http://elecraft.85.s1.nabble.com/KPA-1500-ATU-not-working-well-tp7642239p7642267.html
OK, note my qualifier, "If". If there are other detrimental issues with greater
intrinsic performance of the transistors, although as I have reported elsewhere
> I have found that if the KPA1500 is feeding a largish SWR (like 1.5:1 as you
> suggest) then the drive power required to maintain a constant output will vary
> significantly as you tune across a band. This means you have to keep adjusting
> the power control within a single band. This appears not to occur if the SWR
> is 1.1:1 or better.
>
> I don't know, but I would guess a solid state untuned amplifier efficiency is
> better into a 1:1 SWR than a 1:5:1. This could lead to the dreaded more fan
> noise.
>
> By the way by suggesting 1.0:1. I did not mean exactly
> 1.0000000000000000000:1. I tired to infer 1 digit resolution/accuracy.
>
> - Paul KW7Y
>
>
> At 11:11 AM 6/22/2018, Wes Stewart wrote:
>> I do not, and probably never will, have a KPA1500. I do have a KPA500 and
>> KAT500 so I think I can comment. In my opinion, the function of these
>> tuners is to provide a match into which the amp can deliver full power. If
>> 1.5:1 does this, then that's good enough in my book. Furthermore, a better
>> match might entail higher tuner losses. So why worry about it? Another
>> thing; a 1.0:1 SWR infers infinite return loss. To measure infinite return
>> loss, you need a directional coupler with infinite directivity or some
>> mathematical correction derived from very well known calibration standards
>> and no other errors, So maybe you say, 1.0:1 can't be measured (you would
>> be correct), let's shoot for 1.22:1.  That's a return loss of ~20 dB. Now
>> I have no idea of what the directivity of the coupler is in the KAT500 or
>> KPA1500 but considering it has to work from 1.8 to 54 MHz and to keep the
>> numbers easy, 20 dB wouldn't be unreasonable. (Note: I'm only considering the
>> directivity error, there are several others, internal mismatches, frequency
>> tracking, detector non-linearities, etc.) If we measure a load with 20 dB RL
>> using a directional coupler with 20 dB directivity the answer can be anywhere
>> between infinity to 14 dB. (Full cancellation of the two reflection
>> coefficients to the sum of the reflection coefficients)Â In SWR terms, a
>> 1.22:1 load can measure anywhere between 1.0:1 and 1.5:1. A "perfect" load
>> will measure 1.22:1. Folks, these things aren't laboratory instruments and
>> until Elecraft builds in vector network analyzers with full error correction
>> this is what we get. Wes N7WS On 6/21/2018 11:17 PM, Paul Baldock wrote: >
>> 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 1.4:1Â 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
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