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K1 Receiver Sensitivity Issue.

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Les Garwood

K1 Receiver Sensitivity Issue.

Dear Fellows,

I Bought a K1 kit at a ham fest several years ago (SN 02197) and recently
finished the receiver section. Although audio is strong, as evidenced by
the hiss, I have nearly no signal on all 4 bands.
I can pump strong rf into it and hear a good side tone/bfo but not
strongly. Once, I heard a very faint CW station that was loud on my big
rig. But no others.
From the best of my repeated testings, all voltages and resistances
provided in the manual match. I have not built an rf probe for my DMM yet
but will. However, I also used the signal generator kit from Elecraft
(the KXGI?). It is only weakly audible too, and only on the 50 microvolt
setting. The AGC setting has no effect. The attenuator kills the weak
probe signal when on.
One post I found after scouring the Net spoke of a very similar problem
that turned out to be a bad 2N7000, in the A Preamp stage, but I can't see
how that would affect signal sensitivity, only audio gain.
I also put a scope on pin one and pin 4 of U1, the Receiver Mixer. The
relative voltage was 3x higher on pin 1 than on pin 4. I would at least
have expected gain instead.

Any comments appreciated.

73
Les
KE7SLX
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Don Wilhelm-4

Re: K1 Receiver Sensitivity Issue.

Les,

Yes, the NE612 should show plenty of gain. When it does not, the usual
reason is little or no oscillator signal to pin 6.

The Pre-mixer Bandpass filter must be aligned before you will get much
of a signal at U1 pin 6.

Since you have a 'scope (hopefully with a 10X probe), I will give you an
alternate method of tuning the Pre-Mixer Bandpass filter.

Since you have the 4 band board, you must follow the proper band order -
adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust
30 meters before 40 meters.
Make a check before starting - align all the slots in the trimmer
capacitors parallel with the long edge of the band board. Then check
the activity of the crystal for each band - put your probe on band board
P1 pin 4 and not the amplitude of the signal as you switch through the
bands - you should have greater than 200 mV peak to peak. The position
of the trimmer slots when tuned should be no more than 30 degrees from
the center position if your toroids are correct.

Then switch to 15 (or 17) meters, and with your probe on P1 pin 6,
adjust the Pre-Mixer trimmer caps for 15 meters for the maximum
amplitude. Switch to 30 meters and do the same for that bands
trimmers. Do the same for 20 meters and 40 meters. You should be able
to get 200 mV peak to peak there on all bands.
Remember that your 'scope probe will load the Pre-Mix filter a bit, so
the trimmers to the right of the filter will not be at their optimum
setting, but it will be enough for receive - you will set the optimum
position when you adjust for transmit.

You should check to see that the Pre-Mix signal is getting to U1 pin 6 -
if it is not, suspect the coax link on the bottom of the board between
J9 and J10.

Once you have a good signal at U1 pin 6, you should see that the output
at pin 4 is much greater than the input at pin 1.

73,
Don W3FPR

On 8/18/2014 5:20 PM, Les Garwood wrote:

> Dear Fellows,
>
> I Bought a K1 kit at a ham fest several years ago (SN 02197) and recently
> finished the receiver section. Although audio is strong, as evidenced by
> the hiss, I have nearly no signal on all 4 bands.
> I can pump strong rf into it and hear a good side tone/bfo but not
> strongly. Once, I heard a very faint CW station that was loud on my big
> rig. But no others.
> >From the best of my repeated testings, all voltages and resistances
> provided in the manual match. I have not built an rf probe for my DMM yet
> but will. However, I also used the signal generator kit from Elecraft
> (the KXGI?). It is only weakly audible too, and only on the 50 microvolt
> setting. The AGC setting has no effect. The attenuator kills the weak
> probe signal when on.
> One post I found after scouring the Net spoke of a very similar problem
> that turned out to be a bad 2N7000, in the A Preamp stage, but I can't see
> how that would affect signal sensitivity, only audio gain.
> I also put a scope on pin one and pin 4 of U1, the Receiver Mixer. The
> relative voltage was 3x higher on pin 1 than on pin 4. I would at least
> have expected gain instead.
>
>

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Message delivered to [hidden email]

Les Garwood

Re: K1 Receiver Sensitivity Issue.

Hi Don,

Extremely helpful and encouraging; thanks. Actually, I was able to get
the trimmers set pretty well, i think, using a strong signal source. But I
will make the measurements you recommended.
Right now, I suspect either low VFO output or something is pulling down the
gain of U1.

