Posted by
Ken Cannaday on
Aug 31, 2010; 10:54am
URL: http://elecraft.85.s1.nabble.com/K2-KPA-100-excessive-power-issue-SSB-mode-some-bands-tp5470018p5482089.html
Thanks much for the comments, all were very helpful and are much
appreciated. I did some further testing along the lines suggested with the
following results:
Settings: SSBA = 1; SSBC = 3 to 1; requested power QRP = 2, QRO = 20;
transmitting into a dummy load; microphone = Heil HC4 (but similar results
have generally been experienced with Icom electret hand mike, HM 36); all
bands tested in both TUNE and SSB modes .
Generally in QRP on TUNE mode, I saw anywhere from 2.8 to 2.3 watts after
the ALC had time to settle in (the ALC seems to start over with any change
in band or certain other settings). In particular, I saw 2.8 watts on 160,
2.3 on 10 meters, with the other bands somewhere in between. In SSB, I
generally saw peaks at one or two bars, with an occasional third bar, for
ALC; and two bars with an occasional third bar for RF. The exceptions were:
80 meters, where there was a very brief initial surge up to 4 or 5 bars
before settling in at 1 to 3 bars for ALC, and 2 to 3 bars for RF; 40
meters, where again there was the initial surge in reading before settling
at 3 to 4 bars for both ALC and RF; 30 meters where the results were similar
to 40 meters except that RF eventually settled to only 2 to 3 bars.
Then switching to QRO, on Tune mode, I saw 19, 20, or 21 watts on all bands
except on 80 meters where the ALC never seemed to settle in and kept
bouncing around between 18 and 22 watts, with 19 being the most stabile
eventual reading. In SSB, I generally saw peaks at 1 (10 and 12 meters), 1
to 2, or 2 to 3 (160) bars for ALC and 2 to 3 bars for RF. On 80 meters,
however, there was again an initial surge, lasting a little longer and
settling in a little slower to an eventual 2 to 3 bars for ALC and a solid 3
bars of RF; on 40 the initial surge was more extreme with the ALC kicking up
as high as 6 bars before settling in at 3 to 4 bars, 2 to 3 bars for RF.
The most extreme results were on 30 meters where I saw readings as high as 5
to 6 bars for ALC and 7 to 10 bars for RF. After a much longer period of
speaking into the microphone, eventually readings settled respectively to 3
to 4 bars with a rare 5th bar and 2 to 3 bars with an occasional 4th bar.
I should add that I can generally get a bit higher readings by screaming
into the microphone, but the results summarized above were obtained by
speaking just a bit louder than normal, as if I am excited on the verge of
working a new, rare DX entity.
Generally a higher RF reading was supported by a higher ALC reading. Does
this indicate that any excess in power output is not likely to be an ALC
problem rather than a KPA/100 problem? How necessary do you think it is to
install the KPA100UPKT given these results? Any observations or suggestions
would be appreciated.
73
Ken
----- Original Message -----
From: "Don Wilhelm" <
[hidden email]>
To: "Ken Cannaday" <
[hidden email]>
Cc: <
[hidden email]>
Sent: Friday, August 27, 2010 12:00 PM
Subject: Re: [Elecraft] K2 KPA/100 excessive power issue, SSB mode, some
bands
> Ken,
>
> That description sounds suspiciously like you are developing a parasitic
> on 40 meters.
> Yes, the first step in getting that under control is to install the
> KPA100UPKT.
> It was developed specifically to address a problem very similar to yours.
>
> There is another possibility (since you mentioned the SSBA and SSBC
> parameters) - that you are driving the mic input too hard. switch the
> display to read ALC. You should have no more than 3 bars with maybe an
> occasional 4th.
> There should be no problem with an SSBC setting of 3:1 or even 4:1, but
> the SSBA parameter will depend on your mic. If you are using the Elecraft
> mics, set SSBA to 1.
>
> 73,
> Don W3FPR
>
> On 8/27/2010 11:42 AM, Ken Cannaday wrote:
>> I had an RF feedback problem on 40 meter SSB, which I brought under
>> control,
>> mainly by winding a foot or two of mike cable through a ferrite core.
>>
>> However, I had been having another problem on 40 meters SSB that had gone
>> unnoticed until the power supply (rated at 30 amp surge) tripped out on a
>> voice peak.
>> Power control seemed okay because the output as measured on the meter in
>> my
>> MFJ tuner was the same as the power setting on the K2 in Tune, Tune +
>> Display (override 20 watt limit), and CW modes.
>>
>> However, on SSB, the circumsatance was very different. If the setting
>> was
>> for 100 watts, the meter in the tuner would often kick up to 100 watts or
>> more on voice peaks, whereas with my Icom transceivers, it generally will
>> not kick
>> any higher than half the power setting (i.e. 50 watts). (I really have
>> no
>> good way of accurately measuring peak power on SSB and always assumed PEP
>> would be the same as the output in continuous carrier mode.) Turns out
>> that
>> on 40
>> and 30 meters, and to a lesser extent on 80, while transmitting into a
>> dummy
>> load, I apparently get two to four times the expected power on voice
>> peaks, judging by the meter in the tuner (and applying the times two
>> formula). This only occurs when the KPA/100 is active. It does not
>> occur
>> with the basic K2 in QRP mode. Moreover, even with KPA/100 active, if I
>> set
>> compression (SSBC) and audio (SSBA) to the lowest levels, the power
>> reading
>> levels appear to be similar to the Icom - about 50% of nominal power on
>> voice peaks.
>>
>> My KPA/100 is revision C and does not have the KPA100UPKT installed.
>> Does
>> anyone have any suggestions for this problem? Would the KPA100UPKT
>> likely
>> solve the problem? On the other hand, would there be any harm in setting
>> the
>> power levels and/or the SSBA and SSBC parameters so that output does not
>> exceed
>> 100 watts, and continuing to operate with the KPA100 as is?
>>
>> Any help would be greatly appreciated!
>>
>> Ken, W4NZC
>>
>> 73!
>>
>> ______________________________________________________________
>> 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>>
______________________________________________________________
Elecraft mailing list
Home:
http://mailman.qth.net/mailman/listinfo/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.html