Posted: 9/12/2016 8:29:10 PM EDT
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I bought a NMO mount, NMO mobile dual band antenna and made a mast that attaches to my truck via the cargo tie down system. I have the antenna installed.
Now I need to make a ground plane for the antenna. 1/4 wave ground plane radials for 2 meter is big. I have seen ground plane kits where the 2 m VHF ground plane has 6 inch radials. Does this work? I was under the impression the radials had to match the vertical wavelength of the antenna. ie. If I have a 2 meter 1/4 wavelength vertical, ( about 19 inches ) do I need 1/4 wavelength radials for the ground plane or can I use a much smaller multiple, say 1/8 wave or 1/16 wave radials and just suffer with a smaller ground plane. Then I have to make it withstand 100 MPH, so the smaller the radials the better, I don't want a hole in my brand new truck and I don't want a magnetic mount so I don't think there is any other way I can use the truck as the ground plane. Thanks in advance. |
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So if I make a ground plane with radials that are 1/16 of the 2 meter wavelength ( will be middle of the 2 meter band freq wise. I know the HAM 2 meter band isn't really 2 meters ) how much loss will there be compared to 1/4 length. Is there a chart or formula I can compute that?
With the metal of the car being 12 inches under the ground plane radials affect performance? Thanks for any info. and yes, I like making stuff. |
| Can you post a photo of your antenna installation? Did you check the antenna with an analyzer or a watt/SWR meter? A separate ground plane section is not common on a 1/4 wave vehicular installation. If you need one then you are doing things the hard way. Please post a photo so we can give you some tips. |
Get a Comet NMO fender mount. They have one for various vehicle years and models. http://www.theantennafarm.com/catalog/mobile-antenna-mounts-264/fender-bracket-mounts-268/nmo-vehicle-specific-mounts-297/ |
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Can you post a photo of your antenna installation? Did you check the antenna with an analyzer or a watt/SWR meter? A separate ground plane section is not common on a 1/4 wave vehicular installation. If you need one then you are doing things the hard way. Please post a photo so we can give you some tips. I will get a photo. NMO mount is at the top. Antenna not screwed on yet. I am pretty sure it is RF isolated from the vehicle and there is no ground plane since the antenna is not sitting on metal. I am trying to optimize a symmetrical radiation pattern by providing a separate ground plane from the vehicle metal, like you would need to do with a base installation of a mobile antenna. Maybe I am misunderstanding something. Best place would be on top of the passenger compartment in the middle with either a hole in the roof or a mag mount, I don't want to do either, so I am trying something different. Radio and SWR show up Wed. |
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http://i966.photobucket.com/albums/ae144/wakerunner_08/Sierra%201500/Radio%20Installs/file-26.jpg http://www.wearecb.com/images/watermarked/1/detailed/5/fender_mount_with_NMO.jpg Get a Comet NMO fender mount. They have one for various vehicle years and models. http://www.theantennafarm.com/catalog/mobile-antenna-mounts-264/fender-bracket-mounts-268/nmo-vehicle-specific-mounts-297/ Having it mounted to that position will produce non-symmetrical radiation patterns and having the antenna below a chunk of the metal part of the vehicle will cause RF shadows. I am trying to optimize the radiation pattern. |
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I will get a photo. NMO mount is at the top. Antenna not screwed on yet. I am pretty sure it is RF isolated from the vehicle and there is no ground plane since the antenna is not sitting on metal. I am trying to optimize a symmetrical radiation pattern by providing a separate ground plane from the vehicle metal, like you would need to do with a base installation of a mobile antenna. Maybe I am misunderstanding something. Best place would be on top of the passenger compartment in the middle with either a hole in the roof or a mag mount, I don't want to do either, so I am trying something different. Radio and SWR show up Wed. http://i228.photobucket.com/albums/ee259/mach_102/6FB3CFBC-D234-4C39-8B14-562DAA5C75E1_zpsghaicy4b.jpg Quoted:
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Can you post a photo of your antenna installation? Did you check the antenna with an analyzer or a watt/SWR meter? A separate ground plane section is not common on a 1/4 wave vehicular installation. If you need one then you are doing things the hard way. Please post a photo so we can give you some tips. I will get a photo. NMO mount is at the top. Antenna not screwed on yet. I am pretty sure it is RF isolated from the vehicle and there is no ground plane since the antenna is not sitting on metal. I am trying to optimize a symmetrical radiation pattern by providing a separate ground plane from the vehicle metal, like you would need to do with a base installation of a mobile antenna. Maybe I am misunderstanding something. Best place would be on top of the passenger compartment in the middle with either a hole in the roof or a mag mount, I don't want to do either, so I am trying something different. Radio and SWR show up Wed. http://i228.photobucket.com/albums/ee259/mach_102/6FB3CFBC-D234-4C39-8B14-562DAA5C75E1_zpsghaicy4b.jpg A ground plane like you are planning will work, but is not really the right way to do it. If you want to try a ground plane then go ahead and try it. The ground plane does require 1/4 wave length radials. If I were you I'd go ahead and do this the right way by drilling a hole top dead center of the roof for an NMO. There is a reason that is the gold standard vehicular arrangement. If you are looking for the best performance in a mobile then you want the best mount possible, and that is the top dead center drilled mount. |
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I'm not being snobby just hear me out.
