Best way to mount a HAM radio antenna

[cruiserlarry]

I finally decided to drill my roof, if I can successfully drop the headliner. I want to install about 4 NMO mounts (maybe 3 NMO and a 3/8"-24 for CB). I want to run a couple of ham, a cell phone, and a CB antenna.

I have a few questions related to the installation, and a couple of general questions:

1. What should the arrangement and spacing be? I have a sunroof, so I will be limited the rear half of the roof.

2. I want an easy way to remove or fold down the antennas for low clearance areas (like my garage). I am not sure if it is practical to unscrew the antenna every time. Currently I have a mag mount and just lay it on it's side. How do you all handle this?

3. I was told that the Larsen mounts are the best. Is this the general consensus?

4. How much weight/force can these mounts handle? The mount seems pretty small, and I have a hard time believing it can hold my diamond 770 at 80 mph.

5. On the mag mount I have now, the threaded connection between the mount and antenna gets very sticky (bare metal on metal), and is very difficult to unscrew. Can I use some kind of waterproof conductive lubricant on the threads to allow it to be unscrewed easily (graphite, lithium grease, other)? Something like this:
http://www.mgchemicals.com/products/846 ... 7d23a7ecda

7. If I add a roof rack in the future, how will it affect performance? Can I remount the antennas on the rack with a short extension jumper and ground strap?

8. Is it worthwhile to install a cell phone antenna? Any experience here?


I'm sure I am forgetting something, but this is enough to get me started.

Thanks for all the help.

I'll quickly address a couple of your questions. The Larson NMO mounts are the best, IMO. They also make a NMO mount base-loaded CB antenna (27Mhz), so you can use all the same mounts. The mounts will not take much lateral force with an antenna attached, but you can remove the antennas fairly easily. You need to space the antennas at least 19" apart from each other and any other conductive / reflective object. Don't bother with a cell antenna. A roof rack will interfere with the performance of the antennas, so mount the rack first, and work around it to mount the antennas.A jumper ground wire will have virtually no effect on performance - you are working with a ground plane, not a ground point. The NMO mounts I've used have not siezed up - the antennas came off easily, even after several years (they o-ring seal w/the threads).

Good luck...

[DaveK]

Eric:

My comments in bold below.

I finally decided to drill my roof, if I can successfully drop the headliner. I want to install about 4 NMO mounts (maybe 3 NMO and a 3/8"-24 for CB). I want to run a couple of ham, a cell phone, and a CB antenna.

I have a few questions related to the installation, and a couple of general questions:

1. What should the arrangement and spacing be? I have a sunroof, so I will be limited the rear half of the roof. If your concern is interference between one antenna and the other, please note that two radios, which transmit and receive, should not be operating at the same time on your roof. There is generally not enough room on your roof for you to safely space these types of antennas. Otherwise, there obviously should be some space between the antennas, but the arrangement will mostly be a function of space and personal preference.

2. I want an easy way to remove or fold down the antennas for low clearance areas (like my garage). I am not sure if it is practical to unscrew the antenna every time. Currently I have a mag mount and just lay it on it's side. How do you all handle this? See my post above

3. I was told that the Larsen mounts are the best. Is this the general consensus? They are excellent. Others are available but Larsen is widely available. A trip to your local Ham radio store should give you an opportunity to actually see what else is available so that you have a better idea about what else might serve your needs.

4. How much weight/force can these mounts handle? The mount seems pretty small, and I have a hard time believing it can hold my diamond 770 at 80 mph. Call Larsen tech support with your specific specs.

5. On the mag mount I have now, the threaded connection between the mount and antenna gets very sticky (bare metal on metal), and is very difficult to unscrew. Can I use some kind of waterproof conductive lubricant on the threads to allow it to be unscrewed easily (graphite, lithium grease, other)? Something like this:
http://www.mgchemicals.com/products/846 ... 7d23a7ecda

7. If I add a roof rack in the future, how will it affect performance? Can I remount the antennas on the rack with a short extension jumper and ground strap? See my post above. I have achieved exceptional performance with my antennas on the roof rack.

