On Sun, 6 Feb 2005 07:52:39 -0800, "Ed Price" wrote:


"Buck" wrote in message
.. .
I want to test a couple of antenna designs and compare them to a
dipole antenna.

I am wondering if my idea is a good way to measure gain or loss from
an antenna. Here goes:

Create a place in which to install the test antenna which will be
consistent. For example, 40 foot high between two power poles (no
power lines etc, though.)

Setup a fixed location with a Field Strength Meter (FSM) that has a
fixed antenna for testing at that location.

Hang a dipole (the reference antenna) and transmit a signal that can
be calibrated to a fixed location on the FSM. Then hang the
experimental antenna in place of the dipole. Take the measurements
without changing anything from the rig. Measuring the power output
required to meet the same setting on the FSM as the dipole should give
me a fair idea about the gain or loss from the experimental antenna.

or maybe not.

What am I overlooking?

Thanks
Buck
N4PGW

--
73 for now
Buck
N4PGW


Put some ferrite tubes (big beads) on the coax near each antenna; this will
minimize radiation off the feedlines. Also, put a 3 dB attenuator on each
antenna, to stabilize the system impedance. Secure the feedlines so that
they are hanging in the exact same position each time. And don't forget that
40' off the ground is not good for frequencies below about 50 MHz.If you
want to dig very deep, there's an IEEE standard on antenna calibration (but
it's not free). You might find an old SAE 958 (IIRC) document on antenna
calibration.

Ed
wb6wsn


Thanks for the info. I am just doing this for personal information
more than professional. I will probably experiment with higher
frequency antennas such as 15-6 meters and then scale them to the
larger antennas as needed. I realize I won't learn much about the
TOA or other characteristics. It isn't for purely scientific research
as much as it is to get a measurement somewhere in the general
ballpark of the antenna.

You are correct about the ferrites, but I hadn't thought about the
attenuators. That sounds like a good idea too.

Thanks for your input.

Buck
N4PGW

--
73 for now
Buck
N4PGW