Power Output Regulation Issue

[Francis Belliveau]

All,

I have been trying to get a handle on how well my K2 controls output power
for a long time.  I have finally acquired an LP-200 Wattmeter/Dummy load
combination in order to provide a reasonable measure of this characteristic.
The results are below:

For a setting of 5 watts
MHz   PWR
 3.50  4.76
 4.00  12.5
 7.00  5.01
 7.30  2.34
10.10  7.07
10.15  7.03
14.00  4.31
14.35  1.95
18.068  6.06
18.168  6.24
21.00  6.41
21.45  5.5
24.89  6.59
24.99  6.47
28.00  9.45
28.75  6.22

For a setting of 10 watts
MHz   PWR
 3.50  4.47
 4.00  12.1
 7.00  16.1
 7.30  8.74
10.10  13.2
10.15  13.1
14.00  17.6
14.35  12.0
18.068  11.7
18.168  12.0
21.00  12.8
21.45  11.9
24.89  11.9
24.99  11.7
28.00  11.1
28.75  10.6

Of greatest concern to my are the main bands 10, 15, 20, 40 and 80 meters.
Where the readings look reasonable at one end of the band, they are way off
at the other end.  I am wondering what might be causing such problems with
power regulation?

The rig only had the SSB, NB and Analog Audio filter options installed when
these measurements were made.

I very much need some advice on where to start looking and troubleshooting
this problem.

Thanks,
Fran

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[Don Wilhelm-3]

Fran,

You most definitely have a problem somewhere in that K2.  We cannot begin to
guess where in the transmit chain the fault lies, so I recommend that you
turn to the Preparing for Transmitter Signal Tracing in Appendix E of the K2
manual and begin there.  In the steps that you will be following, you will
be validating several points along the transmit path, and hopefully you will
be able to determine a failing stage.  Either you have a stage that does not
have sufficient gain or the power detection/control loop is not functioning
properly.

Your power variation within a band (I am looking at 80 meters at 5 watts as
the first example) indicated that the power control is not working, but
having similar output levels (on 80) when set to 10 watts indicate that one
of the transmitter stages has a fault.  In troubleshooting we usually assume
that there is only one fault, but for a recently constructed transmitter
which might have bad solder connections, etc., there can be several faults.
The only way to find them is one at a time using an orderly troubleshooting
technique as outlined in the manual's Transmit Signal Tracing section.  Find
the first stage that shows a problem and correct that, then re-check to find
the second one.

Once you have identified a failing stage, do the related DC voltage
measurements at that stage and then we can help you localize it to the
component level if you give us the relevant information.

73,
Don W3FPR

> -----Original Message-----
> All,
>
> I have been trying to get a handle on how well my K2 controls
> output power
> for a long time.  I have finally acquired an LP-200 Wattmeter/Dummy load
> combination in order to provide a reasonable measure of this
> characteristic.
> The results are below:
>
> For a setting of 5 watts
> MHz   PWR
>  3.50  4.76
>  4.00  12.5
>  7.00  5.01
>  7.30  2.34
> 10.10  7.07
> 10.15  7.03
> 14.00  4.31
> 14.35  1.95
> 18.068  6.06
> 18.168  6.24
> 21.00  6.41
> 21.45  5.5
> 24.89  6.59
> 24.99  6.47
> 28.00  9.45
> 28.75  6.22
>
> For a setting of 10 watts
> MHz   PWR
>  3.50  4.47
>  4.00  12.1
>  7.00  16.1
>  7.30  8.74
> 10.10  13.2
> 10.15  13.1
> 14.00  17.6
> 14.35  12.0
> 18.068  11.7
> 18.168  12.0
> 21.00  12.8
> 21.45  11.9
> 24.89  11.9
> 24.99  11.7
> 28.00  11.1
> 28.75  10.6
>
> Of greatest concern to my are the main bands 10, 15, 20, 40 and
> 80 meters.
> Where the readings look reasonable at one end of the band, they
> are way off
> at the other end.  I am wondering what might be causing such
> problems with
> power regulation?
>
> The rig only had the SSB, NB and Analog Audio filter options
> installed when
> these measurements were made.
>
> I very much need some advice on where to start looking and
> troubleshooting
> this problem.
>
> Thanks,
> Fran
>
>

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