VHF antenna -- bidirectional in the horizontal plane
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VHF antenna -- bidirectional in the horizontal plane


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  1. #1
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    VHF antenna -- bidirectional in the horizontal plane

    - It seems to be accepted theory that an "omnidirectional" UHF antenna can achieve modest gain (about 2.8 dB over a dipole) by eliminating the z dimension. In other words, it doesn't radiate signal (or look for signal) from above or below, only in the horizontal plane.

    - It's also common to refer to a dipole as a "bidirectional" VHF antenna, but it clearly does nothing to eliminate the z dimension.

    Well, it just so happens I could use a bidirectional VHF antenna, and I don't think a simple dipole is going to cut it! Isn't it possible to make a VHF bidirectional antenna without the wasted gain from a dipole radiating in the z dimension?? I can't find anything available commercially.


    Rick

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    The problem with a dipole as an omni is that it must be oriented vertically and US broadcast TV uses horizontal polarization as the default (some stations do include a vertical component, but its a lesser share of the stations). Commercial antennas that claim to be omni rarely are truly omnidirectional and usually exhibit peaks and nulls of up to 10 db, and in severe cases, up to 20 dB in various directions.

    For bidirectional VHF, the only thing commercially available that I can think of would be a ClearStream 5 without the reflector grid. If your budget permitted it, you could conceivably create a VHF equivalent of a ClearStream 2 loop with two of the C5 loop elements combined vertically.

    If you want to build your own, a 2-bay or a 4-bay scaled to high VHF would be your best bet. See Hi-VHF 2-Bay Bowtie - NO Reflector and Hi-VHF 4-Bay Bowtie - NO Reflector Keep in mind that they are TALL.
    Last edited by ProjectSHO89; 12-31-2013 at 04:30 AM.
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    Rick the bidirectional VHF antenna is of great interest to me and with good reason in the area I live. As are all DIY easy to build VHF antennas. The simple loop will have slight gain over a dipole and is easily constructed.
    VHF Square & Circular Loops
    The next one is of great interest to me. Simple, compact, not real difficult to build, a bit of gain over a simple loop.
    Hi-VHF (+UHF) Twin Rectangular Loops
    The next step up gets a bit large and more complex to build correctly, but has significant gain over the simple loop.
    Hi-VHF Hourglass Loop
    The high VHF bow tie would be by far highest gain. I do have some construction ideas in my head for both the VHF hour glass loop, and the 2 bay VHF bow tie.
    I've built and used and recommended the home brew 4 bay with no reflector for bidirectional gain on UHF, and VHF gain about equivalent to a dipole. It works good for me.
    mclapp's M4 (10.0x9.5) 4-Bay - NO Refl.
    I've not yet built a GH0n but everything about the computer models, and real world plans look very promising.
    nikiml's Antenna pages - GH0n UHF/VHF-hi combo antenna
    That's about all I can add to this in a few simple links. Turning optimized computer models into practical real world antennas is not always an easy project.
    Steve
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    Rick,

    Which hi-VHF channels are you trying to receive?

    Jim

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    Quote Originally Posted by ProjectSHO89 View Post
    The problem with a dipole as an omni is that it must be oriented vertically and US broadcast TV uses horizontal polarization as the default (some stations do include a vertical component, but its a lesser share of the stations). Commercial antennas that claim to be omni rarely are truly omnidirectional and usually exhibit peaks and nulls of up to 10 db, and in severe cases, up to 20 dB in various directions.
    But this is a choice on the part of the antenna company, right? (Maybe a devious choice.) I think they have those wrinkles all worked out, on a smaller scale, for cellular antennas. I had a link about that in another thread. People don't expect to lose phone signal just by turning around in place.

    For bidirectional VHF, the only thing commercially available that I can think of would be a ClearStream 5 without the reflector grid. If your budget permitted it, you could conceivably create a VHF equivalent of a ClearStream 2 loop with two of the C5 loop elements combined vertically.
    Brilliant suggestion, I never thought of that! But I think I can get by a little cheaper. Those Clearstream prices are kwazy.

    Thx,
    Rick

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    Quote Originally Posted by RF Steve View Post
    Rick the bidirectional VHF antenna is of great interest to me and with good reason in the area I live. As are all DIY easy to build VHF antennas.
    ...
    I've not yet built a GH0n but everything about the computer models, and real world plans look very promising.
    nikiml's Antenna pages - GH0n UHF/VHF-hi combo antenna
    That's about all I can add to this in a few simple links. Turning optimized computer models into practical real world antennas is not always an easy project.
    Wow, looks like I hit the motherload on this! That GH0n looks very impressive.

