[Antennas] Frank Witt's Tuner Loss Test - More!

[George, W5YR]

As mentioned in the previous posting, there is some likelihood that the
presence of the metal cabinet of the MFJ 989C tuner could lower the Q of the
inductor and otherwise increase the losses in the tuner.

In order to evaluate this possibility, I simply removed the top cover and
repeated the 20 meter test reported earlier, using the first set of
adjustments.

With the cover removed, the tuning adjustments were slightly differerent
from before, but not by very much. The results were that the loss decreased
from 0.53 dB with the cover on to 0.33 dB with the cover removed.

The percentage of power loss went from 11.5% to 7.3% and the output power
for a 5-watt input increased from 4.43 watts to 4.63 watts.

The net effect appears large numerically, but the practical effect can be
expected to be small. The calculated loss decrease and power output increase
lie within the bounds of experimental and instrumentation error and should
not be regarded as definitive

However, these results do suggest that the cabinet metal around the inductor
does appear to increase tuner loss probably due to a decrease in the Q of
the inductor.

On the basis of these results, it would be very instructive if someone with
one of the smaller MFJ tuners in which the coil is very close to the small
metal cabinet could make these measurements for comparison. And the new
metal cabinet BLT is a good candidate for comparison with other forms of the
Z-match using non-metallic cases.

I will replace the tuner cover for the sake of appearance and keeping the
dust out, and for any shielding it might provide.

Hope this is interesting to someone else!   <:}

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"Starting the 58th year and it just keeps getting better!"
w5yr@att.net