If you want max performance put an nmo in the center of your roof. Even with your setup using radials your radiation patter will be effected by the cab. I understand the hesitation in drilling, however there are thousands of NMO mounts on the road between public service and hams, there is a reason it is the go to. Aircraft antennas are the same through body type of instillation. If the mount is properly installed you will have years of trouble free performance. You probably already have a hole for the XM antenna, your third brake light posses just as much risk as leaking. Have you met anyone who wishes they never put an nmo on? |
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Need more info. Antenna type (model number or link). What type mast, wood, aluminum? A pic would help or MS Paint. 
ETA - Oh, I see that pic is the mount. What's the mast made of metal or some insulator like wood or fiberglass? Metal, although version 2.0 will be an extend able fiberglass to get 3 times the height above the vehicle when stopped. |
Or you could just drive to higher ground with your permanent NMO mount. 
Seriously, there is a recurring theme here and I'm pretty sure that the drilled NMO will not only be the most suggested solution in this thread, but will also prove to be the best performing in the real world. |
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failureToExtract and GCW,
I am very hesitant to put a hole in the roof, I just bought this thing. I figured I would try this first and if I really get into this hobby ( Just got my Tech Saturday, still don't have my call sign, so I am a noob ), I may put a hole in the roof eventually, or maybe a hole in the CAP I may end up buying. |
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failureToExtract and GCW, I am very hesitant to put a hole in the roof, I just bought this thing. I figured I would try this first and if I really get into this hobby ( Just got my Tech Saturday, still don't have my call sign, so I am a noob ), I may put a hole in the roof eventually, or maybe a hole in the CAP I may end up buying. Fair enough, but consider this... With a properly installed NMO on the roof, not only is the antenna installed in the most optimal configuration, but the feedline is also routed easily and hidden all within the cab. With your frankentenna solution the metal of the cab is still present in the nearfield of the antenna (will yield unexpected results). Also, how do you plan to cleanly route the feedline into the cab while both protecting it and keeping water out? |
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A hole from an NMO mount won't detract from the vehicle value. If you sell it or trade it in. There are caps you install over the unused mount and it looks like a small GPS puck or sat radio antenna.
I understand you not wanting to drill into a new vehicle, but properly done won't hurt it. As far as radials when you are stationary, solid copper wire with some crimp type ring terminals could be bolted to the antenna base. |
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Fair enough, but consider this... With a properly installed NMO on the roof, not only is the antenna installed in the most optimal configuration, but the feedline is also routed easily and hidden all within the cab. With your frankentenna solution the metal of the cab is still present in the nearfield of the antenna (will yield unexpected results). Also, how do you plan to cleanly route the feedline into the cab while both protecting it and keeping water out? Quoted:
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failureToExtract and GCW, I am very hesitant to put a hole in the roof, I just bought this thing. I figured I would try this first and if I really get into this hobby ( Just got my Tech Saturday, still don't have my call sign, so I am a noob ), I may put a hole in the roof eventually, or maybe a hole in the CAP I may end up buying. Fair enough, but consider this... With a properly installed NMO on the roof, not only is the antenna installed in the most optimal configuration, but the feedline is also routed easily and hidden all within the cab. With your frankentenna solution the metal of the cab is still present in the nearfield of the antenna (will yield unexpected results). Also, how do you plan to cleanly route the feedline into the cab while both protecting it and keeping water out? No doubt, NMO in a hole in the roof is the best solution and keeps the feedline inside.. I will be putting a hole in my Civic
The metal of the cab and likely the bed will influence the antenna because much of it will be within a wavelength. How much I don't know. I guess i will find out. I scoped out a rubber grommet into the cab with a wire harness going through it. So I will use that. |