Les
On Aug 18, 2014 3:00 PM, "Don Wilhelm" <[hidden email]> wrote:

> Les,
>
> Yes, the NE612 should show plenty of gain. When it does not, the usual
> reason is little or no oscillator signal to pin 6.
>
> The Pre-mixer Bandpass filter must be aligned before you will get much of
> a signal at U1 pin 6.
>
> Since you have a 'scope (hopefully with a 10X probe), I will give you an
> alternate method of tuning the Pre-Mixer Bandpass filter.
>
> Since you have the 4 band board, you must follow the proper band order -
> adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust 30
> meters before 40 meters.
> Make a check before starting - align all the slots in the trimmer
> capacitors parallel with the long edge of the band board. Then check the
> activity of the crystal for each band - put your probe on band board P1 pin
> 4 and not the amplitude of the signal as you switch through the bands - you
> should have greater than 200 mV peak to peak. The position of the trimmer
> slots when tuned should be no more than 30 degrees from the center position
> if your toroids are correct.
>
> Then switch to 15 (or 17) meters, and with your probe on P1 pin 6, adjust
> the Pre-Mixer trimmer caps for 15 meters for the maximum amplitude. Switch
> to 30 meters and do the same for that bands trimmers. Do the same for 20
> meters and 40 meters. You should be able to get 200 mV peak to peak there
> on all bands.
> Remember that your 'scope probe will load the Pre-Mix filter a bit, so the
> trimmers to the right of the filter will not be at their optimum setting,
> but it will be enough for receive - you will set the optimum position when
> you adjust for transmit.
>
> You should check to see that the Pre-Mix signal is getting to U1 pin 6 -
> if it is not, suspect the coax link on the bottom of the board between J9
> and J10.
>
> Once you have a good signal at U1 pin 6, you should see that the output at
> pin 4 is much greater than the input at pin 1.
>
> 73,
> Don W3FPR
>
> On 8/18/2014 5:20 PM, Les Garwood wrote:
>
>> Dear Fellows,
>>
>> I Bought a K1 kit at a ham fest several years ago (SN 02197) and recently
>> finished the receiver section. Although audio is strong, as evidenced by
>> the hiss, I have nearly no signal on all 4 bands.
>> I can pump strong rf into it and hear a good side tone/bfo but not
>> strongly. Once, I heard a very faint CW station that was loud on my big
>> rig. But no others.
>> >From the best of my repeated testings, all voltages and resistances
>> provided in the manual match. I have not built an rf probe for my DMM yet
>> but will. However, I also used the signal generator kit from Elecraft
>> (the KXGI?). It is only weakly audible too, and only on the 50 microvolt
>> setting. The AGC setting has no effect. The attenuator kills the weak
>> probe signal when on.
>> One post I found after scouring the Net spoke of a very similar problem
>> that turned out to be a bad 2N7000, in the A Preamp stage, but I can't
>> see
>> how that would affect signal sensitivity, only audio gain.
>> I also put a scope on pin one and pin 4 of U1, the Receiver Mixer. The
>> relative voltage was 3x higher on pin 1 than on pin 4. I would at least
>> have expected gain instead.
>>
>>
>>
>

Don Wilhelm-4

Re: K1 Receiver Sensitivity Issue.

Les,

If you can get at least 200 mV peak to peak out of the Pre-Mixer
bandpass, the VFO level is OK.
The VFO and band module xtal oscillator are mixed in U7 and the output
of that mixer (after the bandpass filter) is applied to U1 pin 6.

If you find you need to check for loading of the U1 output, lift one
lead of C22 to isolate it.

73,
Don W3FPR

On 8/18/2014 6:08 PM, Les Garwood wrote:

> Hi Don,
>
> Extremely helpful and encouraging; thanks. Actually, I was able to get
> the trimmers set pretty well, i think, using a strong signal source. But I
> will make the measurements you recommended.
> Right now, I suspect either low VFO output or something is pulling down the
> gain of U1.
>
> Les
> On Aug 18, 2014 3:00 PM, "Don Wilhelm" <[hidden email]> wrote:
>
>> Les,
>>
>> Yes, the NE612 should show plenty of gain. When it does not, the usual
>> reason is little or no oscillator signal to pin 6.
>>
>> The Pre-mixer Bandpass filter must be aligned before you will get much of
>> a signal at U1 pin 6.
>>
>> Since you have a 'scope (hopefully with a 10X probe), I will give you an
>> alternate method of tuning the Pre-Mixer Bandpass filter.
>>
>> Since you have the 4 band board, you must follow the proper band order -
>> adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust 30
>> meters before 40 meters.
>> Make a check before starting - align all the slots in the trimmer
>> capacitors parallel with the long edge of the band board. Then check the
>> activity of the crystal for each band - put your probe on band board P1 pin
>> 4 and not the amplitude of the signal as you switch through the bands - you
>> should have greater than 200 mV peak to peak. The position of the trimmer
>> slots when tuned should be no more than 30 degrees from the center position
>> if your toroids are correct.
>>
>> Then switch to 15 (or 17) meters, and with your probe on P1 pin 6, adjust
>> the Pre-Mixer trimmer caps for 15 meters for the maximum amplitude. Switch
>> to 30 meters and do the same for that bands trimmers. Do the same for 20
>> meters and 40 meters. You should be able to get 200 mV peak to peak there
>> on all bands.
>> Remember that your 'scope probe will load the Pre-Mix filter a bit, so the
>> trimmers to the right of the filter will not be at their optimum setting,
>> but it will be enough for receive - you will set the optimum position when
>> you adjust for transmit.
>>
>> You should check to see that the Pre-Mix signal is getting to U1 pin 6 -
>> if it is not, suspect the coax link on the bottom of the board between J9
>> and J10.
>>
>> Once you have a good signal at U1 pin 6, you should see that the output at
>> pin 4 is much greater than the input at pin 1.
>>
>> 73,
>> Don W3FPR
>>
>>

