[Lowfer] Slow to rise antenna current #2

[Andy - KU4XR]

Hi all:

After reading some very helpful tips from Jay - W1VD, I began
to examine my setup. I started with a dummy-load, and my RF
Ammeter. Thanks to John - W1TAG, he has an article on his
website about RF current meters. I found out that my meter,
a Weston model 425 is a 1930's vintage Thermocouple type.
The first mistake I had made was removing the .33 uF Cap that
the PA feeds into. I found out that it wants that cap. I put
it back in circuit, and a lot of the flakiness went away.
I also found that I had a mismatch in my " TEE " network
following the capacitor. Using the dummy load, and ammeter,
I experimented with the shunt cap. until I had max RF current
at min. PA current. At this point, the slow rising current
went away. Every time I keyed the xmtr, it instantly went to
full current reading, and the PA transistors were cold as a
cucumber. So you guys were right ! a mismatch was ONE of the
problems, along with the series cap in the PA output. I was
now operating into a 50 Ohm resistive load, and the xmtr was
happy.
Chapter - 2 :::::   Using the calculations that Jay told me
about ( I hate math ), I calculated my input power at 1.268 W.
RF current^2 X R-50 equaled .93845 W. into the dummy load.
If my figures are right; that is about 74% PA efficiency.
I think it should be higher than that, and I noticed that when
feeling the transistors for heat; one of the string of 4 diodes
would kill the output if my finger touched it. It's the one
coming from the base of Q1 to the PA output. This might be
normal, I'm not sure. I'll look into that more. After connecting 
to the ant. using the 74% power ( .93845 ) and ant. current of
.145 A. squared to .021025 A. these figures calculated an ant.
system resistance of around 44.63 Ohms ( I hate math ). this is
with the variometer in line and tuned to resonance ( peak output )
I did have to decrease the shunt capacitance a little on the
actual ant. to get back to Max. RF current / Min. PA current.
On the ant. the current rise started again, but after lots of
experimentation with the shunt capacitance in the " TEE "network,
instead of a 25mA rise, it's down to a 15mA rise, and faster.
The transistors are a little warm on the ant. vs the dummy load.
I feel that I have made progress today, finding a better match
for the PA at least. There are still some big antenna issues to
work out, and I plan to check components in the PA to make sure
none are bad. I will swap transistors around to try to find a
better matched pair ( higher output with less PA current ) in 
the hope of increasing the PA efficiency. The accuracy of my
RF ammeter is not known yet, I plan to try John - W1TAG way
of checking the accuracy in a 60Hz circuit at another time.
Thanks to all who gave me tips to look for, and of course if
I have made gross errors in my math ( I hate math ) please
point out my error, so the info will be correct for myself, as
well as anyone else who reads the info. But please be kind !
correcting an error, and critisizing my method are not the
same thing.

73 to all :::


Andy - KU4XR - EM75xr - Friendsville, TN.
LOWfer Beacon " XR " @ 185.29893 KHz ( QRSS-60 )
Coordinates:  N:  35* 43' 54" - W:  84* 3' 16"
http://www.myspace.com/beaconxr