Want a true omni antenna for FM--recommendations?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K3RW, Oct 3, 2019.

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  1. K3RW

    K3RW Ham Member QRZ Page

    Basic problem: I would like a vertically polarized omni antenna for FM, monoband if possible, and with some 'gain'.

    I run a PAR omni-angle for SSB/CW/digi on VHF+ and it works really well. Don't need a beam for the closer-in guys, and it tells me if I need to swing a beam. Supposedly its a 'true' omni, and unlike the M2s I had before, it does seem to be. But those are for horizontal polarization.

    I'm running about 50/50 FM to SSB on recent contests. More people here seem to have 223 FM but DX is 222 SSB.

    I have a Diamond X200A dual-band and it doesn't cover 1.25m. 'Gain' listed on their page seemed decent, until I pulled up the radiation pattern on their website. Unlike the PAR antenna HO loop, it doesn't look omni-enough to me!

    [​IMG]
    [​IMG]
    I suppose if I know which way the lobes were going I could orient it mostly N/S and pickup everything up and down I-5 where the main population is anyway. But this seems awful for an omni. I'm not going to get a perfect circle, but the lobes seem really distorted. Its hard to get more than 2 grids here on FM, but I make up for that with a ton of FM QSOs. If I want longer DX, of course I point with a beam, but I've lost a lot of the backend and sides with closer guys.

    I run over to radiation patterns for a quarter-wave vertical 'omni' and they look basically like a circle. Ok. I'd like to squish the top part of the donut since I'd probably be higher than anyone else locally. But

    Well, not to make this post verbose, but if the half or 5/8ths or another collinear had 'gain' but a more omni-looking pattern, I'd be in the running for that.

    Well, I'd be willing to tradeoff something here for a more omni pattern, but can't seem to find decent comparisons between a quarter vs 5/8ths, vs Ringo II, etc. Also seems that on 223 I'm limited finding anything that has a decent power rating. FM-only I couldn't run QRO anyway in a contest, but limited/unlimited multiop I sure can.

    Bottom-line, is there a decent monoband antenna for omni FM that has a more true omni pattern AND some gain? And do they make a 223 one? :)

    please reply to this thread so I get the notification
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Those are polar radiation plots indicating omnidirectional radiation with all the gain at 0 degrees elevation angle, and about -10 dB at 30 degree elevation angle (looks like about -3 dB at 20 degrees elevation angle) on 2 meters; and all the gain at 0 degrees, and about -3 dB at ~8 degrees elevation angle on 70cm. The smaller lobes on 2m appear to be about -9 dB at 65 degrees elevation and another one on the other side of the vertical about -13 dB at 60 degrees elevation. I'd forget about those.

    On 70cm, the smaller above-horizon lobes are all down -6 to -12 dB and I wouldn't worry much about those, either.

    These plots are a "side view" of the vertical, taken from any side you want, all the way around the vertical. They are not "top down" views of horizontal plane radiation.

    BTW I should mention those plots are so imperfect I suspect they're from actual antenna range testing and not computer simulation. Computer simulation usually look a bit smoother as they can't take into account every single thing about the installation and environment.
     
    Last edited: Oct 3, 2019
    K7JEM likes this.
  3. K3RW

    K3RW Ham Member QRZ Page

    Excellent point on the polar plot. I see now why it appeared awful looking to me.

    My current setup is the Diamond X200A, but because I want to dedicate a 2m FM-only rig and a 446 rig, and not really run diplexers, etc., I'd like a monoband antenna for each. And with 223, same thing.

    Not sure what 'gain' I'm giving up by going to a half, 5/8ths, really long collinear, over a standard quarter wave. And a bit concerned about the feedline issues and fragility of the Ringo I and II's. Its not feasible in my situation to run a 20ft collinear. Maybe 8' is pushing it since it needs to go on the house but potentially go in the car for a mountaintop run. But if I can get a decent omni pattern with some 'gain', whether that is 0deg, 6deg, etc., I'm hoping not to have deep nulls 4000' up in the mountains.

    Any recommendations on way to go on an omni-FM antenna, monoband? I could go all Ringo II's, all white radome collinears, etc. But not sure other than takeoff angle how much is changing between a quarter wave, half, 5/8ths, etc. Seems manufacturers are posting ridiculous gain figures making comparisons about impossible.
     
