G3rzp@aol.com wrote:
> In a message dated 19/03/2005 22:27:10 GMT Standard Time,
> philc@texascellnet.com writes:
>
> but are useless if you
> > actually want to know the power output.
>
> +/-5% works out, according to my calculator as +/- 0.22dB. Prodigious!!!
It is simply not achievable on Bird 43's - at least not on a regular
basis. My new element was out of spec the day I got it.
> If we go look at professional standards for 'Type Approving'
> equipment, we see that an approved accreditation lab is supposed to
> measure to +/- 0.75dB at 99.9% certainty. That's nearly 19%.....
I don't know what 'Type Approving' equipment is, but RF power can be
measured to a lot better than 19%. Using a water Calorimeter an amateur
should be able to do better than that using a DC/RF substitution method.
The advantage of that, compared to other techniques, is that it does not
rely on getting lots of bits of kit calibrated at great cost.
> So personally, I trust the '5%' claim as much as I do a politician.....
Same here. I *know* is is rubbish. I'm surprised they have manged to
get away claiming it for so long.
> There has been a lot of work done at ETSI, the European
> Telecommunications Standards Institute, on measurement uncertainty.
> The reports are pretty major things, but you can download them free
> from www.etsi.org <http://www.etsi.org>
> The ones on measurement uncertainty are TR100 028-1 V1.4.1 and TR100
> 028-2 V1.4.1
>
> They should help you get to sleep.....
I know there were people who spent most of their working life perfecting
the measurement of RF power in standards labs. That's not my idea of
fun, so I won't read the documents.
> 73
>
> Peter G3RZP
--
Dr. David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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