[Yaesu] FT-ONE - low output.

[Jerry Flanders]

At 12:23 PM 6/1/2011, Dr. David Kirkby wrote:
>On 05/29/11 12:49 PM, Rob Atkinson wrote:
> > I don't argue about the Bird accuracy but if you don't like a 43, how will
> > you be content with any hammy hambone watt meter out there 
> marketed to hams?
>
>I think my point is that hams don't really require great accuracy in power
>measurement.
>
>Unfortunately I've never tested any ham meters in a lab, so I don't know how
>good/bad they are.
>
> > If you want to achieve accuracy on a budget, consider getting a 
> thermocouple
> > RF amp meter (they show up at hamfests for a few dollars/pounds/euros but
> > are often hidden under junk because most hams don't give them much value
> > which is good for you) that measures 6 A and a good 50 ohm non-reactive
> > dummy load.   Mount the meter in an aluminum box in series with UHF jacks
> > mounted on the sides.  Measure your current into 50 ohms and calculate the
> > power.   Actually with your legal limit a 2 or 3 A meter is fine.
>
>I don't have much clue about how accurate that would be. I'm not an 
>expert in RF
>power measurement, but when it comes to Bird meters, I probably know 
>more than
>99.99 % of hams.  At least one review on eHam describes the meter as "lab
>grade". The reviewer is seriously mistaken.
>
>I think my main issue with Bird is the claimed accuracy and the cost. If the
>accuracy was as good as Bird state, then I'd have no problem with the cost.
>
>But when Bird claim +/- 5% of FSD, and I know some don't even meet 
>10% of FSD,
>then I do have a problem with the meter.
>
>I've often wondered how difficult it would be for hams to make a water
>calorimeter. For high power, that's how its measured in a standards lab. Of
>course, this would require that you transmit for a time sufficient to reach
>thermal equilibrium, which would exceed the duty cycle of most ham 
>rigs. Making
>one would be a major project, but an interesting one and within the 
>capabilities
>of a dedicated constructor.
...

Not difficult at all, actually - just different from the way most ham 
measurements are done. In a quantitative analysis college chemistry 
course I was astonished at how accurate, yet simple  calorimeters 
are. Years later when I wanted to check the output of a QRP 
transmitter I remembered this. I took a couple of styrofoam cups and 
a few ounces of water and it all worked just as well as the college 
lab equipment. I checked my system by comparing heat from my TX 
against heat from a measured known DC source using the same immersed 
load resistor

You have to look up conversion constants to convert units back and 
forth (BTUs to Watts, e.g.) and use common sense about test design.

Google says there is an article on calorimeter use in  the ARRL 
Antenna Handbook15th ed., p. 27-13 . I haven't read it.

Jerry W4UK