[Elecraft] KX-1 20 Meter Deafness

[Kurt Pawlikowski]

Mike,

    While my pride as a builder says, "No way!" you are probably right 
and I'll probably have to rebuild that board. To paraphrase a quote: "We 
hates it Mr. Baggins..."

    Regards,

    kurtt

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

Mike wrote:
> Kurt,
>
> For what it's worth, when I built my KX-1 I had very similar problems.  I wound up sending a pic of my LPF board to Don, who spotted the slightest hint of enamel insulation in one of the toroid solder joints.  I had to look at it 4 times before I could even see it.  Anyway, I wound up pretty much rebuilding that board and it was fine after that.  It's *very* finicky.
>
> --
> 73,
> Mike, KC0KBC
>
>  -------------- Original message ----------------------
> From: Kurt Pawlikowski <kurtt at pinrod.com>
>   
>> Don,
>>
>>     I'll check the LPF board closely.
>>
>>     As far as whether the signal increase, I believe it does. Since, 
>> when I touch it, signals I an hearing on my other receiver become 
>> apparent in the KX-1 also. And, I believe the XG-2 signal is increasing 
>> (only by ear). I say that because the increase is very noticeable: From, 
>> "Is it there?" to "I have to turn it down." Which is quite a jump 
>> (probably 9dB).
>>
>>     Anyway, I'll look it over more closely (maybe rebuild that board) 
>> and report back. Thanks.
>>
>>     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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