On Sat, 20 Sep 2003 18:41:21 -0700, "Ed Price"
wrote:

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

Perhaps, but very few bench techs are found here.


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.

Arguable. Calibration is not what you do to something, that is tuning
or adjusting. Calibration is knowledge.

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

There are many ways to accomplish the calibration, again, there are
too few bench techs here to care.

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.

The Bolometer is a classic load, there are many others (like a
barreter).

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.

A good method that employs the easier methods of measuring differences
rather than absolutes. However, you must eventually obtain some
standard to make the final determination.

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


Hi Ed,

I've never run across a need for batteries, except to light the meter.
There are better meters than a Bird. The AN/URM-120 is easily better,
and sells cheaper, has all the same qualities, but for its advantage
it also is larger and presents its readings with the meter horizontal.
If those were the only down-sides, then it is much like personal
choices in tie color.

73's
Richard Clark, KB7QHC