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Build Your Own Antenna - Discuss topics for building your own antenna.

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  #1 (permalink)  
Old 02-08-2018, 10:19 PM
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Default Source for commercial grade fold-over trailer mount?

We're looking to install a five foot(ish) tall UHF antenna, a heavy fiberglass rod type, on a trailer roof. The reasons for that antenna don't matter here, please let's not get distracted with questions like "use a magmount".

The idea is to put the antenna on the forward edge of the trailer roof, on a fold-over hinged mount of some type. Because the trailer roof is about nine feet high, there's no convenient way to send someone up to raise and lower a mast, and we want something simple and reliable. So, a fold-over antenna that could be erected by simply pulling down on a cord attached to the base, extending forward from the hinge and trailer, would be ideal. Cord gets pulled down, antenna rotates up, no fuss. Release the cord, nudge the antenna, and it folds down on the roof so it doesn't hit overheads on the road. And we can live with the antenna base having a lopsided ground pattern as it will be connected to the trailer frame and roof.

But for the life of me, I can't find anything in a rotating or hinged antenna mount, except one kludgy ham unit built out of metal bar/tube stock. I'm looking for something that doesn't look homemade, and is robust and simple.

Anyone seen a source for that? Anything remotely similar, or other good options?
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Old 02-08-2018, 11:16 PM
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How about something even simpler to operate, a motorized mobile antenna mount. Install and adjust the mount on your trailer (they make several different mounting types so simply pick the one that will work best for your trailer), install the antenna onto the mount, run the coax and power for the motor and get ready to operate. Use the convenient switch to change it from upright for operation or down for travel, it couldn't be simpler. With a simple relay and some ingenuity you could probably even automate the operation so the mount moves up and down when you 1) turn on/off the radio or 2) connect/disconnect the trailer to the tow vehicle (by all means fully test this automation prior to relying on it).

Diamond® Antenna ~ K9000LRM Motorized Luggage Rack Mount <-- is one type, but there are others on the market that work similarly. Since you provided very few details on your antenna choice (is that a firm choice or how flexible are you with the exact antenna?) I can't say if that type of mount will work for you, but for most mobile UHF antennas they work just fine. If you do require that specific antenna, check when you order the mount to verify that it will indeed handle the weight and mounting requirements for that antenna.
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Old 02-09-2018, 1:07 AM
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Sounds like n5ims and I are thinking of two different types of antennas. Sounds to me like you are talking about a UHF base antenna, am I incorrect?

I think this is a case where some custom fabrication is in order. I've seen mounts like what you are probably looking for before, but they were all custom.

A pair of heavy aluminum angle stock uprights bolted to the trailer with a pivot at the top with a short pole to support the antenna. Pivot the antenna to 90º and put a pin/bolt through to hold it in place.
Not glamorous, not automatic, but simple and durable.

Probably something similar could be done with some unistrut.

Another option might just be a length of pipe welded/bolted to the front of the trailer or the trailer tongue. A pice of pipe that fits inside there with the antenna on top. Take it out of the trailer, drop it in place, hook up the coax.
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Old 02-09-2018, 4:55 AM
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N5-
Thanks, but that won't work. This antenna is over four feet long (close to six if I remember correctly, definitely a good 5+) and about as thick as a broomstick, or your thumb. It is also ground dependent, the base is meant to be firmly clamped to a ground, typically a tripod mount with an 8' tall pole to further elevate the antenna.

McK has the right picture. The problem is, "custom". I was told in no uncertain terms "This has to look professional" because the Powers That Be will be judging that critically. And if I go to a machine shop and start saying "I need this and this per these plans" I just KNOW what East Coast machine shops charge to fab up shiny stainless these days. Or even shiny anodized aluminum, or brass.

Can't "drop it in place" because the "place" will be nine feet up, and we're not allowed to levitate in public. (It tends to start religions.) Also, the coax connection on these is at the bottom of the antenna, facing straight down.

The Antenex FG4505 is very similar:
FG4505 - Antenex Fiberglass Base Station Antenna (450-460MHz, 5Bd)
except it is maybe half the height, less gain, different freq range. I just don't have a model number on the one we're trying to match, not sure it is made any more but it probably is. Used to be advertised on the back of QST as being used on Mount Washington and surviving the winters there. These are "overkill" antennas, yes.
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Old 02-09-2018, 10:02 AM
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If you can mount something to the roof of the trailer where someone can reach up from the inside and operate it, here is a mount designed for what you need. It terminates in a 1"-14 thread for marine antennas but you can screw on a short SS extension tube and mate that with your antenna base. When installed you just use the crank handle inside the trailer to raise and lower the antenna.

GS-890: Grand Slam 890 Universal Mount | TACO Marine
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Old 02-09-2018, 3:04 PM
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I believe the Tarheel Lift & Lay mount is the solution. Scroll to about the bottom of the page - http://www.tarheelantennas.com/mounts

- Automated with actuator installed as part of the mount
- Read some reviews/use here: Tarheel Lift & Lay Antenna Mount Product Reviews
- A quick check with Tarheel on the size of mast for mounting and the weight it will lift should answer questions. Still, right off it appears reasonably robust enough to lift the antenna you noted.

