Roof rack mounted antennas

[AlbanyTom]

Please school me. Why do the rails need to be electrically secure at both ends of the vehicle roof?

I currently have antennas mounted to tabs on a steel drop in basket that sits on top of the factory roof rack rails of my Nissan Xterra (3' Firestik for CB at the left rear corner; Larsen NMO 2/70 SH at the right rear corner). Since the rack rails are not very well grounded to the vehicle, I grounded the drop in basket to the vehicle by running short lengths of 1/2" copper strap from near the antenna tabs at the left and right rear corners of the drop in basket to the vehicle body under the rear hatch.

Should I have also run copper strap from the front of the drop in basket to the vehicle body? Why would that result in an improvement in either reception or transmission on CB and 2m/70cm?

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I think you did really well. I have the same truck. The basket itself is giving you a ground for the 2m/440 antenna, and the copper strap is giving you the ground for the firestick to the truck. And that the brackets are welded on means they will have a great connection.

For mine, I had an NMO mount put in the middle of the roof, and use a flexible 1/4 wave whip for 2m. Works fine, and it doesn't get hurt when I pull in and of my garage, with only a couple of inches clearance about the roof.

 

[jwhutch]

I think you did really well. I have the same truck. The basket itself is giving you a ground for the 2m/440 antenna, and the copper strap is giving you the ground for the firestick to the truck. And that the brackets are welded on means they will have a great connection.

For mine, I had an NMO mount put in the middle of the roof, and use a flexible 1/4 wave whip for 2m. Works fine, and it doesn't get hurt when I pull in and of my garage, with only a couple of inches clearance about the roof.

What is the brand of the flexible quarter wave 2m antenna? I have thought about a 4 Runner type vehicle. Comet and Diamond, (I believe) make a mount that will clamp on to the lip of the hatch back. The mount is an NMO and is pretty much fully adjustable, to have the antenna oriented vertically. I would like to try that. You can always get a 27mhz Larsen nmo antenna for the CB, and have one on each side of the hatch.

 

[AlbanyTom]

What is the brand of the flexible quarter wave 2m antenna? I have thought about a 4 Runner type vehicle. Comet and Diamond, (I believe) make a mount that will clamp on to the lip of the hatch back. The mount is an NMO and is pretty much fully adjustable, to have the antenna oriented vertically. I would like to try that. You can always get a 27mhz Larsen nmo antenna for the CB, and have one on each side of the hatch.

It's a sti-co. I think the flexi-whip. It's a commercial antenna. A friend of mine, who is a ham and a tech at a local mobile radio dealer, recommended it. You can tie the thing in a knot without hurting it. I think it comes in a 20" or so length, you cut it down to the band you want. Absolutely love it. I had the radio shop do my install...not cheap, but safest and easiest way I know to have it mounted in the middle of the roof. Works great, looks great.

If you're looking at 4runner, take a look at xterra, too. A little bit smaller, a bit less payload and gvwr, part time 4wd (which I like), and way less expensive. I test drove both and liked the xterra better, although that wasn't the only thing that swayed me. Just bought it a few months ago, and love it. Not my first SUV, but my first Nissan. New truck, new antenna....I'm spoiled.

 

[Frdmskr]

Larsen NMO270B...Flexible, Indestructible. Uses NMO. Cheap enough to buy more than 1.

 

[Robert Bills]

Since pictures are worth thousands of words, here is my antenna setup with the drop-in roof rack basket on my Xterra. I welcome any comments to improve the system.

Specifications

Vehicle: 2005 Nissan Xterra with factory roof rack

Drop-in Basket: Manufactured by Tony Hepler of Heps Designs, available through XterraPerformance.com http://www.xterraperformance.com/DE...RD-ROOF-RACK-2005-2015-NISSAN-XTERRA_p_8.html

Modifications to Drop-in Basket: antenna tabs, light tabs, footman loops and Rotopax can mounts welded to basket prior to powdercoating.

Antenna mounts: 2m/70cm (passenger side) - Breedlove NMO Roof Mount with ring terminal connection #78; CB (driver side) - Breedlove Pedestal Stud Mount #008 with Firestik medium spring and Breedlove quick disconnect coupling #002. breedlovemounts.com.

Antenna: 2m/70cm - Larsen NMO 2/70 SH; CB - Firestik 2' (in forested areas with low overhangs) or 3' Firefly (in desert areas).

