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-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> On Behalf Of Paul Baldock Sent: Friday, June 22, 2018 2:36 PM To: Wes Stewart <wes_n...@triconet.org>; elecraft@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) 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
