Based on another thread a few weeks back in which Horizontal dipoles
were being compared to Vertical antennas, and from a little chiding from
Roy, W7EL, I decided to do some testing on my own personal versions of
the two.


My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Part one of this experiment is to calibrate the S-meter. I found that
trying to calibrate the thing with on-air signals was a nuisance, and
probably wouldn't be as accurate, so I used a signal generator.

I started out with a +20 signal, then worked my way down.

+20 start
S9 -18 db
S8 -23 db
S7 -26 db
S6 -29 db
S5 -32 db
S4 -35 db
S3 -37 db
S2 -39 db
S1 -41 db

All in all, I would have to say that the meter tracks very well from S8
to S4, and the only place that wasn't that great was from S9 to S8. But
considering the transient nature of the signals we are receiving, I
would have to day that the S-meter is of reasonably close accuracy.

With my newly calibrated S-meter I am ready to start looking at what the
two different antennas are doing for me. I have a coaxial switch to jump
back and forth between the two. My initial impressions are that there
are some surprises. The difference in noise levels varies by antenna by
band. On some bands the vertical is noisier, and on others it is the OCF
dipole. Especially intriguing is that on PSK mode, where I can see
several signals at one time, switching between antennas will attenuate
some signals, while other signals increase in strength. I think that my
vertical works better than I gave it credit for, but If I definitely
want *both* antennas.

Next installment will be the band to band comparison of the two antennas
with some numbers.

Installment three will be an investigation of that PSK signal strength
business.

- 73 de Mike KB3EIA -

On Sun, 05 Mar 2006 19:29:12 -0500, Mike Coslo
wrote:

Based on another thread a few weeks back in which Horizontal dipoles
were being compared to Vertical antennas, and from a little chiding from
Roy, W7EL, I decided to do some testing on my own personal versions of
the two.


Mike, this sounds interesting.

My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

Another, are the antennas coupled significantly, eg is one within the
near field zone of the other? It is pretty hard to avoid in a
residential block on the low bands, and it will confuse the results
somewhat.


Part one of this experiment is to calibrate the S-meter. I found that
trying to calibrate the thing with on-air signals was a nuisance, and
probably wouldn't be as accurate, so I used a signal generator.

I started out with a +20 signal, then worked my way down.

+20 start
S9 -18 db
S8 -23 db
S7 -26 db
S6 -29 db
S5 -32 db
S4 -35 db
S3 -37 db
S2 -39 db
S1 -41 db

Not only is the shape of the scale an issue, but the granularity or
resolution, especially with LCD meters, or any meter where there are
discrete steps in the meter current (such as where a D/A converter
drives the meter movement).

If you want to move beyond S meters, you could try FSM
(www.vk1od.net/fsm) and organise some constant carriers at known
distances / radiation angles that you could make a series of
measurements of and produce summary statistics (median and inter
quartile range) for each antenna type.


All in all, I would have to say that the meter tracks very well from S8
to S4, and the only place that wasn't that great was from S9 to S8. But
considering the transient nature of the signals we are receiving, I
would have to day that the S-meter is of reasonably close accuracy.

With my newly calibrated S-meter I am ready to start looking at what the
two different antennas are doing for me. I have a coaxial switch to jump
back and forth between the two. My initial impressions are that there
are some surprises. The difference in noise levels varies by antenna by
band. On some bands the vertical is noisier, and on others it is the OCF
dipole. Especially intriguing is that on PSK mode, where I can see
several signals at one time, switching between antennas will attenuate
some signals, while other signals increase in strength. I think that my
vertical works better than I gave it credit for, but If I definitely
want *both* antennas.

I described a technique for assessing the relative performance of
mobile stations by having them transmit known constant carrier, each
station space about 200Hz and turning circles in a carpark near each
other, and to observe them at typical propagation distances with an
audio spectrum analyser, watching the relative strength of the
carriers.

Your PSK setup is affording you the same type of comparison, and
provides a ready (and recordable) assessment of the relative strength
of the stations under the two antenna scenarios. Be great if you could
orchestrate stations at known distances as part of an organised test.


Owen

Next installment will be the band to band comparison of the two antennas
with some numbers.

Installment three will be an investigation of that PSK signal strength
business.




