On Aug 12, 3:42*pm, JIMMIE wrote:
On Aug 12, 3:21*pm, dave wrote:

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service

On Aug 12, 3:42*pm, JIMMIE wrote:
On Aug 12, 3:21*pm, dave wrote:

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!
So what is it on the other side of the coin is what this thread is
posing to those who are familiar with respect to radiators.

You stated that MOST commercial antennas are CP. Having been in that
business to some extent, I know that statement to be false. I'm simple
asking you to prove it.

Also where is this information that shows linear antennas have 30dB of
attenuation? When? How? What conditions?

And when do the CP antennas have 3dB by comparison? Give references.

I know you can't since all these things are figments of your addled brain.

tom
K0TAR

tom wrote:
Art Unwin wrote:
The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

Please provide examples of commercial antennas that are CP. Space
communication antennas are not ok to include.

FM and TV broadcast.

dave wrote:
tom wrote:
Art Unwin wrote:
The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

Please provide examples of commercial antennas that are CP. Space
communication antennas are not ok to include.

FM and TV broadcast.

I asked him, not you because he wouldn't know any answers.

Now you've given it all away!

And he said "the majority" which is untrue.

tom
K0TAR

I have been looking for a decent CP design to try out on my
repeaters .
For many years I have been looking at the reasoning for FM
broadcasters having used CP pol with great success.

I also have a small indication that linear antennas (eg:linear
collinears)and non-linear antennas(eg:folded loop dipoles) by design
may have slightly different characteristics in the far field that
tend towards a greater degree of cross/CP from the mechanical design .

Anyone had good success with installing a CP repeater antenna(2m or
70cm) to assist with the deap fade nulls in mobile uplink to the
repeater.
I want to try rhp for TX and lhp for RX - anyone tried this
combination before?

wrote in message
...
I have been looking for a decent CP design to try out on my
repeaters .
For many years I have been looking at the reasoning for FM
broadcasters having used CP pol with great success.


In the UK, Band II VHF FM sound radio broadcasting began to fixed receivers
using horizontal polarisation (HP) for reasons including a belief that
interference from car ignition systems was predominantly vertically
polarised, and because it was found easier to achieve a good
omni-directional pattern in the horizontal plane from a transmitting antenna
based on a vertical slot (Babinet's principle) - several such slot antennas
were stacked vertically to obtain some gain and to avoid illuminating the
sky.

Later, as transistors became available and vehicular VHF receivers of
sensible size became practical, a new market emerged but it was poorly
served by the HP transmissions*. When local radio was launched in the UK,
in Band II, the new transmitters were equipped with antennas that radiated a
VP component as well as HP, and in time all Band II transmissions were
converted to mixed polarisation. Circular polarisation is one example of
mixed polarisation, but its ability to provide cross-polar discrimination is
not used in FM broadcasting.

Take a look at: http://downloads.bbc.co.uk/rd/pubs/reports/1970-35.pdf

The experience in other countries has probably been similar - same physics.



I also have a small indication that linear antennas (eg:linear
collinears)and non-linear antennas(eg:folded loop dipoles) by design
may have slightly different characteristics in the far field that
tend towards a greater degree of cross/CP from the mechanical design .


Huh?

* HP is less effective than VP for VHF communication with mobiles because
the ever-present ground reflection has reversed polarity (i.e. it's in
antiphase with the signal propagating over a direct path).



Anyone had good success with installing a CP repeater antenna(2m or
70cm) to assist with the deap fade nulls in mobile uplink to the
repeater.
I want to try rhp for TX and lhp for RX - anyone tried this
combination before?

If you use the same antenna for transmitting and receiving, and it is
fundamentally circularly polarised, then it will provide and respond to the
two different senses of CP automatically because the definition of the sense
of circular polarisation depends on the direction of propagation. But do
you think the horizontally-polarised component will help with deep nulls?

