OK, note my qualifier, "If". If there are other detrimental issues with greater
load mismatch then they might need to be addressed. Unfortunately, Elecraft
doesn't specify a load requirement for rated output. Gain ripple that you
observe is possibly a reflection (no pun intended) of the LPFs rather than the
intrinsic performance of the transistors, although as I have reported elsewhere
K3S IMD is frequency sensitive, but not overly so within a band.
One point I would like to make is that guys who wring their hands because the
SWR meters on the K3, KAT500 and KPAs all read differently should lighten up.
There are reasons why this can be without there being product defects.
Wes N7WS
.On 6/22/2018 12:36 PM, Paul Baldock wrote:
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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