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Author Topic: ATAS 120 on ROOF RACK & Foldable, -Can it be d  (Read 6425 times)
DEANSANDERS
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Posts: 15




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« on: September 23, 2005, 05:53:18 PM »

A buddy of mine has an Atas 120 and has given up on trying to mount this as a foldable on his roof racks of the SUV.

Called up HRO and Diamond and they both said that Diamond doesnt make a strong enough foldable bracket for this.

Because apparently most that successfully do it, have a custom bracket

Has anyone done this? or have ideas?

Where can we get a custom made bracket that will permit luggage rack mounting and is foldable.

Thanks,
Dean (NEW TO HAM RADIO)
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KG4RUL
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« Reply #1 on: September 23, 2005, 08:55:15 PM »

Tarheel Antennas has a motorized mobile mount that looks like it could handle a 40 meter beam on a tower.  Pricey but, it does look sturdy.

Dennis KG4RUL
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K0BG
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« Reply #2 on: September 24, 2005, 04:54:45 AM »

At least two manufacturers make electrically operated fold over devices. The mag mount one was touted in the pages of QST of all places. The other one, like you need, looks like it could hold a big antenna, but it can't. The gear set is plastic which should tell you a lot. And...there is a problem with any mount which offsets any antenna away from its groundplane, regardless of how big groundplane might be (not large in a vehicle).

The ATAS is already a minimal antenna. Improper mounting just adds to the ground and overall system losses. Yes, you'll make contacts, but not when the going gets tough. Just keep the safety issues in mind when using such devices.

Alan, KØBG
www.k0bg.com
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KE3HO
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« Reply #3 on: September 24, 2005, 07:21:02 PM »

I am not familiar with the ATAS 120, but I will caution you that the roof rack on most cars and trucks is NOT grounded. They are typically attached with sheet metal screws into plastic plugs. If the antenna requires a good ground, you will have to provide a good RF ground to the mount.

73 - Jim
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KC2OOS
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« Reply #4 on: September 24, 2005, 08:54:28 PM »

The ATAS-120 is not a particularly heavy antenna, nor is it of such a dimension that I would expect extremely high wind loads. I have mine mounted on a Diamond K601 hideaway trunk lip mount on my VW Passat. Of course, the thing doesn't fit in the trunk without dismounting the whip, but hey, it works just fine at speeds up to 90 mph or so. I *do* need to do a little bit of adjustment, though.

I would be very surprised if you couldn't find a commercially available mount, but you might want to investigate adapting a marine mount to your SUV.

The above issues with grounding also need to be considered. The ATAS-120 is a fine antenna for what it is, but many of the eHam reviews point out the need for good grounding of this particular antenna system.
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KC2OOS
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« Reply #5 on: September 24, 2005, 08:59:34 PM »

The ATAS-120 is not a particularly heavy antenna, nor is it of such a dimension that I would expect extremely high wind loads. I have mine mounted on a Diamond K601 hideaway trunk lip mount on my VW Passat. Of course, the thing doesn't fit in the trunk without dismounting the whip, but hey, it works just fine at speeds up to 90 mph or so. I *do* need to do a little bit of adjustment, though.

I would be very surprised if you couldn't find a commercially available mount, but you might want to investigate adapting a marine mount to your SUV.

The above issues with grounding also need to be considered. The ATAS-120 is a fine antenna for what it is, but many of the eHam reviews point out the need for good grounding of this particular antenna system.
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K0BG
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« Reply #6 on: September 25, 2005, 06:08:03 AM »

Here we go again. There is a distinct difference between DC ground and RF ground. Neither should be confused with ground plane.

It doesn't make any difference if the roof rack is DC grounded or not. In view of the fact that the mount is secured to the rack is enough to DC ground it (via the coax) in most cases.

An RF ground is much harder to devise than a DC ground. But that's not the problem here. The major problem with mounting an antenna to a roof rack, DC grounded or not, is it adds to the ground losses which are already high. Overcoming this typically requires drilling holes, which is why most people opt for the rack in the first place.

It is all a matter of how efficient you want your mobile system to be.

