[time-nuts] OT: Power level reference

[Joseph Gray]

I'm not ready for "power nuts" yet, but thanks to all for the
suggestions. I was considering the o'scope method, but thought I'd see
what others had to say. It's always interesting to see how different
people tackle a problem.

Joe Gray
KA5ZEC

On Tue, Dec 1, 2009 at 5:00 PM, J. Forster <jfor at quik.com> wrote:
> Scopes tend to have non-flat frequency response. I'd consider a precision
> load and something like an HP 3400A True RMS meter for up to a hunderd MHz
> or so.
>
> Above 10 MHz the HP 432A would be my choice.
>
> FWIW,
> -John
>
> ===============
>
>
>> At 11:41 PM 11/30/2009, Joseph Gray wrote...
>>>We all have our various highly accurate frequency and perhaps time
>>>references. Is there a relatively simple and inexpensive method of
>>>making an accurate RF power level reference?
>>>Joe Gray
>>>KA5ZEC
>>
>> Since you're a ham, I'll assume you're primarily concerned with the
>> simple case (50 ohm source impedance, sine wave, HF-VHF). Use an
>> o-scope to measure the p-p voltage across a precision 50 ohm load (I
>> use the Caddock thick film resistors available through Digikey, which
>> are 1%, with minimal inductance).
>>
>> The power is then W=((Vpp/2)^2)/100
>>
>> Not time-nuts precision, but good "bang for the buck," and you can get
>> better accuracy than a Bird wattmeter (which is only 5%), assuming you
>> have a decent scope. Without an o-scope, you can make a peak detector
>> and use a voltmeter, with some loss of low level accuracy.
>>
>> You asked for "simple and inexpensive." For higher frequencies,
>> different impedances, non-sine waves, the other more expensive
>> solutions are needed.
>>
>>
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