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Author Topic: SG7900 mounting  (Read 2516 times)
KB9WXQ
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Posts: 2




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« on: December 22, 2004, 07:09:07 AM »

I have a Diamond SG7900 NMO mount version, and just purchased a new vehicle (a minivan).  I have two issues (other than the cold weather...) to deal with in the vehicle move that I'm looking for advice for.

First, and most pressing...  When I removed it from my old car, I found that the NMO mount seems to have corroded into it - the mount fell apart, and is stuck inside the base of the antenna.  How do I best remove it?  How would I best prevent that on the new vehicle/mount?  The whole point of using the NMO mount was for weather resistance...

Second, mounting.  The SG7900 was already a bit tall mounted on the trunk of my old car.  Now, on the roof of a minivan, it could be a bit obnoxious.  I'm considering getting a K9000LRM motorized mount for it.  This would allow me to easily raise and lower the antenna when entering parking garages.  It would also seem to be a lot better than using the foldover as I did in the past when going hiking/backpacking and traveling down the miles of dirt road with low tree branches.  That foldover seemed to take a beating in the folded position over those distances/bumps.

Of course, the K9000LRM isn't "recommended" for the SG7900.  Actually, no mount is - if you went with recommended mounts, it'd be an antenna with no mounting options.  Even a hard mount requires serious reenforcement of the roof with such thin sheet metal on today's cars. So, the second question - anyone have any experience with the K9000 mounts?  Is it fairly robust?  Will it last 3 or 4 years being overloaded with the tall/stiff SG7900, or just crumble quickly? At $100 a pop, it's kind of an expensive mount to order blind just to test it...
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K0BG
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« Reply #1 on: December 22, 2004, 08:14:03 AM »

High-quality NMO mounts are made from brass, and the cheaper ones from aluminum. As I recall, the inner portion of the Diamond is also made of aluminum. Unless you put a liberal coat of NoOx on the threads, the aforementioned is usually the result. If you're careful with a Dremel tool, you can cut away enough to loosen it up so it will come out. It isn't easy.

A better choice would be the Larsen NMO2/70. It is shorter and a little less prone to damage and has brass parts. It's about half the price of the Diamond.

You could also mount the antenna on the front of the vehicle. As for the motorize mount, they're typically more trouble than they are worth.

Alan, KØBG
www.k0bg.com
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N3ZKP
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Posts: 2008




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« Reply #2 on: December 22, 2004, 02:28:52 PM »

<< Even a hard mount requires serious reenforcement of the roof with such thin sheet metal on today's cars. >>

having installed roof mount antennas on about a dozen vehicles in the last 10 years, I do not find this to be the case for the typical ham 2m/440 antennas. I haven't had one fail or leak yet.

I agree with Alan, go with the larsen 270NMO. If you want an open coil whip, get the 270B. That's what I have been using for several years on four different vehicles.

Lon
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KB9WXQ
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« Reply #3 on: December 23, 2004, 05:27:02 AM »

I guess it's important to note that the SG7900 is not a typical 2m/70cm antenna.  It's very stiff, very heavy (almost 13 oz), and 62" tall.  It's a 7/8 wave on 2m, and 3 5/8 wave on 440.  

I have a friend (KC6ETE) who mounted one to a Ford Expedition, and, well, several of us were involved, along with some creative engineering, trying to reenforce the roof enough to keeep the roof intact at highway speeds.  We've got pictures of the installation (and of Dave holding the antenna for perspective - important to note that Dave is a rather tall person -  and a description that's an amusing read...:
http://www.inchase.org/outflow/events/installnic2002/f5mount.html

Also probably important to note that I already own the antenna (bougt it over 2 years ago) and really like it.  So the relative cost of the Larsen vs. the Diamond (I actually have the black/open coil version of the Larsen NMO 2/70 as well) isn't a consideration.  The fact that there's 11" of snow on the roof of the van probably means that I won't be drilling holes in it before spring, though Smiley

I'd still like to hear folks' opinions on the motorized mount - one opinion does not a concensus make, though it does direct my thoughts...  If I do opt to hard mount in the middle of the roof, it'll be more difficult to fold over when needed than it was on the car trunk lid, because it will be harder to reach.  It takes a fair amount of force to lift up the antenna to fold it over.

As for the corroded NMO mount - I think I'll call Diamond today and see how much just replacing the part is, and remember to periodically shoot it with NoOx in the future.  Unless it's too expensive, in which case I'll be spending some quality time with the dremel tool.  Most of their parts are fairly inexpensive...
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N3ZKP
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Posts: 2008




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« Reply #4 on: December 23, 2004, 01:36:00 PM »

I'm familiar with the antenna - I had one for a month and sold it just because it is a non-flexible antenna and is not really well suited to mobile use. They are very easy to knock off or damage. I'm not sure what those sticks ARE suited for. Smiley

As to the motorized mount, I personally know five hams who have had them and sold them to some unsuspecting sucker (er, ham) within a few weeks for a variety of reasons, all being they just didn't perform well in one aspect or another.

The interesting thing about the big Diamonds (and Comets, for that matter) is the performance difference between them and the smaller Larsens is not measurable in the real world - and the Larsens are half the cost and virtually impossible to tear up.

I agree that you might get Diamont to sell you just the bottom portion, it surely won't hurt to ask.

Lon
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N3ZKP
Member

Posts: 2008




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« Reply #5 on: December 23, 2004, 01:36:45 PM »

I'm familiar with the antenna - I had one for a month and sold it just because it is a non-flexible antenna and is not really well suited to mobile use. They are very easy to knock off or damage. I'm not sure what those sticks ARE suited for. Smiley

As to the motorized mount, I personally know five hams who have had them and sold them to some unsuspecting sucker (er, ham) within a few weeks for a variety of reasons, all being they just didn't perform well in one aspect or another.

The interesting thing about the big Diamonds (and Comets, for that matter) is the performance difference between them and the smaller Larsens is not measurable in the real world - and the Larsens are half the cost and virtually impossible to tear up.

I agree that you might get Diamont to sell you just the bottom portion, it surely won't hurt to ask.

Lon
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N3ZKP
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Posts: 2008




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« Reply #6 on: December 23, 2004, 01:37:48 PM »

Sorry for the double post.
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