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

[Don Wilhelm]

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
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