Hello Fellow Drake Fans,
To recap: The wattmeter on my Palstar AT1500DT reports that I'm getting
variable output from my L-4B on dedicated 120v house circuit. On 40 it looks
like 800-900 watts out, but on 15 maybe 500. The matched 3-500Zs are about 5
years old, the power supply was rebuilt from kit (Evan may even remember my
plaintive cries for help) and I keep a muffin fan over the power supply sucking
warm air out. So I promised to do some testing and report back. Here's what I
found.
First, the setup:
Yaesu FT-1000MP Mark V via RG-8X to Drake L-4B
L-4B output via RG-213/U to Palstar AT1500DT
Output via RG-213/U to Balun Designs 1:1 choke balun (unun) 5 kW model 1115du to
Heath Cantenna via RG-8/U patch cable
10+ minute warmup
2600 volts key up in SSB mode
120v AC on a dedicated 15a. circuit
Grid current @ 200ma.
The results:
Band Freq est.drive volts/keydn ma/keydn meter on usual antenna
80 3545.41 40w 2250 520 800w 700w
40 7012.54 72w 2250 520 800w 900w
20 14063.85 68w 2250 520 700w 600w
15 21045.28 70w 2250 550 700w 500w
10 28045.11 80w 2200 620* 600w 450w
Caveats:
The Cantenna is by no means the best dummy load but it worked.
I have no idea whether the Palstar wattmeter is anywhere near calibrated and it
may be frequency-sensitive.
Have no idea how accurate the L-4B meters are, but the voltage readings seem to
be spot-on, e.g., 1700v in CW/Tune and 2600v in SSB modes.
Notes and Observations:
1. Regardless of the accuracy of the Palstar wattmeter, I WAS cranking up the
RF power knob on the Yaesu, so I am sure the variation in required input drive
is real, though the actual readings are open to question.
2. Also, I only allowed the amp to draw 620 mils on 10 for a few seconds, for
test purposes, to keep the drive @ 200 grid mils common. When I backed the
drive down to 550 ma on the plate on 10, the grid showed 160 ma. and the
wattmeter read 500w.
3. The higher the frequency, the more a minor SWR imbalance showed on the
Palstar meter, though never more than 1:1-1. I suspect that this means the
Cantenna is not a perfect 50 ohm resistive load; but then, we knew that.
4. The output readings on the dummy load differ sufficiently from what they are
with my antennas connected (see above) that it suggests I could do well by
doing some work on the transmission lines, coax switch, etc.
Nevertheless, something seems to be sub-optimal with the L-4B. It may be time
to do some work on the RF deck. The question is, what?
Your thoughts and wisdom most welcome,
Peter W2CDO
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