roof structural integrity and NMO mounts?

apco25 · Post by **apco25** » Wed Jun 18, 2003 8:47 pm

Ok engineer types... How many antennas is too many to roof mount on a long roof as on the 03 suburban I have?

If I went nuts I could find room for 12 - will this weaken the roof structure too much?

USPSS I were discussing this - he thinks its too much or I'd need additional roof bracing.

I had 8 antennas on the last truck a 95 Yukon 2 door with signifcantly less roof real estate. I didn't notice any problems.

I could cut down and place less used and or critical stuff on some glass mounts, i.e nextel hard install kit, VHF data radio etc etc

werdnuts · Post by **werdnuts** » Thu Jun 19, 2003 6:42 am

Well, I am not an engineer, but I have a Masters in the Obvious and one in Common Sense.

1. The more holes you put in your roof, the higher the chance for leaks.

2. Unless you put them all close together, in theory you shouldnt have a problem. Remember, sheet metal is the skin. (Uh... well, we must not negelct the unibody.)

3. Don't forget, placing antennas may cause reflection.

4. 12 Radios. You have a problem. No offense, but 12 antennas screams "I'M A TOOL!!!" Consolidate. You can't talk on all at once. If you do... you will cook you nuts... Actually, that might not be a bad thing... Probably cheaper than a vasectomy.

That's my 4 cents!

-werdnuts

USPSS · Post by **USPSS** » Thu Jun 19, 2003 7:00 am

APCO25 you missed what I put after that statement (LOL)

jcobb · Post by **jcobb** » Thu Jun 19, 2003 7:40 am

A "TOOL"? Craftsman? Skil? Makita?

I think 12 antennas simply means a lot of radios.

Seems like a cubicle and "casual Friday" screams "TOOL" louder than anything.......

Just my 2 pesos worth.

Jack

apco25 · Post by **apco25** » Thu Jun 19, 2003 9:01 am

Yep, I must have missed it! Never hurts to ask though. I was tired as hell when we discussed it so my brain must have switched off.

a lot of antennas does not make me a tool. No offense taken, but maybe I do need them?

I use VHf and UHF professionally, along with 800Mhz trunking on both Motorola and MA/COM formats. That's 4 radios right there. Also need and antenna for nextel car kit, 802.11b WiFi would be nice to have, lowband antenna, GPS antenna, maybe one spare mount and a VHF data radio for APRS.

davkenrem · Post by **davkenrem** » Thu Jun 19, 2003 9:08 am

I was with a friend yesterday in his Bronco. He had 3 antennas mounted on the roof. He installed a steel plate on the inside of the roof and then drilled his NMO holes through both the roof and the stell plate. This provided a much more stable platform for his antennas. You said you were going to used the "whipless" Maxrad's? There shouldn't be much wind torque on those short antennas.
Do take lots of pics.

jim · Post by **jim** » Thu Jun 19, 2003 9:09 am

The sheetmetal roof skin is not really structural. It is merely a cosmetic skin. The "monocoque" inside of the roof (the members and bracing) is where the strength comes from. As long as you don't cut any of the internal metal away, such as when you miss-drill a hole, you aren't weakening anything. Keep the holes in only the skin and not hitting anything inside and you'll be fine.

12 antennas? Does this truck look like a porcupine?

n1pfc · Post by **n1pfc** » Thu Jun 19, 2003 4:30 pm

if it were me, I'd consolodate as many things into multi band antennas as possible. I'd go with some type of diplexer and or triplexer arrangement for them. That way you'll also get the isolation so you don't fry the recievers in the other radios that happen to be on a harmonic of the ones transmitting at any given time.

Kurt

KF6HHS · Post by **KF6HHS** » Thu Jun 19, 2003 4:36 pm

As others have mentioned, don't think structural integrity is an issue. However, structure of the NMO mount and 'oil canning' from wind load, that low tree branch, or whatever is. I prefer the 3/8" type NMO mounts. I use these and a thin large area 'fender washer' in combination to spread the load and cut down on oil canning of the roof panel. (Rather break an antenna than pull out a mount or dimple the roof.)

After drilling the 3/8 mount hole I scuff the underside surface of the roof panel and one side of the washer - then bond the washer using Devcon Plastic Steel to the underside of the roof. Now you have beefed up the roof panel and "spread the load". The plastic steel does have metal in it and makes a good ground for the NMO mount retainer, and the cad plated washer resist oxidation better than the bare roof metal. I put the Devcon on the washer and use a 3/8" bolt to center and snug/pull the washer in place (by hand), and then use duct tape to hold it, then remove the bolt. The Devcon sets in about an hour, full cure is 12 to 24 depending on temperature.

