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Author Topic: Quarter wave on the roof, or half wave on the hood?  (Read 7727 times)
KC3AYG
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Posts: 27




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« Reply #30 on: February 19, 2017, 03:01:59 PM »

"These do not use a little self-tapping screw to screw to the inside of the fender (that's a complete other story and are weak)."

That's very good to know; I did not appreciate the difference between that and the self-tapping screw type mount.
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W8JX
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Posts: 12038




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« Reply #31 on: February 20, 2017, 06:23:33 AM »


These do not use a little self-tapping screw to screw to the inside of the fender (that's a complete other story and are weak).  


I worked in flight mod/test for many years for DOD and when objects were attached to a air frame they were never attached to a existing bolts/fasteners. Typically a new mount area was beefed up/gusseted and used for a mount. The whole flaw with using brackets mentioned above it that they are a after thought and the bolt being used was NEVER designed to support a antenna mount but rather that someone (that did not design car) is changing the bolts purpose.  Once again it does not matter how strong the add on bracket is, the weak link is were it attaches and a large bracket increases the stress/leverage applied to mounting bolts.  Also one again a add on bracket should be designed to yield before causing damage to vehicle but in this case someone just make a bracket using a existing hole in a jobber shop that they sell without and stress tests on the design to insure bracket will fail before there is damage to vehicle when stressed to far.

I would use a thru fender mount on side of truck and place a gusset/metal plate about 5 inches in diamenter inside fender that mount bolts to thru fender and it will provide a very strong attachment.
« Last Edit: February 20, 2017, 06:26:21 AM by W8JX » Logged

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Ham since 1969....  Old School 20wpm REAL Extra Class..
KD5BVX
Member

Posts: 106




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« Reply #32 on: February 20, 2017, 07:45:28 AM »

"These do not use a little self-tapping screw to screw to the inside of the fender (that's a complete other story and are weak)."

That's very good to know; I did not appreciate the difference between that and the self-tapping screw type mount.

Yes, these that are designed to attached to the structure and are very sturdy with no issues to be expected (despite someone who has never used one posting things to the contrary).  Highly recommended if a roof mount isn't an option (and the bed mount can't be used due to the cap).  

I guess folks can either take my opinion/input - which is input from someone who has actually used the product and is speaking from first-hand experience - or the "advice" of someone else who hasn't and is simply surmising and posting whatever stuff they think or want to believe is the case.  Completely up to the ham.  I just wanted to share what I know about it since I actually use it.  

Best wishes in getting your antenna mounted!  

73,
Mark
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Mark
W8JX
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Posts: 12038




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« Reply #33 on: February 20, 2017, 12:22:25 PM »


Yes, these that are designed to attached to the structure and are very sturdy with no issues to be expected (despite someone who has never used one posting things to the contrary).  Highly recommended if a roof mount isn't an option (and the bed mount can't be used due to the cap).  

You need to clarify that these are designed by after market, not maker of car, to use existing bolt holes. I have not doubt they are not stress tested to make sure they fail before they damage car. Cars/trucks are simply not as strong in body and some would like to believe to be able to support simple bolt on brackets. That body bolt and metal around it is seeing far more stress/leverage on mounting point than it was designed for with a mount hanging off it.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KD5BVX
Member

Posts: 106




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« Reply #34 on: February 20, 2017, 12:56:05 PM »

A 1/4 antenna is not stressing the bolt and entire vehicle structure...sorry, but no.  They're designed for an NMO antenna mount - I've seen people post pictures with a 5/8 wave or a 2m/70cm dual-bander like the Larsen 2/70 or a Comet/Diamond variety - and if something hits the antenna, the antenna is going to break long before the vehicle suffers any damage...at least from the mount.  Smiley
« Last Edit: February 20, 2017, 01:00:03 PM by KD5BVX » Logged

Mark
W8JX
Member

Posts: 12038




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« Reply #35 on: February 20, 2017, 02:39:48 PM »

A 1/4 antenna is not stressing the bolt and entire vehicle structure...sorry, but no.  They're designed for an NMO antenna mount - I've seen people post pictures with a 5/8 wave or a 2m/70cm dual-bander like the Larsen 2/70 or a Comet/Diamond variety - and if something hits the antenna, the antenna is going to break long before the vehicle suffers any damage...at least from the mount.  Smiley