    Thx,
    Rick

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    Quote Originally Posted by Fringe Reception View Post
    Which hi-VHF channels are you trying to receive?
    OK, here's my situation. My New Years resolution is to upgrade the second half of my antenna setup, like I said I would over a year ago. You might remember that I have a CM-4221HD indoors, pointed north toward Milwaukee. I also have a goofy little Monoprice "omnidirectional" antenna, enclosed in plastic, with a home brew tin can reflector, pointed south toward Chicago. The 4221HD goes in through the coax connector on back of the TV. The Monoprice goes in to a converter box, then into the RCA jacks on front of TV.

    Here is my TV Fool report: TV Fool

    Rough guess on how much signal I lose by being indoors, with only east facing windows: about 45 dB in either direction!!

    I get everything from Milwaukee above NM=34 (the green), and everything from Chicago above NM=40, very reliably. The four channels I want, or want more reliably are:
    11 PBS(RF47) NM=39 from Chicago
    49 CBS/IND(RF48) NM=31 from Milwaukee -- good IND stuff on 49.1
    10 PBS(RF8) NM=31 from Milwaukee
    2 CBS(RF12) NM-30 from Chicago. No subchannels.

    11 PBS should be no problem with a decent antenna pointed at Chicago. I get it close to half the time already.

    Might have to give up on 49 CBS/IND, since my good 4221HD is pointed at Milwaukee already. Only thing might be to get it closer to the east facing window. It's about 30 inches away perched on top of a desk. Maintenance guy already complains the desk is too close to the window -- hard to get to the air conditioner.

    Assuming I can get 11, 10 PBS becomes less important -- two PBS stations is probly enough. I rarely get 10 PBS now, and never get 2 CBS. Since I already get CBS on channel 58 (RF46), the two VHF stations are my least important, although Channel 2 news has a history for me.

    Anyone think 2 (RF12) would come in with this Hoverman? AntennaCraft 4 Bay UHF Antenna HDTV Outdoor TV Aerial for Local Off-Air Digital HD Four Bay Signal Fringe Reception, LIGHT GREEN ZONE, Part # G1483

    I thought if I could get a bidirectional VHF with directional UHF antenna, maybe I could get 11, 10 and 2 in one shot. Then I could also try pointing the 4221HD at Chicago and the other at Milwaukee, in hopes of snaring 49.

    But more and more I go back to the Hoverman, which is dirt cheap on Summit Source. If the Hoverman gets nothing on VHF, then I can try adding VHF elements later. I'm thinking I could put it right in the middle in front of either antenna, and get added gain from the directionality. So ultimately I might wind up with two UHF and two VHF antennas. (Gilda Radner voice: "It could happen.")

    Antennas that I eliminated from my search, due to high price and/or limited UHF or VHF functionality:

    Stellar Labs Model #30-2440 combo UHF/VHF -- just a little too long to install inside.
    Audiovox/RCA ANT751R -- UHF gain probably no better than my Monoprice/tin can.
    Winegard HD-1080 Not good for Hi VHF.
    Winegard Squareshooter Too expensive! Looks like my MonoPrice.
    ClearStream C2-V-CJM Too expensive. $67.49 used very good. $65 open box on eBay.
    ClearStream 5 C5 Not too big, but way too expensive! Doesn't do much on UHF.
    Winegard FreeVision FV-30BB or FV-HD30 Poor gain on UHF according to the chart I downloaded.
    The Y5 and Y10 7-13's -- 5 and 10 feet long. Way too big for me.

    Rick

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    Quote Originally Posted by Rickideemus View Post

    10 PBS (RF8) NM=31 from Milwaukee
    2 CBS (RF12) NM-30 from Chicago.

    Rick
    Rick,

    Your stations are truely in opposite directions, so here is a wild idea for you. I haven't tried it nor have I heard of anyone else doing this: build a 5-bar "cut-to-RF-10" Yagi without a reflector element and on the same boom, built a 5-bar "cut-to RF-12" Yagi using a single driven element (dipole) in the center of the boom.

    The first director element of each half of the antenna would work instead of the usual reflector elements. Since the driven element is a dipole (cut to channel 8 or 12 or somewhere in between, the impedence will be around 300 ohms like any other Yagi.

    Sadly, I see you have eliminated a Y7-13 on your list and my idea would be twice as long ... but I'd love to try it.

