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L1 vs W1 Power Reading

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akiwi ham

L1 vs W1 Power Reading

I recently put together a DL1 dummy load and W1 wattmeter.

I have the DL1 connected to my KX1 through the W1. I have the W1 connected
to a computer using the W1 software. I have a significant difference between
the power reading from the W1 and the power calculated from the voltage
measured on TP1 of the DL1 using a digital volt meter.

For example:

W1 reading = 4.04W

TP1 volts on DL1 = 8.97V => 3.29W

Is this magnitude of difference to be expected?

Bryan, Zl1NI
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Don Wilhelm-4

Re: L1 vs W1 Power Reading

Brian,

Unless you used a very accurate wattmeter to calibrate the W1, I would
believe the DL1.
HOWEVER: The formula in the DL1 manual is not correct. 8.97 volts
measured from the DL1 properly indicates 3.44 watts.
The correct formula for the DL1 is (Vdmm + Vdiode)^2/25. You can
measure the actual forward voltage drop of you diode in the DL1 and
substitute into the formula above, or assume the diode drop is 0.3 volts.

I believe an updated DL1 manual may be due with the corrected power
formula - I submitted the power formula derivation to Bob Friess (he
designed the DL1) and he accepted it.

73,
Don W3FPR

akiwi ham wrote:

> I recently put together a DL1 dummy load and W1 wattmeter.
>
> I have the DL1 connected to my KX1 through the W1. I have the W1 connected
> to a computer using the W1 software. I have a significant difference between
> the power reading from the W1 and the power calculated from the voltage
> measured on TP1 of the DL1 using a digital volt meter.
>
> For example:
>
> W1 reading = 4.04W
>
> TP1 volts on DL1 = 8.97V => 3.29W
>
> Is this magnitude of difference to be expected?
>
> Bryan, Zl1NI
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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akiwi ham

Re: L1 vs W1 Power Reading

Thanks Don.

The only calibration I did for the W1 was the procedure in the manual.

Bryan, Zl1NI

> Brian,
>
> Unless you used a very accurate wattmeter to calibrate the W1, I
> would
> believe the DL1.
> HOWEVER: The formula in the DL1 manual is not correct. 8.97 volts
> measured from the DL1 properly indicates 3.44 watts.
> The correct formula for the DL1 is (Vdmm + Vdiode)^2/25. You can
> measure the actual forward voltage drop of you diode in the DL1 and
> substitute into the formula above, or assume the diode drop is 0.3
> volts.
>
> I believe an updated DL1 manual may be due with the corrected power
> formula - I submitted the power formula derivation to Bob Friess (he
> designed the DL1) and he accepted it.
>
> 73,
> Don W3FPR
>