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Old 06-24-2014, 07:06 PM   #1
NN5I
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Default Sermon on the Mount

Sermon on the antenna mount, that is. Last Saturday my new screwdriver arrived from KJ7U. So of course I started thinking how to mount it on my motor home.

At length I decided to make a mount that would attach to the horizontal (athwartship) 3" square steel bar that's part of the Class IV hitch receiver. I figured I could use big square U-bolts, so I went shopping.

At a big trailer-hitch place I bought big square galvanized U-bolts, sized to fit over a 3" square tube. Then at Lowe's I bought galvanized nuts and lockwashers. At a metal place I bought a cut-off end, 34.5 inches, of 6" steel structural channel. Back to Lowe's to buy 1/4-20 hardware for grounding connections. All that was yesterday.

This morning I got up early (before noon, even) and sanded and primed the channel so I could handle it without instantly becoming filthy dirty. Then I started drilling all the necessary holes. This was actually quite a lot of work. Here's the mount with all the holes drilled, and final paint.


This end mounts to the hitch. The big holes are for the U-bolts, and the small holes are for braid connections to the coach's chassis. The holes for the U-bolts are at an angle, because I wanted the mount to stick out at an angle.


This end sticks out in the rear of the coach and is where the antenna is attached. The big hole is for the antenna mounting post, and the small holes are for grounding screws.


Here are the U-bolts. They are pretty strong; the thread is 1/2-13, and they require 1/2-inch holes.


For good grounding, it is necessary to remove paint around the holes where the ground connections go. I did this with a carbide burr on both the top and the bottom surfaces of the mount.


The ground straps (braids) are pretty substantial too, about 1" wide and 1/8" thick. One end is attached to the nice new mount, and the other end will be connected to the frame rails of the coach. I haven't done that yet.


The ground connections are made with capscrews and what I have learned are called keps nuts, with attached star washers for good electrical contact.


Here's the mount with all ground studs mounted, ground straps attached, and the antenna mounting post installed.


Here are a couple views of the mount on the coach, with the antenna mounted.



Here's an underside view of the U-bolts holding the antenna mount to the hitch receiver under the coach. You can see the two grounding braids hanging down because I haven't connected them to the coach's frame rails yet.



Still to do: connect the ground-braid straps to the frame rails. Run coax and the control/power wires from the front end of the coach to the back end. The IC-7000 is mounted on the driver's console, so this is a non-trivial task.
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Old 06-24-2014, 08:17 PM   #2
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That's downright righteous.

Blessed are they who know how to use tools, for they shall make cool stuff. And thanks for all the pics. Very good job!
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Old 06-25-2014, 05:30 AM   #3
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Beautiful work, Carl.

When I mounted my Icom-7000 in my Towncar I went to an automotive stereo shop and paid them to run all of the wiring and they also attached a couple of ground straps to the body as well.

Cheap. Less than $100 for sure and the wires are "gone". I have no idea how these auto guys hide the wires in the vehicle like that!

The owner of the stereo shop told me that lots of folks have him install "CB" radios in their vehicles. Not sure if that comment applies to just this shop, all auto-stereo shops or was just total BS :-)

But the price was right, the work was well done and the wires are very hidden! Not sure you want to trust your RV rig to an auto-stereo shop, though .

Good luck putting the finishing touches on the install. That really is nice work there Carl !
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Old 06-25-2014, 07:26 AM   #4
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lt looks real nice, in fact that's how I"d do it,,,, The only thing I'd change is that full width broom that can sweep rocks and debris onto my towed.
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Old 06-25-2014, 08:59 AM   #5
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lt looks real nice, in fact that's how I"d do it,,,, The only thing I'd change is that full width broom that can sweep rocks and debris onto my towed.
Actually that broom, which doesn't touch the ground, keeps rocks, gravel, and oil from hitting the toad after the coach's tires pick them up and throw them.
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Old 06-26-2014, 11:43 AM   #6
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Naa, that's what the mud flaps are for.. By the way I use what Blue Ox used to call an "RV Underskirt" I think they calli t protect-a-tow or some such now, A mesh cloth that goes between coach and car, Does a real good job.

