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Old March 18th 05, 04:01 AM
Lex-Lutor
 
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Default Circular V.S. Vertical antenna polarization !

I'm interested in real results between this two antennas, urban area, same
power, same high etc. Running circular we have only 50% of power, compared
to normal dipole, but there are many positive feedbacks about circular
polarization in urban area!



Is this really true?





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Old March 19th 05, 03:45 PM
Scott Dorsey
 
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Lex-Lutor wrote:
I'm interested in real results between this two antennas, urban area, same
power, same high etc. Running circular we have only 50% of power, compared
to normal dipole, but there are many positive feedbacks about circular
polarization in urban area!


For FM, yes, circular polarization is a very good thing. Part of it is
because the antenna orientation no longer matters; your listener can have
a vertical whip in a car or a horizontal dipole and still get good reception.

In addition there are some serious benefits in reduced multipath, many of
which really only apply if the listener has a circularly polarized receive
antenna, but some of which are of benefit even with a whip.

Is this really true?


Yes. Pretty much everyone today is running some sort of circular polarization.
The real difference is in the antenna patterns and how low the angle of
radiation is. You don't want to waste your signal by sending it out into
space or into the ground.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Old March 19th 05, 03:45 PM
Bob Haberkost
 
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"Lex-Lutor" wrote in message
...
| I'm interested in real results between this two antennas, urban area, same
| power, same high etc. Running circular we have only 50% of power, compared
| to normal dipole, but there are many positive feedbacks about circular
| polarization in urban area!

| Is this really true?

In a manner of speaking, yes, it's true. The reason why you have 1/2 the power
that you would with a straight dipole is because half the power transferred goes
into the other polarisation (10kW ERP = 5kW Horiz + 5 kW Vert). And the reason
why one uses vertical polarisation is for the number of automobile receivers
that have vertically-oriented antennas. But, other than that (with one
exception which I'll cover presently) there's no good reason why you'd run
C-pol. For the rare individual who has a C-pol receiving antenna, (s)he'd be
picking up both polarisations, and therefore get 3dB better
signal-to-noise....but in an urban area, that effort is for naught, since
there's already plenty of RF, and twice more than plenty is still more than
plenty. For the rest of those using dipoles in random orientations, they're
just as susceptible to multipath, fading, and other propagation effects that
would be experienced with a single polarisation. Still, there's some value in
this since it wouldn't make any difference which orientation a simple dipole was
in, if it had a C-pol signal to work with.
--
-----------------------------------------------------------------------------
Men born to freedom are naturally alert to repel invasion of their liberty by
evil-minded rulers. The greatest dangers to liberty lurk in insidious
encroachment by men of zeal, well-meaning but without understanding." -- Justice
Brandeis
-----------------------------------------------------------------------------
For direct replies, take out the contents between the hyphens. -Really!-


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Old March 19th 05, 03:45 PM
David Eduardo
 
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"Lex-Lutor" wrote in message
...
I'm interested in real results between this two antennas, urban area, same
power, same high etc. Running circular we have only 50% of power,
compared
to normal dipole, but there are many positive feedbacks about circular
polarization in urban area!


I did extensive empirical testing in Quito, Ecuador in the mid 60's on
HCTM1, using both horizontal and vertical polarization. I ended up with only
vertical, which reduced the multipath from the reflection of the hills and
mountains considerably. At that time, HCTM1, 95.1, was the only FM on the
air in that city of 700,000 lying in a valley in the Andes, so it was a good
test of signal. Since we were the only FM for about 1000 miles around, we
could do pretty much whatever we wanted.


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Old March 20th 05, 09:00 PM
Robert J Carpenter
 
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Lex-Lutor wrote:
I'm interested in real results between this two antennas, urban

area, same
power, same high etc. Running circular we have only 50% of power,

compared
to normal dipole, but there are many positive feedbacks about

circular
polarization in urban area!


Very, very much not an urban setting, but West Virginia Public Radio
was exclusively horizontally polarized at most, if not all, their
dozen mountain top transmitters. The chief emgineer contended it
worked better in the mountainous terrain. Their situation might have
assumed a fixed transmitter power out, thus the circular would result
in half the ERP (per polarization).

I note that they have recently obtained construction permits to
convert to circular. Perhaps they are buying new transmitters - which
will have much higher efficiency. This way the power bill and wires
up the mountain need not change (much) to get the higher transmitter
output needed to maintain the same horixontal ERP when going to
circular.




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Old March 21st 05, 05:41 PM
Scott Dorsey
 
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Robert J Carpenter wrote:

Very, very much not an urban setting, but West Virginia Public Radio
was exclusively horizontally polarized at most, if not all, their
dozen mountain top transmitters. The chief emgineer contended it
worked better in the mountainous terrain. Their situation might have
assumed a fixed transmitter power out, thus the circular would result
in half the ERP (per polarization).


I think this was the case at the time when most listeners were at home
with horizontal folded dipoles.

I note that they have recently obtained construction permits to
convert to circular. Perhaps they are buying new transmitters - which
will have much higher efficiency. This way the power bill and wires
up the mountain need not change (much) to get the higher transmitter
output needed to maintain the same horixontal ERP when going to
circular.


The big deal is that in the past 15 years or so, radio listenership has
moved very much into the car (even for NPR which tends to have more home
listeners than most stations) which has made vertical components that
much more important.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Old March 22nd 05, 06:50 PM
Robert J Carpenter
 
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Default


"Scott Dorsey" wrote in message
...
Robert J Carpenter wrote:

Very, very much not an urban setting, but West Virginia Public

Radio
was exclusively horizontally polarized at most, if not all, their
dozen mountain top transmitters. The chief emgineer contended it
worked better in the mountainous terrain. Their situation might

have
assumed a fixed transmitter power out, thus the circular would

result
in half the ERP (per polarization).


I think this was the case at the time when most listeners were at

home
with horizontal folded dipoles.


The chief engineer claimed that it worked better in his car as well.
YMMV.




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