[Elecraft] K3 TX Calib Dummy Load Recommendations

[Walter Underwood]

Sorry, that is twenty resistors, not fifty.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Aug 25, 2018, at 5:35 PM, Walter Underwood <wunder at wunderwood.org> wrote:
> 
> I built the Oak Hills Research RFL-100 dummy load kit. It is supposed to be good to
> 144 MHz, so it should be fine at 50. If you’ve never built a kit, this is a good one to
> start with. The kit is $50. I got the $5 BNC option, since my shack is 100% BNC.
> 
> http://www.ohr.com/rfl100.htm
> 
> Here are some photos of my build. Mine measured 49.9 Ω, which is within 0.2%.
> My Ohmmeter is accurate to +/-0.5%, so I’ll take that as a solid 50 Ω. Because the
> dummy load is built with 50 resistors, part tolerances will average out.
> 
> https://observer.wunderwood.org/2016/12/31/building-a-dummy-load/
> 
> wunder
> K6WRU
> Walter Underwood
> CM87wj
> http://observer.wunderwood.org/ (my blog)
> 
>> On Aug 25, 2018, at 4:49 PM, Mark Goldberg <marklgoldberg at gmail.com> wrote:
>> 
>> A good one that you know is 50 ohms over the range of frequencies and power
>> you want to use it at. Unfortunately, any particular model may be good or
>> bad, depending on how it has been used or abused. Is there any way you can
>> get access to an analyzer to determine if the dummy load is good? I have a
>> Vector Network Analyzer, but few hams will have one of those.
>> 
>> Also, if you really want to do a real calibration, you should have a
>> calibrated reference to check against. Lots of devices can be 5-10% off if
>> not calibrated, worse if abused or damaged. A Bird meter is only specified
>> to I think 5% of the full scale. So if it is a 200W full scale, it could be
>> 10W off. So 100W might read 110W or 90W.  I've got a calibrated Spectrum
>> Analyzer and Signal Generator that I use to calibrate all my other stuff
>> against, but again, few Hams will have similar or spend to keep them in
>> calibration.
>> 
>> In general, oil filled dummy loads with fins like the Birds shown lower on
>> this page are going to be good, but expensive:
>> 
>> https://www.birdrf.com/Products/Test%20and%20Measurement/Loads/Coaxial-Terminations.aspx
>> 
>> You can find similar ones used, hopefully not abused and not filled with
>> PCBs.
>> 
>> I've got a similar one that must be decades old and it works well and is
>> pretty close to 50 ohms over the HF range. I have not opened it to see what
>> it is filled with!
>> 
>> 73,
>> 
>> Mark
>> W7MLG
>> 
>> 
>> On Sat, Aug 25, 2018 at 4:09 PM, Steve Lawrence via Elecraft <
>> elecraft at mailman.qth.net> wrote:
>> 
>>> What are recommended dummy loads to consider for use when running the K3
>>> TX Calibration?
>>> 
>>> Thanks - Steve WB6RSE
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