  4. K7JEM

    K7JEM Ham Member QRZ Page

    Basically, if the antenna is designed properly, gain will be proportional to length. On 2M, in order to get 3dBd of gain, the antenna has to be 8-10' in length. To get 6 dB of gain, the antenna has to be 18-22' long. You won't have a 10' long antenna with 6dBd of gain, it just isn't possible. A 10' antenna on 2M will have around 3dBd of gain, a 10' antenna on 440 will have around 7dBd of gain, and a 10' antenna on 220 will have around 5dBd of gain.

    Most commercial antennas are configured as HW dipoles, either collinear or phased arrays spaced vertically. Some collinear antennas use two or more 5/8 wave antennas. There are lots of possibilities depending on your budget and overall length that you want to use, the degree of ruggedness will usually determine the price.
     
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  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The LMR commercial/industrial antennas are all built better than the "amateur radio" antennas, and their published gain figures are very realistic by comparison. But they're generally heavier and cost more -- usually, a lot more. And some models would not be available for 222 MHz, since that's not a commercial LMR band.

    For "separate" antennas for each band, it's hard to go wrong with the Hustler G6-G7 series. They're quite strong and well-made, easy to assemble or disassemble, and work. The inexpensive fibreglas radome verticals are a bit more fragile, inside and out; they generally use a very thin brass rod or wire as the radiating element(s), and the collinear designs have phase shift networks made of very small copper wire and tiny, fragile capacitors, plus radiator "splices" that are dissimilar metals and hold the elements in place with tiny setscrews -- it all "works," but can also all fail, and for the collinear models, there are mechanical splices in the fibreglas tubing that can be weak points or points for potential water ingress. I've used a lot of these over the years and never felt very confident about any of them.

    Those models also usually have a "transmitter power level" limitation, sometimes as low as 100W or so. That's due to their design, using tiny capacitors in the phase shift and matching networks. Those caps will fail at high power. You won't find anything like that in the LMR commercial/industrial antennas, which are generally rated in the 600W+ power handling range.

    I have a Hustler G7-144 which is an aluminum collinear with fibreglas sections to house the phase-shift networks (very well done, everything is all sealed at the factory and there's no way to open them) and I think it's rated "600W" but I've put a kW into it lots of times and it's fine. It's about 15-16' long and has about 4.5 dBd "real" gain (not "ham radio" gain).:p

    But...its angle of radiation is about 0 degrees, with all energy focused on the horizon. For an average home station, that's what we'd generally want; but if you want to use a similar antenna for "mounaintopping," if you want to cover the lower elevation surroundings, especially those fairly close (like maybe within 10 miles), a "downtilt" antenna could be better to fill in the shadows. As hams, we're often not very concerned about this and just want "DX," so the 0 degree antenna may be all we ever need for a temporary mountaintop stint.
     
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  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The truth be known, the segment between 220.0 MHz and 222.0 MHz is a Land Mobile Radio band. That thanks to the United Parcel Service attempt to get that segment for "narrow bandwidth" technology. Then, after they got their way, UPS tried to get the FCC to allow "normal" +/- 5 kHz deviation FM instead of the narrow bandwidth equipment. When the FCC refused to give in, UPS abandoned their system. However, the FCC did not return that segment for amateur radio use and continued to designate it for LMR use.

    A fair number of base station antennas are available for the 220.0 MHz band including:

    https://www.theantennafarm.com/catalog/laird-technologies-fg2200-4111

    https://www.theantennafarm.com/catalog/sinclair-sc225m-sf7snm-4113

    https://www.theantennafarm.com/catalog/pctel-boa2175-4122

    https://www.theantennafarm.com/catalog/pctel-boa2177-4123

    https://www.theantennafarm.com/catalog/telewave-ant220f2-4115

    https://www.theantennafarm.com/catalog/telewave-ant220f6-4116

    With the exception of the very first antenna in the list, which is just a unity gain antenna, the antennas are definitely not cheap!

    Glen, K9STH
     
  7. K3XR

    K3XR Ham Member QRZ Page

    The G-7 series for 220 has been up over 20 years at this location with no problems. As WIK indicates it's a very well made antenna.
    https://www.dxengineering.com/parts/hsr-g7-220/
     
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  8. N8EKT

    N8EKT Ham Member QRZ Page

    Hustler G6-440 and Hustler G7-144 are the two best built highest gain ham grade antennas made.
     
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