[Elecraft] KPA-1500 ATU not working well

[Paul Baldock]

First let me say that other than some issues with 
the ATU, I am after a week of use, very happy with the KPA1500.

So here's the ATU issues:

I find that the ATU very rarely will learn a 
setting to get the SWR below 1.2:1 on any band. I 
can usually tweak it down to 1.0:1 using the 
Utility Program.  And yes, before anybody asks, I 
have ATU STOP TUNE and the ATU BYPASS set at 1.0:1.

On 6M into a perfect load (laboratory quality to 
8GHz) with the ATU bypassed, the internal SWR 
meter reads 1.4:1  I would have expected it to be 
1.0:1, but Elecraft tell me it is normal. So the 
ATU on 6M will have to tune out what is left when 
the 1.4:1 internal mismatch sees your external 
antenna mismatch. Maybe this is contributing to 
your problem. Try adding a quarter wave of coax, 
maybe it will achieve a better match. Fortunately 
my 6M antenna is flat enough that I can work CW, SSB and FT-8 in BYPASS.

For your interest, on 10M in to perfect load with 
ATU bypassed the internal SWR meter reads 1.2:1. Not 1.0:1.

Another issue I have with the ATU is that the 
internal frequency counter has 8KHz resolution 
which according to one of the Elecraft techs can 
lead to a 16KHz error in measurement. It appears 
that during "learning" that the ATU is based on 
the internal frequency counter measurement, not 
the frequency you transceiver sends to the 
KPA1500.This means that on the bands that have 
10KHz or 20KHz segments, you cannot be sure which 
segment you are using, and when you use the tuner 
it could be in a different segment. Being off by 
a segment could be a problem with a high Q antenna.

Apparently the counter originally had 1KHz 
resolution but was changed to fix some other 
problem. An Elecraft tech told me they currently 
have no plan to change it back to 1KHz. I am not 
suggesting that the tuner should change segments 
exactly on their edge. Clearly there has to be 
some hysteresis to stop hunting. 25% of a segment 
width might width be a good number to choose, but 
this would require the current frequency counter to have improved resolution.


- Paul  KW7Y

At 08:53 PM 6/21/2018, K9MA wrote:
>Dick, Have you tried manually adjusting the 
>ATU?  I haven't used mine on 6 meters, but on 
>other bands, no matter what I do, it sometimes 
>doesn't get a very good match automatically, and 
>I can do better manually.  On the other hand, 
>it may be that the L and C step sizes are just 
>too big to get a good match on 6. Or there could 
>actually be something wrong. If you have a good 
>50 MHz dummy load, try that with the ATU in. 73, 
>Scott K9MA On 6/21/2018 22:40, Dick via Elecraft 
>wrote: > I'm wondering if anyone else is having 
>problems with their KPA-1500 ATU on 
>6-meters?  My antenna is cut for 50.100 and has 
>a 2.2:1 SWR at the 50.313 FT-8 frequency.  The 
>very best the ATU will do is to lower the SWR 
>from 2.2:1 down to 2.0:1 which is almost no 
>improvement.  The 2.0 to 1 is with exciter 
>power, when I switch the KPA-1500 to operate 
>and transmit at 1,200 watts the SWR increases to 
>aprx. 2.2 to 1 and the KPA-1500 will fault and 
>trip off occassionally.  Hoping there's a fix 
>for this. >   > I'm using the latest KPA-1500 
>firmware. >   > Thanks, > Dick- K9OM >   >   > > 
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