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A hole from an NMO mount won't detract from the vehicle value. If you sell it or trade it in. There are caps you install over the unused mount and it looks like a small GPS puck or sat radio antenna. I understand you not wanting to drill into a new vehicle, but properly done won't hurt it. As far as radials when you are stationary, solid copper wire with some crimp type ring terminals could be bolted to the antenna base. Did not know about the caps, makes sense. I was thinking about welding some steel rod onto a small base for the radials, but the copper wire is a good idea, I would be able to see how much they bend in the wind. |
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Just ground the vertical pole to the frame of the truck and your Good to go.. Nothing else needed. The truck will do the rest. would actually be better if you drilled the ant to the top of the cab.. The cab would be the ground plane.. Prosise My understanding is that the RF doesn't need it to be common to the shielding, it just needs a big metal surface close to the bottom of the vertical. I though if I brought the antenna down to just above the cab, I would get ground plane from the cab, mostly forward signal probably though. |
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http://i.imgur.com/A7RBUnI.jpg http://i.imgur.com/UAasnPP.jpg http://i.imgur.com/mnptCTe.jpg Go drill your civic and see how easy it is and overcome your worries What is on the other side of that NMO connector, mine requires a 5/8 hole for the SO-239 to fit through. That looks like a very small hole, just the core of the NMO sticking through? And that looks like the same antenna I bought at the Ham Fest. Opec VU-1509 and the one I am mounting to my truck ETA: Shit, maybe I installed it into the bracket wrong. |
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No doubt, NMO in a hole in the roof is the best solution and keeps the feedline inside.. I will be putting a hole in my Civic
The metal of the cab and likely the bed will influence the antenna because much of it will be within a wavelength. How much I don't know. I guess i will find out. I scoped out a rubber grommet into the cab with a wire harness going through it. So I will use that. Quoted:
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failureToExtract and GCW, I am very hesitant to put a hole in the roof, I just bought this thing. I figured I would try this first and if I really get into this hobby ( Just got my Tech Saturday, still don't have my call sign, so I am a noob ), I may put a hole in the roof eventually, or maybe a hole in the CAP I may end up buying. Fair enough, but consider this... With a properly installed NMO on the roof, not only is the antenna installed in the most optimal configuration, but the feedline is also routed easily and hidden all within the cab. With your frankentenna solution the metal of the cab is still present in the nearfield of the antenna (will yield unexpected results). Also, how do you plan to cleanly route the feedline into the cab while both protecting it and keeping water out? No doubt, NMO in a hole in the roof is the best solution and keeps the feedline inside.. I will be putting a hole in my Civic
The metal of the cab and likely the bed will influence the antenna because much of it will be within a wavelength. How much I don't know. I guess i will find out. I scoped out a rubber grommet into the cab with a wire harness going through it. So I will use that. Amateur radio is all about experimenting and having fun. You are doing both right off the bat. Good on ya! Although we are all saying that your way isn't optimal and to drill the hole, your experiment is worthwhile and educational. I think you will learn that you can get away with a lot with antenna installations. The truth it that even a bad antenna installation can work pretty well. Many people have seriously poor installs, yet they are perfectly content with them. Why? Because they are working as far as they are concerned. I say have fun and experiment. Ever heard of fox hunting? I learned a lot about how the signals travel and reflect off of things by foxhuntig. Loads of fun! |
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Amateur radio is all about experimenting and having fun. You are doing both right off the bat. Good on ya! Although we are all saying that your way isn't optimal and to drill the hole, your experiment is worthwhile and educational. I think you will learn that you can get away with a lot with antenna installations. The truth it that even a bad antenna installation can work pretty well. Many people have seriously poor installs, yet they are perfectly content with them. Why? Because they are working as far as they are concerned. I say have fun and experiment. Ever heard of fox hunting? I learned a lot about how the signals travel and reflect off of things by foxhuntig. Loads of fun! Quoted:
