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Thread: 210 mhz 3 element yagi ?

  1. #1

    210 mhz 3 element yagi ?

    I cannot find any cut and dry info on building a 3 element yagi between channels 12 and 13 Hi VHF TV 210mhz 12db band witdth.
    I get all the basics and then confusion on all the rest.
    Metal boom - pvc boom - wood boom ??
    I want to use a 1" square boom from an old TV antenna. I have the elements and the insulators for them.
    I want to feed my coax into a 75 ohm transformer which is 300 ohms at the driven element.
    Do not need a folded dipole at that frequency. I have the info that the reflector is 5% longer and the directors are 5% shorter.
    I also have dimensions for the complete antenna with the spacing. However it is for a wooden boom with the elements raised off of it.
    In the ARRL hand book it gives a lot of info but it is also not cut and dry.
    Wade makes single band antennas. If I could find there dimensions for the channel 12 and the channel 13 yagi.
    Then just build one using the difference between them. I need the bandwidth to be very tight only the 12 db with a drastic cut off on each side.
    I do get major interference every so often it actually kills the TC signals for both 12 and 13 so sometimes no reception at all.
    I have tried VHF filters. The do help but I need something far better to clean out the interference.
    I have tried a 7-13 yagi with no help on the problem.
    Any suggestions?

  2. #2
    I'm asking an expert to weigh in and we'll see if we can get you the answer you need.

  3. #3
    Thanks. The other possibility (But it looks expensive) is a band pass filter (Notch) just to pass 12 & 13 and dump everything else.

  4. #4
    Join Date
    Feb 2012
    Location
    Orlando FL
    Posts
    402
    There are a few things that don't seem to make sense.
    12 dB isn't a bandwidth
    A bandpass filter is the opposite of a bandstop [notch] filter.
    Your "interference every so often" may be due to multipath.

    Building an antenna or filter that have a narrow bandwidth and skirts with sharp rejection require a lot more than 3 elements.

    This might be helpful to model your antenna design(s) Martin E. Meserve - K7MEM - VHF/UHF Yagi Antenna Design
    At the bottom of the page is an example of a 144 MHz, 12 element, and 222 MHz, 16 element, yagi and estimated performance.
    Last edited by VOS; 06-04-2014 at 03:46 AM.

  5. #5
    Join Date
    Feb 2012
    Location
    Orlando FL
    Posts
    402
    For some idea of what you're in for a 210 MHz Yagi Design:

    3 Elements, 4.0 dBd Estimated Gain, Electrical Boom Length of 16.9"
    6 Elements, 8.2 dBd Estimated Gain, Electrical Boom Length of 56.2", with 49.9 Degrees Horizontal Beam Width
    10 Elements, 11.5 dBd Estimated Gain, Electrical Boom Length of 123.6", with 38.1 Degrees Horizontal Beam Width
    13 Elements, 13.0 dBd Estimated Gain, Electrical Boom Length of 185.5", with 33.2 Degrees Horizontal Beam Width

  6. #6
    What I meant was 12mhz band width not 12db my mistake.
    Low end of ch12 and upper end of ch13 sorry for that.
    You are also correct. Notch filter. Making one is not possible for me at that frequency.
    So gain is not the problem. Interference is and multipath might not be the problem.
    No buildings other than homes. All lower than the antenna. Only transmissions are cell towers, non are close to me.
    This is not a continuous situation. It could be for a couple of seconds to maybe several minuet of both 12 and 13 going out.
    Sometimes just 13 gets pixelized and 12 is OK never the other way around.
    Personally, it is either a dirty FM pirate transmitter or an amateur transmitter that is dirty.
    Nether station engineer can help. I tried the FCC and I must first find what is causing the problem before they will do anything.
    Currently 2 antennas one UHF and one VHF. The UHF has a UHF filter. Kills VHF. The VHF has the opposite.
    Then combined and then an FM trap into Very Low Noise 12db preamp (At the antenna) to make up for the filters and the 75 ft RG6quad cable run.
    This might happen several times a day, it may not happen for many days. It was only around noon each day, now mostly in the evening. Usually at prime time for viewing.
    If I remove the filters. it is much worse.

  7. #7

    Built the antenna

    Quote Originally Posted by Danny View Post
    What I meant was 12mhz band width not 12db my mistake.
    Low end of ch12 and upper end of ch13 sorry for that.
    You are also correct. Notch filter. Making one is not possible for me at that frequency.
    So gain is not the problem. Interference is and multipath might not be the problem.
    No buildings other than homes. All lower than the antenna. Only transmissions are cell towers, non are close to me.
    This is not a continuous situation. It could be for a couple of seconds to maybe several minuet of both 12 and 13 going out.
    Sometimes just 13 gets pixelized and 12 is OK never the other way around.
    Personally, it is either a dirty FM pirate transmitter or an amateur transmitter that is dirty.
    Nether station engineer can help. I tried the FCC and I must first find what is causing the problem before they will do anything.
    Currently 2 antennas one UHF and one VHF. The UHF has a UHF filter. Kills VHF. The VHF has the opposite.
    Then combined and then an FM trap into Very Low Noise 12db preamp (At the antenna) to make up for the filters and the 75 ft RG6quad cable run.
    This might happen several times a day, it may not happen for many days. It was only around noon each day, now mostly in the evening. Usually at prime time for viewing.
    If I remove the filters. it is much worse.
    Update, 12/7/2017
    Well I built the VHF antenna 13 element at 210 mhz. Still no luck. More update information. The problem is just starting again. Coinciding with the return of the snowbirds. Starts at 10:00am and usually ends at about 11:00PM As the hours pass it progressively get much worse. Yesterday it started with channel 13 at 10:00AM at about 9:00PM channel 13 was totally unwatchable. Up until that time Channel 12 was fine. Then At 10:00PM channel 13 came in crystal clear then channel 12 went out. These are channels 5 & 12 West Palm Beach. 5 on 12 and 12 on 13. Moving the antenna over 100ft one way and then the other changed nothing. I have noticed that Biomedical Telemetry is also in that range. No hospital or doctors anywhere near in that direction. Anyone know if that can be in a home? What else can cause this? No multipath problems. The pixelization is getting very aggravating.

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