[Elecraft] Re: the Yagi problem

[wayne burdick]

Ed,

A couple of other thoughts on this, assuming that no relays are 
switching as you vary power from 80-120 W (see previous e-mail).

We need to get an o'scope on your TX output at the time the SWR goes up 
to see if the PA is unstable. If it isn't, then perhaps the SWR bridge 
transformers are getting saturated, or there's RF getting into the SWR 
bridge op-amp.

If it's the PA going unstable, the next step is to have you put in the 
KANT3 module rather than the KAT3.

Wayne


On Sep 17, 2007, at 9:26 AM, Ed Muns wrote:

>> On your 100W+ SWR problem (going wild after having been
>> 1.0:1):  once this has occurred, doing a TUNE (not an ATU
>> TUNE), does reducing the power back below some threshold
>> restore the SWR, or does it remain high?
>
> The higher SWR is only at 115 and 120 watts.  No problem reducing 
> power and
> having the SWR return to 1.0:1, so I'm assuming there is something 
> still
> going on in the KPA3.  All measurements are done by using TUNE to read 
> the
> actual power and SWR.  (I did a TUNE at 5 and 50 watts on all bands 
> before
> redoing the measurements.)  Attached are updated tables of data for:
>
> 1.  50 ohm load, KAT3 bypassed.
> 2.  Antennas, KAT3 bypassed.
> 3.  Antennas, KAT3 tuned.
>
> It was at a power request of 120 watts and inflated SWR on 20 meters 
> that
> K6XX heard the problem with my signal.  At 100 watts, the problem went 
> away
> (as does the inflated SWR).  For FCS, maybe the firmware should limit 
> power
> to 100 watts, at least until the KPA3 can be fixed at the higher power
> levels?
>
> Ed
> <Power Output.xls>

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