Reflected power

[Stephen Rabinowitz]

Many thanks to all of those who responded to my message and shared their
experiences and thoughts: Dave WO2X, Mike VA3MW, Bob K4TAX, Jim K9YC, Victor
4X6GP, and Alan N1AL. With a dummy antenna (Cantenna) on 7MHz, and a 1.1:1
match, using 10w drive the KPA-1500 puts out 605w at first, then settles
down two seconds later to 384w with 8w reflected power. With 25w drive, the
initial output is 1431w, settling down to 1105w after two seconds, with 20w
reflected power. So, the fault seems to be in the antenna, not in the
amplifier.
The same initial power surge occurs on 14MHz using the dummy antenna. I
don't know if it originates in the transceiver or the amplifier, but it
doesn't have much effect on reflected power except with the defective
antenna. Answering some of the questions that were posed, the double bazooka
in this case is the high power version from Radiowavz, two years old. A
common mode choke from DX Engineering sits between the end of the feed coax
and the antenna. Several Mix 31 snap-on chokes from Palomar are on various
short coax jumpers in the shack, and the ground system is very good.
The double bazookas I use on 80m and 30m work well and are from
iacantennas.com. I am ordering a 40m version from them to replace the one
that seems to be faulty. I will try to report the result after I install it.
Many thanks again to all,
73, Steve K2SN

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[Dave wo2x]

Steve,

What radio are you using to drive the amp? Are you using ALC? Sounds like power setting on radio is such you see the higher power until ALC drops exciter power.

Dave wo2x

Sent from my iPad

> On Sep 16, 2019, at 10:58 AM, Stephen Rabinowitz <[hidden email]> wrote:
>
> Many thanks to all of those who responded to my message and shared their
> experiences and thoughts: Dave WO2X, Mike VA3MW, Bob K4TAX, Jim K9YC, Victor
> 4X6GP, and Alan N1AL. With a dummy antenna (Cantenna) on 7MHz, and a 1.1:1
> match, using 10w drive the KPA-1500 puts out 605w at first, then settles
> down two seconds later to 384w with 8w reflected power. With 25w drive, the
> initial output is 1431w, settling down to 1105w after two seconds, with 20w
> reflected power. So, the fault seems to be in the antenna, not in the
> amplifier.
> The same initial power surge occurs on 14MHz using the dummy antenna. I
> don't know if it originates in the transceiver or the amplifier, but it
> doesn't have much effect on reflected power except with the defective
> antenna. Answering some of the questions that were posed, the double bazooka
> in this case is the high power version from Radiowavz, two years old. A
> common mode choke from DX Engineering sits between the end of the feed coax
> and the antenna. Several Mix 31 snap-on chokes from Palomar are on various
> short coax jumpers in the shack, and the ground system is very good.
> The double bazookas I use on 80m and 30m work well and are from
> iacantennas.com. I am ordering a 40m version from them to replace the one
> that seems to be faulty. I will try to report the result after I install it.
> Many thanks again to all,
> 73, Steve K2SN
>
> ______________________________________________________________
> 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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