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KPA100 tools

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lstavenhagen

KPA100 tools

Hi all,
And speaking of the K2... I can't recall if I asked this several years ago on my first K2 build when I was contemplating this exact same question the first time, :), and I couldn't find this specifically in the reflector archives either.

Are there any specific tools for building/aligning/testing the KPA100 _other_ than the ones listed in the manual that are either required or very strongly suggested?

I may go QRO in my now-being-built K2 but have rejected my "plan A" of an external amp. So may do the KPA100. It looks like a wattmeter is almost mandatory, but are there any other alignment tools needed?

I have a 100W dummy load, will get a large batt (that I'll use with it /p) and have a DMM. And the compliment of tools spelled out in the manual which I'm using to build the K2 to start with.

tnx es 73,
LS
W5QD

Don Wilhelm-4

Re: KPA100 tools

LS,

The tools listed in the KPA100 manual are quite sufficient.
To set the PA bias, you do need a means of measuring the current rise
for the PA idle current, and most DMMs will suffice - you will have to
measure a current rise of 400mA. I use a dedicated DMM on the workbench
set on the 10 Amp scale for that purpose. Since you are doing only one,
a dedicated DMM for that purpose is not economical. Use your existing
DMM connected to measure current.

The only other things I use are a precision 25 ohm and precision 100 ohm
dummy load. Those 2 dummy loads allow me to more accurately set C1 than
I am able to do by measuring the DC voltage null as instructed in the
manual. When the wattmeter bridge is correctly balanced, the SWR shown
by both those loads will be the same. After adjusting C1 so the SWR
reading for both loads is the same, I can easily set the REFL pot
exactly for a 2.0 SWR.

If you do not have the capability to produce a 25 ohm and a 100 ohm
dummy load, then simply follow the instructions in the manual, and it
will be close enough for proper operation. The KPA100 throttles power
back if it detects an SWR in excess of 2.0, so this is not a critical
setting and those tools are not required - this is just a refinement
that I do on my repairs.

73,
Don W3FPR

On 3/21/2016 4:06 PM, lstavenhagen wrote:

> Hi all,
> And speaking of the K2... I can't recall if I asked this several years ago
> on my first K2 build when I was contemplating this exact same question the
> first time, :), and I couldn't find this specifically in the reflector
> archives either.
>
> Are there any specific tools for building/aligning/testing the KPA100
> _other_ than the ones listed in the manual that are either required or very
> strongly suggested?
>
>

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lstavenhagen

Re: KPA100 tools

Ok thanks Don. That reminds me, my dummy load is eons old, so I should check and see if it's still 50 ohms. And I believe my DMM has a 10amp setting that may work for the bias setting, but I'll check. Also I have a very old MFJ manual ant. tuner with an analogue wattmeter in it (assuming it still works). Will that be sufficient for the items requiring a wattmeter or will I need something more precise than that?

Thank you,
LS
W5QD.

Don Wilhelm-4

Re: KPA100 tools

LS,

The KPA100 wattmeter calibration will be as accurate as the accuracy of
the external wattmeter used.
The real question is -- How much can you trust your wattmeter at the 20
watt and 100 watt levels?

73,
Don W3FPR

On 3/21/2016 5:03 PM, lstavenhagen wrote:

> Ok thanks Don. That reminds me, my dummy load is eons old, so I should check
> and see if it's still 50 ohms. And I believe my DMM has a 10amp setting that
> may work for the bias setting, but I'll check. Also I have a very old MFJ
> manual ant. tuner with an analogue wattmeter in it (assuming it still
> works). Will that be sufficient for the items requiring a wattmeter or will
> I need something more precise than that?
>
> Thank you,
> LS
> W5QD.
>
>
>
> --
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lstavenhagen

Re: KPA100 tools

Ah, gotcha, thanks Don. I'll see if I can borrow an accurate one for that part...

Thank you,
LS
W5QD