K2: Various Receive Problems

[jperelst]

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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[L. D. Ingram]

Jon,

I wonder if you are tuning at the fastest rate - at that rate the
signals would seem to jump in and out as you are describing and since
they would not be in the center of the filter passband most of the
time it might explaing the seeming lack of sensitivity.

Larry Ingram  AG4NN

At 11:06 AM 11/8/2008, you 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.
>

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[David Woolley (E.L)]

Jon Perelstein wrote:
>

> 1.  Receive sensitivity is not good.  Using the same antenna, and with
> AGC on:

The K2 is somewhat short on overall gain.  However that is not the same
as receiver sensitivity, which is related to noise, rather than gain.
Sensitivity is the minimum signal that will exceed the internally
generated noise.

>  
> 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)?

R1 adjusts the AGC threshold.
>  
>  
> 2. On receive, stations are either there or not there.
>  
See below.

> Along with this, there is no interference from adjacent signals.  I'm
> always hearing the strongest station and only the strongest station at

That's good. If there were a way of achieving that which wasn't being
used, it would be considered a fault.  There is no capture effect with
SSB, so the only way of achieving this is good selectivity and good IMD
performance.

> 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.

Note that FL1,2,3,4 are selections from a memory.  You need to set
sensible filter parameters for each of these.

> 3.  As I tune across a CW station's signal, there is no change in audio
> frequency.

Combined with (1), this indicates that the reference oscillator
frequency isn't being modified.  You should be able to confirm this by
using the frequency counter on it.

However, there is an explicit check for this during the assembly process
and the VFO calibration would fail if it wasn't working.  I don't know
what happens if you never run the calibration.

>  
> 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).

You do not need the SSB module to receive SSB, and, in fact, if you use
the standard SSB setup, FL3 and FL4 settings on SSB do not use the SSB
module for receive.


--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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[Don Wilhelm-4]

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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