8. Is it worthwhile to install a cell phone antenna? Any experience here? An external antenna is always preferable to one located inside your metal box (the vehicle). All of the on-star systems rely on external antennas (they are all cell phone based). Practically speaking however, I've seen very little difference when I have used an external antenna when I am in the boonies. I've tried the booster kits with an external antenna and I've also taken a mag mount Cell antenna 20 feet over the vehicle. If there was a difference, I've not seen it. Perhaps if you can hook up with someone who is a skilled and knowledgeable antenna guy, maybe they can set you up with something that will improve your performance.


I'm sure I am forgetting something, but this is enough to get me started.

Thanks for all the help.

[sdnative]

Thanks for the quick replies!

I'll look in to the On-Star to see how they manage the antenna.

I do not have a roof rack now, and I may or may not add one in the future, so I wanted to know what my options are once that happens.

I saw the Larsen CB antenna. I am looking for something a little shorter, like the firestik 2' or 3'. Sure wish it had an NMO mount.

[hmfigueroa]

In the NMO mounts I have had antennas fail before the mounts do, Too fast, low branch Comet SSB5 or SBB7 antenna (I forget which) very thich whip broke the antenna base but he mount held firm.

There are adapters for NMO to various bases, such a N, 3-28, UHF etc. http://www.eur-am.com/nmo.htm or http://www.pl-259.com/page5.html

Stuff like a roof rack in the near field of the antenna will have an effect on the impedance You can allleviate this effect with an antenna that has a raised radiating element.

[cruiserlarry]

Keep in mind that the Firestik 2' or 3' CB antennas are much less flexible than the Larson base-loaded 27 Mhz antenna. It may be taller, but the majority of the antenna is a very flexible thin-wire whip...

[Nadir_E]

A question for the gurus from the peanut gallery:

I have a soft-topped vehicle - no metal roof of which to speak. I *am* about to install a roof rack, though it won't have a metal floor (just the frame for now, possibly with some marine board as a deck). Am I correct in presuming I have no ground plane in this set-up and should choose an antenna designed to operate without one?

How significant a difference in performance will I experience without the ground plane compared to someone equipped with one?

Very, very new to HAM radios - just passed the test for my Technician's license a few days ago!

Thanks for your insight!
-Nadir

[sdnative]

First off, congrats on your ham ticket.

Man, a lot has changed since I posted those question. I have drilled my roof, used Larsen NMO mounts, ditched the thought of the firestik and went with the Larsen 27B in addition to my SBB1. Very happy with the install. One of these days I will post some pics.


Back to your question. If you dont have a large metal surface for a groundplane (counterpoise), you can use an antenna that doesn't need one. Namely a halfwave type. Quarterwave antennas need a groundplane.

For 2m use, I have run the diamond NR770HBNMO with great success, although I am not to impressed with the tab where it connects to the mount. I would look at the comet SBB5, a very similar antenna, which (I believe) has a spring loaded pin instead of the tab. Most everyone on this board has one flavor or another of the halfwave, open-coil antennas.

http://www.rfparts.com/diamond/nr770hbnmo.html

http://www.cometantenna.com/products.ph ... &childID=4

[OLLIE]

A question for the gurus from the peanut gallery:

I have a soft-topped vehicle - no metal roof of which to speak. I *am* about to install a roof rack, though it won't have a metal floor (just the frame for now, possibly with some marine board as a deck). Am I correct in presuming I have no ground plane in this set-up and should choose an antenna designed to operate without one?

How significant a difference in performance will I experience without the ground plane compared to someone equipped with one?

Very, very new to HAM radios - just passed the test for my Technician's license a few days ago!

Thanks for your insight!
-Nadir

Nadir,

In additon to the advise you get from some of the knowledgable members here, try calling these guys and asking your questions or drive down there. They are great people and more than willing to help you out. Let them know you're from this site.

Jun's Electronics
(310) 390-8003
5563 Sepulveda Blvd, Culver City, CA 90230
Cross Streets: Between Playa St and Berryman Ave
http://www.hamcity.com

[David]

I would consider a tailgate mount. there are many mounts that slip on the edge of the tailgate and screw down tight. it will work great. dont to the roof thing. if you are near Ham Radio Outlet in Anahiem, go there and look at the many mounts available.
David

[Nadir_E]

A question arose as I was thinking about this - if I were to install a piece of sheet metal on the roof rack deck and ground that to the truck's chassis, would that be a way of creating the ground plane that a hard top vehicle's roof offers?

thanks, Everyone!
-Nadir