From: firstname.lastname@example.org (Bob Wilson)
Subject: Re: designing an HF Powermeter
Date: Sun, 08 Sep 2002 05:18:09 -0000
Organization: Your Organization
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In article ,
>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
>>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.
The ARRL handbook has (or at least had) a basic design concept of this. As
you say, nothing but a meter, a couple of diodes and a cap or two. I built
one many (many!) years ago and it worked great.