[Elecraft] KX-1 20 Meter Deafness
Don Wilhelm
w3fpr at embarqmail.com
Thu May 22 08:57:58 EDT 2008
Kurtt,
If you suspect the KXB3080 board strongly enough, disconnect one end of
the A, B and C wires to that board and it will be removed from the front
end circuits. It is easy to remove the A and B wires from the KXB3080
board (solder them back on the top of the board). The C wire is the
hardest to remove - but if you have a de-soldering gun, you can suck the
solder from both ends of the wire and pull it straight out - to replace,
just put a long wire through both holes, solder and clip the ends.
Do not remove T2 and the board capacitors added with the KXB3080 - those
should tune to 20 and 40 with the KXB3080 removed, but you will have to
re-peak the trimmers to compensate for the stray capacitance on the
KXB3080 board and the wires.
73,
Don W3FPR
Kurt Pawlikowski wrote:
> Don,
>
> I suspected that. At any rate, I've either blown something else
> (seems 40 "almost" worked before I started troubleshooting!) or more
> than that one component was damaged. Gonna have to maybe mess with the
> LXB3030 with it's SMT stuff. I'm thinking that if that's damaged, its
> the most expensive single part of the 3080 kit! Of course, the more I
> think about it, the more it seems it'll be at least part of the
> remaining issues...
>
> Regards,
>
> kurtt
>
> Kurt Pawlikowski, AKA WB9FMC
> The Pinrod Corporation
> kurtt at pinrod.com
> (773) 284-9500
> http://pinrod.com
>
> Don Wilhelm wrote:
>> 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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>>>
>>
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