VHF/UHF antenna polarization and testing

Discussion in 'Amateur Radio News' started by KJ4YZI, Apr 20, 2017.

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  1. WA1ZJL

    WA1ZJL Ham Member QRZ Page

    Interesting discussion and everything appears factual. I spent almost my whole career as a broadcast engineer and did both FM and TV. Early on FM was horizontal only same as TV. That way you could use your TV antenna to receive FM as well. As time went by FM radios started appearing in vehicles and portable radios with whip antennas as well. Now FM was faced with the dilemma of serving both home receivers hooked up to a TV antenna and the new mobile and portable radios. That's when CP came into the picture. CP receive antennas also have decided advantages if the transmitted signal is CP. Forgive me in not remembering specifically what the advantages were but I remember only reading that they were there but in spite of that CP receive never caught on. CP never caught on with TV as well although there never was the compelling reason to use CP. Economics had a major part to play in CP or not CP. Economics plays the same role in the two way industry as well. We're in the same boat they are and maybe even more so. Many of us are fortunate to be able to have a repeater in operation using older surplus commercial equipment. My repeater is an old Micor which just keeps running and running. Now, enough of the history. Some have mentioned directional CP. Shivley and ERI (I think) offer directional CP FM broadcast antennas. They use a parasitic element with their standard CP antenna. As I recall they can get at least a 10 dB null on the tower side of the antenna. Another option is to use crossed dipoles with appropriate phasing harness. Scala makes them and I used an array of two on a translator that was shoehorned in between two other stations. There's advantages to each type of polarization but we end up living with standards set years ago. It's not unlike analog TV. We lived with NTSC color (sometimes refered to as "never the same color") when the European PAL standard was much better.
     
  2. NA7OM

    NA7OM Ham Member QRZ Page

    Interesting that WA1ZJL mentioned Scala. I did a stint as a test technician and assembler for Scala Div. before Kathrein made the decision to move cell panel production to Mexico and spin off Scala Gold Line products to limited contract mfg. The reason I'm chiming in here is just before the final boot out the door, I pitched to what has to be, the most talented group of antenna guys I'd ever worked with to build for amateur use. I brought to the discussion a few examples of popular antennas used by amateur repeater owners and a ARRL repeater book. Just for giggles, we dissected a few mechanically wise, (great fun and laughs around) and ran them thru the anachoic test chamber and all were in most ways, pretty sad compared to what we built for commercial applications. That idea is still alive, but it comes down to this, who wants a antenna capable of surviving 100 mph winds, operate encased in ice or pulled by it's coax from the sea for two weeks after a Gulf hurricane and upon breaking the surface, transmit. Certainly I would if I had a repeater, but I don't, so I can't say I'd buy one for $ 500 plus. What's the market?
     
  3. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    I believe this was mostly due to power density. SSB is only 3khz bandwidth where FM is 15khz wide.
     
  4. UT7UX

    UT7UX Ham Member QRZ Page

    Mobile communications require circular pattern in horizontal plane: all mobile/portable users won't care direction to the relay while most relays try to cover as far as possible in all directions. Obviously, vertical polarization is most suited for this. Stationary users may work with directional antennas at distant relays but also obviously they must be compatible in terms of polarization. So let's leave mobile FM in vertical polarization as is.
    Horizontal polarization is mechanically better for Yagis and most directional antennas: it is much easier isolate (I mean RF, not DC) horizontally polarized antenna from a mast. So again it is obvious that for weak signal modes, where omnidirectional patterns mostly are not welcome, the horizontal polarization is widely used. Additional benefit: local FM relays are attenuated for approx 20dB.
    Circular polarization is a good idea for SATs and probably EME: you may work stations regardless their angle of polarization (vertical, horizontal, diagonal) but lose 3dB. So it may be a better idea to switch two orthogonal antennas rather then combine them both to one circular.

    Yep. Theoretically it is possible to create as narrow FM as SSB is (with appropriate filters, not just to reduce deviation) and acheive pretty similar communication distance. But the big advantage of FM is tolerance to frequency accuracy. Wider deviation means greater tolerance. That's why FM (FM itself and FM-based digital modes) is commonly used in channelized commercial applications. And that's why deviation cannot be too narrow. BTW, in Europe we are still using 5kHz deviation and 25kHz frequency step.
     
  5. W0AAT

    W0AAT XML Subscriber QRZ Page

    Publish the design, hams are an enterprising lot and could build it themselves.
     

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