    Jim

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    Rick I have followed this forum long enough to realize a bit about your situation. I too had wondered why you asked about VHF antennas.
    I don't think the out of the box Hoverman from summit Source would do it. With the addition of NARODs it might. It would certainly be a big step up from the Monoprice.
    I agree with the too expensive comments.
    Signal levels on 8 and 12 are at the almost indoor doable level. Sounds like 47 should be there with a bit better antenna.
    As best I recall VHF gain on the CM-4221HD is off the back side, and VHF swr is excessive. In my experiments a 24'' wide reflector on a UHF bow tie antenna puts the VHF gain off the back side. It acts more as a director.
    I still like this one.
    Techorator - A blog about tech and more: Homemade $20 super antenna out of paper and tape!
    It wouldn't work for me inside this metal building, and would be a wind sail outside.
    Jim I like the wild idea. There must be some reason it wouldn't work.
    Steve

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    Quote Originally Posted by Fringe Reception View Post
    build a 5-bar "cut-to-RF-10" Yagi without a reflector element and on the same boom, built a 5-bar "cut-to RF-12" Yagi using a single driven element (dipole) in the center of the boom.

    The first director element of each half of the antenna would work instead of the usual reflector elements. Since the driven element is a dipole (cut to channel 8 or 12 or somewhere in between, the impedence will be around 300 ohms like any other Yagi.
    Cool idea, but shoot! I already think I put in too much work, attaching the tin can to the Monoprice and taping it to a box "mount." If I only had two or three other channels, I might feel differently.

    Sadly, I see you have eliminated a Y7-13 on your list and my idea would be twice as long ... but I'd love to try it.
    I think the ANT751R, at 36 inches, is my limit. Landlady already looks funny at what's there now, plus anything longer will be a hassle to balance up there, on top of the desk.

    But now, couldn't I just as well make two VHF loops, cut to size? Like the C5, but one loop bigger than the other. No reflector. Very honestly, even that would be a project way down the road. I'll probably try dipoles first, in front of the UHF antenna reflectors. If that doesn't work, I'm only out about 8 bucks.

    Thanks,
    Rick

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    Quote Originally Posted by RF Steve View Post
    I don't think the out of the box Hoverman from summit Source would do it.
    Yeaaaaaaah... I doubt it myself. But it should get 47, and who-knows-what-else. And the collapsible rod reflectors will be fun to play with. On good days, I could probably get by with just that antenna going to the converter box -- which has a much better UI than the TV tuner. I'm intrigued by the Hoverman. One expert thinks it's better than the 4221HD. Had an idea once it might be better indoors than the 4221. Can't remember why...

    I agree with the too expensive comments.
    Well, too expensive for me... They should charge whatever the market will bear.

    Signal levels on 8 and 12 are at the almost indoor doable level.
    Yes. You know I got those both off a wire connected to ground -- which is all that's left of our once proud outdoor antenna. But I can't imagine what splicing that together with one of the other antennas would do for multipath! Only two inputs to the TV, both occupied.

    As best I recall VHF gain on the CM-4221HD is off the back side,
    I didn't know that! Now on this antenna: http://www.mcmelectronics.com/conten...ts/30-2440.pdf Doesn't it look like VHF comes off the backside? I think they should mention that in the ad.

    I still like this one.
    Homemade $20 super antenna out of paper and tape!
    Yeah, $20 plus about $120 for my effort!

    Rick

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    I didn't know that! Now on this antenna: http://www.mcmelectronics.com/conten...ts/30-2440.pdf Doesn't it look like VHF comes off the backside? I think they should mention that in the ad.
    No, it is received from the front.
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    When I first added a 24"x24" reflector to a simple home brew 2bay. I got the gain I was looking for on UHF. Channel 7 and 8 off the back side came up a bit, but channel 10 off the front side went way down. I've since then learned that to act as a reflector on VHF frequencies it needs to be wider, and spaced farther back. The close spacing also made the already poor impedance match of a UHF 2bay at VHF frequencies worse. It is not unusual for a UHF antenna to have its best VHF gain off the back or sides. The reflector on the C5 is about 29" wide, and as best I can tell about 11" behind the driven element. Those who build 4bay antennas for dual band directional gain go quite a bit wider on the reflector. There is a good discussion of reflector width in the first page of this thread.Kosmic Antennas: SuperQuad 4 Bay Bowtie
    On the Stellar Labs antenna. Take a look at the change they've made to the driven element, and the reflector of dual band model. I'm not certain what kind of antenna magic they might be pulling off with that one. I'm quite curious about that antenna.
    $120 I think you've under estimated that. I have a hard time every time I try to build something. The first 4 bay I built went together with a lot of frustration, and mistakes. I had a hell of a time getting it right. Even the simplest single bow tie or 2bay antenna can turn into a 2 day failed project for me.
    Steve

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    Quote Originally Posted by ProjectSHO89 View Post
    No, it [VHF] is received from the front.
    So then what is the VHF element? Doesn't the UHF reflector also act as a VHF reflector? If not, does the UHF reflector double as the VHF element?? Is the added rectangular piece the VHF reflector?? Is there any VHF reflector??? You would think so, since they quote a VHF front to back ratio.

