[Elecraft] Re: KX-1 20 Meter Deafness

Wed May 21 11:27:25 EDT 2008

Don,

    Thanks for the tips. Here are some comments...

    XG-1: Well, when I hook it up to my vintage Yaesu 757, besides 
showing signal strength difference (S-0 and S-9 respectively), the tone 
audio volume is very noticeable. Also, on 40 and 80 with the KX-1, I can 
hear a marked difference between the two settings. When I say that there 
is no difference, there isn't even a "switch-click" between the two 
settings. Very, very weird. Also, the relative position of the XG-1 to 
the KX-1 seems to have no affect (which, if the signal was somehow being 
directly coupled, bypassing the antenna lead, I would expect). Also, I 
expect that the signal at 50 uv should be blasting in. It only sounds 
like a moderate level at this time.

    Touching pre-mixer: I did notice that once my "crossed" wires on the 
LFP board were fixed, I could get a "noise only" increase on at least 
one other band (don't remember which) when touching the area, but on 20, 
it was a true signal volume increase (confirmed with the PC's band scope 
on the audio).

    I'll dig up the old yellow core toroids and put them in for now.

    Pre-3080: Since everything was built at the same time, its existence 
as a "straight" KX-1 was a very short time and some months ago. I can't 
remember most of yesterday, so who knows? {'-)

    It may come down to actually measuring components or finding someone 
willing to take a look at it for me (maybe who already has the proper 
test equipment or has a known good KX-1 for a side-by-side comparison?). 
Anyway, it's all I can do for right now. Thanks again for your help.

    Regards,

    kurtt

    Kurt Pawlikowski, AKA WB9FMC
    The Pinrod Corporation
    kurtt at pinrod.com
    (773) 284-9500
    http://pinrod.com

