Doesn't 440Mhz penetrate objects in the environment better than the 2-meter band?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KC0BUS, Jul 27, 2017.

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  1. KM4DYX

    KM4DYX XML Subscriber QRZ Page

    K9STH, it sounds like this is a subject that you have some expertise in.

    I posted the old military study because I found it interesting, and relative. I don't have a lot of formal training in the matter, but I can tell you from military experience that UHF was generally preferred for elements that were primarily operating inside buildings. The short antennas suitable for UHF was one factor; the superior propagation due to reflection was another.

    Of course, VHF was favored for rural terrain. Longer, more efficient antennas were practical and VHF "punches through" foliage better, in most cases.

    One thing Big Army lost when they moved away from HF was Surface Wave Propagation. Most of the literature about HF focuses on Sky Wave, but Surface Wave provides a unique capability in favorable terrain.

    Gotta run. Enjoy what remains of the evening.

    73,
    Al
     
  2. K9STH

    K9STH Ham Member QRZ Page

    DYX:

    My foliage experience goes back to like late May, maybe early June, 1966. I was in my senior year at Georgia Tech and had just established the first portable / pager repair facility owned by Motorola away from the Schamburg, Illinois, plant.

    In like January and February Motorola had installed a 450 MHz control system along a pipeline in north Georgia. The terrain was very mountainous and stations were installed on mountain tops about 15-miles apart. This system consisted of 100-watt output (they really ran about 90-watts output) feeding into LPY antennas, vertically polarized, aiming at the next station in line. At each station, there was another LPY antenna feeding the receiver.

    When the system was installed, it was found that the 100-watt amplifiers were not needed and the system worked fine with the 12-watt exciters. Then, came late March and the system "cratered". Technicians were sent to each site and everything checked out. Finally, the 100-watt amplifiers were put in line and the system started working again. But, by late May, the system "cratered" again and yet the equipment was meeting all technical specifications. The Motorola Area Vice President was a graduate of Georgia Tech and decided that I needed to accompany the field engineers working on the problem.

    One thing was that, at night, one could stand at the equipment location and, using a flashlight, send code to someone at the sites on either side. But, no r.f. was making the trip! Horizontally polarization was tried on the antennas to no avail. Then, every angle between horizontal and vertical was tried but no luck. Finally, someone suggested trying circular polarization. That not only worked, but the system again worked with only the 12-watt exciters. After everything was said, and done, there were 2-each circular polarized antennas left over. I was told to "get rid of them" and Motorola was not going to "say anything" about what it took to get the system working again. I still have both antennas in my attic waiting to find something to do with them! I just could not bring myself to throw away 2-each perfectly new antennas!

    The problem source turned out to be all the pine needles in the valleys between the stations. In the winter, with not much moisture in the pine needles, there was little attenuation. Then, as the weather warmed up, the sap started flowing into the needles and the attenuation started increasing. This was a factor even though the r.f. was actually physically above all the pine trees in the valley.

    Because of this, Motorola started looking into foliage losses and came to the conclusion that pine, and cypress, attenuated the 450 MHz, and higher frequency, signals by a significant amount.

    I worked with one of the design engineers for the Atlanta, Georgia, cellular telephone system. After working there, he came to the Dallas, Texas, area. He said that, because of all the pine trees in the Atlanta area, they had decided to install 4-times the "normal" number of cells. Well, that did not work out! They ended up installing about 9-times the "normal" number of cells to get reliable coverage of the Atlanta area.

    My youngest daughter, who started with Nortel here in Richardson, Texas, "took to" a particular computer program that was being used to verify the performance of the PCS telephone systems being installed around the country. When they were finished with the Dallas area systems, Nortel made her a "deal she couldn't refuse" to go to Atlanta to use the system. In the late 1990s, they were paying something like $45.00 per hour, guaranteeing her 50-hours per week (with overtime for all over 40-hours) and a $600.00 a week per diem! At 19-years of age, this was a fantastic salary!

    After Nortel was through with the PCS system, she was made the vice president's personal assistant at a very good salary. She met her now husband at Nortel and she still lives in the Atlanta area.

    Nortel found the same foliage problems as Motorola and the cellular telephone people. Pine trees definitely attenuate the higher frequencies considerably.

    Glen, K9STH
     
  3. KM4DYX

    KM4DYX XML Subscriber QRZ Page

    Great story! Thanks for sharing.

    73,
    Al
     
  4. AB8MA

    AB8MA Subscriber QRZ Page

    My new Lacrosse Atomic Clock, sitting in my basement, picked up the 60 kHz signal from Ft. Collins, Co. (~1200 miles) within 5 minutes at 4 in the afternoon.
     
  5. AI3V

    AI3V Ham Member QRZ Page

    Quoted for the OP.

    Search the phrase "waveguide beyond cutoff" for more info about wavelength vs hole size.

    Another neat and related phenomenon is a "slot antenna"

    Rege

    Edit: about low frequency's being better able to penetrate materials, well, consider a all metal building, sometimes called a Faraday cage, all frequencies will be equally affected.

    A wood house, with brick veneer, different frequencies would penetrate differently, probably favoring low frequency's.

    Add a hole, to a metal building, and all of a sudden high frequencies leak out better.

    So yeah, maybe 2m, or maybe not. :)
     
    Last edited: Sep 17, 2017 at 3:24 AM
  6. K9STH

    K9STH Ham Member QRZ Page

    In the late 1960s, here in Richardson, Texas, at the Collins Radio Company "new" corporate headquarters, a new "screen room" was built so that equipment could be tested on frequencies from "daylight to dark" without any external signals coming into the situation.

    The engineers who had designed the screen room were basking in glory. Well, that "glory" only held for a couple of days after the screen room was put into operation. The screen room was being "shown off" to a number of representatives from several companies that were purchasing Collins equipment. Suddenly, a pager, carried by one of the representatives, activated and the voice message came through without any problem.

    The pager was operating on a frequency in the 450 MHz to 470 MHz band and the signal was definitely getting into the screen room without any problems. It was back to the drawing board for the engineers who had designed the screen room. After a considerable amount of testing, it was found that the r.f. seals around the door had minute physical gaps and that allowed the higher frequencies to make it into the screen room. These seals had to be redesigned so that the higher frequencies could not penetrate the screen room.

    Glen, K9STH
     

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