[Elecraft] Mic Gain Changing

[Don Wilhelm]

Steve,

Your "confession" should be preserved in bold type for others to heed 
and lessons to be learned.

Attempting to do calibrations with 'almost good enough' dummy loads (or 
other equipment too) will result in 'funny behavior' - one cannot obtain 
precision results with 'almost good enough' equipment.

An accurate dummy load is the basis for many amateur measurements and 
calibrations.  1% 50 ohm dummy loads are not difficult to come by.  A 
100 watt dummy load can be built from a thick film power resistor 
(Caddock MP9100-50), a heat sink and a BNC, UHF, or N connector.  These 
50 ohm 1% resistors, when mounted on a heat sink with zero length leads 
to the connector, will be flat up to 200 MHz or more depending on the 
construction techniques.  That kind of dummy load and a precision 
voltage reference (along with some basic math) have become the basis for 
calibrating other equipment on my workbench.  I practice the "trust no 
measurement tool until it has proven its accuracy" rule.

Good calibrated equipment does not need to be expensive, nor of 
laboratory quality, but it must be used intelligently with respect for 
its shortcomings.

73,
Don W3FPR


list1 wrote:
> Hi Everyone,
>
> OK I seemed to have "removed" the problem.
>
> I added 11 small resistors in parallel to my MFJ 949E dummy load to change
> its resistance from about 56.5 Ohms to close to 50.0 Ohms.  I then ran the
> "Calibrate Transmitter Gain" procedure from the configuration Menu of the K3
> utility.  Now I can talk with 100 Watts and 6 bars of ALC all the time
> regardless of the temperature of the radio.  No more fiddling with the Mic
> gain.  Changing the Mic gain affects the power out and ALC reading now as
> expected.
>
> I think when I built my K3 I skipped the "TX Gain Calibration" step.  I may
> have thought that it was optional like the Wattmeter calibration, but with
> my dummy load being off I think I was afraid that I would do more harm then
> good.
>
> I can now see how some people have problems with the K3 by not following
> instructions.  I am a bit amazed the radio worked as well as it did in spite
> of the "loose nut in operator's chair" syndrome I was experiencing.
>
> OK, now to have even more fun with the radio, now that is it perfect.
>
> Steve, W2MY
>
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