Posted: 3/15/2012 4:22:40 AM EDT
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Hey guys, I'm planning to install mobile type 90 UHF radio in my truck to communicate with my dad and wife via GMRS. My application form is filled out, but I haven't sent in in yet. I need some help selecting an antenna... Here is where I was hoping to install the antenna since I have limited mounting options on a non-personal vehicle.  I'd use a fender mount like this one  Do I need a No-Groundplane type antenna for this location? I realize the vehicle groundplane is a lot less than ideal, but what else can I do without drilling holes in a company vehicle? Please suggest some options and antenna options. Thanks guys. |
| Be sure to read K0BG's VHF page. It's amateur-radio centric, but most anything he has to say about 70 cm should apply to GMRS. |
that is a dual-band antenna. mount & antenna purchased here. hope that helps, not really up on GMRS. 
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| Mag mount to roof? Route coax down along the window somewhere inconspicuous to the bottom of the cab. Then find one of many precut holes in the floorboard, they usually have solid rubber grommets. My Ford Ranger has quite a few of these. You can drill through one of those, or cut 2 slits in the shape of an X. Feed coax through there and now its in the cab. When the time comes to remove its as simple as can be. The grommet can be replaced (Ace Hardware has a great selection) or just fill it with RTV/silicone. |
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Quoted: Mag mount to roof? Route coax down along the window somewhere inconspicuous to the bottom of the cab. Then find one of many precut holes in the floorboard, they usually have solid rubber grommets. My Ford Ranger has quite a few of these. You can drill through one of those, or cut 2 slits in the shape of an X. Feed coax through there and now its in the cab. When the time comes to remove its as simple as can be. The grommet can be replaced (Ace Hardware has a great selection) or just fill it with RTV/silicone. I don't particularly want a mag mount since they don't typically work very well from my understanding. Plus they can destroy the paint under magnet. It was my understanding a mag mount was sort of a secondary to fender mounting; am I mistaken? |
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different schools of thought.
Mag allows you to mount in center of roof for optimal pattern, front fender mount displaces some of the plane....of course I have no complaints on where mine is, I can talk all-over. Mags can come off in collisions and harm paint underneath. I reckon any 440 Ham-tenna would work for your application. A second idea would be a Bed Stake Hole Mount. Prolly would work about like fender mount, except you wouldn't be able to watch your antenna sway in the wind 
lastly some will ask you to drill a hole and put in roof that way.... 
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Mag mount to roof? Route coax down along the window somewhere inconspicuous to the bottom of the cab. Then find one of many precut holes in the floorboard, they usually have solid rubber grommets. My Ford Ranger has quite a few of these. You can drill through one of those, or cut 2 slits in the shape of an X. Feed coax through there and now its in the cab. When the time comes to remove its as simple as can be. The grommet can be replaced (Ace Hardware has a great selection) or just fill it with RTV/silicone. I don't particularly want a mag mount since they don't typically work very well from my understanding. Plus they can destroy the paint under magnet. It was my understanding a mag mount was sort of a secondary to fender mounting; am I mistaken? My mag mounts are working great, low SWR, and haven't messed up my paint in a year and a half so far.  They have a protective film of some sort to prevent paint damage, I think. Center of roof is the optimum location, fender not as much, right?
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Quoted: page 43 in the latest QST mag from ARRL shows different mounting positions and the relative patterns. Yes center of roof is optimum.....but isn't everything a compromise This is certainly true! If I were to roof mount an antenna, I'd need to use a shorter, 1/4 wave antenna to prevent issues when in parking garages or on job sites with low areas. If I fender mount, I should be able to use at least a 5/8 wave size. |
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Here's a list from Universal.
