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From: firstname.lastname@example.org (Tom Bruhns)
Subject: Re: RF power measurement (again)
Date: 18 Nov 2002 16:44:29 -0800
NNTP-Posting-Date: 19 Nov 2002 00:44:29 GMT
o Do you know that the scope is good for the frequency you're
o Does the resistor get warm? Can you compare with
a similar resistor excited with DC?
o Do you know that the transmitter is designed to output
power to a 50 ohm load?
o Are you sure the resistor looks reasonably like 50
ohms at your operating frequency?
Since the transmitter is taking more than 2 watts input power, it
should be apparent what gets warm. Is it the load, or the transmitter
(or both)? I'd think you'd get a watt or more output for that much
input, if the load is correct for the transmitter.
Paul Burridge wrote in message news:...
> Hi all,
> I've just stripped a radio control transmitter to try to ascertain its
> output power. This is one of those hand-held Futaba ones with the
> telescopic ariel; runs of 12v battery. total DC current drain was
> 220mA on transmit; although that includes a couple of fairly large and
> bright LEDs. Anyway, discounting say 20mA for those, that still
> amounts to DC input power for the whole circuit at 2.4 Watts. Anyway,
> on removing the ariel and soldering a 50 ohm carbon resistor from
> ground to where the ariel was, an oscilloscope showed a pk-pk output
> voltage across the resistor of only 0.25 volts. By my calculation that
> means only 1.25mW output power. Can this possibly be right? It seems
> very low indeed to me. BTW, there does not appear to be a PA stage as
> such on the circuit board at all.
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