My First Permanent NMO Install

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Here are some pictures of my first NMO install. I purchased all Antenex products from Economy 2-Way Distributors INC at a really good price. I am not really familiar with installs and ran into a few problems and have a lot of questions. Maybe someone could help me out a little.

I ran into a few problems with the installation:

Problem 1. No directions came with either of my NMO mounts so I had to figure it out myself. I think I over tightened the rear mount because the rubber gasket split (I replaced the gasket). I wasn't sure on how much to tighten the mounts.

Problem 2. The center section of both mounts stick up a little to high and I can't use Antenex's regular 1/4 wave with a shallow base because it doesn't make a good seal with the roof. Not sure if this is because the sheet metal is so thin, or because I originally tightened them down a little to much, or because i installed them wrong. Any ideas?

http://www.antenex.com/c_search.asp?txtFunction=browse2&selFamily=QUA&txtSubFamily=UNITY+GAIN+MODELS

Problem 3. I Had no directions with the crimp on and solder connectors so I had to use trial and error. I ended up using the crimp on connectors and wasting only one.

Problem 4. A few problems with routing the cables and finding good spots to drill the holes due to the roof in the Dodge having two sections of sheet metal for the front 3/4 of the roof. I had to install one mount right above the dome light and one right were the two sections turned into one. Is this normal for every vehicle?


A few questions:

Q 1. How much do you tighten the mounts down? Just snug them?
Q 2. Should I cut the extra 4 ft. of cable I have or should I just leave it?
Q 3. Should I use silicone grease, teflon grease or Vaseline on the rubber o-rings? I have heard of people mentioning all three. Which one should I use?
Q 4. Does the spacing between the antennas look OK? What is the general rule on spacing?
Q 5. Should I shut off and unplug my scanners antenna coax when I transmit on my 50 watt VHF-HI two way radio? Will this ruin my scanners front end?
Q 6. Does anyone have general directions on how to install crimp on connectors? Like how much to cut and strip each part of the coax etc..
Q 7. Should I have the coax and antenna SWR checked before I transmit? Or is it OK since I am using a VHF-HI antenna cut using a cutting chart provided by Antenex?
Q 8. Does the SWR matter on receive only antennas? If the SWR is tuned in on receive only will this allow for better reception?

Thanks in advance for any help.

 

[MB]

More Pictures

Here are some more pictures.

I can also post pictures of my radios if any one wants to see them. BC 780 XLT, ICOM IC-F521, and BR330T.

I also have a few more close ups of the mounts if anyone wants to see them let me know - I would hate to post to many pictures on this forum.

 

[OpSec]

Not too bad...sent you a PM.

 

[spitnsand]

Looks very smooth

Did you drill into the top or what I am about to attempt my first one as well

 

[RESCUE4NFD]

NMO Install

Looks fine to me.......

 

[MB]

Yes, I used the 3/4" Antenex HS34 X-ACT Hole Saw. Worked great once I found the center and a good spot to drill (which can be really tricky).


http://www.econ2way.com/catalog/public/miscellaneous_accessories.htm

Did you drill into the top or what I am about to attempt my first one as well

 

[kyguy]

nice antenna setup, now let's see the radios.

 

[kingpin]

A few questions:

Q 1. How much do you tighten the mounts down? Just snug them?
A:I get mine pretty snug. I don't overtighten them.

Q 2. Should I cut the extra 4 ft. of cable I have or should I just leave it?
A: 4 ft really is not going to make a difference. Lay it flat and don't roll it in a coil and you should be fine.

Q 3. Should I use silicone grease, teflon grease or Vaseline on the rubber o-rings? I have heard of people mentioning all three. Which one should I use?
A: I use silicone on all of mine. I put some in the o ring track on the brass nut and place the o ring in there and using my fingers, rub the underside with silicone and then screw onto the base and tighten. Never had a leak after 100+ installed.

Q 4. Does the spacing between the antennas look OK? What is the general rule on spacing?
A: General rule of thumb is 1/2 wavelength apart if they are transmitting. Receiving shouldn't be a problem there on the spacing.