Alan, KØBG
www.k0bg.com
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DEANSANDERS
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« Reply #7 on: September 26, 2005, 02:42:52 PM »

Thanks for the info

However still none of the retail stores have a bracket that will work.

So, does anymone have any additional tips for me on mounting a atas 120 to a roof rack so that its foldable.

Also, how exaclty will I RF ground this one I mount it.
Any part # would help.

Thanks,
Dean
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KE3HO
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« Reply #8 on: September 27, 2005, 07:22:36 AM »

Well Dean, I am sorry to say that the solution to this problem will not be found in a parts catalog. There won't be any "part number" solution.

The ATAS 120 would work best if it were mounted on a large very low impedance ground plane. "Large" being relative to the wavelength, and "very low impedance" being RF impedance. Obviously, in the case of HF mobile, you are not going to get this no matter what you do. The best you can hope for is to make use of the body of the vehicle and its capacitance to earth in place of the ground plane. It is a low efficiency proposition when done correctly. You want to avoid adding any losses that you don't need to add. In the case of a luggage rack mount, you want to have a very low rf impedance connection between the antenna mount and the body (the roof in this case) of the vehicle. That will be difficult to do. If the luggage rack were bolted solidly to the roof, metal to metal, ( and if we ignore the issue of corrosion) you might get away with putting the antenna mount as close as possible to one of the points were the rack is attached to the roof (and if Alan is reading this, he is probably reaching for his Ronco Pocket Defibrilator right now :-). However, the roof rack is not likely to have a low RF impeance to the roof. In fact, its only connection (in RF impedance terms) to the roof is most likely a VERY small capacitance. This means that if you mount the ATAS 120 to the rack you will probably have a very high SWR that you will not be able to tune out, and even if you were "lucky" and could tune the SWR low enough to use the antenna, the ground losses would be so high your antenna would be an expensive dummy load. The only way I can think of to solve this problem would be to drill a couple of holes in the roof directly below the antenna mount and use several pieces of copper braid (where the braid is wide, and as short as possible - a few inches at most, with heavy ring terminals soldered to both ends) bolted solidly to the roof and to the antenna mount. Of course, you probably want to use the rack mount to avoid drilling holes in the roof, so this is probably not a solution that you would want to use. If that is the case, I would suggest not using the luggage rack at all.

This is long-winded, and even so it is just scratching the surface of the problem. The bottom line this: I am assuming that your goal is to have fun. Period. If your goal is to have the best possible HF mobile performance, you would not be using the ATAS 120 or any other small antenna. You would have a 16 foot homebrew antenna with a big coil in the middle with guy stays, and so on. I met a guy at a hamfest who put a 75M hamstick on a bumper mount on the back of a full size van. It would be hard to make a less efficient system than this. However, when asked about how the antenna worked, he was very pleased with it and said he "gets good signal reports" all the time. I only mention this to illustrate that you may be able to be happy with your results without creating the best mobile antenna installation of all times.

Personally, I would suggest not using a luggage rack mount. Maybe someone here can give a suggestion for another mount that might meet your needs. Please let us know that your restrictions are (for example, are you willing to drill holes in the body, etc.).

73 - Jim
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DEANSANDERS
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« Reply #9 on: September 27, 2005, 01:30:38 PM »

Thanks KE3HO for you detailed answer. I can't tell you how a rookie like myself appreciates this.

I originally thought that this could be simply done because I have seen many people that successfuly have it like this and even the picture I saw of this from yaesu.
see for yourself:
http://www.comdac.com/yaesu/atas120.jpg (doesn't look like its drilled in to me)

And since I need to get into my garage, I wanted it to fold over. Also worried about theft and prefer it mounted  high up on the roof and again, its more discrete when not in use and wont attract too much attention.

(1)
So can ground it through a ground strap mounted somehow to the roof racks? How exactly do ground straps work?


(2) If I do drill holes can you explain this process. This would be my worst case scenario.

(3) Since I am not an engineeer, I  undestand the basic concept, but still think there must be a professional way without overkill.