- 73 de Mike KB3EIA -
--

Owen Duffy wrote:
On Sun, 05 Mar 2006 19:29:12 -0500, Mike Coslo
wrote:

Based on another thread a few weeks back in which Horizontal dipoles
were being compared to Vertical antennas, and from a little chiding from
Roy, W7EL, I decided to do some testing on my own personal versions of
the two.


Mike, this sounds interesting.

Sorry for the delay getting back on-line...

My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Another, are the antennas coupled significantly, eg is one within the
near field zone of the other? It is pretty hard to avoid in a
residential block on the low bands, and it will confuse the results
somewhat.

Almost certainly there is some interaction. It isn't a very big yard.

Part one of this experiment is to calibrate the S-meter. I found that
trying to calibrate the thing with on-air signals was a nuisance, and
probably wouldn't be as accurate, so I used a signal generator.

I started out with a +20 signal, then worked my way down.

+20 start
S9 -18 db
S8 -23 db
S7 -26 db
S6 -29 db
S5 -32 db
S4 -35 db
S3 -37 db
S2 -39 db
S1 -41 db

Not only is the shape of the scale an issue, but the granularity or
resolution, especially with LCD meters, or any meter where there are
discrete steps in the meter current (such as where a D/A converter
drives the meter movement).

If you want to move beyond S meters, you could try FSM
(www.vk1od.net/fsm) and organise some constant carriers at known
distances / radiation angles that you could make a series of
measurements of and produce summary statistics (median and inter
quartile range) for each antenna type.

All in all, I would have to say that the meter tracks very well from S8
to S4, and the only place that wasn't that great was from S9 to S8. But
considering the transient nature of the signals we are receiving, I
would have to day that the S-meter is of reasonably close accuracy.

With my newly calibrated S-meter I am ready to start looking at what the
two different antennas are doing for me. I have a coaxial switch to jump
back and forth between the two. My initial impressions are that there
are some surprises. The difference in noise levels varies by antenna by
band. On some bands the vertical is noisier, and on others it is the OCF
dipole. Especially intriguing is that on PSK mode, where I can see
several signals at one time, switching between antennas will attenuate
some signals, while other signals increase in strength. I think that my
vertical works better than I gave it credit for, but If I definitely
want *both* antennas.

I described a technique for assessing the relative performance of
mobile stations by having them transmit known constant carrier, each
station space about 200Hz and turning circles in a carpark near each
other, and to observe them at typical propagation distances with an
audio spectrum analyser, watching the relative strength of the
carriers.

Your PSK setup is affording you the same type of comparison, and
provides a ready (and recordable) assessment of the relative strength
of the stations under the two antenna scenarios. Be great if you could
orchestrate stations at known distances as part of an organised test.

I'll probably be doing the next best thing, which is to do a lookup of
the various callsigns as I see them.

The more I see of waterfall displays, the more I like them. I would love
to see one as standard on an HF rig.

- 73 de Mike KB3EIA -

On Tue, 07 Mar 2006 14:18:47 -0500, Michael Coslo
wrote:

....

My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Mike, I understand that feedline radiation is an un-escapable
characteristic of an OCF dipole, caused by the asymmetric feed. Some
even claim it as a major advantage (eg Caroline Windom). Whilst no
dipole is perfect in that respect, the OCF dipole is less perfect, and
it may be worth modelling the thing to comment in your findings on the
probably magnitude of the contribution by the feedline.

Great project, look forward to follow-ups.

Owen
--

On Tue, 07 Mar 2006 14:18:47 -0500, Michael Coslo
wrote:

Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Hi Mike,

Not all 4:1 BalUns exhibit enough (or sometimes any) common mode Z.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Tue, 07 Mar 2006 14:18:47 -0500, Michael Coslo
wrote:

Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?
There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Hi Mike,

Not all 4:1 BalUns exhibit enough (or sometimes any) common mode Z.

Okay. Perhaps I might better characterize my experiment as a comparison
of a vertical and an OCF dipole of indeterminate vertical vs horizontal
performance. I was under the impression from the designers of this
flavor of dipole that they were not radiating from the feedline unless
you wanted that "feature". In that case you would feed the antenna with
balanced line. Certainly the antenna doesn't seem to be radiating RF
from anywhere but the antenna bits.

p.s. forgive the spelling, I am using a beta of Thunderbird for my
newsgroups, and it seems to have a few quirks that make it hard to see
what I have written!!

