"Richard Clark" wrote in message
...
On 20 Sep 2003 22:23:36 GMT, (Radio913) wrote:
I've heard that the Bird Model 43 is very accurate.

Hi OM,

Now you know different. Besides, NO ONE is accurate without
comparison to a known Standard.

A Bird can be made accurate, better, in fact, than the manufacturer's
claims. I doubt you would spend the money to do it the first time,
much less each time required to keep it accurate (much less more
accurate).

It makes more sense to invest in a good load and calibrate it. It is
not at all difficult, except for the cash-and-carry tech who shuns
benchwork.

73's
Richard Clark, KB7QHC


I'll bet you'd love an invitation to expand on your comments about a "good
load" and "calibrate it."

The only good load is one that presents the desired, purely resistive
impedance. Maybe you can adjust the load, but you don't make it better by
calibration.

Or perhaps you are assuming a good load, and by calibration, you are meaning
some type of thermal calibration to indicate power.

I don't use loads to measure power, I use attenuators (sufficient for the
expected power), and put a bolometer on the end of the attenuator string. Of
course, I have the luxury of other test equipment, so I can check the
attenuators, with low power, against my spectrum analyzer and signal
generators.

All that said, I still think that a Bird 43 (and yes, a good load or
attenuator string [once you get 60 dB or so on the attenuator string, an
open-end reflection is quite minor]) is the best route for a ham. A ham
typically doesn't need even the factory accuracy of a Bird, but the
versatility of forward and reverse power, with multiple power ranges and
multiple frequency ranges, is very nice. Plus, it doesn't even need
batteries, and it's small and light. (Anybody who ever lifted HP gear can
now grin.)

For the 100 MHz region, you can think about a directional coupler. Nice, but
you still need either a bolometric power meter or a calibrated spectrum
analyzer. If you don't already have those two goodies, then the Bird is the
champion choice.

Ed
WB6WSN