Accuracy of K1's built-in power / swr meter?

[Stephanie Maks]

Hi everyone,

I am wondering how accurate is the built-in metering of the K1?

For all of my testing and alignment etc. I've been running the K1  
through an MFJ cross-needle HF meter, and I've noticed that there is  
a very consistant difference in the display on the MFJ meter and what  
the K1 reports.  The MFJ meter is always reporting between 1 watt and  
1.5 watts lower power than the K1 indicates.  For example, with the  
K1 set to 2 watts out, in Tune mode, the display on the K1 wanders  
around between 1.9 and 2.2 while the MFJ meter seems quite stable at  
1 watt.  At higher powers, such as when finding a peak during  
alignment, the K1 indicates as high as 7+ watts, while the MFJ only  
goes as high as about 5 watts.

Normally, I tend to trust the analog meter over the digital stuff,  
but in this case the MFJ meter was dropped last month and might have  
sustained some damage.  Plus, it's not really intended as a QRP meter  
so it might not be that accurate at low powers.

I also have the KAT-1 and I understand that its meter is 'more  
accurate' than what's in the base K1, but not really sure how much more.

Thanks!

73 de Stephanie
va3uxb

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[Stephanie Maks]

Thanks Jim!

Sorry I should have clarified, when I was testing / comparing the  
KAT1 to the MFJ I had the KAT1 set to CLP which bypasses/disables the  
tuning.  I know if the KAT1 is set to TUN then it's not going to  
present 50 ohms on the antenna jack.

73 de Stephanie
va3uxb

On 03-Jan-2006, at 17.48.57, k4zm wrote:

> Stephanie:
>
> If you have the KAT1 in the K1 and have the MFJ meter connected to  
> the output of the K1 you are looking at an inaccurate reading on  
> the MFJ because it is located between the antenna  and the input of  
> the tuner.  The only place to read it accurately would be to place  
> your MFJ meter between the KAT1 and the K1.  This is almost  
> impossible to do. Since you are between the antenna and the KAT1  
> your MFJ is not looking at 50 load and the reactances of the  
> antenna that are tuned out by the tuner are destroying the  
> accurately of the MFJ Meter.
>
> 73
> Jim Younce K4ZM
>
>

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[Don Wilhelm-3]

Stephanie,

If you really want to know which is the more accurate, you will have to have
a good 50 ohm non-reactive dummy load and a means of measuring the RF
voltage across it.  The Elecraft DL1 will do both nicely because it has a
built-in RF detector and has a nice chart of voltage out vs. power.  You may
want to obtain one to calibrate the wattmeter in the KAT1 (the accuracy will
only be as good as your calibration technique).

As for how much you can trust your MFJ wattmeter (dropped or not)?, look at
its specs to determine that.  I am not certain, but I would venture a guess
that is is speced at 10% of full scale - so the next question is what scale
are you using?  Multiply that by the accuracy specification and you will
know how much it could be in error and still be in spec - and that amount of
error will be possible no matter what the power level used (it is NOT a
percentage of the power level indicated, but a percentage of the full scale
reading) - so if you are using a 10 watt scale, and the speced error is 1%,
the MFJ could read as much as 1 watt high or 1 watt low - i.e. if the actual
power is 2 watts, you may obtain a reading anywhere between 1 and 3 watts.
An RF Probe and an accurate dummy load is much better for lower power
measurements.

If you are drawing comparisons when feeding an antenna instead of a known
good dummy load, then the simple RF detector in the K1 will not indicate the
actual power output with accuracy.  The KAT1 will do that for you if you
calibrate it properly.

73,
Don W3FPR

> -----Original Message-----
>
> I am wondering how accurate is the built-in metering of the K1?
>
> For all of my testing and alignment etc. I've been running the K1
> through an MFJ cross-needle HF meter, and I've noticed that there is
> a very consistant difference in the display on the MFJ meter and what
> the K1 reports.  The MFJ meter is always reporting between 1 watt and
> 1.5 watts lower power than the K1 indicates.  For example, with the
> K1 set to 2 watts out, in Tune mode, the display on the K1 wanders
> around between 1.9 and 2.2 while the MFJ meter seems quite stable at
> 1 watt.  At higher powers, such as when finding a peak during
> alignment, the K1 indicates as high as 7+ watts, while the MFJ only
> goes as high as about 5 watts.
>
> Normally, I tend to trust the analog meter over the digital stuff,
> but in this case the MFJ meter was dropped last month and might have
> sustained some damage.  Plus, it's not really intended as a QRP meter
> so it might not be that accurate at low powers.
>
> I also have the KAT-1 and I understand that its meter is 'more
> accurate' than what's in the base K1, but not really sure how much more.
>
> Thanks!
>
> 73 de Stephanie
> va3uxb
>
>

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