Grounding. : 1/2" copper strap from adjacent to the CB mount to the vehicle body under the rear hatch, and a second 1/2" copper strap from adjacent to the NMO mount to the vehicle body under the rear hatch. Powdercoat/paint sanded to bare metal under connections to drop in basket and vehicle body.

Gear Bag: custom Blue Ridge Overland Gear Bag - compresses from 6" tall (height of stacked Rotopax gas and water cans to 3" tall (single can) to allow low profile. http://www.blueridgeoverlandgear.com/



Photos:

 

[4x4junkie]

Since pictures are worth thousands of words, here is my antenna setup with the drop-in roof rack basket on my Xterra. I welcome any comments to improve the system.

Specifications

Vehicle: 2005 Nissan Xterra with factory roof rack

Drop-in Basket: Manufactured by Tony Hepler of Heps Designs, available through XterraPerformance.com http://www.xterraperformance.com/DE...RD-ROOF-RACK-2005-2015-NISSAN-XTERRA_p_8.html

Modifications to Drop-in Basket: antenna tabs, light tabs, footman loops and Rotopax can mounts welded to basket prior to powdercoating.

Antenna mounts: 2m/70cm (passenger side) - Breedlove NMO Roof Mount with ring terminal connection #78; CB (driver side) - Breedlove Pedestal Stud Mount #008 with Firestik medium spring and Breedlove quick disconnect coupling #002. breedlovemounts.com.

Antenna: 2m/70cm - Larsen NMO 2/70 SH; CB - Firestik 2' (in forested areas with low overhangs) or 3' Firefly (in desert areas).

Grounding. : 1/2" copper strap from adjacent to the CB mount to the vehicle body under the rear hatch, and a second 1/2" copper strap from adjacent to the NMO mount to the vehicle body under the rear hatch. Powdercoat/paint sanded to bare metal under connections to drop in basket and vehicle body.

Gear Bag: custom Blue Ridge Overland Gear Bag - compresses from 6" tall (height of stacked Rotopax gas and water cans to 3" tall (single can) to allow low profile. http://www.blueridgeoverlandgear.com/

I think that if your SWR is good (and you're not experiencing any rattling or crackling/static noises as you're driving over bumps), you probably don't need to worry about it. That rack does look to have a fair amount of mass extending forward of your antennas to act as a ground plane, and the ground straps you have at the rear to the roof provide a connection to act as a ground plane toward the rear.
Certainly there's no harm in grounding the rack up at the front somewhere (maybe to the bolts holding the factory rails) just to see if anything changes though... If it does improve things, then all the better.

The bigger issue I see (at least on the CB side) is that tiny rubber-ducky (size) antenna you have on there. I'd bet you could triple or even quadruple your effective range (not just outgoing, but incoming too) by putting something better (taller) on there (you have the spring... trees, etc. shouldn't hurt a taller antenna unless you're passing under 4" diameter limbs @ like 60MPH or something). My Francis 5.5' on a spring atop the roof of mine has been fine for 10+ years now even through the tight twisty trails in the forests of the Sierra-Nevadas.

 

[Robert Bills]

. . . The bigger issue I see (at least on the CB side) is that tiny rubber-ducky (size) antenna you have on there. I'd bet you could triple or even quadruple your effective range (not just outgoing, but incoming too) by putting something better (taller) on there. . . .

That's not a rubber ducky. Your eyes are playing tricks on you.

Note from my post with the photos that for CB I use a 2' Firestik only when I'm on a forested trail with low overhangs otherwise I use a 3' Firefly on the highway and in open terrain. (The 2' antenna is pictured.)

I experimented with a 4' antenna but reception really wasn't appreciably better than with the 3'. I haven't had any difficulty communicating with others in my group either in transit to a trailhead or on the trail. In fact, when compared to a setup I had on another vehicle using a 5' antenna mounted on the cowl, my 2' above the roof gets about the same range as the 5' on my other rig and the 3' gets better range.

.

 

[4x4junkie]

You missed the "(size)" in my post.

I guess if it's working well enough for you, then no need to change it. You did say you were open to comments to improve your setup though.
I've done tests in the past of switching out numerous different antennas on the same vehicle while parked in an open elevated spot and there were immense differences between antennas that were 3 feet or less tall vs. ones 5½ feet or taller. My signal would drop from S-9 to about S-5 simply by switching out a 102" whip for a 3' Firestick, where my 5.5' Francis was still a bit over S-8 or so (seems the performance tipping point was somewhere between 4½-5 feet, or about 55-60% of a quarter-wavelength).

