[Elecraft] [K1] Unusual ATU Problem

[Don Wilhelm]

Steve,

Yes, that certainly sounds like strange behavior.  Your tuner and 
antenna do work on 30 meters because your 4 band board works OK with 
them, so they are not the likely cause of your failure.
I can guess that the 'light display/relay chatter' symptom is a result 
of the resettable fuse creating an effective power off/on cycle.
If you can follow my thinking below, you should have several things to 
check.  It would be best if you do the checks in the order I have listed 
if you can.
The power cycling brings up the next question of why the power draw 
would be sufficiently great on 30 meters to cause that behavior - from 
your description it is confined to 30 meters on the 2 band board.  Check 
the solder on the relays for possible solder bridges first.
If the soldering is OK, then I would first guess that the transmit 
frequency may not  be correct, and if the frequency is correct, then the 
low pass filter for 30 meters could be at fault.
Do you have any way to determine the frequency out of the Pre-mixer 
bandpass filter?  A frequency counter would be great, but a receiver 
that can tune to the vicinity of 15 MHz could do that check.
The Pre-Mixer output frequency should be around 15 MHz (the 18 or 18.1 
MHz crystal minus the VFO frequency of approximately 3.0 MHz). - You can 
do the exact math based on your exact VFO frequency.
If you do have a 15 MHz signal out of the pre-mixer bandpass, then check 
the signal out of the RF Bandpass filter to be certain it is in the 
vicinity of 10.1 MHz.

If the frequencies are OK, then check the Low Pass filter.  The best 
check is to sweep the low pass filter with an antenna analyzer - to do 
that, set the board relays to 30 meters and remove the board from the K1 
- terminate the low pass filter with a 51 ohm resistor temporarily 
soldered between P3 pins 1 and 3  and  solder (or otherwise connect) J2 
pin 1 to the center conductor of the analyzer output and J2 pin 3 to the 
'shield' of the analyzer.  You should find a low SWR at frequencies 
below 10.7 MHz but the SWR should increase rapidly above 12 MHz.
If the Low pass filter cutoff is not correct, check the toroids - an 
extra turn will result in a cutoff frequency in the vicinity of 9.5 
MHz.  Recently I did find one 30/40 meter LP filter that was tuned too 
low even though the number of turns was correct - due to a pair of cores 
that were too high in permeability was my assumption, but removing one 
turn from each toroid made the filter tune correctly.

Good luck with it.

73,
Don W3FPR

Elecraft Reflector wrote:
> Hi Guys! I wonder if you can help with a bewildering problem please?
>
> I have a K1 with a 4 band board (40, 30, 20, 15m) and the internal ATU. All function perfectly and match to an inverted Vee cut for 30m. On 30m my analyser shows a Vswr of around 1.1-1.3.
>
> I have recently added a 2 band board for 80/30m with the same Elecraft ATU. The ATU matches 80m to the same antenna with no problems. However when I activate tune or key up with the 30m part of the board, strange things happen. The screen goes clear,  the following lights show in sequence: Attn light fashes - green RIT - red RIT - some relay chatter - Attn light - Display resumes. 
>
> If a power meter is installed in line with the antenna feed, the same sequence occurs and no power registers.  It gets stranger...!
>
> If I connect the K1 directly to a dummy load the ATU tunes up as normal. No problem.
>
> If I put a 1:1 or 2:1 balun in series with the antenna the problem occurs but if I put a 4:1 balun in series it works just fine.
>
> I have remelted every solder joint on the board and checked no components on the board are touching above or below. 
>
> Without the ATU the board provides 5W to the antenna on 30m easily.
>
> If I pop back the 4-band board and ATU combination, 30m works via the tuner with no problems at all.
>
> I am bewildered and perplexed. Any ideas would be much appreciated. Thanks Guys
>
> Steve - M0ECS
>   
>