    Anyone feel free to jump in here.

    Rick
    Last edited by Rickideemus; 01-02-2014 at 08:58 PM.

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    Rick On the Stellar Labs antenna. Take a look at the change they've made to the driven element, and the reflector of dual band model.
    Compare it to the UHF only model. You will see the driven element has been designed for both bands on the dual band antenna.
    Take a look at the added large reflector elements at the back of the dual band antenna. How all the elements interact with each other to produce the desired results is beyond my simple understanding of antennas. The driven element may not be a full size half wave length at VHF frequencies, but it is not the first time capacitance loading of elements has been used by TV antenna manufactures. The interaction of all parasitic elements of the antenna play into the final performance of the finished product.
    The UHF only.
    http://www.mcmelectronics.com/conten...ls/30-2155.pdf
    The VHF/UHF.
    http://www.mcmelectronics.com/conten...ts/30-2440.pdf
    I would say the added rectangular piece is part of the dual band reflector assembly and all parts of the reflector assembly work together with the driven element and directors to produce the desired results.
    Steve

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    Quote Originally Posted by RF Steve View Post
    Rick On the Stellar Labs antenna. Take a look at the change they've made to the driven element, and the reflector of dual band model.
    Compare it to the UHF only model. You will see the driven element has been designed for both bands on the dual band antenna.
    I did look at that. I just don't know how you can say the two Y shaped elements on the dual band antenna were "designed for both bands." They look just like the main elements on many UHF bow-tie antennas, but smaller. (Smaller means HIGHER RF frequencies, right? VHF low, UHF high??)

    I really would like to understand this. I was assuming the rectangle in the rear was the VHF element. They are adding VHF and that's the only added section.

    Thanks,
    Rick

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    Rick those bow ties have a center dipole right through the middle of them. Or at least that's the way my eyes see the pdf drawing.
    Steve
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    Quote Originally Posted by RF Steve View Post
    Rick those bow ties have a center dipole right through the middle of them. Or at least that's the way my eyes see the pdf drawing.
    Whew! At least I know I'm not going crazy. Just blind. I never would have seen that if you hadn't pointed it out. Thanks, buddy.

    Rick

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    Quote Originally Posted by RF Steve View Post
    Rick On the Stellar Labs antenna. Take a look at the change they've made to the driven element, and the reflector of dual band model.
    Compare it to the UHF only model. You will see the driven element has been designed for both bands on the dual band antenna.
    Take a look at the added large reflector elements at the back of the dual band antenna. How all the elements interact with each other to produce the desired results is beyond my simple understanding of antennas. The driven element may not be a full size half wave length at VHF frequencies, but it is not the first time capacitance loading of elements has been used by TV antenna manufactures. The interaction of all parasitic elements of the antenna play into the final performance of the finished product.
    The UHF only.
    http://www.mcmelectronics.com/conten...ls/30-2155.pdf
    The VHF/UHF.
    http://www.mcmelectronics.com/conten...ts/30-2440.pdf
    I would say the added rectangular piece is part of the dual band reflector assembly and all parts of the reflector assembly work together with the driven element and directors to produce the desired results.
    Steve
    Steve,

    That looks like the 'triple-yagi' from Televes (Europe) that was badly panned and dismissed several years ago, much like the Chinese wonders currently marketed on Craigslist with (similar) totally absurd dB gain numbers. I'll go back and try to find links (if they still exist).

    Jim
    Last edited by Fringe Reception; 01-02-2014 at 10:03 PM.

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    Jim I had suspected it to be a Chinese copy of a European design. Very similar to the current Televes antennas. The VHF gain claim of 7-10 db I would have to assume to be dbi in order for it to have any sort of credibility. I've followed this line of import antennas for quite some time now where ever they show up. I had been watching the mcm catalog ones for over a year before I found them mentioned on the forums. I found it interesting that shortly after they were mentioned on this forum mcm expanded there line of Stellar Labs antennas.
    While a different antenna I thought quite interesting that this company would use an out of U.S. band peak gain in their marketing.
    I thought channel 51 ended at 698 MHZ
    http://manuals.solidsignal.com/hdb4x-gainchart.pdf
    I found it interesting the same company would post some very real world numbers on another antenna they just added to their brand line.
    Solid Signal Xtreme Signal HD1080X 2-Bay Bowtie UHF and High Band VHF TV Antenna 35 Miles UHF/VHF (HD-1080x) from Solid Signal
    You may need to click on specifications.
    I think publishing gain figures is fine, but the playing field is not level. For the most part Winegard has done a good job, and I would suspect Antennacraft's numbers are on the conservative side.
    Steve

 
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