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KX1: 40M low power, 20 not working on transmit

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John Donovan

KX1: 40M low power, 20 not working on transmit

I just finished building my KX1 and the receiver works great. I get 2W
out on 40 but nothing measurable on 20. The odd thing is in receive on
the base of Q4 I get 2x the signal on 20 that I do on 40; OTOH when I go
into TUNE mode that signal ramps way up on 40 but remains insignificant
on 20; by the collector of Q5 it's barely there. I checked the voltages
on Q1/4/5/6 and they're OK, except that the source of Q1 is only 1.2V. I
checked solder joints and they all seem fine; ditto inductors, though T1
looks to be a tricky bit of work.

Any suggestions would be greatly appreciated. I'd hoped to take this rig
camping with me this Labor Day weekend, but it doesn't look like that's
going to happen.

73,
John K6YLG
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Don Wilhelm-4

Re: KX1: 40M low power, 20 not working on transmit

John,

Sorry that I could not help before the Labor Day weekend, but the Shelby
Hamfest called and I just arrived back home.

While the change on RF voltage on Q4's base between transmit and receive
may appear disconcerting, it may or may not be the problem. The DDS
operates 4913 kHz lower than 14 MHz during receive, or 4913 kHz higher
than the RX frequency when on 40 meters, while during TX, the DDS
frequency is shifted to the TX output frequency.

It is wise to check and double-check the 14 MHz Low Pass Filter
following the DDS for correct values and good soldering. L4. L5, C50.
C51, and C52.

1.2 volts on the source of Q1 is normal.

Once you have solved the lack of output from the DDS LPF on 20 meters,
you can move on to the PA LPF. Count the turns on L1 and L2 (count the
number of times the wire passes through the center of the core), and
check the capacitors for correct values.

73,
Don W3FPR

On 9/3/2011 12:19 PM, John Donovan wrote:

> I just finished building my KX1 and the receiver works great. I get 2W
> out on 40 but nothing measurable on 20. The odd thing is in receive on
> the base of Q4 I get 2x the signal on 20 that I do on 40; OTOH when I go
> into TUNE mode that signal ramps way up on 40 but remains insignificant
> on 20; by the collector of Q5 it's barely there. I checked the voltages
> on Q1/4/5/6 and they're OK, except that the source of Q1 is only 1.2V. I
> checked solder joints and they all seem fine; ditto inductors, though T1
> looks to be a tricky bit of work.
>
> Any suggestions would be greatly appreciated. I'd hoped to take this rig
> camping with me this Labor Day weekend, but it doesn't look like that's
> going to happen.
>
> 73,
> John K6YLG
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Help: http://mailman.qth.net/mmfaq.htm
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John Donovan

Re: KX1: 40M low power, 20 not working on transmit

Hey Don,

That fixed it, thanks!! I had the wrong value for C52--close, but no
cigar. Now to do final assembly, work a few contacts, then build the
antenna tuner. Happy, happy!

73,
John K6YLG

On 9/4/2011 4:19 PM, Don Wilhelm wrote:

> John,
>
> Sorry that I could not help before the Labor Day weekend, but the
> Shelby Hamfest called and I just arrived back home.
>
> While the change on RF voltage on Q4's base between transmit and
> receive may appear disconcerting, it may or may not be the problem.
> The DDS operates 4913 kHz lower than 14 MHz during receive, or 4913
> kHz higher than the RX frequency when on 40 meters, while during TX,
> the DDS frequency is shifted to the TX output frequency.
>
> It is wise to check and double-check the 14 MHz Low Pass Filter
> following the DDS for correct values and good soldering. L4. L5, C50.
> C51, and C52.
>
> 1.2 volts on the source of Q1 is normal.
>
> Once you have solved the lack of output from the DDS LPF on 20 meters,
> you can move on to the PA LPF. Count the turns on L1 and L2 (count
> the number of times the wire passes through the center of the core),
> and check the capacitors for correct values.
>
> 73,
> Don W3FPR
>
> On 9/3/2011 12:19 PM, John Donovan wrote:
>> I just finished building my KX1 and the receiver works great. I get 2W
>> out on 40 but nothing measurable on 20. The odd thing is in receive on
>> the base of Q4 I get 2x the signal on 20 that I do on 40; OTOH when I go
>> into TUNE mode that signal ramps way up on 40 but remains insignificant
>> on 20; by the collector of Q5 it's barely there. I checked the voltages
>> on Q1/4/5/6 and they're OK, except that the source of Q1 is only 1.2V. I
>> checked solder joints and they all seem fine; ditto inductors, though T1
>> looks to be a tricky bit of work.
>>
>> Any suggestions would be greatly appreciated. I'd hoped to take this rig
>> camping with me this Labor Day weekend, but it doesn't look like that's
>> going to happen.
>>
>> 73,
>> John K6YLG
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>