[Elecraft] KX-1 20 Meter Deafness

[Don Wilhelm]

Kurtt,

The KX1 should receive just fine with Q7 removed.  Any other receiver 
troubles are a different problem.

73,
Don W3FPR

Kurt Pawlikowski wrote:
> Don, Et Al,
>
>    Looks like the unit may have had a static discharge through the 
> antenna. Q7, part of the receiver mute circuit was blown. I'll order 
> one tomorrow and go from there. Once I removed this component, 20 
> meters seems to be up there where it should be. Nothing else seems to 
> be receiving correctly right now, but I'll attribute that to either 
> this (now missing) part or some issue I accidentally introduced while 
> troubleshooting. We'll see!
>
>    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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