[Elecraft] KPA1500 delivery

[Bill Johnson]

Update:  ordered 4/24 has been shipping today.  From everything I have read and know about the amp, can't wait to wire into 240v and get on the air.  Need more power!!!@  Tired of not making marginal contacts on all bands to 6m. QRPpp is my preferred mode when condx are there.

72 & 73,
Bill
K9YEQ
FT'er for K2, KX1, KX3, KXPA100,  KAT500, W2, etc. 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of Paul Baldock
Sent: Friday, June 22, 2018 2:36 PM
To: Wes Stewart <wes_n7ws at triconet.org>; elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA-1500 ATU not working well

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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