Circular versus linear polarization
On Aug 11, 3:28*pm, JIMMIE wrote:
On Aug 10, 11:11*am, Art Unwin wrote:
On Aug 10, 9:04*am, "christofire" wrote:
"Art Unwin" wrote in message
....
The majority of antennas used today are (commercial) circularly polarized
That probably isn't true for VHF/UHF. *Take a look at the website of a major
supplier of professional antennas such ashttp://www.amphenol-jaybeam.com/base-station-antennas-search.php. *Entering
CP in their search engine for base-station antennas yielded 2 results wheras
entering VP yielded 365!
One of the reasons for greater use of linear polarisations in professional
applications is frequency re-use on the orthogonal polarisation some
distance away - i.e. the value of the limited VHF/UHF spectrum. *That's
certainly true in Europe.
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" ?
Extensive use is made of 'mixed polarisation' *for transmitting VHF FM
broadcast services in Europe. *It may not be pure circular but it contains
significant vertically- and horizontally-polarised components. *The mobile
and portable receiving antennas have whatever polarisation they end up with,
more or less by accident, and fixed rooftop antennas are usually linearly
polarised. *DAB and terrestrial television are transmitted using V or H
linear polarisation.
Chris
Hmm * * *A bit too technical for me! *When I model my antennas it
shows *gain for cp being 3 db above the gains of vertical and
horizontal for the same antenna. Is that what you call "mixed
polarization? *In other words, it picks up all polarizations with a
max deviation in signal strength of only 3 db.
I find it hard to make any sort of comparison when using reflective
waves at HF because it is not clear to me exactly what sort of
rotations *occur at the reflections on earth and of its layers
together with possible rotation in transit in between in the absence
of true comparison experiments.- Hide quoted text -
- Show quoted text -
Describe the circular antenna you are modeling? With the gain you are
claiming it doesnt seem to be an apples to apples comparison. I
suspect you are comparing a fullwave loop to a halfwave dipole. Show
the data you are using for your model or be prepared for most to
suspect you of the usual handwaving.
Jimmie.
NO
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