Jon,
At first glance it might seem as though your problem may be simply that
there is too much AGC. Turn the AGC Threshold down to 3.6 volts as a
starter - but I seriously doubt this is the problem, so set the AGC
threshod down anyway as a starter just to get that out of the way.
The most significant item is your statement that you hear the signals
with a constant pitch. That tells me that you may have a PLL/VCO
problem and the VCO is not actually on the correct frequency. Check the
VCO frequency at the low end of each band against the chart at the lower
left corner of the Schematic Key sheet in Appendix B of the manual. To
check the VFO frequency, put the internal probe into TP1 and tune to the
low end of each band - then in the menu select CAL FCTR to read the VCO
frequency. If it differs from the chart by more than 0.040 KHz, you
have a VCO/PLL problem. Re-check the PLL range as a first response if
this is the case.
You could also have a situation where your CAL PLL run was not done
correctly - put the K2 bottom panel in place and re-run the CAL PLL routine.
If you have rework eliminators in place or have changed C71 to allow for
the K60XV installation, you must enter the secondary menu and set D19 to
Yes. Failure to do so will create the problem that you state on 40 meters.
If these things do not help, ask again, and prepare yourself for Receive
Signal Tracing as described in Appendix E of the K2 manual (build the
oscillator and the RF Probe).
73,
Don W3FPR
Jon Perelstein wrote:
I just finished building the K2 and am in process of checking it out.
All voltage tests, current tests, power tests, alignment tests and
alignment activities were completed successfully. I've been through
the receiver alignment twice just to make sure, and got good peaking
on each band.
I'm hitting various receive problems that are just strange and I'm
going to have a little trouble explaining some of them, so please bear
with me.
1. Receive sensitivity is not good. Using the same antenna, and with
AGC on:
o Without the pre-amp on, the K-2 is nowhere near as sensitive as my
K-1, nor is it as good as my FT-897 (but the K-1 is better than the
FT-897).
o With the pre-amp on, the K-2 is about as good as the FT-897, but
still not as good as the K-1.
The situation is better with AGC off, as good as or better than the
FT-897, but still not as good as the K-1.
It seems as if the AGC is having too much impact since I have to crank
the AF Gain almost all the way clockwise to get decent audio volume
with the AGC on (both headphones and speaker)?
2. On receive, stations are either there or not there.
In a correctly operating radio, as you tune across a station's signal,
the signal strength starts out lower and then picks up in strength and
volume as you reach the station's actual transmit frequency.
Furthermore, if two stations are near each other, you typically hear
both of them.
In this case, if I hear a signal, I hear it at the same volume as I
tune across the signal's bandwidth. The perceived signal strength
simply does not change. The S-Meter does change value, but not the
perceived signal strength in the headphones or speaker.
Along with this, there is no interference from adjacent signals. I'm
always hearing the strongest station and only the strongest station at
whatever spot that my VFO is tuned to. Any other stations are simply
not there, as if some sort of really good DSP has completely
eliminated all but the strongest station at that point in the VFO (and
I mean *completely* eliminated). As you tune across, you can hear the
specific point where one station stops being heard and a different one
starts being heard.
I do not have DSP -- this is a bare bones K-2 without noise blanker or
anything else. I have AGC turned off. The problem also appears with
AGC on. In addition, it appears in both VFO A and VFO B.
I have the squelch turned off.
I have checked, and I'm in filter 1 and I'm getting the correct
readings from aligning FIL1. When I go to FIL2, there's a similar
effect -- except that the bandwidth range across which I can hear the
signal is much smaller (to be expected with a tighter filter). At
FIL3 I can hear only the strongest of stations, and then across an
extremely narrow signal bandwidth. Finally, at FIL4 I cannot pick up
even the strongest signals.
3. As I tune across a CW station's signal, there is no change in
audio frequency.
In a correctly operating radio, as you tune across a CW signal, there
is a change in the audio frequency of the signal, until you're at
zero-beat, at which time the audio frequency is whatever you've set
your sidetone at.
In this case, once I hear a signal, I hear it at the same audio
frequency across the entire bandwidth of the signal for as long as I'm
hearing that signal (see problem 2 above).
The audio frequency at which I'm hearing the signal is not
particularly my sidetone frequency. It seems to be different for each
different station, but is the same for the same station. For example,
I'm hearing a station at 14.100. As I tune across his signal, the
audio on his signal is at about 800 Hz. As I tune past that (up), I
hear another station and I'm hearing the audio at something much
lower, like about 500 or 600 Hz. If I keep tuning across the dial,
I'll hear other stations, each of which may or may not have a
different audio frequency than 800Hz. However, if I go back to the
station at 14.100, I'll again hear him at about 800 Hz and not some
other frequency. I can hear this particular station from about 14.099
to about 14.101, and his audio frequency does not change as I tune the
2KHz range between .099 and .101
I get the same result with SSB signals. There is no change in the
audio, and thus most SSB signals are unintelligible because there is
no way to tune in on the station's actual transmission frequency.
Every so often, an SSB station is intelligible, and then no amount of
tuning across its bandwidth makes it unintelligible.
Note that I do not have the SSB module installed, and I'm not sure if
I'm supposed to be able to hear SSB in a bare-bones K-2 without the
SSB module installed (although it is my understanding that I should be
copy SSB).
*****
I've been through the manual twice and can't find any features that I
may have inadvertently turned on to get these results.
Any suggestions would be appreciated. Thanks in advance.
Jon
KB1QBZ
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