- 73 de Mike KB3EIA -

On Wed, 08 Mar 2006 09:47:18 -0500, Michael Coslo
wrote:

I was under the impression from the designers of this
flavor of dipole that they were not radiating from the feedline unless
you wanted that "feature".

It is pretty well known that an OCFD is a bear when it comes to common
mode current on the feedline. Usally requiring more than one common
mode choke to tame the sucker.

Danny, K6MHE

On Wed, 08 Mar 2006 09:47:18 -0500, Michael Coslo
wrote:

I was under the impression from the designers of this
flavor of dipole that they were not radiating from the feedline unless
you wanted that "feature".

Hi Mike,

This is not outside the realm of possibility. Whose antenna is it?

73's
Richard Clark, KB7QHC

Michael Coslo wrote:
Okay. Perhaps I might better characterize my experiment as a
comparison of a vertical and an OCF dipole of indeterminate vertical vs
horizontal performance. I was under the impression from the designers of
this flavor of dipole that they were not radiating from the feedline
unless you wanted that "feature".

Unfortunately, even if the designers don't intend the feedline to
radiate, it's very difficult to avoid. A single balun at the feedpoint
is very likely not enough to prevent it.

In that case you would feed the
antenna with balanced line.

That would make no difference at all in determining whether or not the
line would radiate.

Certainly the antenna doesn't seem to be
radiating RF from anywhere but the antenna bits.

The amount of feedline common mode current and therefore radiation will
vary from band to band, probably a great deal. It's easy enough to make
up a simple current probe with a clamp-on core and make quantitative
measurements if you're interested. They've been described on this
newsgroup several times.

Roy Lewallen, W7EL

I'm glad to see that my chiding has had a positive result.

Be sure you calibrate your S-meter on each band you'll be using it on,
and that the RF gain control and any preamplifier and input attenuator
settings are the same as they are when making measurements.

Especially when comparing horizontal and vertical antennas, you'll
likely have to make several measurements over a period of time. I've
seen many cases where one antenna is a good 20 dB stronger than the
other, then over the next minute or so their relative strengths reverse.
This is due to polarization rotation of the received signal. On 40 and
80 meters at least, this is common and often has a period of around a
minute or more. Really makes me chuckle when I hear "Ok, this is antenna
1. Now this is antenna 2. Which is stronger?"

If neither antenna is consistently stronger than the other, you can put
a fixed attenuator is line with one of the antennas and the step
attenuator in line with the other to make comparison easier.

People who blindly assume the marks on their S-meters are 6 dB apart
should take a good look at your calibration results.

Roy Lewallen, W7EL

Mike Coslo wrote:
Based on another thread a few weeks back in which Horizontal dipoles
were being compared to Vertical antennas, and from a little chiding from
Roy, W7EL, I decided to do some testing on my own personal versions of
the two.


My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Part one of this experiment is to calibrate the S-meter. I found that
trying to calibrate the thing with on-air signals was a nuisance, and
probably wouldn't be as accurate, so I used a signal generator.

I started out with a +20 signal, then worked my way down.

+20 start
S9 -18 db
S8 -23 db
S7 -26 db
S6 -29 db
S5 -32 db
S4 -35 db
S3 -37 db
S2 -39 db
S1 -41 db

All in all, I would have to say that the meter tracks very well from S8
to S4, and the only place that wasn't that great was from S9 to S8. But
considering the transient nature of the signals we are receiving, I
would have to day that the S-meter is of reasonably close accuracy.

With my newly calibrated S-meter I am ready to start looking at what the
two different antennas are doing for me. I have a coaxial switch to jump
back and forth between the two. My initial impressions are that there
are some surprises. The difference in noise levels varies by antenna by
band. On some bands the vertical is noisier, and on others it is the OCF
dipole. Especially intriguing is that on PSK mode, where I can see
several signals at one time, switching between antennas will attenuate
some signals, while other signals increase in strength. I think that my
vertical works better than I gave it credit for, but If I definitely
want *both* antennas.

Next installment will be the band to band comparison of the two antennas
with some numbers.

Installment three will be an investigation of that PSK signal strength
business.

- 73 de Mike KB3EIA -