Les Garwood

Re: K1 Receiver Sensitivity Issue.

Hi Don,

Success!!!
I mostly followed your advice--I say mostly because I got diverted when I
found a clue. I would still be searching without your insights and
expertise, however.

I was getting about 150 mv out of pin 4 of u7. I traced it to pins 1and 2
of J6, which was still hot on the scope through the secondary winding of T1
ON THE FILTER BOARD but was dead upon arrival at pin 6 on the return leg.
This sent me on a merry chase of testing all the relay solenoids for
continuity, and their contact leads. They all checked good so then I leapt
at the conclusion that the controller IC was at fault. I tried resetting
it to factory default but no apparent change resulted.
So, I went back to the scope and finally found the exact dead end: C15 was
wrongly mounted. Somehow, I misread the silkscreen hole indicator, I'm
embarrassed to say. Anyway, I resoldered it in the right holes
and, instantly, robust CW screamed at me. I'm thrilled and humbled.

Thanks again, Don

73

Les
KE7SLX

On Monday, August 18, 2014, Don Wilhelm <[hidden email]> wrote:

> Les,
>
> If you can get at least 200 mV peak to peak out of the Pre-Mixer bandpass,
> the VFO level is OK.
> The VFO and band module xtal oscillator are mixed in U7 and the output of
> that mixer (after the bandpass filter) is applied to U1 pin 6.
>
> If you find you need to check for loading of the U1 output, lift one lead
> of C22 to isolate it.
>
> 73,
> Don W3FPR
>
> On 8/18/2014 6:08 PM, Les Garwood wrote:
>
>> Hi Don,
>>
>> Extremely helpful and encouraging; thanks. Actually, I was able to get
>> the trimmers set pretty well, i think, using a strong signal source. But
>> I
>> will make the measurements you recommended.
>> Right now, I suspect either low VFO output or something is pulling down
>> the
>> gain of U1.
>>
>> Les
>> On Aug 18, 2014 3:00 PM, "Don Wilhelm" <[hidden email]> wrote:
>>
>> Les,
>>>
>>> Yes, the NE612 should show plenty of gain. When it does not, the usual
>>> reason is little or no oscillator signal to pin 6.
>>>
>>> The Pre-mixer Bandpass filter must be aligned before you will get much of
>>> a signal at U1 pin 6.
>>>
>>> Since you have a 'scope (hopefully with a 10X probe), I will give you an
>>> alternate method of tuning the Pre-Mixer Bandpass filter.
>>>
>>> Since you have the 4 band board, you must follow the proper band order -
>>> adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust
>>> 30
>>> meters before 40 meters.
>>> Make a check before starting - align all the slots in the trimmer
>>> capacitors parallel with the long edge of the band board. Then check the
>>> activity of the crystal for each band - put your probe on band board P1
>>> pin
>>> 4 and not the amplitude of the signal as you switch through the bands -
>>> you
>>> should have greater than 200 mV peak to peak. The position of the
>>> trimmer
>>> slots when tuned should be no more than 30 degrees from the center
>>> position
>>> if your toroids are correct.
>>>
>>> Then switch to 15 (or 17) meters, and with your probe on P1 pin 6, adjust
>>> the Pre-Mixer trimmer caps for 15 meters for the maximum amplitude.
>>> Switch
>>> to 30 meters and do the same for that bands trimmers. Do the same for 20
>>> meters and 40 meters. You should be able to get 200 mV peak to peak
>>> there
>>> on all bands.
>>> Remember that your 'scope probe will load the Pre-Mix filter a bit, so
>>> the
>>> trimmers to the right of the filter will not be at their optimum setting,
>>> but it will be enough for receive - you will set the optimum position
>>> when
>>> you adjust for transmit.
>>>
>>> You should check to see that the Pre-Mix signal is getting to U1 pin 6 -
>>> if it is not, suspect the coax link on the bottom of the board between J9
>>> and J10.
>>>
>>> Once you have a good signal at U1 pin 6, you should see that the output
>>> at
>>> pin 4 is much greater than the input at pin 1.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>>
>>>
>