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Author Topic: fender bracket NMO mount -or- lip mount?  (Read 2941 times)
KE7PMY
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Posts: 22




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« on: November 05, 2007, 08:28:20 AM »

Which is preferred?  A vehicle specific fender/hood bracket, or a SO-239 trunk lip mount used on the hood as shown in the attached picture?

Link to fender/hood bracket:
http://www.theantennafarm.com/catalog/index.php?main_page=index&cPath=264_268_297

Link to trunk lip mount on side of hood:
http://www.qrz.com/uploads/post-5-73603-IMG_5679_800_600.jpg
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K0BG
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« Reply #1 on: November 05, 2007, 08:57:54 AM »

Any antenna mount which uses any form of SO239 is not very sturdy. The hood seam mount shown isn't very sturdy either.

If you have to mount an antenna using a seam mount, use the Larsen NMO style, and go with an NMO2/70BK. You'll never be sorry.

Alan, KØBG
www.k0bg.com
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KE7PMY
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« Reply #2 on: November 05, 2007, 09:31:33 AM »

You're saying the Larsen NM02/70BK performs better than a Comet SBB-5NMO?

According to the specs:

Comet - 146MHz has 3.0dBi and is 1⁄2 wave.
Comet - 446MHZ has 5.5dBi and is 5⁄8 wave x 2.

Larsen - VHF has 1.6dBd/3.8dBi and is center loaded 1/2 wave.
Larsen - UHF has 3.5dBd/5.2dBi and is collinear.  I'm not sure how 5/8 wave x 2 compares to collinear.  I did read this:
http://www.larsen-antennas.com/docfiles/ASB8/Mobile/MobileIntroduction.pdf

I'd say their pretty darn close when it comes to performance.  I really don't know much when it comes to which antenna is better than others.  I do appreciate your information on them.  Can you explain why you favor the Larsen?
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KE7PMY
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Posts: 22




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« Reply #3 on: November 05, 2007, 09:37:07 AM »

I forgot to add that I am definitely going with something like the Larsen TMB34D for a mount.  After all, I have a '97 Dodge Ram Cummins Turbo Diesel.

Hopefully I don't get to much noise.  I already have experienced, what I believe to be, alternator noise with my VX-6R and E-DC-5B (cigarette lighter adapter with built in noise filter).  No noise when powered only by the Li-Ion battery.  Since this is an older Dodge with a mechanical fuel pump, I can't imagine it would be anything other than alternator whine.
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K3GM
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« Reply #4 on: November 05, 2007, 10:40:27 AM »

I ran an FT-8900 for 4 years in a 2nd generation Turbodiesel, and I had no problems with noise.  I used 2 fender mounts with the right side pushed little farther forward so to clear the broadcast antenna.  Use the large hole plug on the firewall (if you have auto trans) to pass the power and coax into the cab.  Goop the underside of the mount with RTV to seal it good.

One other comment.  Check that Comet NMO mount to make sure it's a true Motorola 3/4" NMO and not the less robust C213-NMO found on other antennas made offshore.
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KE7PMY
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« Reply #5 on: November 05, 2007, 11:05:16 AM »

Thanks for the info.  What year 2nd gen did you have?  Mine is a '97, so I should definitely be good to go for noise.  Although, I was a little puzzled to have alternator whine passing through on Tx when using the VX-6R with the noise filtered cigarette lighter adapter.

Regarding the NMO mount.  I don't know the difference between the two you mentioned.  Perhaps the Larsen is the one to go with?
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K0BG
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« Reply #6 on: November 05, 2007, 01:08:06 PM »

Roy, that is exactly what I'm saying. Published gain figures are almost always hyped, and Comet is one of the worst in that respect. What's more, relying strictly on the published figures is playing the Gain Game. Unfortunately, far too many amateurs play the game, but don't understand the rules.

If these antennas were as good as Comet claims, you'd see commercial two way shops using them. You don't.

Here's another facet. In a lot of cases, especially in urban areas, a standard 1/4 wave antenna will out perform one with lots of gain. It's a case of comparing HAATs of the repeater and the mobile in question.

You might want to spend some time looking over http://www.w8ji.com and reading about VHF verticals.

