showed up in the form of the BFO frequency being drastically
shifted. I cooled the chip and normal operation of the receiver resumed.
After 2 more minutes when the chip heated up again, the problem surfaced
again. I cooled the chip once more, and once more, the receiver resumed
normal operation.
The Digi-Key part number is: MC14569BCPOS-ND They have 1743 of them in
stock at a price of $2.47 if you order less than 25 pieces.
This receiver was a stumper, but since it is only a collection of parts,
it was inevitable that would eventually get fixed. Now, if only Radio
Shack has that part in
stock............................................. ..........

Pete



Can you explain this problem a little more? I did notice that sometimes
after I get a lock on a signal, and move out of range a little and you get
that howl, I have to move the dial quite a bit around to get another lock.
But, it then locks well below the frequency it locked at before.

Is this what you mean?

Lucky