[Premium-Rx] Measurement of Oscillator Output Power

[George Georgevits]

Hello to the Group,

I know this is not directly on topic, but I was hoping someone in the Group
may be able to offer some advice on a rather difficult problem I am
currently grappling with?

I have been trying to make a measurement of the radiated power of a low
power transmitter running on 433MHz. It consists of a simple one transistor
oscillator, whose frequency is controlled primarily by a SAW device in the
base circuit, plus a coil as the collector load and two capacitors. It has
no antenna as such. It relies on the coil to radiate, in much the same way
as a grid dip oscillator. The coil is just a PCB track in the shape of an
arc, about the diameter of a half dollar coin. My problem is that I would
like to make an estimate of the radiated output power. Due to the nature of
the oscillator, it is not possible to measure the radiated power by direct
connection because not all of the radiation comes from the coil, and in any
case, connecting to the circuit anywhere disturbs the operation drastically.

Its radiation pattern is far from isotropic, so measuring the field strength
at a given distance is no help.

So how does one measure the radiated power of something one cannot connect
to?

My best guess has been to measure the DC input power, and subtracted the DC
dissipation in the circuit. The difference should be the total RF power
(dissipated + radiated). However, this still leaves the big unknown of
oscillator efficiency.

Any advice at this point would be most appreciated.



Also, I came across a very good site for information on how to make precise
measurements of the frequency, phase and frequency stability of precision
oscillators. I thought it may be of interest to some members of the Group.
See http://tf.nist.gov/phase/Properties/sumintro.html

Regards,
George Georgevits