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

Raleigh fading? (Addition or subtraction of reflected signal from the
main - or flutter you hear on VHF)

You dont mention the freqency in use or the distance between antenna and
FSM. There is some kind of optimum or minimum distance (in wavelengths)
that I dont remember off hand

You dont seem to be allowing for ground effects and the desired angle of
measured radiation. (If that is important..)

Having said that how you have described it is probably how I would
attempt it!

Cheers Bob VK2YQA


Buck wrote:
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

On Sat, 05 Feb 2005 07:01:34 +1100, Bob Bob
wrote:

You dont mention the freqency in use or the distance between antenna and
FSM. There is some kind of optimum or minimum distance (in wavelengths)
that I dont remember off hand

You dont seem to be allowing for ground effects and the desired angle of
measured radiation. (If that is important..)
'

It is for testing HF antennas, but no reason it can't work for VHF as
well.

After writing this, I was thinking of the G5RV, it has a cloverleaf
pattern so it might register as a loss since the antennas would be
broadside to each other.

I don't know the distance for the FSM. I suspect it would have to be
a good distance away. probably a wave length or more.


This would work best with a beam antenna as the lobe would be
consistent. but a 3/2 wave antenna would have different radiation
lobes so it might register a loss instead of the gain it actually has.

It is a thought, but I may have to reconsider it.

Thanks

Buck
N4PGW

--
73 for now
Buck
N4PGW

Buck,
Using more than one 'station' for the FSM should take care
of the radiation pattern variatons. The more 'stations', the
better (as in 180 of them, or more, depending on the antenna?).
'Doc

On Sun, 06 Feb 2005 01:08:37 GMT, 'Doc wrote:

Buck,
Using more than one 'station' for the FSM should take care
of the radiation pattern variatons. The more 'stations', the
better (as in 180 of them, or more, depending on the antenna?).
'Doc

I think you are correct. Either that or a rotatable antenna.


If the antenna is supposed to have a clover leaf pattern, then maybe
just setting up the FSM in the angle of the lobe.

Just a thot.


--
73 for now
Buck
N4PGW

"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

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

On Fri, 04 Feb 2005 13:28:21 -0500, Buck wrote:

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

If you are trying to get a feel for the pattern of the antennas in
"the real workd" you want to have your receiving antenna far enough
away to be making far field measurements. I don't have a definition
at hand, but it think it's somewhere between 5 and 20 wavelengths.

Regards,
Ed