The transmissions are typically circularly polarized to reduce multipath interference, or, if the station is feeling fancy, elliptically polarized to provide a horizontal component for rooftop antennas.

The conversion to elliptical polarization is mainly for ATSC 3.0. We shift to OFDM (from trellis-coded 8VSB) with ATSC 3.0, like the rest of the sane world for DTV. With OFDM, mobile reception is possible (unlike 8VSB), so also pushing energy to the V plane makes sense when receivers are in motion. Non-horizontal receiving antennas will see an improvement.

https://www.eriinc.com/wp-content/uploads/2020/09/ATSC-3-brochure-Final.pdf

https://www.dielectric.com/wp-content/uploads/2020/05/ATSC-3.0-SFN-and-Antenna-Design-1-May-2020.pdf

POLARIZATION
The channel characteristics are not the same for
transmitted horizontal polarization (HPOL) and
transmitted elliptically polarized signals (EPOL). This can
be explained by understanding that elliptical polarization
helps mitigate the effects of small scale, fast fading which
is present both indoors and outdoors at handheld receiver
heights. Testing has confirmed that transmitting elliptical
polarization to a linearly polarized receiver in motion in a
heavy scatter environment provides 5 to 7 dB of margin
improvement (MI) over transmitting a linearly polarized
signal to the same receiver [6]. This improvement is
directly proportional to an increase in the carrier to noise
ratio.
...
This can be
interpreted as saying approximately 35% more people will
have access to reliable mobile service in harsh conditions
with the use of elliptical polarization transmission.

 

Before the advent of satellite and cable TV feeds, the closest TV broadcast towers here were 90 miles south and 60 miles north. There were a lot of 30-40' backyard towers with very large log periodic antennas mounted on rotating masts. And even then, what you got was still a bit fuzzy... Especially if you were used to living in a town with a broadcast tower. Haven't had or even seen a TV in years that still used an antenna much less a set of "rabbit ears". I do remember having as a child a "portable" 17" black and white TV in the house that had a set of built in telescoping "rabbit ears" that were pretty much useless as the closest broadcast tower was quite distant.

 

Before the advent of satellite and cable TV feeds, the closest TV broadcast towers here were 90 miles south and 60 miles north. There were a lot of 30-40' backyard towers with very large log periodic antennas mounted on rotating masts. And even then, what you got was still a bit fuzzy... Especially if you were used to living in a town with a broadcast tower. Haven't had or even seen a TV in years that still used an antenna much less a set of "rabbit ears". I do remember having as a child a "portable" 17" black and white TV in the house that had a set of built in telescoping "rabbit ears" that were pretty much useless as the closest broadcast tower was quite distant.

Lots of people have and use outdoor TV antennas here for locals. In a past 'life', during the 70's, I had a FCC Radio Telephone Operator 1st class commercial license so I could legally operate, setup and control commercial broadcast stations as the engineer.

Example, not mine:

My last ticket is at my mom's house, somewhere.

 

I had a FCC Radio Telephone Operator 1st class commercial license so I could legally operate, setup and control commercial broadcast stations as the engineer.

Me to. +radar. Made good money with that piece of paper. Funny my date was also mid 197x.
I was operating two 100kw FM stations one mid-sized and two small, and one large AM. But I could not get a HAM ticket. I just could not hear the code.

 

I also had to await the removal of the code requirement. And the strange thing is that it does not seem to have damage amateur radio the way it was predicted to. And then i upgraded without ever taking a practice exam. And still get no respect from some folks. Oh Well

 

I also had to await the removal of the code requirement. And the strange thing is that it does not seem to have damage amateur radio the way it was predicted to. And then i upgraded without ever taking a practice exam. And still get no respect from some folks. Oh Well

I never had a problem with code or radio. I was in the donut shop too long for it to be a hobby but it was a first love and first loves usually break your heart.

 

Lots of people have and use outdoor TV antennas here for locals. In a past 'life', during the 70's, I had a FCC Radio Telephone Operator 1st class commercial license so I could legally operate, setup and control commercial broadcast stations as the engineer.

I had one of those, but no radar endorsement. It was a long time ago. I was mostly working in radio stations.

 

I never had a problem with code or radio. I was in the donut shop too long for it to be a hobby but it was a first love and first loves usually break your heart.

While some folks still regard those without the Morse Code endorsement, very few of them can look at a schematic diagram and know what to check when a transceiver does not function correctly. That is often an interesting undertaking. But since diagnosing system issues in a customer plant is sort of similar, it all depends on adequate drawings and accurate descriptions of problems.

(Back to the thread) Long ago, "POPULAR ELECTRONICS" magazine published an article on RESONANT TV antennas for fringe reception. That was quite interesting, especially the claims for distance reception. And I guess that it actually did work as well as claimed. But like other things, every portion needs to be done right. And while aluminum is an easy material to work with, every electrical joint is a source of potential future problems. So there is always that compromise.

 

Thank you, fellows. The geometry of the radiowave and electric/magnetic components is understood, and the electric field position naming the polarization.

----> The wave polarization goes with the plane of the loop or with the position of the feedpoint or both or none ? <----

===================================================================================

In other words, this loop below works on vertical or horizontal polarization wave? :

View attachment 337095

=========================================================================================

About directionality , From the fourth image in post #10 above, for these loop antennas below to receive optimally in the pictured position; the RF signal source should be coming from either the left or right ( or above ! ) of the guys in the image; correct ?

View attachment 337096

Hi,

Yes. Not sure if they use them anymore, but small aircraft used to use those for direction finding. By turning the whole plane in different directions, they could figure out which way to fly in order to reach the destination transmitter location. The loop would be mounted on top in a fixed position. They probably improved this over the years though by making it rotate.
This only works at circuit frequencies though, because skip and all that will mess up the directionality of the signal, it may appear to be coming from everywhere. This is very critical when you are flying over the ocean and running low on fuel and have to get to the right place before you run out. Also flying over land and trying to find the nearest airport.

If the signal is normal to the plane of the circular loop it creates a null. If the signal reaches one edge of the circle before the other (parallel to the plane of the loop) you get a maximum. This makes a lot of sense because if you superimpose the signal shape over the loop shape, you only get a high on one side and a low on the other side if the signal is coming in from a direction parallel to the loop.

LIKE THIS FOR A MAX (signal from the left side of the loop here):
------> O

LIKE THIS FOR A NULL (signal from the front or back here):
------> |

I think the smaller loop allows detecting if the signal is coming from the back or the front, which can confuse the interpretation of the direction of the null if you don't know which is which.