rf power fluctuations

[Frank DL4KQ-2]

G`day,


I`m running a K2 + EC2(KAT100/KPA100), fully loaded, actual fw`s, which seemed to work fine.
But driving an external linear amplifier (tune situation) I noticed inacceptable rf output fluctuations of the KPA100.
(measured on antenna as well as on dummy-load)


K2 (alone): obviously no output fluctuations
K2+KPA100 (independant of KAT100 settings: bypass or auto mode):
1. jumping output fluctuations of 10 to 15 W on all bands
2. height of fluctuation nearly independant of K2 power knob setting; f.e. 10 W jumps at 30 W as on 50 W or any other driver setting.
3. fluctuation depends on K2 power knob setting, there exist ranges with and without fluctuation (on same band), obviously different ranges for different bands.


Asked a friend to come along with his K2+EC2 (also fully loaded, actual fw`s) for test changing of components.
But his K2+EC2 showed same behaviour.
Btw, another K2/100 + KAT100 (all but KX60V options) showed same behaviour but fluctuation was less (max. 8 W).

10-15 W jumps are a bit "much" ...   :-((

Any ideas?

Frank, DL4KQ
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[Stewart Baker]

Hi Frank,

You might like to search the Elecraft Email List User Group for references to
R98.
There are a lot of mails concerning changing that resistor value to reduce the
basic K2 power jumping. Things of course worsen with the KPA100 fitted.
I changed my R98 from 270 ohms to 1k, and it made quite a difference.
It reduces the overall gain in the BFO ALC loop.

73
Stewart G3RXQ

On Mon, 5 Dec 2005 09:04:21 +0100, Frank DL4KQ wrote:

> G`day,
>
>
> I`m running a K2 + EC2(KAT100/KPA100), fully loaded, actual fw`s, which
> seemed to work fine.
> But driving an external linear amplifier (tune situation) I noticed
> inacceptable rf output fluctuations of the KPA100.
> (measured on antenna as well as on dummy-load)
>
>
> K2 (alone): obviously no output fluctuations
> K2+KPA100 (independant of KAT100 settings: bypass or auto mode):
> 1. jumping output fluctuations of 10 to 15 W on all bands
> 2. height of fluctuation nearly independant of K2 power knob setting; f.e. 10
> W jumps at 30 W as on 50 W or any other driver setting.
> 3. fluctuation depends on K2 power knob setting, there exist ranges with and
> without fluctuation (on same band), obviously different ranges for different
> bands.
>
>
> Asked a friend to come along with his K2+EC2 (also fully loaded, actual fw`s)
> for test changing of components.
> But his K2+EC2 showed same behaviour.
> Btw, another K2/100 + KAT100 (all but KX60V options) showed same behaviour
> but fluctuation was less (max. 8 W).
>
> 10-15 W jumps are a bit "much" ...   :-((
>
> Any ideas?
>
> Frank, DL4KQ
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com

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[Don Wilhelm-3]

Frank,

The internal transmit ALC loop settling is causing this power fluctuation.
It can be reduced by reducing the loop gain.  R98 on the RF Board can be
increased to accomplish that, but increasing R98 will also reduce the gain
on 10 and possibly 12 meters, so the amount of 10 meter gain reduction that
you are willing to tolerate will limit how much you can increase R98.

You may wish to temporarily use a variable pot and increase the resistance
until you see the 10 meter output being reduced - measure it and install the
next lower standard value resistor.

73,
Don W3FPR

> -----Original Message-----
>
> I`m running a K2 + EC2(KAT100/KPA100), fully loaded, actual fw`s,
> which seemed to work fine.
> But driving an external linear amplifier (tune situation) I
> noticed inacceptable rf output fluctuations of the KPA100.
> (measured on antenna as well as on dummy-load)
>
>
> K2 (alone): obviously no output fluctuations
> K2+KPA100 (independant of KAT100 settings: bypass or auto mode):
> 1. jumping output fluctuations of 10 to 15 W on all bands
> 2. height of fluctuation nearly independant of K2 power knob
> setting; f.e. 10 W jumps at 30 W as on 50 W or any other driver setting.
> 3. fluctuation depends on K2 power knob setting, there exist
> ranges with and without fluctuation (on same band), obviously
> different ranges for different bands.
>
>
> Asked a friend to come along with his K2+EC2 (also fully loaded,
> actual fw`s) for test changing of components.
> But his K2+EC2 showed same behaviour.
> Btw, another K2/100 + KAT100 (all but KX60V options) showed same
> behaviour but fluctuation was less (max. 8 W).
>
> 10-15 W jumps are a bit "much" ...   :-((
>
> Any ideas?
>
> Frank, DL4KQ

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