antenna placement and type

[kvp]

Hello all,

I don't have a radio or antenna yet as I don't know if I can make it work on my rig.

Thoughts?

[Lscott]

The higher up you can mount the antenna the better. The ideal location in somewhere in the center of the camper's roof. I'm guessing the roof is aluminum so you will likely need to drill a hole for an NMO type mount and buy a matching antenna.

https://theantennafarm.com/shop-by-categories/shop-all/mobile-antennas/vhf-uhf-dual-band/451-commercial-dual-band/219-high-gain-dual-band-antennas/5582-laird-connectivity-c150-450cs-detail

It's a dual band antenna so you can use it for both a license free MURS VHF radio and for GMRS on UHF. It has a spring base so if it hits a tree limb it won't break or get ripped off the roof easily.

You can try one of these too. It has an optional spring base, have to buy separately. It has a claimed wide band performance so if you ever get you Ham license yo can use the same antenna on the Ham bands.

https://theantennafarm.com/shop-by-categories/shop-all/mobile-antennas/vhf-uhf-dual-band/451-commercial-dual-band/219-high-gain-dual-band-antennas/8128-comet-ca-2x4srnmo-detail

https://cometantenna.com/wp-content/uploads/2013/09/CA-2x4SR.pdf

https://cometantenna.com/wp-content/uploads/2013/09/CA-SPR-instructions-x-1.pdf

As long as the measured SWR at the radio end of the coax cable is 2:1 or less the radio should be OK. I have a work buddy that mounted one, the Comet antenna, on the fender of his pickup truck with the spring base installed. The measure SWR was under 2:1 and he used it for a while with a hand held radio while out doing sales calls around the Midwest area.

If you locate the antenna in a different spot the SWR will likely be different.

[kvp]

Thanks for the rely.

The roof is fiberglass.

I wondered if I could mount someplace on truck but figured the camper and truck would block pattern.

[Lscott]

You might have room to put a metal plate under the fiberglass. Also some aluminum tape, used on furnace duct work would likely work just as good on the roof too. Just a couple of suggestions to think about.

[WRPG745]

it looks like you have an air conditioner up there... is it possible to attach to a point on that instead of penetrating the camper roof?

perhaps a clever bracket with a ground plane kit. There maybe a way to chase the antenna wire through this access too.

I could be wrong, I've never had an RV or camper air conditioner, do you have a photo that shows the top area there?

[wayoverthere]

45 minutes ago, WRPG745 said:

it looks like you have an air conditioner up there... is it possible to attach to a point on that instead of penetrating the camper roof?

perhaps a clever bracket with a ground plane kit. There maybe a way to chase the antenna wire through this access too.

I could be wrong, I've never had an RV or camper air conditioner, do you have a photo that shows the top area there?

Good eye! If the outside is metal, it could be enough for a 1/4 wave and mag mount, and bring the cable down to the back window or back door seal. Failing that, fiberglass isnt as much fo an issue as metal in the way, so mounting at the hood line, either lip mount or bracket might be an option, with something longer like the ca2x4sr @Lscott mentioned (and I've had good results with), or I've also had good results with the browning 1713br (which is uhf only 5/8 over 5/8). The comet is ~36", and the browning is ~32"

[kvp]

Good info guy, thanks. I'm learning. Antenna theory is fascinating and mysterious. Smoke, mirrors and magic.

From what I've found looks like for gmrs, a disc of metal 6 - 8 inches works, doesn't even need to be a disc just the equivalent surface area if odd shaped.

Then I see 1/4 wave vs 1/2 wave etc. with no ground plane needed for 1/2 wave. I'm probably mixing disciplines here.

I'm getting a new truck but the camper will be the same. This photo is more up to date. I have three solar panels on the front now.

High on the roof would be ideal but I'm not sure practical with canoe. I may be able to mount a pole on the back of camper at roof height and mount there. This roof moves up and down so that would present a problem with needing coax slack and slapping in the wind.

 

[PACNWComms]

No matter which antenna you end up using, I would highly recommend 3M 5200 sealant for use on the coax penetration. Years of adding radio antennas and satcom equipment to RV's for emergency communications has shown that sealant to work very well for keeping the water out. It is also used by Bayliner/Sea Ray/Meridian for their vessel hull penetrations. 

As others have mentioned the Air conditioning unit would be a good place to mount to the metal under the plastic cover, perhaps even having the antenna poke out through one of the vent holes in the plastic. You would also have the opening to the inside for the coax run. Just use a lot of good quality sealant on that roof. Although, I live in the Pacific Northwest, and everything gets wet, eventually, you may have a different climate or use case for that camper. Good luck. 

[wayoverthere]

So...one thing it just hit me that I haven't seen asked or answered: is the plan to be able to use the radio in the truck (possibly in motion, based on the comment about cable slap), or in the camper at rest?

If the former, that may limit the usefulness of a mount drilled into the camper roof (which puts the cable inside the camper), unless there's then good access from in the camper to run the cable into the truck.

