HELP-Antenna for enclosed aluminum trailer!

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Mike445

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Hey y’all. I am in the process of building a small travel camper based on an aluminum 5 x 8 enclosed trailer. I’m going to be putting an STS 100 and an ICOM IC R-10 in it. I have everything I need to split the antenna between two 2 radios already. That isn’t an issue.

what I want is an antenna that mounts through the side. I do not want any holes in the roof. When I am traveling and I stop for a night on the road I want to be able to turn on the scanner without setting up my base antenna. I was thinking of using a side mount CB antenna mount and found several 3/8x24 scanner antennas but have been told by many they become useless as the frequency increases due to the mount. I have found a couple side mount AM/FM antennas that would work. They are extendable from 18” to 55” I have a Motorola to bnc adapter already. Is there any reason I could not use this and adjust it to the length of a dual band antenna for general scan receive?

Any other recommendations would be awesome!
 

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prcguy

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The AM/FM antenna will be a compromise and I would try to use an antenna designed for the the frequencies you want to scan. How about an NMO type antenna on a small L bracket on the trailer side at roof level? Something like this, the maybe a Larsen Tri-band antenna or similar?

 

Mike445

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The AM/FM antenna will be a compromise and I would try to use an antenna designed for the the frequencies you want to scan. How about an NMO type antenna on a small L bracket on the trailer side at roof level? Something like this, the maybe a Larsen Tri-band antenna or similar?

Thank you for the speedy reply! That is what I was hoping to use. The question is how do I route the cable in? I don’t want to have to drill a hole and fill it with caulking. If you can figure me out and neat way to get an SMA in there I have a brand new Larsen NMO with SMA and that very bracket sitting here in front of me. I also have several spare Larson tri-band antennas without the spring.
Mike
 

prcguy

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You will have to drill a hole to get the cable in. Here is one type of waterproof cable entry thing and there are others. This one has a flange that mounts on the outside over the hole then you pass the cable through and tighten a ring to squeeze a rubber grommet around the coax. You might be able to pass an SMA connector through it but I would pass just the cable then install the connector afterward.



Thank you for the speedy reply! That is what I was hoping to use. The question is how do I route the cable in? I don’t want to have to drill a hole and fill it with caulking. If you can figure me out and neat way to get an SMA in there I have a brand new Larsen NMO with SMA and that very bracket sitting here in front of me. I also have several spare Larson tri-band antennas without the spring.
Mike
 

Mike445

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You will have to drill a hole to get the cable in. Here is one type of waterproof cable entry thing and there are others. This one has a flange that mounts on the outside over the hole then you pass the cable through and tighten a ring to squeeze a rubber grommet around the coax. You might be able to pass an SMA connector through it but I would pass just the cable then install the connector afterward.

Thank you!! That’s a great idea. Thank you. Hopefully the preinstalled sma can fit through!
Mike
 

prcguy

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I think it will pass through ok. You can take the thing apart and pass the cable with connector through the metal cover and internal rubber part separately, then reassemble. You might also look at a West Marine type catalog and see if there is a better cable entry solution, then find it cheap on Ebay.

Thank you!! That’s a great idea. Thank you. Hopefully the preinstalled sma can fit through!
Mike
 

Mike445

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I think it will pas through ok. You can take the thing apart and pass the cable with connector through the metal cover and internal rubber part separately, then reassemble.
Awesome! Thank you! I think that’s the route I’m going to go!
Mike
 

chief21

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Another possibility for cable entry is a short section of small diameter PVC pipe, with a 45 or 90 degree fitting on the outside, facing down. This allows you to route the cable slightly upwards into the trailer so that water will not enter. Leave a drip loop on the outside and you can pack any open space in the PVC with foam rubber to prevent any air or insect entry. I've used this home-brew method to route multiple, full-sized cables into several buildings successfully - using larger PVC, of course.
 

Mike445

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Another possibility for cable entry is a short section of small diameter PVC pipe, with a 45 or 90 degree fitting on the outside, facing down. This allows you to route the cable slightly upwards into the trailer so that water will not enter. Leave a drip loop on the outside and you can pack any open space in the PVC with foam rubber to prevent any air or insect entry. I've used this home-brew method to route multiple, full-sized cables into several buildings successfully - using larger PVC, of course.
That’s a very interesting idea! Thank you!
Mike
 

MUTNAV

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Is there going to be electricity in your trailer? Maybe a panel would be worth it if your are going to have multiple penetrations through the trailer.
Just a thought
Thanks
Joel
 

Mike445

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Is there going to be electricity in your trailer? Maybe a panel would be worth it if your are going to have multiple penetrations through the trailer.
Just a thought
Thanks
Joel
Yes there will be. I have a special plug that attaches to the side (watertight) that you connect an external cord to. I never thought about a panel!
Mike
 

WB9YBM

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"They are extendable from 18” to 55” I have a Motorola to bnc adapter already. Is there any reason I could not use this and adjust it to the length of a dual band antenna for general scan receive?"

