K3S - Alpha 87a combo - loss of keying amp

[Kimo Chun]

In a K3S tested with two Alpha 87a amps using RF sensing to change band and
tuning the K3S appears to easily trip the amp into Fault mode. When amp is
cycled between Operate and Standby to clear the Fault, K3s can no longer
key the amp unless you cycle power to the radio. Then it works properly
again.

1. Manually change bands on the radio, with amp still sitting on prior band
and with the drive turned down to 5 to 8 W to try to ensure we won't trip
the amp while possibly transmitting into a momentarily high SWR of the
wrong band input circuitry? When keyed on the new band to have the amp
auto-tune it trips into Fault.
2. After cycling the amp from Standby back to Operate the K3S can no longer
key the amp. It is transmitting in apparent bypass mode as indicated by the
low RF level still indicating on the built in Watt meter of the amp.
3. This was tested with two 87a amps. Same issue.
4. Pulling the key line and shorting RCA plug at radio end does
successfully key the amp.
5. Another K3 radio with updated syn) doesn't do this.
6. I believe the pertinent default settings of the two radios were set to
be the same, though perhaps the band by band default drive setting or limit
may not have been mapped (If I understand correctly).

I am the new owner of the K3S and I have zero experience with the radio or
type. I've not set up my station yet (working on rebuilding tower and
antennas) since buying the radio.  It is about 3 years old but only used
for 6 months by the prior owner and once by my group at last year's Field
Day. The radio and P3 are being loaned to a friend to use in an SO2R entry
in a contest.

Has anyone experienced this? Any ideas on what may be wrong?
Can my K3S be sending a spike of power, anyway, to cause the trip? We
haven't gotten further into verifying this or other things as we only
started this today.Thank you for any help you may provide.

Kimo Chun, KH7U
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[Edward H Russell]

Kimo,

In order to keep my 87a from tripping into fault on band change, I sometimes
need to lower the drive power. About 10w seems ideal.

On my 6700 and 890s I am able to configure a low drive power for the TUNE
function. I'm not sure but think the K3 has a similar function. Of course
make sure the antenna is matched before TUNE is activated.

TKS,
73 ED W2RF





-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of Kimo Chun
Sent: Tuesday, October 20, 2020 7:22 AM
To: [hidden email]
Subject: [Elecraft] K3S - Alpha 87a combo - loss of keying amp

In a K3S tested with two Alpha 87a amps using RF sensing to change band and
tuning the K3S appears to easily trip the amp into Fault mode. When amp is
cycled between Operate and Standby to clear the Fault, K3s can no longer key
the amp unless you cycle power to the radio. Then it works properly again.

1. Manually change bands on the radio, with amp still sitting on prior band
and with the drive turned down to 5 to 8 W to try to ensure we won't trip
the amp while possibly transmitting into a momentarily high SWR of the wrong
band input circuitry? When keyed on the new band to have the amp auto-tune
it trips into Fault.
2. After cycling the amp from Standby back to Operate the K3S can no longer
key the amp. It is transmitting in apparent bypass mode as indicated by the
low RF level still indicating on the built in Watt meter of the amp.
3. This was tested with two 87a amps. Same issue.
4. Pulling the key line and shorting RCA plug at radio end does successfully
key the amp.
5. Another K3 radio with updated syn) doesn't do this.
6. I believe the pertinent default settings of the two radios were set to be
the same, though perhaps the band by band default drive setting or limit may
not have been mapped (If I understand correctly).

I am the new owner of the K3S and I have zero experience with the radio or
type. I've not set up my station yet (working on rebuilding tower and
antennas) since buying the radio.  It is about 3 years old but only used for
6 months by the prior owner and once by my group at last year's Field Day.
The radio and P3 are being loaned to a friend to use in an SO2R entry in a
contest.

Has anyone experienced this? Any ideas on what may be wrong?
Can my K3S be sending a spike of power, anyway, to cause the trip? We
haven't gotten further into verifying this or other things as we only
started this today.Thank you for any help you may provide.

Kimo Chun, KH7U
[hidden email]
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[Jim Brown-10]

On 10/20/2020 4:22 AM, Kimo Chun wrote:
> In a K3S tested with two Alpha 87a amps using RF sensing to change band and
> tuning the K3S appears to easily trip the amp into Fault mode.

For a couple of years, I have had two 87As on my operating desk, each
driven by a K3, and I the only time I experienced any issues when
changing bands was when I screwed up and transmitted into the wrong
antenna.Both of those 87As have the auto-tuning feature, which was added
several years after the amp was introduced. Not all 87As have it, older
amps require the replacement of a PROM, and after the company has been
sold several times, it's no longer available.

The auto-tuning system must be trained, by band segment. It's covered in
the manual, which can be downloaded. That training can be tricky,
depending on what the previous owner might have done. And the feature
must be turned on, by simultaneously pushing two of the buttons. I found
that it works quite well when working into reasonably well matched
loads, but its tuning range is pretty limited, and falls apart as the
mismatch approaches 2:1. It's a Pi-L output network, not an antenna
tuner.

One of those 87As has been replaced by a KPA1500, and it DOES
occasionally go into Fault mode when changing bands, but it matches a
FAR greater range of loads. I didn't replace the 87A because I was
unhappy with it, but to get legal limit on 6M.

73, Jim K9YC
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