Tom Horne wrote:
Is it possible to ask questions here without triggering an arcane debate
about competing views of theory. I'm about to find out. I asked
earlier in another thread what measuring instruments I would need to
have the use of in order to compare the effective radiated power of
different antennas. As near as I can tell there was no answer.

I built a collinear J pole using copper tubing. I'd like to know if it
is more or less effective at radiating whatever works to the stations
I'd like to be able to talk to under conditions of emergency operation
then say a collinear ground plane or any other omni directional antenna.

I would like to deploy the most effective practical antennas that field
testing can devise and not have to wait until the next breakthrough in
physics to be able to get my local governments Email out to my county's
government, the state government and the responding relief forces.

My question, again, is what measuring instruments can be effectively
applied to the comparison to provide results that will be born out by
real world performance.


In order to answer your question, one would need to know...
How accurately do you want to measure? If you want to know to tenths of
a dB, that's a very different matter from, say, to the nearest 3 dB.

In most practical field antenna installations, local conditions and
installation can result in field strength variations of +/- 3dB without
needing to come up with absurd scenarios.

This is why most commercial emergency HF comm systems rely on fairly
simple antennas which are fairly insensitive to surroundings (e.g.
loaded folded dipoles, or wires with autotuners at the feedpoint, and so
forth) and having enough RF power to accomodate the inevitable
variations in performance.

Note that this is a VERY different scenario than the typical ham setup,
where the ham wants to get the very best performance from limited power.


So, maybe your testing might be to work out the deployment details
(what's easy to put up), and just do simple RF testing to make sure that
your easy to deply scheme isn't "terrible" and is "good enough".

OTOH, if you're looking to do antenna shootouts with cases of beer
riding on the results, a whole nother measurement methodology would be
called for.

Now to practicalities...

Something like a Icom PCR1000 computer controlled HF receiver has a
pretty accurate signal strength measuring feature, certainly, it's
pretty good over small variations (10-20dB) in signal strength. You
could put it at some distance (a mile away?) with a short whip (so the
receiving antenna is nondirectional) and make your measurements. You'd
put a fixed amount of power into the test antenna (i.e. set up your rig
for, say, 10W out, and "put a brick on the key"..)

Actually, almost any receiver will do, if it has a reasonably stable way
to check if the received signal is at the same level. You put a
variable attenuator on the input, and just adjust it until the audio
output voltage is the same, or the S-meter hits the same tick mark on
the scale, etc. Since the receiver is always seeing the same level,
things like nonlinear AGC or uncalibrated meters don't make any
difference. It's all in the variable attenuator.

What's also important is making sure the transmitter power is really the
same each time. You don't much care exactly what it is, just that it's
the same. Almost any power meter can do this, as long as the system
isn't too horribly mismatched. Remember, you're looking to hit the same
mark, not have some absolute value. Big changes in mismatch mean that
the quality of the forward and reverse balance in the meter will have an
effect.

Easy way is to have
transmitter: power meter: tuner: feedline: antenna system.

Adjust the tuner for no reverse power on the meter, and there you go.
(Of course, feedline and tuner losses are now part of your measurement)


People literally spend their entire lives doing this kind of thing
professionally, so you need to take a step back and decide what level of
measurement you need. For all you know, just doing some A/B comparisons
when receiving WWV might be good enough.