From: Don Pearce
Subject: Re: designing an HF Powermeter
Date: Sat, 07 Sep 2002 12:48:41 +0100
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On Sat, 07 Sep 2002 11:32:35 GMT, "amdx" wrote:
>> Could you explain what you mean by the phase angle of the >signal. I mean,
>it is 25 to 75 degrees with respect to what?
>> And is this to be an absorption power meter, terminating the line >or is
>it a throughline like a Bird?
> A phase angle means the current and voltage are not in phase.
>The current can lead or lag the voltage, if the voltage leads, the
>circuit is inductive, if the current leads the circuit is capacitive.
>ELI the ICE man is a useful phrase to remember.
>In ELI the E (volts) comes first (leads) the I (current), and the L means
>In ICE the I (current) comes first (leads) the E (volts) the C means
> Most of my loads will be capacitive (25 to 70 degrees) but the
>meter should measure inductive and capacitive loads.
> The design is throughline, I'll put it between the amp and the load.
>I plan on UHF connectors in and out.
> Battery operation may be preferable but not mandatory.
OK, if it is throughline, using a directional coupler for sniffing the
signal, then the phase angle is taken care of automatically by
measuring the forward power and subtracting the reverse power.
Provided you can terminate the coupled line nicely both ways you can
put diodes both ends and make both measurements at once - just use a
pushbutton to select which you are measuring..
I can't think offhand of any kind of chip that would help you here.
Just the diodes, smoothing capacitors and a moving coil meter would
appear to be what you need. You shouldn't even need any batteries -
there is plenty of power coming in on the RF.