It is true that a 1/4 wave has little stress to induce on mount but it does not change the fact that such bolt on mounts are over rated and a 1/4 wave on a side mount is kinda stupid and would have very limited performance. You could also duct tape a metal plate to top of camper shelf and use a mag mount 1/4 wave antenna attached to it. It would work far better than any side or fender/hood mount.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KD5BVX
Member

Posts: 106




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« Reply #36 on: February 20, 2017, 08:06:47 PM »

The point of these types of forums is sharing information and ideas and that's what makes them so great.  When I know an answer I will speak up and share it but I don't speculate about something without saying I'm just guessing.  I respect other's input and even their opinions but I don't like seeing someone post things as if they are factual that I know 1) aren't true and/or 2) they are just guessing or surmising.  So I share not to be argumentative but to clarify the facts.

However, this thread continues to grow longer and longer with a back-and-forth that is going nowhere (and continually changing the focus of the topic, it seems) so it's best if I choose to bow out of it gracefully.  You're certainly free to post again - I'm sure you will - but I think I'm done since I've made the facts clear based on my first-hand experience.  Not much else to say beyond: 

My final summary:  the mount is sturdy, the bolt is sturdy (it holds part of the car together, after all!), and using the mount does not compromise the vehicle structure - the bolt is lengthy and tightens down the same after attaching the mount as it did before - so there are no concerns there at all.  Same as I've said more than once now.  Best case would be an NMO mount on the roof.  Not an option?  This mount I've mentioned is a viable option but certainly not the only one.  Fortunately, most everyone else who has read this thread understands all of this.

Have a good day and 73!

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Mark
W8JX
Member

Posts: 12038




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« Reply #37 on: February 21, 2017, 04:01:32 AM »


My final summary:  the mount is sturdy, the bolt is sturdy (it holds part of the car together, after all!), and using the mount does not compromise the vehicle structure - the bolt is lengthy and tightens down the same after attaching the mount as it did before - so there are no concerns there at all.  Same as I've said more than once now.  Best case would be an NMO mount on the roof.  Not an option?  This mount I've mentioned is a viable option but certainly not the only one.  Fortunately, most everyone else who has read this thread understands all of this.


Your opinion only with no hard data to back it up. (I would not make claim that it will NOT damage vehicle either unless you are willing to pay for any damages) It is merely a mount that uses existing body bolts and I am sure that you will not find any statement in owners manual that those bolts are rated for a antenna mount. Unlike you I am well aware of the weakness in modern cars in body metal and how easy it is to damage them. When you attach a external after market mount to existing bolt holes it acts as a large lever and multiplies the force placed on mounting point from antenna far beyond what the point was designed for. Sure it might work for a while but when over stressed it will likely damage car and fixing that will cost far more than mount. 25 years ago car had thicker bodies and even thicker before that and clip on or bolt on mounts was not a problem but not today and mount such as you suggest induce a false security as implying it is a sturdy mount. Once again it does not matter how rugged bracket is, it is how weak attaching point is.  
« Last Edit: February 21, 2017, 04:09:12 AM by W8JX » Logged

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Ham since 1969....  Old School 20wpm REAL Extra Class..
K1DA
Member

Posts: 715




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« Reply #38 on: March 03, 2017, 10:59:22 AM »

Larson sells an eighth wave in a polycarbonate "radome" which is not far down in db  from the quarter and takes the kind of beating being on top of a rescue wagon passes out.
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W4KVW
Member

Posts: 68




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« Reply #39 on: June 09, 2017, 08:58:43 PM »

At least that 1/2 wave is not in need of a ground plane.I did not see a mention of what band or bands but a Larson 2/70 is a tough antenna to beat on those 2 bands.

Clayton
W4KVW
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WB4M
Member

Posts: 245




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« Reply #40 on: June 22, 2017, 10:47:42 AM »

I have a Diamond SG7500, dual bander, and it is designed to be folded over for situations you described with the parking garage.   Of course getting out of the truck and folding it over would get old very quick if it had to be done on a regular basis.   I personally am not a fan of drilling a hole so I would go with the hood/fender mount.  You'll never have to worry about parking garages again.
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