For VHF/UHF when parked, I sometimes put a channel like that atop my flabpole.. Can'd do that for a bit though, Need the flag pole for,,, other uses... next week. (Like it's intended use on July-4)
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Old 06-26-2014, 01:59 PM   #7
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Naa, that's what the mud flaps are for.. By the way I use what Blue Ox used to call an "RV Underskirt" I think they calli t protect-a-tow or some such now, A mesh cloth that goes between coach and car, Does a real good job.

For VHF/UHF when parked, I sometimes put a channel like that atop my flabpole.. Can'd do that for a bit though, Need the flag pole for,,, other uses... next week. (Like it's intended use on July-4)
To each his own.

Looking in my mirror, I see quite a lot of flab, but (thank goodness) I don't yet see anything that could be called by your word "flabpole".
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Old 06-27-2014, 11:11 AM   #8
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Opps FlaGpole... Dang fat fingers hit the wrong key.. I seem to have Typelexia.

Usually for HF I toss around 83 feet of wire in the air, From the KAT-1 Auto-tuner on the rear of the rig up a fish pole around 25 feet high then over a tree limb.. Where I am now (Cathead Creek Ranch RV park and cowboy church, Townsend GA) the nearest tree is 2 fields away,,,, Much too far for my long wire plus leader cord.. So I parked the flaGpole (And yes I typed it wrong again) under the right front tire (Well the mount at least) and strung my 50' wire.. JUST reaches the flag pole.. I'll have to re-configure slightly in a few days so I can fly the flag under the wire (Put a small ring (Plastic" on teh end of the wire and put the final on the pole) This pole usually carries my Wi-Fi hardware.
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Old 06-27-2014, 11:39 AM   #9
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Me, I like to operate HF while in motion. Can't do that with a wire over a tree, unless the wire is rather long.
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Old 06-28-2014, 07:30 AM   #10
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Carl, that's a great looking mount and well worth preaching about. Me, I'm not that ambitious. I just hang my Comet CHA250 onto my rear ladder and communicate on all bands, with or without the tuner. Now, riding down the road with it attached would be a bit challenging and since it only takes about ten minutes to take down (or put up), I stow it before going mobile.
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Old 06-28-2014, 09:29 AM   #11
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Me, I like to operate HF while in motion. Can't do that with a wire over a tree, unless the wire is rather long.
The nice thing about the KAT-1 Tuner is it can use a multitude of different length wires,, 83 feet over tree limbs is my favorite. 50 feet run from a fishing pole to a flag pole one mounted on the rear of the RV and the other in a "Park on base" under the right front tire (The pole will also hold a flag in a few days) is the current antenna. On the road there is a bit over 30 feet of COPPER TUBING with a CB sprial wound on the end of it about 2 inches above the roof, Does not work well on low bands but actually better on the higher bands.

That said,, Mobile I use mostly VHF/UHF since I do not care for tuning.
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Old 08-16-2014, 02:54 PM   #12
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You have your antenna mounted too low on the vehicle..

The maximum amount of current is at the base of the antenna and the tip of the antenna has the least.
When you mount the antenna low - most of the signal ends up underneath the vehicle.

A better suggestion would have been to mount the antenna in the middle of the roof and build a tip up antenna mount. Drive to where you are going and then tip it up and operate...

Even if it was at the rear of the vehicle and high - it would talk several times better then where you have it.
I'm surprised that you aren't complaining about a high SWR ...
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Old 08-16-2014, 04:48 PM   #13
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Me, I like to operate HF while in motion. Can't do that with a wire over a tree, unless the wire is rather long.
Just drive faster!
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Old 08-16-2014, 04:54 PM   #14
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You have your antenna mounted too low on the vehicle..

The maximum amount of current is at the base of the antenna and the tip of the antenna has the least.
When you mount the antenna low - most of the signal ends up underneath the vehicle.

