[Elecraft] DL1 - Measuring Coax Loss

[EricJ]

Excellent post, John. You don't mention that there is even more useful 
information about this on your web site.

I have always thought it would be very useful for Elecraft to post "App 
Notes" of this kind about all their mini-kits. I know several people who 
have built them seemingly to satisfy their kit addiction, but then toss 
them in a drawer and never use them. There is plenty of information 
around about how to use them, but I think it would be very helpful to 
see them used almost in a tutorial fashion as you have done here. 
Specific hook ups and tests on Elecraft gear with the noise generator, 
2-tone generator, etc.

Many of us have used equipment like this over decades, but Elecraft has 
introduced whole new generations to ham radio who could really benefit 
from knowing how to routinely use this test equipment, and enjoy a new 
aspect of the hobby at the same time.

I think the work you show on your web site could be the first of these 
App Notes.

Eric
KE6US

On 8/24/2013 5:28 AM, John Oppenheimer wrote:
> How many of you have an Elecraft DL1? It's an amazing piece of test
> equipment for only $26 when coupled to an accurate DVM.
>
> The DL1 is a simple 50 ohm dummy load with a peak detector diode. The
> load on the diode is the input impedance of the voltmeter, normally
> 10 Meg Ohm, which results with a rather flat 0.25 Volt diode loss.
>
> One use is to measure coax loss along with the KX3. The KX3, having an
> active power control, has a very stable and repeatable power output.
> The Fluke 87V has four significant digits when measuring 10 watts. The
> KX3 output is repeatable, using the 87V AutoHOLD feature, within +-2 LSB
> digits (+-0.02V) resulting with a resolution of about 0.022 dB.
> Measuring coax requires two measurements, therefore, the coax loss
> computation is within about 0.044 dB.
>
> Some additional loss error may be caused by the DL1 50 ohm RF impedance.
> I suspect that the DL1 is well within 2% in the HF region, probably
> within 1%.
>
> As a test, I measured and plotted a 100 foot piece of RG-58A/U. And
> solved for K1, conductor loss, and K2, dielectric loss, constants.
> Loss = K1 * SQRT(F) + K2 * F
>
> http://www.kn5l.net/Elecraft/DL1RG58Loss.png
>
> The Red line is for constants computed from
> http://vk1od.net/calc/tl/tllc.php. The Green line is a least squares fit
> to the measurements. The Blue ticks are the RG-58A/U measurements using
> the KX3, DL1, and 87V.
>
> John KN5L
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