Most SUV's and vans have corrugated roofs. On regular car roofs I use two 2" x 6" metal strips in addition and bond these next to the washer for added strength and load spreading using a high quality RTV. Frequency of installs using this method, 6m, 2m, 220, 440, 900, and 1.2GHz - no 800 or cell. No problem tuning antennas to low vswr.

I'm about to start on my new Excursion, been starring at that massive headliner - giving due consideration to letting an upholstery shop to do R & R of it for me. Interested in hearing from any that have done an Excursion headliner, do's - don'ts ??

Just my 2 cents, works well for me. Good luck with yours.

Regards, Hugh KF6HHS

FMROB · Post by **FMROB** » Thu Jun 19, 2003 5:14 pm

Tool,,,,,That is really funny....But I had the same problem with my 02 yukon xl. I don't have as many antennas as you are going to need, but I completely agree with a diplexer/tri setup. The loss in this set-up is negligible, and will make the installation and appearance of the vehicle much better. In my vehicle from front to back is the lowband, 900, vhf. In line with the VHF on opposite sides are the two uhf antennas (one for MCS and other for VRS)....I will try to post the pics...
P.S. This was taken when the vehicle was under contruction......Thats why there are no mics on the 2 spectras....

Happy Installation, Rob

http://firemarshal.freecyberzone.com/

apco25 · Post by **apco25** » Fri Jun 20, 2003 5:14 am

Rob,

Looks like you've been down the same install path I will be on. I too have the factory console in the truck (looks slightly different for 03 model year) and am custom designing a steel faceplet from a machine shop that will support troy console stock rails and faceplates.

This will look identical to what you did in the storage box area. How was your's made? Plastic? Painted steel stock?

At this point I need to mount 2 A9 spectra, a W7 spectra, MA/COM Orion and some type of intergrated siren/light controller.

I'll keep the VRS, but the motorola Siren/PA is just too big and single function to keep at this point.

I need a smartsiren or a unitrol touchmaster

sglass · Post by **sglass** » Fri Jun 20, 2003 6:43 am

I have 4 antennas on the cab on my 1994 chevy s-10 pickup (standard cab - not extended)

it looks like this

uhf 1/4 wave

900 1/4 wave vhf 5/8 larsen dual band (vhf uhf)

zero problems

plans for the 1991 blazer are (in front)

uhf 1/4 wave

900 vhf 5/8 larsen vhf 1/4 wave

in back

low band (left rear)

this gives me vhf and uhf for my dual band rig, 1/4 vhf for aprs, 900 for well 900 ham, and low band for 6m

FMROB · Post by **FMROB** » Fri Jun 20, 2003 9:28 am

Actually I made that myself. I got piece of 30/30 aluminum and bent and cut it all by hand using a hammer, jig saw, and hand files. To top it off I bought color matched vinyl from a local installation supply shop and vinyl wrapped the center console piece. The top part of the dash is the original factory plastic cut out to fit the MCS head and then I vinyl wrapped that as well..I was happy with the results. By the way,,,,,,,Keep your siren and vrs.. I believe that you can combine the two units into one case...If you add in the unitrol or the smart siren you have to deal with another head issue, keep it on your spectra or syntor head....Good Luck...BTW if you want the web address of the supply house that carries all of the vinyl, carpet, and installation supplies I will get it for you...

apco25 · Post by **apco25** » Fri Jun 20, 2003 9:46 am

Yes I know about combining the VRS and Siren/PA I've that on other radios. The reason I was looking at the smartsiren or touchmaster was that I need lighting control as well and would prefer to keep all the A+ wiring in a remote location and use a control head to handle it.

I'm not really fond of the systems 9000 lighting switch box. I like slide switching for primary control.

Also I may be migrating to all MA/COM Orions over time.

007 · Post by **007** » Fri Jun 20, 2003 12:24 pm

You need a regular SS2000 or an SS2000SM? I have a SS2kSM, and I just got a astro siren for my spectra, and I'm looking for a switch box now. I love my SS, but it takes up too much room......you with the 'burb on the other hand, have plenty of room.

davkenrem · Post by **davkenrem** » Fri Jun 20, 2003 1:53 pm

Is your SS2000SM for sale. I might be interested if Apco25 isn't.

kc7gr · Post by **kc7gr** » Tue Jun 24, 2003 7:03 am

apco25 wrote:Ok engineer types... How many antennas is too many to roof mount on a long roof as on the 03 suburban I have?

If I went nuts I could find room for 12 - will this weaken the roof structure too much?

I've never done any structural design stuff, but common sense tells me that (as others have pointed out):

(1) The more holes in the roof, the greater the possibility of leaks.

(2) The more holes in any metal sheet, the less strength it will have.

Suggestion: You may want to look at my page to see how I dealt with multiple antennas with minimal holes. If your 'burb has a roof rack, and you don't mind using the thick-metal version of the NMO mounts, your problems can be solved with a few rack panels, and some creative clamping and grounding.

http://www.bluefeathertech.com/kc7gr/thevan.html

Good luck! 12 radios is a load, even by my standards, but I have seen it done by another local ham in a heavily-modified Jeep called 'Hunt-1.'