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failureToExtract and GCW, I am very hesitant to put a hole in the roof, I just bought this thing. I figured I would try this first and if I really get into this hobby ( Just got my Tech Saturday, still don't have my call sign, so I am a noob ), I may put a hole in the roof eventually, or maybe a hole in the CAP I may end up buying. Fair enough, but consider this... With a properly installed NMO on the roof, not only is the antenna installed in the most optimal configuration, but the feedline is also routed easily and hidden all within the cab. With your frankentenna solution the metal of the cab is still present in the nearfield of the antenna (will yield unexpected results). Also, how do you plan to cleanly route the feedline into the cab while both protecting it and keeping water out? No doubt, NMO in a hole in the roof is the best solution and keeps the feedline inside.. I will be putting a hole in my Civic
The metal of the cab and likely the bed will influence the antenna because much of it will be within a wavelength. How much I don't know. I guess i will find out. I scoped out a rubber grommet into the cab with a wire harness going through it. So I will use that. Amateur radio is all about experimenting and having fun. You are doing both right off the bat. Good on ya! Although we are all saying that your way isn't optimal and to drill the hole, your experiment is worthwhile and educational. I think you will learn that you can get away with a lot with antenna installations. The truth it that even a bad antenna installation can work pretty well. Many people have seriously poor installs, yet they are perfectly content with them. Why? Because they are working as far as they are concerned. I say have fun and experiment. Ever heard of fox hunting? I learned a lot about how the signals travel and reflect off of things by foxhuntig. Loads of fun! I am just approaching this like I approach everything else. Experimenting, making stuff, and trying new things. Yeah, I am enjoying this. Never heard of fox hunting, will look into that. Thanks. |
| Mine is one of the 3/8" nmo mounts vs the common 3/4". Yes that's the antenna I picked it up at a hamfest and it seems to work fine. Another thing I like about the NMO is I keep a 5/8 wave dual band high gain behind my seat for road trips or in the sticks. Same for the whip on my screwdriver, in town the smaller antennas are less noticeable but perform fine. |
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Mine is one of the 3/8" nmo mounts vs the common 3/4". Yes that's the antenna I picked it up at a hamfest and it seems to work fine. Another thing I like about the NMO is I keep a 5/8 wave dual band high gain behind my seat for road trips or in the sticks. Same for the whip on my screwdriver, in town the smaller antennas are less noticeable but perform fine. That's a good idea. I will need to do that. |
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FWIW, I've been on 2 Meters since the mid-'70s and never drilled for an antenna mount. I've either used a 1/4 wave mag mount on the vehicle roof or a 5/8 wave trunk-lip mount.
If you use a mag mount, make sure the protective plastic disc stays on the bottom of the magnet. For both mounts, periodically remove them and apply a little auto wax underneath to prevent discoloration and/or rust. |
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Did not know about the caps, makes sense. I was thinking about welding some steel rod onto a small base for the radials, but the copper wire is a good idea, I would be able to see how much they bend in the wind. Quoted:
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A hole from an NMO mount won't detract from the vehicle value. If you sell it or trade it in. There are caps you install over the unused mount and it looks like a small GPS puck or sat radio antenna. I understand you not wanting to drill into a new vehicle, but properly done won't hurt it. As far as radials when you are stationary, solid copper wire with some crimp type ring terminals could be bolted to the antenna base. Did not know about the caps, makes sense. I was thinking about welding some steel rod onto a small base for the radials, but the copper wire is a good idea, I would be able to see how much they bend in the wind. The copper will bend in the wind. I suggested it for stationary use. Some NMO mounts do require a fairly large hole, some don't. IIRC mine uses the 5/8 3/4 in hole. |
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Update.