They have what you might call "manual" versions of the lift where you could use your rope idea, but you would need a cantilever, as the angle of the rope being pulled downward would not be friendly to lift it. You could build something that had an L shaped bracket and the antenna would connect to the vertical part of the L. Then when laid back the smaller part of the L would be vertical. It would be at that top point of the small part where you would attach the rope/line whatever. You could then pull it forward and down to raise the antenna and tie the rope off near the front hitch/lift. (The longer the bottom bar that the rope attaches to, the easier it will be to lift/pull down) Something exactly like the shape of their MT-4 mount.

The difference is this will cost about $500 versus about $50 if you make it yourself. You noted that "homemade" looking is out, so get the checkbook.
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Old 02-09-2018, 4:04 PM
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Thanks guys.

PRC-That boat mount looks interesting, but this antenna doesn't have the 1"x14 base thread it requires. So that becomes problematic. Also, I think the interior height is a full eight feet, so that crank would be mounted out of reach, requiring a step or other "but people can fall down from it and trip over it". We really are looking to make accidents impossible, if there's no step, no one can fall off it.

Vagrant-
The tarheel tilt overs are the type of concept I'm looking for, but in this case we want the base to overhang the edge of the trailer, so that someone can pull down on the overhang, like a permanently affixed gin pole. All the tarheel bases seem meant to be affixed to a flat plane, with someone walking over and doing the raising manually on the antenna itself--no gin pole, no counter balance.

"There's got to be a pony in this pile!" Don't tell me, Archimedes and the Pharoahs were last people to actually USE lever arms??

Maybe I should just buy a plasma cutter....(sigh)
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Old 02-09-2018, 9:44 PM
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Well then, just do it differently. Turn it upside down.

At the base of the trailer edge, on whatever side you want, just put a short pole mount on a hinge that is attached to the trailer. You could use some of those ready made mounts that Tarheel offers, like the MT 5, and initially lock it in with the cotter pin. Just mount it vertically at the side base of the trailer. Then slide on whatever size pole you want to the base mount. The pole you use does not even need to be snug onto the tilt mount. It will simply work as an anchor point. Use some wing nuts on the antenna mount itself and make it easy to secure that onto the pole(s). This would allow whomever to add the poles and antenna horizontally, regardless of their height. No one would need to climb anything.

Now when you walk/push the pole(s) with the antenna on top upward, which should be very easy to do now that the hinge is at the base of the trailer, you will want it to be reasonably vertical. At about five feet up from the trailer base you will want to put in a bracket or hook or something. You may need to re-enforce the inside of the trailer with a plate for the bolts to go through, or not, but basically that bracket or fastener would be an easy to secure solution for the pole once it is vertical. Hell, it could be a Velcro strip if it is not a permanent install. Velcro is pretty damn strong.

I really do not understand the need for a counterbalance. I have walked up 40' of push-up pole using an anchor point hammered into the ground for temporary use. I guess if the people raising this antenna only had the strength of children you could also use a rope. At the top or top side of the trailer, where the pole will be next to it, install some kind of metal loop. Then just slip a piece of rope through that and secure it to the pole before lifting. One child could pull on the rope while the other pushed up the pole until it was vertical.

If these suggestions do not satisfy, someone is trolling you with a task they may never find acceptable.


Hmm...I just looked at that MT 5 base again there is a flaw in my plan, but it can be resolved. If that mount were rounded my suggestion would work fine. As it is reasonably squared once you slide the pole over that mount and start to lift, it would probably bind as it got to the corner since the pole/mast would probably be larger in diameter and not slip between those plates. A way to overcome that would be to fasten a pipe clamp on the pole mount and slip a large washer or piece of metal over the pole where it would rest on the pipe clamp. Then when the pole/mast is slipped on, it would only come down to the secured point and never touch/bind on the corner when raising or lowering.

In case someone wonders about the 40' push up pole raising, there are two holes on the side at the base of the Rohn push up. You can slip a bolt through there. The bolt also goes through this which can be purchased at most any hardware type store. Just hammer that into the ground first and there you go.

https://mobileimages.lowes.com/produ...7376003424.jpg
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Last edited by vagrant; 02-09-2018 at 10:09 PM..
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Old 02-10-2018, 1:27 PM
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A "push up" mounted vertically on the front side might be of some use, but that would also require a pulley system since a separate "push rod" becomes one more thing to lose, etc.

When you mention mounting a tilt-over at the 'base' of the trailer, you realize the "base" is down at ground level, the top is about 8' up from that, and the tilt-over has to be mounted UP THERE on the roof, not at the base, in order to make sure the antenna is above the ground plane formed by the roof?

Also, stowing the antenna flat on the roof when it is not deployed makes the whole thing look cleaner when the powers that be are walking around it.

As I said at the start, there are reasons we'd like to just do a simple tilt-over mounted up top. No loose parts, no clutter, no etcetera. I should just fly in a local machinist from a third-world country where this kind of custom work is their every day normal.(G)
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Old 02-10-2018, 1:55 PM
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Oh! A motorized one, hiding way down the page.

Now that's an elegant solution, even if it is pricey. I think they may just say "Order it. How soon can it get here?"

I'd hoped to keep the budget well under that, but this just could be worth it. My only reservation would be how reliable is that motor system?
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Old 02-10-2018, 3:01 PM
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FWIW, I have a Tarheel MT-3FB that I use to support a mast in temporary situations. It is very nicely made. All stainless steel that has been shotpeened for a consistent finish. Welds are ground smooth. Hardware is factory finish SS, also.
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