73 de KC7GR

FMROB · Post by **FMROB** » Tue Jun 24, 2003 6:44 pm

Bruce,
Looked at the website....Seems interesting. As long as the nmo mount is instaled correctly with correct hole saw, clean surface, o-ring, sealant, and rubber gasket at base of antenna it should never leak.....Only if you are using a larger scale antenna i.e. lowband whip, hi-gain style etc...where the unit is subject to impact damage which loosens the mount and/or destroys the hole. It seems however very tough to get a good ground plane for that rack you have created, I much rather have my nmo mount directly contacting the vehicle shell sheet metal than trough a wire or clamp...Just an observation. P.S. He couls also cut down on some of the antennas by using a di/triplexer or just eliminating some triplicate radios...Which if you were going to install tweleve units I really don't see the reason????

apco25 · Post by **apco25** » Tue Jun 24, 2003 7:28 pm

3 of the antennas really aren't for regular radios those being 802.11b WiFi, GPS and Nextel.

I really need 5 RF antennas at this point. VHF, UHF, 800 x 2 and lowband. No duplicate radios. I'm going to put the nextel as on an on glass mount, along with the 802.11b and VHF no ground plane on glass model for APRS.

So that leaves me with 8 actual NMO mounts to install which I don't think is that bad.

I might try using a maxrad diplexer for the VHF and UHF spectras. They say its rated for 150w and the insertion loss isn't really measurable.

007 · Post by **007** » Tue Jun 24, 2003 7:40 pm

davkenrem wrote:Is your SS2000SM for sale. I might be interested if Apco25 isn't.

Sorry....Apco and I have a deal worked out

davkenrem · Post by **davkenrem** » Tue Jun 24, 2003 7:41 pm

Can't you use a diplexer for the 2-800mhz antennas? I would want as few as possible unless you really like the look of a bunch of antennas.
I don't particularly, but some do.

http://www.rfwiz.com/AustinAntenna/Aust ... lexers.htm

davkenrem · Post by **davkenrem** » Tue Jun 24, 2003 7:42 pm

007 wrote:
davkenrem wrote:Is your SS2000SM for sale. I might be interested if Apco25 isn't.
Sorry....Apco and I have a deal worked out

NP

apco25 · Post by **apco25** » Tue Jun 24, 2003 8:12 pm

I had forgotten about Austin Antennas. The di, tri and quad plexors look nifty and I'd be interested in using them.

Drawbacks I see. All of their antennas look to be VERY rigid, don't have shock springs and are fairly tall at 33inches when places on top of an already very tall 3/4 ton suburban.

I'm betting the lowband performance just sucks

My original plan was to use the maxrad MLPV type whipless antennas for everything except VHF which would be black 1/4 waves and lowband which would be only mounted when needed. Overall antenna height would be quite low.

I could see using two of these quad plexor setups which would allow me to run 2 UHF radios (spectra and VRS) 2 VHF radios (spectra and APRS data radio), 2 800 trunked radios then leaving room for the lowband, nextel, GPS and 802.11b antennas

I'd be down to 6 antennas at that point.

interesting.

apco25 · Post by **apco25** » Tue Jun 24, 2003 8:47 pm

Ok going to try and think this through again.

screw nextel its going on a glass mount

Discrete antennas 1 per radio

GPS
VHF 110w
UHF 110w
VHF APRS 25
UHF VRS repeater 2w
800 smartnet 35w
800 edacs 25w
Low Band 110w

Ok that's 8 done probably as 2 rows of 4 mounts 20 inches apart in all directions

mixed discrete antennas and 2 diplexer

GPS
VHF/UHF
APRS/VRS
800
800
Lowband

That's 6

Only 2 discrete antennas the rest on tri or quadplexer

GPS
Lowband
VHF/UHF/800
VHF/UHF/800

That's 4

Hmm.

Obviously GPS needs to be by itself as does lowband because of the physical size of the antenna.

ARG!
HEADACHE!

davkenrem · Post by **davkenrem** » Tue Jun 24, 2003 9:15 pm

I'd go for option 3.

apco25 · Post by **apco25** » Tue Jun 24, 2003 9:22 pm

Anyone have experience on how well these antennas hold up physically and how well they perform RF wise?

Anyone got an antenna analyzer to play with?

Is this just askig for all sorts of wacky RF interaction and intermod to occur?

I have NEVER liked the ham quality diplexers, but that was the problem they were ham quality and generally sucked at isolation, insertion loss etc etc.

roof structural integrity and NMO mounts?

roof structural integrity and NMO mounts?

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Re: roof structural integrity and NMO mounts?