Q 5. Should I shut off and unplug my scanners antenna coax when I transmit on my 50 watt VHF-HI two way radio? Will this ruin my scanners front end?
A: yes and no. Depending on how far apart the antennas are. My 110 watt kenwood's 3 db gain antenna is 4 feet from my scanner antenna and after a year, I've never had a problem. Not a bad idea though to turn off your scanner while transmitting.

Q 6. Does anyone have general directions on how to install crimp on connectors? Like how much to cut and strip each part of the coax etc..
A: I love me some crimp on connectors after soldering for so many years. I first slide the outer crimp collar on the coax. Then I strip 3" of the outer insulation so I see the braid. Using small wire cutters, I trim all but 1" of braid so then I have 2" of dielectric sticking out. I then strip 1.5 inches of that off, exposing the center conductor. Fan the braid back and slide the outer threaded colar on followed by the connector itself. Once it's on, I crimp the tip and then slide the colar up and then the braid over the connector tail. Then slide the crimo collar over the braid and crimp.

Q 7. Should I have the coax and antenna SWR checked before I transmit? Or is it OK since I am using a VHF-HI antenna cut using a cutting chart provided by Antenex?
A: Never never never rely on just the cutting chart. Always check with an SWR meter to make sure you get it as low as possible. I use the same antennas on deputy cars as well as dump trucks and the mounting can make a fool out of that chart. When I do a mirror mount on a dump truck, I usually have to trim it an inch more than the chart says.

Q 8. Does the SWR matter on receive only antennas? If the SWR is tuned in on receive only will this allow for better reception?
A: No because there is no SWR when you are receiving. No power is transmitted to the antenna and reflected on a scanner so it doesn't matter. However, using an antenna tuned for the target band you are wishing to listen to the most provides better results. I have a 1/4 wave VHF NMO whip on my truck for most days but when I head to Mobile, I swap it out with an 800 whip for optimum reception over there. I also keep a UHF whip in the truck as well.

Thanks in advance for any help.

Hope these answers help!

 

[MB]

Finally someone answered my questions! Thanks kingpin!

1. I have found that I can snug them pretty good just using my hand, and it seems to work ok. Do you just use your hand to snug them?

7. Question about SWR. I transmit on frequencies from 151 to 159MHz so how would I tune the antenna? If I center tuned it for 155MHz I would have a bad SWR at 151 and 159. So what do you do in this case?

I know many police EMS and fire agencies that transmit on a wide range of frequencies using a single antenna. The Sheriff's dept. transmits on frequencies from 154 - 173Mhz. How are these agencies not ruining their radios with bad SWR? I don't understand.


I will post some pics of my radios soon.

Hope these answers help!

 

[crayon]

Well done kingpin.

Awsome install MB. That is something ya should be proud of!!!

 

[kingpin]

Finally someone answered my questions! Thanks kingpin!

1. I have found that I can snug them pretty good just using my hand, and it seems to work ok. Do you just use your hand to snug them?

7. Question about SWR. I transmit on frequencies from 151 to 159MHz so how would I tune the antenna? If I center tuned it for 155MHz I would have a bad SWR at 151 and 159. So what do you do in this case?

I know many police EMS and fire agencies that transmit on a wide range of frequencies using a single antenna. The Sheriff's dept. transmits on frequencies from 154 - 173Mhz. How are these agencies not ruining their radios with bad SWR? I don't understand.

1. I tighten mine using a cresant wrench. For those with coils, hand tightened is ok.

2. You're going to have to find a broader range antenna. I am lucky in that my cars pretty much have a 5 MHz bandwidth so I center tune for 156 and I'm good. I use 1/4 wave tunable maxrad antennas for pretty much everything in my fleet. WHat antenna are you currently using?

