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KPA1500 Operation on 6 Meters

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Ed G

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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Larry (K8UT)

Re: 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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Ed G

Re: 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

Jim Brown-10

Re: KPA1500 Operation on 6 Meters

In reply to this post by Ed G

On 6/15/2020 6:48 AM, Ed G wrote:
> 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.

Look for something breaking down in your antenna system or between the
power amp and the antenna. High power has a way of finding weaknesses
that low power lives with.

73, Jim K9YC

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Adrian-3

Re: KPA1500 Operation on 6 Meters

Did you see this part in Ed's earlier post ;

"

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."

This would also should any power breakdown, but it doesn't ?
Adrian Fewster

On 16/6/20 6:30 am, Jim Brown wrote:

> On 6/15/2020 6:48 AM, Ed G wrote:
>> 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.
>
> Look for something breaking down in your antenna system or between the
> power amp and the antenna. High power has a way of finding weaknesses
> that low power lives with.
>
> 73, Jim K9YC
>
>
>

Elecraft mailing list

Re: KPA1500 Operation on 6 Meters

That means that he needs to check the connectors, adapters and cable that run from the KPA500 to the LPA-100 and potentially the LP-100A itself.

The directional coupler is the last component in the KPA500 chain. For reflected power, it simply reports the conditions it sees from the antenna connector out.
That means the connectors, adapters and cable that follow it. Especially look at any adapters, they are notorious (especially right-angle adapters) for failing at hight power.

This is a problem that many have seen, and is always an issue in the antenna system. Jim’s advice is spot-on here.

73!
Jack, W6FB

> On Jun 15, 2020, at 4:46 PM, Adrian <[hidden email]> wrote:
>
> Did you see this part in Ed's earlier post ;
>
> "
>
> 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."
>
>
>
> This would also should any power breakdown, but it doesn't ?
> Adrian Fewster
>
>
> On 16/6/20 6:30 am, Jim Brown wrote:
>> On 6/15/2020 6:48 AM, Ed G wrote:
>>> 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.
>>
>> Look for something breaking down in your antenna system or between the power amp and the antenna. High power has a way of finding weaknesses that low power lives with.
>>
>> 73, Jim K9YC
>>
>>
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Larry (K8UT)

Re: KPA1500 Operation on 6 Meters

In reply to this post by Ed G

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 <https://go.microsoft.com/fwlink/?LinkId=550986> for
>Windows 10
>
>
>
>From: Larry (K8UT) <mailto:[hidden email]>
>Sent: Monday, June 15, 2020 10:09 AM
>To: Ed G <mailto:[hidden email]>; [hidden email]
><mailto:[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—
>
> >
>
> >
>
> >
>
> >
>
> >--
>
> >This email has been checked for viruses by Avast antivirus software.
>
> >https://www.avast.com/antivirus
>
> >______________________________________________________________
>
> >Elecraft mailing list
>
> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
>
> >Help: http://mailman.qth.net/mmfaq.htm
>
> >Post: mailto:[hidden email]
>
> >
>
> >This list hosted by: http://www.qsl.net
>
> >Please help support this email list: http://www.qsl.net/donate.html
>
> >Message delivered to [hidden email]
>
>
>
>
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Adrian-3

Re: KPA1500 Operation on 6 Meters

In reply to this post by Elecraft mailing list

I don't agree,...

Any issue between the LP-100A and KPA1500 is extremely unlikely, and any
issue in the antenna system would reflect on both LP-100A and KPA-1500
swr indications.

I find the LP-100A consistent readings at all drive levels discounts the
antenna system thereafter as a cause.