I bought the cheap OPEK Dual-Bander, would like a 'nicer' one....in black for the look. |
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page 43 in the latest QST mag from ARRL shows different mounting positions and the relative patterns. Yes center of roof is optimum.....but isn't everything a compromise This is certainly true! If I were to roof mount an antenna, I'd need to use a shorter, 1/4 wave antenna to prevent issues when in parking garages or on job sites with low areas. If I fender mount, I should be able to use at least a 5/8 wave size. I would look for a co-linear dual 5/8 wave antenna, unfortunately there are little option for this in a single band antenna. Here is one option for you CA-2x4SRNMO http://www.cometantenna.com/products.php?CatID=1&famID=4&childID=4 It is a wide band search and rescue dual band antenna. It guarantee's a 1.5 or better SWR in the ham bands, and 2:1 or better on marine, LMR, and FRS/GMRS. I can tell you it is less than that. It is about 1.5:1 on GMRS. It also has a fold over feature. Usually wide band antenna's can be very efficient, a dummy load is very wide banded, this is not the case on this antenna. I can key up the W4RAT repeater in Richmond from the VA/NC boarder, it has excellent gain. It is a 1/2 wave on VHF, and seems to have better gain than a 5/8 wave mag mount I had before it. It will also work if you ever decide to get your amateur license, and after seeing the capabilities a mobile radio gives you, it may happen
I am not saying this is the best antenna for your situation, but it is an option. It can also be tuned to center it into the GMRS band if you wanted to do that. BROADBAND VHF/UHF ANTENNA
Dual band, designed to assist Search & Rescue Volunteers and Professionals 1.5:1 or less SWR: 144-148/440-450MHz 2:1 or less SWR: 140-160/435-465MHz Gain: 3.8/6.2dBi Max Power: 150 watts Length: 40 inches Connector: NMO Fold-over hinge included The CA-2x4SRNMO is a broad-band antenna designed for those needing voice communications on the ham radio, land mobile, and/or FRS frequency ranges. When the amateur radio community is working together with local search and rescue and other public service agencies, the CA-2x4SRNMO antenna allows TX and RX capability in both bands! The coverage area and gain provided by the CA-2x4SRNMO is remarkable. Whether used on VHF or UHF or both, it is an asset to the communications needs of amateurs and land mobile users simultaneously. |
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I know many forum members here swear by the SBB5 NMO antenna, and by the popularity, there is a good reason. I chose to go with the one above because of the wide band, it has a little higher gain figures than the SSB5, and it is only 2 inches taller.
Most of these antenna's can be adjusted to bring the resonance into the FRS band. |
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Both of those Comets look nice, but they also seem like overkill for me... If they're really the best option, then so be it. However, does anyone have any opinion on the Larsen NMO450C? |
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Both of those Comets look nice, but they also seem like overkill for me... If they're really the best option, then so be it. However, does anyone have any opinion on the Larsen NMO450C? should work fine, but with half the gain of those StanP posted..... |
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I have a basic understanding of gain and it's relationship to antenna performance. Per my understanding, the higher the gain on these antenna, the more horizontal the signal radiation (ie less vertical). How does gain affect distance of transmission in real world use? For instance with these 2 antenna models, the Comet SR has a UHF gain of 6ish dB and the Larsen boasts 3.4 dB. What am I really looking at? Technical answers are ok, I can sort though the jargon...  |
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1/4 or 1/2 wave on the roof would do as well as a gain antenna on the fender. Plus that front fender mount puts the antenna right in the driver's sightline and is really annoying (IMO). Mag mount on the roof could be my choice, route the cable through one of the body plugs under the back of the cab (in most pickups). If you have any really low clearances to deal with, a Sti-Co flexible 1/4 wave will fold over flat and pop back up.
Second choice would be a stake hole mount on the drivers side of the truck bed. |
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Quoted:
I have a basic understanding of gain and it's relationship to antenna performance. Per my understanding, the higher the gain on these antenna, the more horizontal the signal radiation (ie less vertical). How does gain affect distance of transmission in real world use? For instance with these 2 antenna models, the Comet SR has a UHF gain of 6ish dB and the Larsen boasts 3.4 dB. What am I really looking at? Technical answers are ok, I can sort though the jargon...