Well, as long as you're not expecting any miracles (great DX for example) it should work. A trick I've used myself--when the car stereo antenna broke off of an old car I had once--was to connect the inner wire of the radios' coax (via capacitor) to the car body. It actually gave me better reception than the original antenna! (Although this was back in the day when cars were still made of metal...)

Taking things a step further: I've heard there are telescopic masts available (or one could DIY them too, I guess). Using one of those will make getting to destination easy when in the "down" position and once on site and extended will very much help whatever antenna you mount to the top. I suppose with some mounting arrangement welded to the back of the trailer would serve...(just thinking out loud)
 

Mike445

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"They are extendable from 18” to 55” I have a Motorola to bnc adapter already. Is there any reason I could not use this and adjust it to the length of a dual band antenna for general scan receive?"

Well, as long as you're not expecting any miracles (great DX for example) it should work. A trick I've used myself--when the car stereo antenna broke off of an old car I had once--was to connect the inner wire of the radios' coax (via capacitor) to the car body. It actually gave me better reception than the original antenna! (Although this was back in the day when cars were still made of metal...)

Taking things a step further: I've heard there are telescopic masts available (or one could DIY them too, I guess). Using one of those will make getting to destination easy when in the "down" position and once on site and extended will very much help whatever antenna you mount to the top. I suppose with some mounting arrangement welded to the back of the trailer would serve...(just thinking out loud)
Yes telescopic would be the only way I would go. Unfortunately I talked to some people who have used them and they are flimsy if they don’t have a spring.
I talked to another gentleman who has done the same thing as I have and he used a magnet mount on the tongue of the trailer and it works well when he travels. One of the stationary for a while he put out a bass antenna just like I am going to do.
I think I’ll skip putting any holes in the side of the unit. Thank you for your idea!
Mike
 

WB9YBM

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"I think I’ll skip putting any holes in the side of the unit"

Check some of the ham store web sites; there are window-mount feedthroughs (basically RF connectors mounted on a long piece of wood) that will let you feed coax runs through windows without having to drill holes. I think MFJ might make them...
 

Mike445

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"I think I’ll skip putting any holes in the side of the unit"

Check some of the ham store web sites; there are window-mount feedthroughs (basically RF connectors mounted on a long piece of wood) that will let you feed coax runs through windows without having to drill holes. I think MFJ might make them...
Thank you for the idea! I’ve seen those before! Totally forgot about their existence! Have a great day!
Mike
 

chief21

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How would I seal then to be watertight?
Which of these types you might use will depend on the thickness of the wall that they need to breach and the exterior surface type. Generally, however, your water-proofing efforts could include rubber gasketing and/or caulking or silicone. In some cases, you might wish to use a small, flat stainless steel panel with a hole for the connector. You could fasten the flat ss panel to the exterior wall, using caulk or silicone between the flat panel and the surface for water-proofing. Dress the interior wall as necessary to make it pretty (another ss panel, perhaps, or a plastic switch cover).
 

Mike445

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Which of these types you might use will depend on the thickness of the wall that they need to breach and the exterior surface type. Generally, however, your water-proofing efforts could include rubber gasketing and/or caulking or silicone. In some cases, you might wish to use a small, flat stainless steel panel with a hole for the connector. You could fasten the flat ss panel to the exterior wall, using caulk or silicone between the flat panel and the surface for water-proofing. Dress the interior wall as necessary to make it pretty (another ss panel, perhaps, or a plastic switch cover).
You can see by the pictures I have attached what the trailer looks like. It is aluminum skin on the outside and plywood on the inside. The aluminum walls are not too thick but they are strong. Every 16 inches there is a 1x1 square tube steel wall and roof trusses. I wouldn’t mind a good rubber gasket but do not wanna have to depend on silicone to seal the hole.
I wouldn’t mind a good rubber gasket but do not wanna have to depend on silicone to seal the hole.
Mike
 

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prcguy

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I would plant a couple of NMO mounts and maybe a 3/8-24 in that roof and be done with it. You can't get a ground plane much better than that and with the ceiling not covered yet you can easily route the cables.

You can see by the pictures I have attached what the trailer looks like. It is aluminum skin on the outside and plywood on the inside. The aluminum walls are not too thick but they are strong. Every 16 inches there is a 1x1 square tube steel wall and roof trusses. I wouldn’t mind a good rubber gasket but do not wanna have to depend on silicone to seal the hole.
I wouldn’t mind a good rubber gasket but do not wanna have to depend on silicone to seal the hole.
Mike
 
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