A better suggestion would have been to mount the antenna in the middle of the roof and build a tip up antenna mount. Drive to where you are going and then tip it up and operate...

Even if it was at the rear of the vehicle and high - it would talk several times better then where you have it.
I'm surprised that you aren't complaining about a high SWR ...
I agree with you at least the coil should be in the clear but the motorized antenna pretty much will match any thing however the efficiency will be pretty poor. A screw driver antenna is pretty much magic any way they really should not work worth a hoot but they do.
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Old 08-16-2014, 04:55 PM   #15
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You have your antenna mounted too low on the vehicle.
And I suppose, if I mounted a ground-mounted vertical in my back yard, you would complain because it was ground-mounted instead of elevated. But when one elevates a vertical monopole, one must also (usually) install elevated radials so that the antenna will be mounted near its ground plane. Therefore, nonsense, say I.

If it were on, say, an all-aluminum trailer, you would be nearer right, for (with the antenna mounted low) the aluminum body would tend to block the signal (and also detune the antenna by bypassing it capacitively). But my motor home's body is mostly fiberglass and, for RF, doesn't exist.

This antenna is some 10-12 feet tall depending on frequency. I can see it now, mounted on top of my 12-foot-tall motor home. I would have to use a tilting mount if I ever wanted to go anywhere, and certainly couldn't operate when moving. Also it wouldn't work worth a flip anyway, being some 12 feet above its ground plane (the frame of the vehicle). That's more than 1/3 of a wavelengh at 20 meters.

But thank you for your advice.
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Old 08-16-2014, 04:58 PM   #16
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I'm surprised that you aren't complaining about a high SWR.
Perhaps there are other surprises in store.
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Old 08-18-2014, 10:53 AM   #17
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NN5I - you would be better off to put it on a Christmas tree stand and deploy it when you are destination, and then throw out a loop of ground radials.
People may refer to you as that nutty old ham that likes to camp by himself, but you would have a much better signal that way...

Had it been say a YUGO - the body would only be about 4' tall, not a lot to worry about if the antenna was mounted 2' off the ground.

I don't operate much mobile, especially while dragging a trailer around...
Too many dumb people on the road, talking on their cell phones / not paying attention, trying to cut you off, or thinking that you can stop on a dime if they pull out in front of you or stop all of a sudden.
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Old 08-18-2014, 12:53 PM   #18
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NN5I - you would be better off to put it on a Christmas tree stand and deploy it when you are destination, and then throw out a loop of ground radials.
People may refer to you as that nutty old ham that likes to camp by himself, but you would have a much better signal that way...

Had it been say a YUGO - the body would only be about 4' tall, not a lot to worry about if the antenna was mounted 2' off the ground.

I don't operate much mobile, especially while dragging a trailer around...
Too many dumb people on the road, talking on their cell phones / not paying attention, trying to cut you off, or thinking that you can stop on a dime if they pull out in front of you or stop all of a sudden.
You're mostly right, except that people already refer to me as that nutty old ham.

I don't drag a trailer around; I drag my toad, a little Ranger pickup that might as well not be there for all the effect it has on driving the motor home.

My motor home is mostly invisible to RF, which is why the antenna can be low.
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Old 08-18-2014, 06:35 PM   #19
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Carl, how efficient have you found your rear (and low) mounted antenna to be? I had an auto tuner, ball mount with 8 foot whip clamped to the rear bumper of my Class C and could not make one qso on 75, 40, or 20 during a road trip a couple of years ago. I grounded antenna to the RV chassis at the rear. Also, mounted a Tarheel II on the left front fender with similar lousy performance. Got lots of RFI from engine. I'm sure the plastic hood on my 2006 Chalet E350 didn't help.

I'm still looking for a practical installation for HF "in motion" communication.

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Old 08-18-2014, 07:04 PM   #20
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I some times remove the TarHeel from the truck and mount it on the camper (roof height) the roof is aluminum and it works pretty good. It's mounted on the rear of my pickup by the tail gate and works great there also. Camper antenna-- 10,12,15 and 17 meters pictured at 17
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