KX1 - >6Watts on 30&40

[Jim - W6VAR]

I haven't used my KX1 in a while, but I noticed it is running over 6 watts when connected to a 13.8 volt power supply on 30 and 40 meters. 20 meters is about 4.2 watts and 80 meters is between 4.7 and 5.0 watts.

Is this excessive and will it cause damage or a dirty signal? If there is a problem, where should I begin my search? Internal batteries generate significanlty lower output:
80M 1.7W; 40M 2.5W; 30M 2.0W; 20M 1.8W

Jim W6VAR

[Don Wilhelm-4]

Jim,

Lower the power when running on the 13.8 volt supply - 4 watts or a bit
less.  The components in the PA output circuit will thank you and live a
longer life.

You can use a slim  flatblade screwdriver and adjust R4 through the hole
in the bottom of the enclosure (and also through the tuner) - that is
why it is there.

73,
Don W3FPR

Jim - W6VAR wrote:

> I haven't used my KX1 in a while, but I noticed it is running over 6 watts
> when connected to a 13.8 volt power supply on 30 and 40 meters. 20 meters is
> about 4.2 watts and 80 meters is between 4.7 and 5.0 watts.
>
> Is this excessive and will it cause damage or a dirty signal? If there is a
> problem, where should I begin my search? Internal batteries generate
> significanlty lower output:
> 80M 1.7W; 40M 2.5W; 30M 2.0W; 20M 1.8W
>
> Jim W6VAR
>  

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[Michael Babineau-2]

Jim :

I made the documented power mod to my KX1 as I was getting too little power out, but then I
had a similar experience to yours when running off of a power supply or a fully charged SLA battery so
I built a "poor mans" voltage regulator that I can put in series with my power cable when powering
the rig from an external source. All I did was to put a couple of diodes in series, with a third that
I can switch in and out and this provides a bit of a voltage drop.  This way I can still get a reasonable
output with the internal batteries without frying the PA when I power the rig from 13.8V.

Michael VE3WMB
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[Jim - W6VAR]

Thanks Don,

I go back and forth between the internal and external batteries, so I'm not crazy about this as the stated life is limited for the potentiometer. Having said that, I dialed it back to get 4 watts into a dummy load and very weak power on internal batteries.

Here's the strange part, my home antenna is a coax fed, parallel dipole, so I need to run the tuner to get a match. When I run through the tuner, to a non 50 ohm load, my power as indicated on the KX1 goes up to about 5.5 watts! As I recall, it used to ALWAYS go down my some small amount.

Thoughts?

Jim - W6VAR

[Don Wilhelm-4]

Jim,

On the power issue, maybe you want to reduce the voltage when you
operate at home and keep R4 set to maximum for the sake of the internal
battery operation.  A couple diodes in series with the power supply
should cut the voltage a bit and keep the KX1 out of the danger zone.

On your SWR/Power situation, it is hard to tell.  You may want to check
the KXAT1 wattmeter balance and re-calibrate the wattmeter just to be
certain that is not the cause.  The other thing is to take a good look
at your antenna asking "What might have changed".
The KX1 power reading is not precise for impedances that differ much
from 50 ohms.  The KXAT1 may be right at the limit of its range when
matching that antenna, and if the SWR does not go down close enough to
1:1, it will vary the power indication.  Yes, I know wattmeters should
be independent of the SWR, but the KX1 wattmeter is quite small, and
that may be the reason, but I suspect the calculation of true power is
not perfect in the firmware (maybe Wayne ran out of room :-) ).

73,
Don W3FPR


Jim - W6VAR wrote:

> Thanks Don,
>
> I go back and forth between the internal and external batteries, so I'm not
> crazy about this as the stated life is limited for the potentiometer. Having
> said that, I dialed it back to get 4 watts into a dummy load and very weak
> power on internal batteries.
>
> Here's the strange part, my home antenna is a coax fed, parallel dipole, so
> I need to run the tuner to get a match. When I run through the tuner, to a
> non 50 ohm load, my power as indicated on the KX1 goes up to about 5.5
> watts! As I recall, it used to ALWAYS go down my some small amount.
>
> Thoughts?
>
> Jim - W6VAR
>  

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[Jim - W6VAR]

It seems the power increase is only on 30 where my antenna is less than perfect. I verified power with a W-1 and the internal watt meter is within .25 watts on all bands...both say I'm pushing 5.5 - 6 watts with the antenna connected, 4 watts with a dummy load.

I'll fiddle some more and also play with the toroids...my 20 meter power on internal batteries is under one watt.

Jim