Don Wilhelm wrote:
> Kurtt,
>
> Forget the 'scope, the levels from the XG2 are too small to drive a 
> 'scope.  The levels will be even less than the output of the signal 
> generator.
> Do you have a crystal around that is somewhere in the 40 meter or 20 
> meter band?  Plus a few parts in your junkbox?  If so, you can build 
> up the crystal oscillator that is shown in the Troubleshooting section 
> of the K2 manual (download the manual from Elecraft website).  And if 
> the oscilloscope is old, you probably do not have a 10X probe for it, 
> so also build the RF Probe.
> At this point, I don't know what else to tell you - you will need some 
> basic test equipment to go much further.  You can do some more visual 
> investigation.
>
> Make certain the PC Trace cut is really cut.  Be certain the added 
> wire is correct and that there is no contact of that wire with the end 
> of L6 nor point 'A'.  Check and recheck the soldering of all the 
> capacitors in the LPF area as well as C1.
>
> How strong is the actual signal from the XG2?  Could it actually be 
> that the KX1 AGC is making the signals sound about equal?  The fact 
> that they sound the same may not be a problem at all.
>
> You will be better off putting the yellow core L1 and L2 in place for 
> the time being.
> One thing that you can check with the 'scope is the Local Oscillator 
> injection to the mixer.  You must have at least 200 mV peak to peak at 
> U6 pin 6 for the mixer to work correctly.
>
> Remember that touching a probe to the area of T2 will always pick up a 
> lot of noise which results in an apparent increase in the signal being 
> picked up, but the actual signal strength usually does not increase.
>
> Did this KX1 work well before you added the KXB3080?  If not, then you 
> may have a problem somewhere other than just the front end of the 
> receiver.
>
> 73,
> Don W3FPR
>
>
>
> Kurt Pawlikowski wrote:
>> Don,
>>
>>    Still frustrated...
>>
>>    I removed the LPF board and removed both L1 and L2. I then "hard 
>> wired" them in, just the way they would be with the board and the 
>> relay "off." This had no affect on the symptoms: The XG-2 signal 
>> still seems to be being coupled direct to the board (1 uv 50 uv 
>> switch does not change tone volume). The next step is to drag down my 
>> boat anchor oscilloscope and take some measurements. I expect the 
>> signal level before T2 to be too small for my old equipment to see (I 
>> don't think it'll do micro volts - I'll have to check though.). 
>> Anyway, with the XG-2 on 20 meters, what signal strength (p-p) should 
>> I be seeing at different points of the circuit? I'm thinking of 
>> several points between the antenna up to the mixer with both the 50 
>> and 1 uv output (I may have a hard time measuring the 50 uv level, 
>> much less the 1!). Any other ideas are welcome...
>>
>>    Regards,
>>
>>    kurtt
>>
>>    Kurt Pawlikowski, AKA WB9FMC
>>    The Pinrod Corporation
>>    kurtt at pinrod.com
>>    (773) 284-9500
>>    http://pinrod.com
>>
>> Don Wilhelm wrote:
>>> Kurt,
>>>
>>> From all you have said, I would believe that the problem is in the 
>>> KXB3080 low pass filter.
>>> While I agree that your continuity test indicates no apparent 
>>> problem with the toroid lead tinning, check all the connections to 
>>> be certain there is a bit of solder on both sides of the board - if 
>>> not, view that connection with suspicion.
>>>
>>> Make certain there is no contact with the green wire from L2 to the 
>>> lower connection of the red wire.  The green wire must wrap around 
>>> to the back side of the LPF board and can inadvertently contact the 
>>> #4 termination of the wire for the red winding.
>>>
>>> The best LPF testing is visual - look for any suspicious solder 
>>> connections.  Yes, you will see a 17 MHz cutoff on the LPF if you 
>>> measure it without regard to disconnecting it from the rest of the 
>>> circuit and failing to properly terminate the filter (it is not 50 
>>> ohms at the PA transistor side, but I have not ever calculated the 
>>> proper termination).
>>>
>>> Perhaps it is helpful if I tell you that the green winding is the 
>>> only active portion on 40, 30 and 20 meters.  The red winding is 
>>> used for 80 meters and SWB band below about 6 MHz only.
>>>
>>> Caution:  The sensitivity of the KX1 is not as great on 20 meters as 
>>> it is on 30 or 40 meters.  Bringing a finger (or antenna) close to 
>>> T2 or many of the receiver tuned circuits after the LPF  will 
>>> normally result in an increase in receiver total output, but that is 
>>> actually an increase in broadband noise - under careful measurement 
>>> conditions, the desired signal strength will not increase even 
>>> though the overall noise level does.  Spectrogram will show that is 
>>> true.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> Kurt Pawlikowski wrote:
>>>> Hi,
>>>>
>>>>    First, thanks for reading. Hopefully, it won't be boring for those
>>>> lucky K3 guys and gals...
>>>>
>>>>    CONFIGURATION
>>>>
>>>>    KX-1, 3080 upgrade. ATU currently removed and antenna jumper
>>>> installed for testing.Using XG-2 as a signal source. I have confirmed
>>>> the XG-2 seems to be working about as expected with another receiver
>>>> (about S-10 at 50uv and S-0 (but still in the speakers) at 1uv).
>>>>
>>>>    SYMPTOM
>>>>
>>>>    With normal operation, receive levels appear normal on 80 and 40 (I
>>>> can make contacts), but the XG2 is not peaking the KX-1's meter (I 
>>>> used
>>>> the XG-2 to calibrate the meter). 20 meters has always seemed deaf to
>>>> me. I don't remember how well the XG-2 was received on 20 when I
>>>> calibrated it. Here's the real "kicker": On 20 meters, with the XG-2
>>>> attached, I hear *no* volume difference between 50 and 1uv (which 
>>>> means
>>>> the KX-1's receiver is picking up the signal by proximity, not through
>>>> the antenna connection). If I touch the RX antenna connection almost
>>>> anywhere between the low-pass filter and the input of the Rx Mixer 
>>>> (U6,
>>>> pin 1), 20 meters comes way up (from nothing to receiving moderately
>>>> weak signals and noise). Touching the RX antenna line on 80 and 40
>>>> appears to have little or no affect. Output power on 20 meters does 
>>>> not
>>>> register full power, but I'm not sure if this is a calibration problem
>>>> as I don't have an accurate power meter. Also, when I couple a grid 
>>>> dip
>>>> meter into the RX, when tuned to 30 or 20 meters, I get a marked "dip"
>>>> just at about 17 MHz.
>>>>
>>>
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