On the slack/slap, if you were dropping down from the roof rack to route in the side door seal or back window, the rack and one of the front jacks could be a place to attach the cable, while leaving some slack tucked inside the vehicle...when parking, just unclip the cable and release the slack and pop the top.

I currently have 2 mag mounts on my truck (cable runs on the roof, rather than the side) and only once experienced any slap, and snugging up the slack resolved that.

[axorlov]

Since you have the roof real estate used up with good stuff (boats, panels, who knows what), I'd say half-wave antenna at any convenient location (front corner on self-fabricated gutter mount) will do.

[SteveShannon]

Is there any reason you can’t combine your antenna with your flagpole?  What is the flagpole material?

[gman1971]

It really depends on what you want to achieve.

For a non-base, non-repeater mobile radio usage (moving), for GMRS, I would just buy a large aluminum plate and drill the NMO hole in the center and use a 1/2 wave NMO no ground antenna, or even a 1/4 wave (6 inch) then secure the AL plate to the roof with heavy duty double sided tape, and run the cable from the radio outside via one of the many electrical connectors you already have poking out from the RV cabin. If cable 

For a stationary base/repeater, I would skip the 1/4 wave, the 1/2 wave and go for a collinear 5/8 over 5/8 mobile antenna.  Know that the gain on those antennas are overly exaggerated, but it will certainly have more gain than the 1/4 wave for sure, with a more concentrated radiation pattern towards horizon, which is probably desirable for a repeater/base setup.

G.

[kvp]

Thanks again guys.

The flagpole is fiberglass and collapses. It's only up when I'm parked someplace that gets a breeze, usually the beach.

I'm looking at getting gmrs to go along with my cb as an alternative when needed. Mobile use unless needed while stopped, so not really a base station.

What do you think about putting a pvc pipe on the back near flagpole that I could raise/lower a few feet for mobile/base use. Running the cable down the inside of pipe, under truck to cab and inside to radio. This would of course require a way to disconnect for when the camper comes off the truck.

Looking on line what are you thoughts here:

Just an arbitrary site I found via google
https://www.arcantenna.com/collections/gmrs-antennas-nmo-mounts

from that site, would this be a good choice?
https://www.arcantenna.com/products/laird-antenex-fg4500-450-470-mhz-5-dbd-7-15-dbi-outdoor-fiberglass-omni-base-station-antenna-with-n-female-connector
looks like I'd need this to mount the above
https://www.arcantenna.com/products/rfmax-rosahdm1-heavy-duty-bracket-wall-or-mast-mount-for-omnidirectional-base-station-fiberglass-stick-antennas

other possibilities,
https://www.arcantenna.com/products/base-loaded-chrome-coil-antenna-for-gmrs-rbc-450-2-s
or this, not sure how it compares to the above.
https://www.arcantenna.com/products/gmrs-mobile-vehicular-antenna-base-loaded-chrome-coil-rugged-no-ground-plane-required-with-spring-rbc-450-5-ns#description

[axorlov]

RBC-450 with or without spring are mobile half-wave antennas not requiring ground plane. Good for the intended application, imo.

Base antennas like FG-4500 will fail quickly on a vehicle. They are rated for 100+mph winds, but not for all-day.

 

[wayoverthere]

1 hour ago, axorlov said:

RBC-450 with or without spring are mobile half-wave antennas not requiring ground plane. Good for the intended application, imo.

Base antennas like FG-4500 will fail quickly on a vehicle. They are rated for 100+mph winds, but not for all-day.

 

This. If a pole mount is the plan, underneath the bed will be an easy route to either do a bulkhead through the back of the cab, or tuck in at the bottom of the door seal. What type of mount is used may be the decider on where to put a disconnect for when removing the camper.

[PartsMan]

In the agriculture GPS world we use metal plates with 3M double sided "trim" tape to mount magnetic antennas.

It is very hard to remove.

I would make a ground plane plate and stick it in the middle of the roof and use a magnetic quarter wave antenna.

[Phenfay]

On 3/23/2022 at 7:14 AM, PACNWComms said:

No matter which antenna you end up using, I would highly recommend 3M 5200 sealant for use on the coax penetration. Years of adding radio antennas and satcom equipment to RV's for emergency communications has shown that sealant to work very well for keeping the water out. It is also used by Bayliner/Sea Ray/Meridian for their vessel hull penetrations. 

 

To PACNWComms, I'm seeing two types of 3M 5200 sealant.  Regular and Fast Cure.  Does the cure time affect performance?  Thanks in advance.

[PACNWComms]

16 hours ago, Phenfay said:

Regular and Fast Cure. 

Performance is the same, the cure time just determines how much time you have to work the pieces together or support it until dry. I use more of the fast cure, as I am often using smaller parts (marine VHF antenna mounts and connectors), where the regular is probably what boat builders use, as they may need to move things a bit to fit pieces together and may need some wiggle room. Since my last post, I have also been shown how this is used in recreation vehicles as well, especially around the TV (over the air digital) antenna, air conditioner, and other penetrations in the roof of that type of vehicle. Buy it at a hardware store (not a boat or RV store) to save some money.