On 16/6/20 10:48 am, Jack Brindle wrote:

> That means that he needs to check the connectors, adapters and cable that run from the KPA500 to the LPA-100 and potentially the LP-100A itself.
>
> The directional coupler is the last component in the KPA500 chain. For reflected power, it simply reports the conditions it sees from the antenna connector out.
> That means the connectors, adapters and cable that follow it. Especially look at any adapters, they are notorious (especially right-angle adapters) for failing at hight power.
>
> This is a problem that many have seen, and is always an issue in the antenna system. Jim’s advice is spot-on here.
>
> 73!
> Jack, W6FB
>
>
>> On Jun 15, 2020, at 4:46 PM, Adrian <[hidden email]> wrote:
>>
>> Did you see this part in Ed's earlier post ;
>>
>> "
>>
>> 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."
>>
>>
>>
>> This would also should any power breakdown, but it doesn't ?
>> Adrian Fewster
>>
>>
>> On 16/6/20 6:30 am, Jim Brown wrote:
>>> On 6/15/2020 6:48 AM, Ed G wrote:
>>>> 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.
>>> Look for something breaking down in your antenna system or between the power amp and the antenna. High power has a way of finding weaknesses that low power lives with.
>>>
>>> 73, Jim K9YC
>>>
>>>
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>

Ed G

Re: KPA1500 Operation on 6 Meters

In reply to this post by Larry (K8UT)

This morning I put my DL2K dummy load right on the KPA1500 amp output (tried both ANT1 and ANT2)…I am still seeing the same SWR anomaly, where lower drive levels are giving high SWR readings on the KPA1500 display. By putting the dummy load right at the KPA1500 output, I eliminated a bunch of coax cables and switchboxes.

So at this point the issue appears to be one internal to the KPA1500. Also appears to be not related to any previously-known high power RF causes, as in my case the problem is there at low drive levels and goes away at maximum drive/RF out. So I remain puzzled.

--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—
>
>
>
>
>--
>This email has been checked for viruses by Avast antivirus software.
>https://www.avast.com/antivirus
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
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>Please help support this email list: http://www.qsl.net/donate.html
>Message delivered to [hidden email]

Ed G

Re: KPA1500 Operation on 6 Meters

In reply to this post by Larry (K8UT)

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—
>
>
>
>
>--
>This email has been checked for viruses by Avast antivirus software.
>https://www.avast.com/antivirus
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html
>Message delivered to [hidden email]

Dr. William J. Schmidt, II

FW: KPA1500 Operation on 6 Meters

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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Adrian-3

Re: KPA1500 Operation on 6 Meters

In reply to this post by Ed G

Just curious to see if you have tried a different length jumper (coax
patch lead between radio & amp) to see if you get the same result ?

On 17/6/20 12:09 am, Ed G wrote:

> This morning I put my DL2K dummy load right on the KPA1500 amp output (tried both ANT1 and ANT2)…I am still seeing the same SWR anomaly, where lower drive levels are giving high SWR readings on the KPA1500 display. By putting the dummy load right at the KPA1500 output, I eliminated a bunch of coax cables and switchboxes.
>
> So at this point the issue appears to be one internal to the KPA1500. Also appears to be not related to any previously-known high power RF causes, as in my case the problem is there at low drive levels and goes away at maximum drive/RF out. So I remain puzzled.
>
> --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—
>>
>>
>>
>>
>> --
>> This email has been checked for viruses by Avast antivirus software.
>> https://www.avast.com/antivirus
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
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>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>
>
>
> Virus-free. www.avast.com
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> ______________________________________________________________
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>
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Ed G

Re: KPA1500 Operation on 6 Meters

Hi Adrian,
Yes, I also substituted a new piece of coax of different length going right from the K3 to the KPA1500 input…same SWR anomaly still observed.
--Ed, N3CW—

Sent from Mail for Windows 10

From: Adrian
Sent: Tuesday, June 16, 2020 11:09 AM
To: Ed G; Larry (K8UT); [hidden email]
Subject: Re: [Elecraft] KPA1500 Operation on 6 Meters

Just curious to see if you have tried a different length jumper (coax
patch lead between radio & amp) to see if you get the same result ?

On 17/6/20 12:09 am, Ed G wrote:

Paul Baldock

Re: KPA1500 Operation on 6 Meters

In reply to this post by Ed G

At 07:30 AM 6/16/2020, you wrote:
>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.

I think the designers will tell you that the SWR meter does not read
well until you have about 20-30 watts passing through it.

