[TowerTalk] steppIR Gain--test method

[Tom Rauch]

> In any event, the 141 series can be quite accurate if you
know
> what you are doing and let the instrument fully warm up.

The problem is people measure something and then several
hours, weeks, or days later measure something else without
having a reference standard. Worse yet they compared what
they measure to something else measured somewhere else by
who-knows-what method (if any method at all).

When a path is long (many wavelengths) small variations in
that path change things a great deal, especially if
polarization does not favor propagation along that path.
That's why it is undesirable to measure HF antennas at any
distance beyond a few wavelengths or far into the farfield
area. Still, people do that. I think it is because they read
how BC stations normalize (not MEASURE, but normalize) FS to
one kM or one mile.
I assume when people read about FS of 199.1uV/m at one mile
(or one km) they assume that's the place where someone
planted the FS meter and the number that came up on the
display.

As for the 141, it's a pretty old and as such unreliable. It
wasn't that gain stable when less than 30 years old, and the
ones floating around for 800 bucks haven't gotten better
with age. They are OK for doing some things, but repeatable
comparisons of things 8 dB apart made 8 days apart isn't
likely in the "good use" column.

Very few casual experiments actually use a Bird wattmeter
correctly, so I doubt they calibrate something like a HP141
and plug-ins accurately. Even if they do the site is likely
so full of variations and the measurement point out on the
slope a large variable attenuator everyone is lucky to be
within 3dB.

This is why we see all the weird gain claims that exceed
theoretical limits, and why with patience we eventually all
the fantasy antenna designs that in a few weeks or years
just flop.

To put it in a few words, anyone buying an antenna based on
a claimed or perceived advantage of  a couple dB or less is
probably not using the best information to make a choice.
Appearance, life, reliability, weight, neat features like
flipping directions instantly....all very good reasons.

Gain, when the data is likely to be off more than the
difference, is not a wise focus.