For every 3 DB you are doubling your effective radiated power. For instance transmitting 5 watts into a 3db has a ERP of 10 watts. With a 6db gain antenna your ERP would be around 20 watts. This is compared to a theoretical antenna. If you take it a little further, 35 watts into a 3.4 db antenna you have an ERP of 76.5 watts, on a 6db antenna 139 watts ERP. Gain also works on receive, not just transmit. |
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Quoted:
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I have a basic understanding of gain and it's relationship to antenna performance. Per my understanding, the higher the gain on these antenna, the more horizontal the signal radiation (ie less vertical). How does gain affect distance of transmission in real world use? For instance with these 2 antenna models, the Comet SR has a UHF gain of 6ish dB and the Larsen boasts 3.4 dB. What am I really looking at? Technical answers are ok, I can sort though the jargon...
For every 3 DB you are doubling your effective radiated power. For instance transmitting 5 watts into a 3db has a ERP of 10 watts. With a 6db gain antenna your ERP would be around 20 watts. This is compared to a theoretical antenna. If you take it a little further, 35 watts into a 3.4 db antenna you have an ERP of 76.5 watts, on a 6db antenna 139 watts ERP. Gain also works on receive, not just transmit. There's also a lot of loss in pattern distortion from the vehicle body as well as propagation loss from the 3 feet lower antenna position. And yes, that's noticable. |
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So a 1/4 wave on the roof is better than the 5/8 wave on the fender? IME, yes. And really, your fender mount is effectively a no ground plane setup, whereas the roof will have a ground plane, so the antenna gain would be roughly equal. I didn't realize the ~3 mounting height would result in a a very noticeable difference... It does make a difference, and moreso the higher you go in frequency. |
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Magnet mounts do not have DC connectivity to the vehicle body for the ground plane, they couple the RF capacitively.
Because of that, the ground plane is slightly less efficient because it electrically appears smaller than if a hole mount was in the same location. The capacitive coupling itself becomes less efficient as the frequency goes down, as the capacitance becomes a lot smaller in comparison to wavelength. So the idea that a magnet mount is less efficient than a fender mount might have some traction at CB frequencies, although I'd still debate the overall effectiveness of the antenna based on mounting locations. At UHF frequencies though the electrical/RF performance difference between a magnet mount and a roof mount are miniscule provided you use a reasonable quality magnet mount base. With the fender mount you've adding losses from missing/distorted ground plane, lower height, and obstruction of the vehicle body. |
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Well I checked with the bosses, and a hole in the roof even if done professionally is a no go. So, mag-mount or fender mount? I'm leaning towards a fender mount 5/8 collinear, but if you think the mag-mount won't degrade the 1/4 whip then I may do that instead. I've got both a 1/4 wave mag mount dual band and a 5/8 wave mag mount VHF . . the 5/8 is a HUGE improvement, even when I run it on the hood near where a fender mount would be (too tall on roof for the country trees). I may try the fender mount, but I'll need a curved unit made to come out below the side of the Dodge hood. Based on my experience, I'd get the fender mount and a 5/8 wave. Possibly would add the spring if I felt it wouldn't bend over at TX Interstate freeway speeds. :) Very pleased with the Hustler 3/8 (not so much for the magnet base mine came with) and you can get the antenna without the magnet. I'd try the Firestick cable made for their fender mount, too. (Sorry, didn't read back to see if you need VHF) In fact, I've been wondering if these could be done on both sides with a co-phase antenna setup (which would probably be overkill, but could be cheap to do considering the price of these antennas). I've been wondering if some BNC T connectors I have would work, but I have yet to catch up with my guru to ask. I'm also considering using a foldover on a trunklip mount on my bedcover (aluminum frame, but I'd use wire to bond the mount to the bed at the hinges on both sides. |