Wes, so well put. The expectations expressed don't include a whole new set of variables when dealing with full power. The good thing: this list may help those challenged to get help to figure out their issues. I can't wait to get mine on the air!
72 & 73, Bill K9YEQ FT’er for K2, KX1, KX3, KXPA100, KAT500, W2, etc. -----Original Message----- From: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> On Behalf Of Wes Stewart Sent: Friday, June 22, 2018 3:45 PM To: Paul Baldock <p...@paulbaldock.com>; elecraft@mailman.qth.net Subject: Re: [Elecraft] KPA-1500 ATU not working well 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) 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 1.4:1 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 >> ______________________________________________________________ >> Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: >> http://mailman.qth.net/mmfaq.htm Post: >> mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net >> Please help support this email list: >> http://www.qsl.net/donate.html Message delivered to >> p...@paulbaldock.com > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to k9...@live.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