3. Are you sure the SO is transmitting above 162 MHz? That's Fed territory there. As far as the SWR goes, the Kenwoods I use (TK-790H's) reduce power when a high SWR is detected in order to help prevent damage to the radio. My SO cars have Customs Net 2 in them with a TX of 171.xxx . They never use it but it's there if they need it. I've never measure the SWR on it as it keys Custom's repeater in Foley. I'm sure the SWR is high but I may be suprised As far as back to your original question, there are some magic fairy dust antennas that are made will cover the 146-174 range with decent SWR across it. They are also high dollar and outside of my budget. $7.50 1/4 waves good enough for us. Me on the other hand, I'm much more picky! LOL

 

[MB]

1. When I first used the crescent wrench I ended up tightening one of them to much which caused the ears to bend back a little. I have found that I can snug them pretty good with just my hands.

2. I am using the Antenex B1443 3dB 144-174MHz tunable for transmitting. I mostly transmit on 151 and 154MHz and occasionally need to transmit on 156 and 158MHz. I have it cut for 154MHz right now. I guess I will either have to purchase or borrow an SWR meter and mess around with it.

Do you think 154MHz is a good center frequency to use?

Any ideas on a broader range antenna?

3. I know the SO transmit quite often between 154 and 159MHz, I guess they must have it center tuned for that. I think they may have some Customs and other Federal frequencies but probably rarely ever use them.

A couple other questions for you:

Any idea where I could get a TK790 for a good price?

Where could I get one of these magic fairy dust antennas that you are talking about? I am also pretty picky, what are you using for antenna's on your personal vehicles? Any suggestions for me?

Also, do you have any pictures of your installs? I would love to see them.

Thanks for all the help Kingpin!

1. I tighten mine using a cresant wrench. For those with coils, hand tightened is ok.

2. You're going to have to find a broader range antenna. I am lucky in that my cars pretty much have a 5 MHz bandwidth so I center tune for 156 and I'm good. I use 1/4 wave tunable maxrad antennas for pretty much everything in my fleet. WHat antenna are you currently using?

3. Are you sure the SO is transmitting above 162 MHz? That's Fed territory there. As far as the SWR goes, the Kenwoods I use (TK-790H's) reduce power when a high SWR is detected in order to help prevent damage to the radio. My SO cars have Customs Net 2 in them with a TX of 171.xxx . They never use it but it's there if they need it. I've never measure the SWR on it as it keys Custom's repeater in Foley. I'm sure the SWR is high but I may be suprised As far as back to your original question, there are some magic fairy dust antennas that are made will cover the 146-174 range with decent SWR across it. They are also high dollar and outside of my budget. $7.50 1/4 waves good enough for us. Me on the other hand, I'm much more picky! LOL

 

[kingpin]

1. When I first used the crescent wrench I ended up tightening one of them to much which caused the ears to bend back a little. I have found that I can snug them pretty good with just my hands.

2. I am using the Antenex B1443 3dB 144-174MHz tunable for transmitting. I mostly transmit on 151 and 154MHz and occasionally need to transmit on 156 and 158MHz. I have it cut for 154MHz right now. I guess I will either have to purchase or borrow an SWR meter and mess around with it.

Do you think 154MHz is a good center frequency to use?

Any ideas on a broader range antenna?

3. I know the SO transmit quite often between 154 and 159MHz, I guess they must have it center tuned for that. I think they may have some Customs and other Federal frequencies but probably rarely ever use them.

A couple other questions for you:

Any idea where I could get a TK790 for a good price?

Where could I get one of these magic fairy dust antennas that you are talking about? I am also pretty picky, what are you using for antenna's on your personal vehicles? Any suggestions for me?

Also, do you have any pictures of your installs? I would love to see them.

Thanks for all the help Kingpin!

I need to get a new picture together. I've changed some radios up and I'm set for now. I do have a TK-790H remote mount I pieced together for about $500 from various auctions on ebay.

I do all of my commercial antenna ordering through Tessco. Check their website for the bandwidth and style you need. I use Maxrad dual band antennas on my ICOM IC-706MKIIG and Kenwood TM-D700A. For my BCT-15, I use a 1/4 VHF whip. My TK-790H uses a Diamond Dual band antenna. My 110 Watt Motorola Spectra uses this same antenna as well though a duplexer. ALl of my radios are in a Jotto Desk Console in my silverado. I'll post some pics soon now that it's all done