Thanks and GOd Bless!
Again, I value your assistance.
Dean
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KE3HO
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Posts: 235




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« Reply #10 on: September 28, 2005, 06:12:08 AM »

Dean,

In the picture that you gave the link for, the roof rack shown is not your typical roof rack on the family station wagon. Not much of the truck is shown in the picture, but the "roof rack" looks like a welded tubular steel external roll cage on a Land Rover or similar vehicle. Is this the kind of roof rack that you are working with, or are you talking about the more common roof rack that simply attaches to the roof in a couple of places?

73 - Jim
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DEANSANDERS
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« Reply #11 on: September 28, 2005, 02:27:02 PM »

Hello:
I am going to install this on a Nissan Xterra with high end racks made for hauling.

see pic of my suv:
http://academic.scranton.edu/student/GIORDANOK2/xterra.jpg

Top of rack:
http://www.theautochannel.com/vehicles/new/showroom/2000/0131/xterra_rack.jpg


What do you think?

and again, can you please touch on ground straps and how that works.

Thanks,
Dean
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VE3VBO
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« Reply #12 on: September 28, 2005, 08:07:47 PM »

Dean,

Jim's observation on the vehicle in the Yaesu brochure is correct; that is a Land Rover Defender 110 with a complete roll cage mounted directly to the frame. As a Land Rover owner I tend to notice these things, and that is the same vehicle in the FT-857D brochure.

I just went outside and looked at my neighboor's Xterra. On the Xterra you may be able to use a Diamond K400 mount on the top edge of the rear hatch. The roof rack is pretty well isolated from the roof, and you would probably have to resort to using the solution that Jim suggested.

Jim: would a well installed K400 be a step up from some of the other alternatives?

Victor
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KE3HO
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« Reply #13 on: September 29, 2005, 08:05:03 AM »

I think the K400 is probably strong enough for the ATAS-120. It does not, however, offer the fold-over feature that Dean is looking for. Aside from the fold-over, I think in this case the K400 is probably a better bet than the luggage rack mount. The luggage rack looks, from the picture, like it may be clear anodized aluminum (at least the tube parts). I can't tell from the picture what the brackets are made of.

If you go with the lip-mount on the rear hatch, there are some issues to be careful of there as well. The rear hatch will need to have a good low impedance RF to the body/chassis. Actually, this is something that you would want anyway for HF mobile, even if you use the rack mount or even a body mount (same for the doors). However, the additional issue with the rear hatch is that it probably has several electrical devices in it - rear wiper motor, center mounted brake light, rear window defroster, maybe an electric rear hatch release, etc. If you don't have a really good RF ground between the hatch and the body, you could end up flowing RF current down the wires for these electrical components. Even if you add ground straps to the hatch, you may want to put ferrite beads over the wires to the hatch as an extra precaution against RF getting into the car's electical system through the hatch components.
If you install the K400, you will want to make sure it has a good electical "bight" into the lip. You may want to add a strap from the mount to the body anyway. This can be easy, or hard, depending on how much room  you have below the lip.

73 - Jim
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VE3VBO
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« Reply #14 on: September 29, 2005, 04:36:55 PM »

Hi,

The K400 will definitely handle the ATAS-120. I am using one on the my rear hatch of my Land Rover Discovery. Similar situation to the Xterra, except my hatch opens to the side, and the Xterra opens upwards.

What I found was that I had to run few inches of braid to the door hinge from the base of the antenna at the bottom of the SO 239 mount. Scratching the paint away under the bolt and adding some "star washers" helped the bite into the bare metal through the paint residue. This was instrumental in getting the ATAS to even get a decent VSWR across the bands.

Another thing that was necessary was to disgard some of the items that came with the mount. It comes with a strip of rubber and metal that is supposed to be put under the set screws. This just seemed to compound the problems getting the VSWR under control. I ended up having the set screws bite into the underside of the hatch lip. This also helped.

The K400 has a version with a large plastic knob that would make it pretty easy to fold it over. The standard one has a alan key. This may be less than ideal, but better than nothing.

Cheers
Victor

 
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