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); [email protected]
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: [email protected]; [email protected]
> 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" <[email protected]>
> To: "Larry (K8UT)" <[email protected]>; "[email protected]"
> <[email protected]>
> 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; [email protected]
> 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" <[email protected]>
> To: "[email protected]" <[email protected]>
> 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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