Alan, KØBG
www.k0bg.com
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K0BG
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« Reply #7 on: November 05, 2007, 01:12:16 PM »

I just noticed your post about powering your radio from the accessory socket. That should NEVER be done. It is the reason you're having alternator whine (it's caused by a ground loop).

As self serving as it may be, after you visit Tom's site, perhaps you should spend a few minutes on mine. The articles, VHF Options and Wiring come to mind.

Alan, KØBG
www.k0bg.com
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KE7PMY
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« Reply #8 on: November 05, 2007, 01:35:53 PM »

It sounds like the best thing to do is to power with a cable that runs all the way to the battery.  Thanks.


I'll be picking up a Larsen NMO2/70BK antenna/coax setup and the TMB34D antenna mount for my Dodge.

I'm also thinking of trading in my Yaesu VX-6R HT for a Kenwood TH-F6A HT.  I think I'd rather have the dual receive capability of the TH-F6A.  Unfortunately, when powered with the Li-Ion battery, the Tx wattages are 5w, .5w, and .05w.  The VX-6R on 2m/440 is 5w, 2.5w, 1.0w, and .3w.  Jumping from 5w to .5w on the Kenwood is kind of lame.  This will be a tough decision.  If I get the TH-F6A, I can put off the mobile purchase for a while longer, because I really want the dual receive.

I'm still unsure which mobile to pickup.  I'm leaning towards the Kenwood TM-V71A and the Yaesu FT-8800R.  They both have cross band repeat, but the Kenwood allows remote control of the unit with my a DTMF capable handheld.  Nice feature.
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K3GM
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Posts: 1791




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« Reply #9 on: November 05, 2007, 02:31:19 PM »

"Thanks for the info. What year 2nd gen did you have?"

Mine was a 2002 24 valve with the VP44 rotary injection pump.  Your truck is a 12 valve with the P7100 inline pump.  You should not any problems with noise.  As I mention earlier, if you have an automatic transmission, you will have a large plastic cover over the hole used for the clutch linkage in a manual transmission.  This is an ideal way to get wires thru the firewall.  It's relatively huge, so you won't have any problems finding it.

As far as the differences in NMO's.  The DIamond antennas in particular use a smaller diameter NMO and it is not compatible with Motorola's.
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KE7PMY
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Posts: 22




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« Reply #10 on: November 05, 2007, 02:37:17 PM »

I'm familiar with the cover you speak of.  My boost line, transmission temp wiring, and exhaust probe wiring goes through the center of the cover.  I figured my coax and power cables can go through it too.

By the way, I'm "royta" on dieseltruckresource.com.
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W3LK
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Posts: 5639




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« Reply #11 on: November 05, 2007, 05:38:44 PM »

The thing that Alan didn't mention is construction.

Larsen antennas are very hard to destroy! My NMO270B is on it's 4th vehicle and has survived more collitions with airport garage beams and other similar objects than I can count. The ONLY damage is the little plastic tip on the end of the whip is gone. There are no joints to tighten, no parts to lose.

The same cannot be said for any of the Chinese-built imports from Comet, Diamond, Opek, Maldol and others.

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
K3GM
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Posts: 1791




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« Reply #12 on: November 06, 2007, 04:19:18 AM »

"By the way, I'm "royta" on dieseltruckresource.com"

I was member 400-something way back when.  There's now 43,000 members.  I sold my diesel in earlier this year after it left me high and dry at a dealer's lot, 50 miles from home and a $3000+ injection pump bill.  Miss the power though....  Good luck with the install.
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KE7PMY
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Posts: 22




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« Reply #13 on: November 07, 2007, 05:45:51 PM »

I assume I will need to seal up the bottom of the NMO assembly where the coax attaches.  Is there a silicone that users have had good luck with?  Black would probably look nicer than white.

Thanks.
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N8EMR
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Posts: 234




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« Reply #14 on: November 08, 2007, 07:23:17 PM »

The whip on the Larsen NMO2/70B seems small and looks like it would lean back at highway speed, How does it hold up at speed? The comets whips look to be about 3x as large in diameter and seem much more stout.
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