[Yaesu] RF Metering

[Bob]

Thermocouples in RF meters are a very POOR choice for measuring SSB 
voice signals, due to the slow response! A Bird 43P is MUCH better for 
SSB peak power, the thermocouple is OK for CW of FM type, AVERAGE power 
readings, but finding a thermocouple with low enough inductance for 
UHF/ MICROWAVE accuracy is likely to be a problem.--73, KC3VO, Bob Curry


-----Original Message-----
From: Dr. David Kirkby <david.kirkby at onetel.net>
To: Rob Atkinson <robk5uj at gmail.com>
Cc: Yaesu <Yaesu at mailman.qth.net>
Sent: Wed, Jun 1, 2011 12:23 pm
Subject: Re: [Yaesu] FT-ONE - low output.


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.

I think for me a spectrum analyser is the easiest solution. It may not 
be the
best, but is good enough. I could calibrate a ham meter against that.


--
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