Posted by
Dr. William J. Schmidt, II on
Jun 16, 2020; 2:41pm
URL: http://elecraft.85.s1.nabble.com/KPA1500-Operation-on-6-Meters-tp7662211p7662279.html
It may be more efficient for you to contact Rene (the KPA1500 support guy) at Elecraft and discuss this with him... ??? I doubt anyone in the forum has seen the schematics or was involved it its development to the point where they could help you.
-----Original Message-----
From:
[hidden email] [mailto:
[hidden email]] On Behalf Of Ed G
Sent: Tuesday, June 16, 2020 9:30 AM
To: Larry (K8UT) <
[hidden email]>;
[hidden email]
Subject: Re: [Elecraft] KPA1500 Operation on 6 Meters
So, summary question for the KPA1500 amp designers:
With 5 watts drive and the amp in STBY, the KPA1500 display reads the correct 1.3:1 SWR. When I switch the amp to OPER, SWR reads 2.5:1 with the same 5 watts drive. All hardware/cabling outside the KPA1500 remains the same for each case. Reminder that this anomaly is seen only on 6 meters; other bands are fine. BTW power out with 5 watts drive is about 150 watts, and internal KPA1500 tuner is bypassed.
What is different inside the KPA1500 as to how the SWR is sensed and displayed between STBY and OPER?
--Ed, N3CW—
Sent from Mail for Windows 10
From: Larry (K8UT)
Sent: Monday, June 15, 2020 9:33 PM
To:
[hidden email];
[hidden email]
Subject: Re[2]: [Elecraft] KPA1500 Operation on 6 Meters
Ed,
Your dummy load choices at 1500 watts range from expensive and good (Bird) to cheap and not-so-good. For example the MFJ-264 is listed as handling 1500 watts but if you read the fine print (the derating curve printed on its case ) you're limited to 8 seconds at 1500 watts. And each time you stress that dummy load its resistor value climbs by a few ohms.
Frustrated with the commercial options available, I built a dummy load using a huge heatsink from a salvage VHF transmitter and a series/parallel combination of four 50 ohm 250 watt resistors purchased on eBay.
https://www.ebay.com/itm/1PCS-Anaren-RFP-250-50RM-RFP250-50-RF-Power-Flanged-Resistors-250-Watts-50-ohm/133028134252?hash=item1ef9183d6c:g:uHQAAOSwyFhcvsvw-larry (K8UT)
------ Original Message ------
From: "Ed G" <
[hidden email]>
To: "Larry (K8UT)" <
[hidden email]>; "
[hidden email]" <
[hidden email]>
Sent: 2020-06-15 10:57:32 AM
Subject: RE: [Elecraft] KPA1500 Operation on 6 Meters
Hi Larry,
Yes, exact same problem is there with a known good dummy load in place of the Steppir yagi I normally use.
--Ed—
Sent from Mail for Windows 10
From: Larry (K8UT)
Sent: Monday, June 15, 2020 10:09 AM
To: Ed G;
[hidden email]
Subject: Re: [Elecraft] KPA1500 Operation on 6 Meters
Ed,
Not seeing that here. SWR value unchanged at 10, 20, 30, 35 watts of drive. Suggest you test into a dummy load to see if the problem goes away, which would suggest some issue with power level into the feedline or antenna.
-larry (K8UT)
------ Original Message ------
From: "Ed G" <
[hidden email]>
To: "
[hidden email]" <
[hidden email]>
Sent: 2020-06-15 9:48:55 AM
Subject: [Elecraft] KPA1500 Operation on 6 Meters
>Folks,
> I am trying to understand some odd KPA1500 operation on 6 meters. When setting the power output of my K3 to give varying amounts of drive to the KPA1500, I am seeing SWR as displayed on the KPA1500 changing by a significant amount depending on the drive level. This is with the KPA1500 tuner bypassed. An LP-100A on the output of the KPA1500 is also used and displays the correct low SWR at all drive levels that I would expect to be seeing on the KPA1500 display.
> For example, with 5 watts drive from the K3, I see 1.3 SWR on the LP-100, and 2.5:1 on the KPA1500 display. As I increase drive, the KPA1500 SWR display goes down proportionally, until I get to about 40 watts drive. At the 40 watt drive level, I am seeing a nice healthy 1600 watts output, and both the LP-100 and the KPA1500 are showing the same 1.3 SWR. 15 watts drive shows 1.3 on the LP100 and 2.0:1 on the KPA1500 display. So I am not sure why the SWR sensing and display in the KPA1500 is behaving this way? I do not see this oddity on any other bands.
> I might also add that attempting to get the KPA1500 internal tuner to bring down the high SWR as seen on the KPA1500 results in a drop in SWR displayed on the KPA1500 to where SWR almost equals that on the LP-100, but using the tuner I would expect that to be even better.
>--Ed—
>
>
>
>
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