I have an old HP calorimeter buried here somewhere. I guess I should dig
it out.
73
Gary K4FMX
David Kirkby wrote:
> G3rzp@aol.com wrote:
>
> Peter, you are agreeing with *all* the comments I have put here. So
> there seems to be little (if any) disagreement between us.
>
>
>
>>Another problem with calorimetry is the time it takes, which with a
>>sweep tube amplifier would be prohibitive - even pulsed!
>
>
> 1) In response to Gary Smith I said " I suspect Bird use Calorimeters
> for internal use, but would not use them to calibrate each and every
> element they sell, as the method is too time consuming."
>
> 2) "Another big problem for amateur power measurement would be line
> voltage variations. Since any such measurement by Calorimetric methods
> will take 10's of minutes at least, there needs to be a way of keeping
> the RF and DC power constant."
>
> 3) I quoted from the book I have " On the other hand, they are bulky,
> expensive to construct, require highly trained personnel, slow,
> difficult to use, have limited dynamic range, and after therefore
> unsuitable for field use outside the laboratory"
>
>
>>
>>I haven't seen a 'scope guaranteed better than 5%, even the new super
>>dooper all singing digital things that can give aliases everywhere.
>
>
> I said that too,
>
> In response to someone I said " I'm not sure I follow your suggested
> technique, but scopes are not normally much better than a few percent
> on the Y-axis, which since the errors are squared for power, I can't
> see that being particularly good."
>
> Rich has said "I used to work in a calibration lab and we calibrated RF
> wattmeters by measuring peak-V across a 50.0-ohm termination with a
> NBS-traceable oscilloscope and doing the math." Whilst I never replied
> to Rich comments, I can't see how anyone can measure power accurtely
> with a scope.
>
>
>>And most of the time, does it matter?
>
>
>
> 1) I said " At the end of the day, you need to ask yourself what
> accuracy do you need. I think for RF power measurements, the answer is
> not very much for amateur radio use. You tend to tweak for maximum,
> keeping an eye not to exceed the current ratings on the tubes.
> Exceeding the anode dissipation by 10-15% will not be a problem if the
> temperature is kept down, so knowing the exact efficiency is not such a
> big deal. I suspect using the temperature rise across the tubes would be
> reasonable to work out anode dissipation."
>
> 2) In response to you I said "For amateur use, we don't need much
> accuracy."
>
>
>
>>73
>>
>>Peter G3RZP
>
>
> So wee seem to be agreeing on just about everything. I would maintain
> *IF* you want the accuracy, which the original poster did since he was
> considering buying new elements, calibrating his elements regularly with
> a Calorimeter would be the best way to do it.
>
> I received the following from someone by private email. I have edited it
> slightly, and removed his name, but otherwise i t is intact:
>
> " Hi David
>
> I my long gone misspent youth I worked at XXXX for a while. They used
> calorimeters for their high power (1kW & 10kW) transmitters. They didn't
> really seem all that complicated - flowing water with a meter -
> thermometers on input and output sides - standard plumbing fittings. The
> actual dummy load was quite small if I recall correctly. I seem to
> remember that the temperature rise was quite small, but the flow rate
> was quite large! I quite fancied making one at the time."
>
>
>
> Berfor making one, I'd certainly read up on what the sources of erorr
> are, and what one needs to do to reduce them, but perhaps someone will
> make one, then offer to calibrate other hams meters for a small fee. He
> might soon recover the cost of making it.
>
> PS I think Calorimeters should be renamed "Jouleometers", since Joule is
> the SI unit of power. However, if a person named Calorie invented the
> idea, then it should be kept its original name.
>
> I don't suppose the latter would go down too well with the American
> hams, as America seems to keep to an odd mix of units. They use seconds
> and Watts, and Watts are just Joules per second. Most of the rest of the
> world has gone to SI, so why not America? (That said, astronomers use
> Parsecs, which is a pretty odd unit. But perhaps there is not a known
> multiplier for metres that makes the use of metres sensible. My
> knowledge stops at Tetra, but there might be some multipliers higher
> than that.)
>
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