Message-ID: <001c01c38276$89597940$3704210a@Hugh>
From: "Hugh M0WYE" <m0wye@thersgb.net>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 24 Sep 2003 09:33:27 +0100
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Subject: LF: Testing soon
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Hi Gary,
I don't have the experience of some of the other operators on this
reflector, but I did face a similar problem last year - i.e. how to test and
set up my TX with next to no test equipment.
I built the RF current meter described in the LF Experimenter's Handbook, to
measure the current, and a simple, peak-sensing voltage probe consisting of
a diode, a
resistor and a capacitor (make sure the diode you use has a high enough
reverse voltage rating !) connected to some cheap (2 for Ł5) Maplin DVMs.

I divided the voltage readings by 1.414 to give me the RMS volts, and I had
a calibration curve for the current meter. Then I multiplied volts by
current together using an uncalibrated pocket calculator, to get the power,
and divided them to get an idea of antenna impedance (resistance).

Getting an accurate power reading this way, depends on the current and
voltage being roughly in phase - but then it should be when the aerial is
fairly well matched to the amp - and will be into a dummy load.

Some ideas for calibrating the current meter were suggested on this
reflector a while back, but once you've got something that produces some
output current you can run it into a resistor load and measure the voltage
across the resistor with the voltage probe to calibrate the current meter.
Ohms law.

Sounds as if you've already been tuning for "maximum smoke" !

I wish you every success.

73
Hugh M0WYE