[opendtv] Re: VHF Stations Seek Solutions for Reception Problems, by D
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 01 Jul 2009 16:45:16 -0700
From Dan,
>Did CP transmissions for UHF ever catch on, or are they still mostly H
polarized? If >CP is common, I would think CP antennas would be
commonplace.
>The article states that the power requirement doubles to power each
polarized
> plane for the same ERP. Any changes there?
Our company constructed UHF stations with full CP where economically
feasible but we often used elliptical polarization when sufficient
transmitter power for full CP was unavailable (read unaffordable).
I don't believe that many other companies did this; it requires a major
capital investment and the increase in operating cost is very significant
(yes, you must double your transmitter power for CP) as many VHF stations
learned after installing UHF DTV transmitters.
I do know that a number of VHF stations upgraded to CP over the years (often
when replacing old antennas) but those capital and operating costs were
relatively minor.
Was it worth it? IMO a yes for VHF but for UHF, Possibly, depending upon
your market dynamics. I do know that in all cases where I was involved, our
CP facilities had significantly fewer OTA reception problems than the other
non CP stations in our markets. This is also the case for a number of CP VHF
facilities.
Dale
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]On
Behalf Of dan.grimes@xxxxxxxx
Sent: Wednesday, July 01, 2009 11:58 AM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: VHF Stations Seek Solutions for Reception Problems,
by D
And how about the tripole CP receive antenna:
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=00115102
How does the helix antenna achieve broad spectrum? Is the (apparent)
rotational speed constant, therefore a fixed radians per change in z axis
for any wavelength? Or is it wavelength/frequency dependant also?
A 1982 IEEE paper for analog about a late '70s installation of a CP
transmitting antenna:
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01456745
Did CP transmissions for UHF ever catch on, or are they still mostly H
polarized? If CP is common, I would think CP antennas would be commonplace.
The article states that the power requirement doubles to power each
polarized plane for the same ERP. Any changes there?
Dan
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Date: Wed, 01 Jul 2009 00:53:37 -0400
From: Cliff Benham <flyback1@xxxxxxxxxxx>
Subject: [opendtv] Re: VHF Stations Seek Solutions for Reception Problems,
by D
I was asking about a circularly polarized antenna being used only for
receiving TV signals. If a circularly polarized antenna has a 90 degree
phase delay between the H&V elements then it follows that it is only good
for one frequency.
This is because the 90 degree delay line is only 90 degrees at one
particular frequency. At a lower frequency it would be less than 90 degrees.
At a higher frequency it would be more than 90 degrees
Therefore a circularly polarized TV antenna used for receiving is only a
"single channel" antenna.
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