From: Mike J Pulley (Mike_J_Pulley@ccm.ch.intel.com)
Text item: Text_1
If you plan to build a 40-40 kit, read on...
Yep, I got my own 40-40 up and running. After the normal cockpit
errors, it went on the air without any smoke escaping from the
Output power was low... only about 160mW. All the tuning
capacitors peaked up just fine. However, driving the transmitter
above 160mW caused wild oscillations and distortion on the output
signal. (Yes, I did make an inaugural QSO or two at 160mW
anyway! 1000m/W, here I come!)
The fuse resistance was too high. Go figure! I used a 1/8 amp
fuse to protect my handiwork during the smoke test phase. Heck,
I build a holder into the chassis just because that's the
conservative kinda guy I am. During transmit, the fuse reduced
VCC down to 10V, preventing the transmitter from developing full
A 1/2 amp or 1 amp fuse works just fine. Now I have a bone
crushing milli-legal kilowatt!
If you use a fuse for protection, make sure its big enough to
support your operating voltage during transmit.
Here's a freebie...
SUPPLY VOLTAGE (VCC) CHARACTERIZATION TESTS
How low can VCC sag before the transmit signal turns to hash?
Properly tuned according to Dave Benson's instructions, I found
the transmitter operates just fine with power supply voltages
down to about 9V. I tested up to 14V, too, before I lost my
nerve. The output power tracks VCC slightly, but never below 1W;
the transmitter produces a squalling racket before the power dips
lower than that.
All tests were performed using a 50 ohm resistive load. YMMV.
Why should you care? Now you know how low you can tolerate
battery voltage before you're forced off the air during FD!
-- Mike, WB4ZKA
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