Here's what mine reads in STBY, in to precision 100W dummy
load connected on the back of the Amp (no coax involved) at 50.1MHz.

60W 1.3
30W 1.3
24W 1.3
18W 1.2
12W 1.2
6W 1.0

Here's what mine reads in OPER, in to a "cantenna" 1000W dummy load at 50.1MHz.

106W 1.3
314W 1.3
447W 1.2
693W 1.2
1071W 1.2

You will see that the AMP SWR meter reads 1.2-1.3 all the way from
12W to 1071W.
It should of read ofcourse 1.0 in to the precision dummy load, not
1.3. It has worked this way since being born about 2 years ago. I
called Elecraft to ask if there was an adjustment for this, and they said no.

By the way on 29MHz in to the precision load the internal SWR meter
reads 1.1, and then from 24.9MHz to 1.8MHz reads 1.0.

Assuming your LP100 sensor is connected directly to the back of the
AMP (no coax involved) and always reads the same at all power levels
then I agree your AMP has an internal problem.

Good luck

- Paul KW7Y

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Kidder, George

Re: KPA1500 Operation on 6 Meters

In reply to this post by Ed G

Internal oscillation suppressed by higher drive level? What does it do
in operate with zero drive?

On 6/16/2020 11:25 AM, Ed G wrote:

> [This message came from an external source. If suspicious, report to [hidden email]<mailto:[hidden email]>]
>
> Hi Adrian,
> Yes, I also substituted a new piece of coax of different length going right from the K3 to the KPA1500 input…same SWR anomaly still observed.
> --Ed, N3CW—
>
>
> Sent from Mail for Windows 10
>
> From: Adrian
> Sent: Tuesday, June 16, 2020 11:09 AM
> To: Ed G; Larry (K8UT); [hidden email]
> Subject: Re: [Elecraft] KPA1500 Operation on 6 Meters
>
> Just curious to see if you have tried a different length jumper (coax
> patch lead between radio & amp) to see if you get the same result ?
>
> On 17/6/20 12:09 am, Ed G wrote:
>> This morning I put my DL2K dummy load right on the KPA1500 amp output (tried both ANT1 and ANT2)…I am still seeing the same SWR anomaly, where lower drive levels are giving high SWR readings on the KPA1500 display. By putting the dummy load right at the KPA1500 output, I eliminated a bunch of coax cables and switchboxes.
>>
>> So at this point the issue appears to be one internal to the KPA1500. Also appears to be not related to any previously-known high power RF causes, as in my case the problem is there at low drive levels and goes away at maximum drive/RF out. So I remain puzzled.
>>
>> --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—
>>>
>>>
>>>
>>>
>>> --
>>> This email has been checked for viruses by Avast antivirus software.
>>> https://www.avast.com/antivirus
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>>
>>
>> Virus-free. www.avast.com
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
> ______________________________________________________________
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Adrian-3

Re: KPA1500 Operation on 6 Meters

In reply to this post by Ed G

Ok on that, My best guess now, as I think you are thinking, is that some
component(s) in the amp 6m circuitry are breaking down, changing impedance

in the amp output sector. Do you have a schematic, or have the link to
it? A good look at that may give more clues ?

On 17/6/20 1:25 am, Ed G wrote:

>
> Hi Adrian,
>
> Yes, I also substituted a new piece of coax of different length
> going right from the K3 to the KPA1500 input…same SWR anomaly still
> observed.
>
> --Ed, N3CW—
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows 10
>
> *From: *Adrian <mailto:[hidden email]>
> *Sent: *Tuesday, June 16, 2020 11:09 AM
> *To: *Ed G <mailto:[hidden email]>; Larry (K8UT)
> <mailto:[hidden email]>; [hidden email]
> <mailto:[hidden email]>
> *Subject: *Re: [Elecraft] KPA1500 Operation on 6 Meters
>
> Just curious to see if you have tried a different length jumper (coax
>
> patch lead between radio & amp) to see if you get the same result ?
>
>
>
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient&utm_term=link>
>
>
> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>