I mounted a 1/4 wave mobile antenna on a mast attached to the cargo tie down channel in my Tundra. I bought and installed a Tram VHF ground plane radial attachment setup that sits 2 feet above my truck. The SWR was 5.00 without the ground plane radials, and was 2.00 with the radials horizontal. I bent them down a little at a time until I got to about a 45 degree angle down while reading the SWR each increment bending down. According to the SWR, I get slightly less than ( slight loss due to SWR I think, .0.2 watts, could just be the radio or loss over the RG-58x ) full power output with a 1.00/1 SWR with 0.00 reflected power. I am not sure I believe it. I am using an MFJ-847 digital power and SWR meter for VHF / UHF. I also set up a 1/4 wave magnetic mount and get 1.07 / 1 SWR with that in the middle of the cab roof, which seems reasonable. My guess is that the SWR is reading a little optimistic. What ball park should a mag mount 1/4 wave wip be reading? My plan is to use the mag mount antenna for now, ( until I put a hole in the roof )and install an expendable and removable 25 foot mast to be used when stationary for HAM fests and camping and field day stuff until I get General and an HF radio and then add an HF antenna too.. By then I will have learned a little bit about antennas and have a 30 foot high VHF antenna for stationary comm in the truck. |
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Update. I mounted a 1/4 wave mobile antenna on a mast attached to the cargo tie down channel in my Tundra. I bought and installed a Tram VHF ground plane radial attachment setup that sits 2 feet above my truck. The SWR was 5.00 without the ground plane radials, and was 2.00 with the radials horizontal. I bent them down a little at a time until I got to about a 45 degree angle down while reading the SWR each increment bending down. According to the SWR, I get slightly less than ( slight loss due to SWR I think, .0.2 watts, could just be the radio or loss over the RG-58x ) full power output with a 1.00/1 SWR with 0.00 reflected power. I am not sure I believe it. I am using an MFJ-847 digital power and SWR meter for VHF / UHF. I also set up a 1/4 wave magnetic mount and get 1.07 / 1 SWR with that in the middle of the cab roof, which seems reasonable. My guess is that the SWR is reading a little optimistic. What ball park should a mag mount 1/4 wave wip be reading? My plan is to use the mag mount antenna for now, ( until I put a hole in the roof )and install an expendable and removable 25 foot mast to be used when stationary for HAM fests and camping and field day stuff until I get General and an HF radio and then add an HF antenna too.. By then I will have learned a little bit about antennas and have a 30 foot high VHF antenna for stationary comm in the truck. How long is the antenna and I assume you are using it on the ham bands? |
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How long is the antenna and I assume you are using it on the ham bands? Quoted:
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Update. I mounted a 1/4 wave mobile antenna on a mast attached to the cargo tie down channel in my Tundra. I bought and installed a Tram VHF ground plane radial attachment setup that sits 2 feet above my truck. The SWR was 5.00 without the ground plane radials, and was 2.00 with the radials horizontal. I bent them down a little at a time until I got to about a 45 degree angle down while reading the SWR each increment bending down. According to the SWR, I get slightly less than ( slight loss due to SWR I think, .0.2 watts, could just be the radio or loss over the RG-58x ) full power output with a 1.00/1 SWR with 0.00 reflected power. I am not sure I believe it. I am using an MFJ-847 digital power and SWR meter for VHF / UHF. I also set up a 1/4 wave magnetic mount and get 1.07 / 1 SWR with that in the middle of the cab roof, which seems reasonable. My guess is that the SWR is reading a little optimistic. What ball park should a mag mount 1/4 wave wip be reading? My plan is to use the mag mount antenna for now, ( until I put a hole in the roof )and install an expendable and removable 25 foot mast to be used when stationary for HAM fests and camping and field day stuff until I get General and an HF radio and then add an HF antenna too.. By then I will have learned a little bit about antennas and have a 30 foot high VHF antenna for stationary comm in the truck. How long is the antenna and I assume you are using it on the ham bands? Using it on HAM VHF band. It is about 19 inches with a center loaded coil, 1/4 wave whip. It sits on a mast about 2 feet above the truck at the front of the bed. I did shave the length just a bit to tune it better for VHF. It is also a dual band for UHF but will not be using it for UHF so I optimized it for VHF HAM band. I just started into this HAM thing, but I have had a little education on antenna theory from my EE degree. ETA: I know just enough to be dangerous.
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5/8" hole NMO mounts are to enable the mount to be installed without access to the underside of the hole.
If you do have access to the underside of the hole you can use a 3/8" hole and an NMO designed for 3/8". NMO mounts designed for thicker mounting surfaces are also typically 3/8" hole and the stop plate on the underside is adjustable so as to get the mount the correct height for the thickness of the surface. Quoted:
Possibly a retarded question, but what about a magnet mount, or would that jack your signals all up? I've seen CB mounts like that, but CB freqs are much different than 2m/70cm Magnet mounts work fine at 2m/440. Magnet mounts couple capacitively to the ground plane, so the ground plane look electrically smaller than it is otherwise - hence, magnet mounts become more problematic the lower you go in frequency. At 6 meters and below it is very noticeable. Less of a problem if you have a physically large vehicle/roof, full size vans are great with mag mounts  . At above 70cm/UHF frequencies, the dimensions of the magnet mount, wiring etc become a substantial fraction of a wavelength so can introduce some eccentricities in performance also.
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My understanding is that the RF doesn't need it to be common to the shielding, it just needs a big metal surface close to the bottom of the vertical. An RF ground plane absolutely has to have connection to the transmission line shield to function as a ground plane, otherwise it's just conductive material in the antenna near field. |