[Elecraft] Monitoring transmitted signal waveforms

[Ron D'Eau Claire]

As George says, it's important that the pickup be a clean sample of the
signal.=20

It's also important to monitor the waveform of the "transmitted" signal =
at
full power as well. That may require an attenuator to protect the scope
input if you have the KPA100 or are running a kilowatt amp and using a
direct connection. The amps change the keying waveform, depending how
"linear" they are, so a clean signal at 5 watts may be nothing like the
signal coming out of an amp at 100 or 1500 watts.=20

One of the very useful bits of test gear that I have around for up to =
100
watts is a 40 dB attenuator "tap" that provides a constant-impedance =
pass
through at 50 ohms and a -40db output for a counter, scope or other
measurement gear. My "tap" is good up through 500 MHz so it has a rather
sophisticated mechanical design to minimize the impedance bump in the 50 =
ohm
line, but for HF work a simple little metal box with two coax connectors =
and
short wire between the center pins would not produce a detectable bump =
in
the line. The -40 dB "tap" consists of four resistors. Three are 820 ohm
1/2-watt metal film in series going to the center pin of the -40 dB =
output.
The fourth resistor is a 51 ohm 1/4 watt from the center pin of the -40 =
dB
output to ground.=20

If you have a copy of the June 2001 QST, look up the excellent little =
power
meter described by W7ZOI and W7PUA. It's part of that system.=20

Ron AC7AC



-----Original Message-----
Paul, the place to start is with one of  your scope probes. Next you =
need a
very low capacitance connection to the center conductor of the coax =
feeding
your antenna output system. I make my connection at the input to the =
Bird 43
wattmeter which connects to the antenna selector switch.

Actual connection is with a T- connector in the coax line. Take a PL-259 =
and
solder a short piece of #12 copper wire in the center pin about an inch =
or
so long. Cover the wire with plastic tubing or "spaghetti."

Clip the scope probe around the insulated wire in the PL-259 which is
plugged into the T-connector. Connect the probe ground to the PL-259 =
shell.

This will give you more than enough signal pickup even with 5 watts QRP.
Where the scope probe is grounded is important in picking up a clean =
signal
uncontaminated with r-f from broadcast stations, RFI, etc....

73, George W5YR