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:
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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); elecraft@mailman.qth.net
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: ed.n...@gmail.com; elecraft@mailman.qth.net
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" <ed.n...@gmail.com>
To: "Larry (K8UT)" <k...@charter.net>; "elecraft@mailman.qth.net"
<Elecraft@mailman.qth.net>
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; elecraft@mailman.qth.net
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" <ed.n...@gmail.com>
To: "elecraft@mailman.qth.net" <elecraft@mailman.qth.net>
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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