Chris

On Mon, 28 Sep 2009 14:13:31 -0700 (PDT), wrote:

I have been looking for a decent CP design to try out on my
repeaters .
For many years I have been looking at the reasoning for FM
broadcasters having used CP pol with great success.

I also have a small indication that linear antennas (eg:linear
collinears)and non-linear antennas(eg:folded loop dipoles) by design
may have slightly different characteristics in the far field that
tend towards a greater degree of cross/CP from the mechanical design .

Methinks you'll be better off with eliptical polarization, where
perhaps 70% of the power is vertically polarized, and the rest is
horizontal. The idea is that most of the energy will be properly
recieved by the traditional vertically polarized mobile antenna. The
remainder will be to fill in the gaps, where the polarization changes
to something not so vertical.

Search Google patents:
http://www.google.com/patents
for "omnidirectional circular polarized antenna". Also, look at FM
broadcast xmit antennas. Some really strange stuff there.

Anyone had good success with installing a CP repeater antenna(2m or
70cm) to assist with the deap fade nulls in mobile uplink to the
repeater.

Yes. I can't find my previous rant on the subject, so I'll try again.
Around 1968 thru 1970, I was at Cal Poly Pomona doing some experiments
with CP UHF antennas. The problem was that the local repeater was
experiencing deep Raleigh fading as mobiles moved along the San
Bernardino Freeway. The ideas was that CP would reduce these fades so
that listening to the repeater didn't sound like it was accompanied by
a machine gun. It worked but with a price. The fades were
dramatically reduced, but so was the coverage area. Antenna gain was
down at least 3dB as was maximum range for the repeater. I thought it
was a good tradeoff, but not everyone agreed. The stations that were
marginal (usually because they were too lazy to install a proper
antenna) were gone. However, the reliability of the local mobiles was
greatly improved. Range won over fade reduction and the antenna was
replaced after a few months of testing.

There was an article on the subject in "The Practical Handbook of
Amateur Radio FM and Repeaters" by Bill Pasternack and Mike Morris.
1981 by Tab Books.
http://openlibrary.org/b/OL4421123M/practical_handbook_of_amateur_radio_FM___repeaters
http://www.alibris.com/booksearch?qsort=p&isbn=0830612122
Sheesh. I paid about $5 at a hamfest.

Since it's not online, I scanned the applicable chapter, chopped out
some irrelevant junk, and posted them to:
http://802.11junk.com/jeffl/circular-polarization/
I'll convert them to a single PDF after I figure out why Irfanview is
generating garbage. Bug me if you have trouble reading the JPG's.

I want to try rhp for TX and lhp for RX - anyone tried this
combination before?

Yep. I tried that to improve TX-RX isolation. I gave up. Mounted on
a single pole, with separate phasing harnesses, I never could get the
antennas anywhere near 50 ohms. There was also just too much coupling
between the RH and LH sections for that to work. Another explanation
might be that at the time, I didn't have a clue what I was doing, but
we won't go there. The rather high VSWR certainly didn't help with
the isolation as it detuned the tx and rx cavities (formerly a
duplexer). Some rather crude testing showed that we were better off
with a single antenna, the stock duplexer, and a single CP
polarization. There was also a problem with distant stations. They
wanted to use CP on the base station to reduce the effects of
multipath (usually off the infamous L.A. smog inversion layer). That
would have required two antennas for each base station. I suggest
that you stick with one circular polarization for now.

Incidentally, note the scanned photo of the Loop Mountain site
http://802.11junk.com/jeffl/circular-polarization/cp-02.jpg
and compare it with the previous intermod factory and post-storm
removal exercise at:
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn02.html
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn03.html
One of the reasons I'm current intact and still sane is that I don't
own any repeaters and find excuses not to do any tower work.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Aug 10, 12:24*am, Art Unwin wrote:
The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

Where did you get the info that most commercial antenna use is
circular polarity?

Jimmie