---------- Original Message ----------
From: Charles Dube <cld@...>
To: JOHN HASERICK <jhaserick84@...>
Date: 11/22/2022 10:18 AM
Subject: Re: Re: [repeater-builder] Circularly-polarized antennas for two-way?
Good morning John-
I'm quite familiar with these designs. We use a similar Jampro out at our Williamstown translator-
And I use single bay CP antennas at several other locations because of cost. More on that later.
Aside from height, which is probably the most important factor in FM antennas, gain is established through
varying bay distance (standardized to 1/2 and full wavelengths apart) and amount of bays.
We also have to factor in human exposure, so in the case of Williamstown we operate 2-bay, 1/2 wave spacing which gives us a 0.7 dB gain factor. If it were full wave spaced the gain would be 1.0 dB, BUT with more downward radiation, which on a building top was not permissible in this case. Regardless, we could only have one ERP factor, so it just means more transmitter power out into a less efficient antenna that alos has less downward radiation. Something broadcasters have to deal with that most repeater systems don't.
The single bay antenna has indeed a 0.46dB gain factor, so more TPO is needed.
CP does have the advantage in broadcasting in serving more receiver antenna styles, from vertical car whips to home T-dipoles (horizontal) to clock radio power cords which are random pol, if there is such a term LOL.
The pattern from a single bay CP antenna is theoretically a globe, so you waste energy up and down the tower- unless your reaching aircraft and illegal campers has any merit. But often it's a compromise in broadcasting because tower space rental is pricy, and often a single bay with more TPO is less expensive than a two or three bay (which could easily use 10-20' of towers space, which could run $1500-5000+ rental depending on market.) It just means you need a bigger transmitter, as long as the antenna is up high enough to pass radiation exposure restrictions.
But for amateur use where few if any are running horizontal polarity, there is no reason to employ CP.
And yes, that reduced gain factor has a big impact on reception. I have used CP antennas for reception
in emergency situations (because they were already at hand and mounted high) and the results are what you'd expect- not stellar. They worked, but only as a temporary solution.
Chuck
From: JOHN HASERICK <jhaserick84@...>
Sent: Monday, November 21, 2022 5:13 PM
To: Charles Dube <cld@...>
Subject: Fwd: Re: [repeater-builder] Circularly-polarized antennas for two-way?
Thought you would be interested in this, Chuck, although you are probably using circular polarization and are well aware of the reasons, but new to me
John.
---------- Original Message ----------
From: Burt K6OQK <biwa@...>
Date: 11/21/2022 12:58 PM
Subject: Re: [repeater-builder] Circularly-polarized antennas for two-way?
[Edited Message Follows]
Matt,
I used a circularly polarized antenna on the WA6TDD repeater back in the 70's and early 80's. The antenna was a single bay antenna made for the repeater by the JAMPRO antenna Company as a test for the 2-way world. It even has de-icers!? If you're familiar with the JAMPRO Penetrator antenna, this was the same antenna with the exception that it was center mounted; the mast was straight down below the white insulator at the feed point. This replaced a (linear) Phelps Dodge 4.8 dB gain Super-Duper Storm Master antenna.? The gain went from approximately +4.8 db to - 3 dB.? The ERP went from 100 watts to approximately 13 watts. Just to clarify, the repeater transmit was now circular and all of the users were linear; none of the users were circular.?
The difference in coverage of transmit was amazing. For example: at the time I worked in a 33 story building with 6 levels of underground parking. With the linear antenna I was able to copy the the repeater with its 100 watts ERP about 25 feet into the parking entrance and that was it. With the circular antenna on the repeater and a 19" spike on the top of my car I was able to copy the repeater solid down to the 2nd level and hear it spotty down to the 5th level.? At some places on the 5th level I could find spots that were almost full quieting.? People that listened to the repeater with radios like the old Patrolmen type receivers claimed that they no longer had to place their receivers near the window and fiddle with the antenna, they could now take the radio anywhere in their homes and hear the repeater with no problems. It was solid through areas like the Santa Ana Canyon and Sepulveda Pass. What was rather humorous and showed a lack of understanding by some users, who were upset that the repeater was no longer ""60 over S9," it was now only "20 over S9." The fact that it had better coverage and penetration was not the point!
Now for the bad news.? It didn't hear very well.? It simply had too small an aperture. While stations could hear the repeater better than ever, and had been solid into the repeater with the 4.8 dB gain linear antenna, they? were now not so solid.? Handhelds that had no problems now had problems.? We eventually went back to the Phelps Dodge Linear antenna.
What did we learn?? We learned that circular transmit to linear receive is a plus.? Yes, circular to circular is best, but not very practical. Think about putting a circularly polarized antenna on your car or handheld radio.
If you have a circularly polarized antenna that truly commutates, it will be optimally coupled to a linear receive antenna even when the polarization of the signal as received is "spun" due to bounces and other propagation anomalies. It really works!
You can read more about this at ? download and read the pdf file.
Hopefully attached is a picture of the Antenna that JAMPRO build for the WA6TDD Repeater.
Burt, K6OQK