At least you do have it mounted up high which is something that can't be said about a lot of radio setups I've seen. Certainly that does help a lot.

 

[Robert Bills]

. . . there were immense differences between antennas that were 3 feet or less tall vs. ones 5½ feet or taller. My signal would drop from S-9 to about S-5 simply by switching out a 102" whip for a 3' Firestick, where my 5.5' Francis was still a bit over S-8 or so (seems the performance tipping point was somewhere between 4½-5 feet, or about 55-60% of a quarter-wavelength).

I'll need to experiment with a longer antennas again. I stopped using them a long time ago after I broke a a half dozen fluorescent tubes in a gas station with the 102" antenna on my jeep.

 

[Frdmskr]

Nice rack LOL...You need to understand that for VHF and UHF that set up is fine. For CB you are asking the questions "What type of compromise am I willing to accept?" Ideal solution is put a Breedlove ballmount and plate on the rear quarter panel, lock in a 102" or 108" steep whip and use that for CB. Even better, stick that on the roof (though in a forest I'd agree to avoid that.) With these smaller antennas they are a coil and not a physical quarter wave or better. So its a compromise antenna that focuses on styling and space as opposed to physics.

With your mount on the roof, the compromises extend beyond the antenna. That basket may not create a good ground and counterpoise. Did you remove the powder coat where you connected the mount? ground strap? Did you use a star washer or something to really make sure you have a tight solid connection? These all play into the game.

The idea? Its all welded/soldered together. That is not practical so we adapt from there. I do like some of what you did and may someday shameless steal your idea for stowing the rotopacks

 

[Robert Bills]

. . . That basket may not create a good ground and counterpoise. Did you remove the powder coat where you connected the mount? ground strap? Did you use a star washer or something to really make sure you have a tight solid connection. . . ?

Yes, yes, and yes. Powdercoat removed from roof basket at antenna mount and under both ends of ground straps (at rack and vehicle body). Star washers were used.

Would adding ground straps from the front of the drop-in basket to the vehicle body add anything for either UHF/VHF or CB (the original question re roof rack rails being "electrically secure at both ends of the vehicle roof" as suggested in an earlier post)?

 

[Frdmskr]

I'd imagine the basket at VHF/UHF is fine. Anything below 100MHZ is where I begin to wonder if there is enough metal.


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[4x4junkie]

I'll need to experiment with a longer antennas again. I stopped using them a long time ago after I broke a a half dozen fluorescent tubes in a gas station with the 102" antenna on my jeep.

BTDT lol.
If they're unavoidable, I just move slow underneath them, this usually keeps them from breaking or falling out (at least with my fiberglass whip... A bare steel whip might need the top 8" or so wrapped with shrink tube or electrical tape to keep from breaking them).

I haven't looked into it to confirm, but I've been told by several people that you aren't liable for damage if they are not covered by a lens or inside a fixture. Take it with a grain of salt though, I'm not sure how much I believe it.

Would adding ground straps from the front of the drop-in basket to the vehicle body add anything for either UHF/VHF or CB (the original question re roof rack rails being "electrically secure at both ends of the vehicle roof" as suggested in an earlier post)?

As I implied a couple posts ago, you probably have to just try it and see.
I agree with Frdmskr in that it's not likely to make any difference on V/UHF, but there might be some possibly it'll allow the CB to work better. Again, the improvements may only be slight though if your SWR is already good.

 

[mm58]

This is an *excellent* site on mobile installations of radios.
K0BG.com
Tons of good info

 

[Robert Bills]

Would adding ground straps from the front of the drop-in basket to the vehicle body add anything for either UHF/VHF or CB (the original question re roof rack rails being "electrically secure at both ends of the vehicle roof" as suggested in an earlier post)?

I agree with Frdmskr in that it's not likely to make any difference on V/UHF, but there might be some possibly it'll allow the CB to work better. Again, the improvements may only be slight though if your SWR is already good.

I don't have my SWR results handy, but my recollection is that with the 3' Firefly is was 1.7:1 with the 2' Firestick it was 2.1:1. Not great but acceptable.

I think that I'll spring for a 4' or 5' antenna to see how much I lower I can get the SWR. To keep things in perspective, I'm not using a full chassis CB, just an all-in-one Cobra 75 WX ST (one of very few radios that can be mounted cleanly in an Xterra). Its purpose is trail communications/convoys with my immediate group.