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Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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  #1 (permalink)  
Old 01-03-2018, 1:47 PM
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Default Diamond K400CNMO - Universal Mount

Hello all, apologies if this topic has been posted (discussed) elsewhere, I searched and couldn't find much.

I am inquiring on your opinion on the Diamond K400CNMO Mount. I have a 2016 Chevy Colorado Duramax Diesel that I plan on installing this on. I am quite hesitant on installing a perm roof mount (as I do not want to drill through my roof) - so I have decided on purchasing this mount.

Any issues with grounding, placement on vehicle, sturdiness, etc ?

https://www.theantennafarm.com/catal...cnmo-4885.html

I plan on installing the Larsen NMO 27B to this mount.

https://www.theantennafarm.com/catal...o27b-6439.html

Thank you in advance for any comments you have regarding this mount (or the Larsen NMO antenna).

-Rich
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  #2 (permalink)  
Old 01-03-2018, 4:42 PM
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I think that would be a poor choice for a mount.

The Larsen NMO-27 requires a ground plane for it to work properly. That mount will not provide the necessary ground. That will result in likely high SWR and poor performance. If all you were doing is listening or not expecting to transmit very far, it might work "good enough", but you can easily do better.

I understand the reluctance to drill a hole in a truck that new. But the trade off is it will really improve performance and I personally think it looks better than these compromise mounts. The clamp type mount you linked to will have to go on either the top of the door or hood, and both of those are going to be lousy. The mounts can move around a bit and require frequent tightening to keep them stable. The coax still ends up running through the door which will eventually lead to cable damage, high SWR, etc.

If a permanent mount is absolutely out of the question, then go with the fender bracket mounts. They'll at least provide a decent ground connection. Keep in mind that anytime you mount the antenna off to the side edge of a vehicle, the ground plane is not sufficient under the antenna and will result in a lopsided radiation pattern. Also, avoid the temptation to mount these to the bed rail directly behind the cab. If you really need to do a bed mount, put it as far back away from the cab as you can.

Here's what I'd suggest:

For the bracket mount: Larsen TMB34 Chrome, $4.95 https://www.theantennafarm.com/catal...mb34-3847.html
or if you want black, Larsen TMB34B, black, $6.95 https://www.theantennafarm.com/catal...b34b-3848.html
Either of these mounts will work with your truck. You mount the bracket to the inside of the fender by the hood. Use the included screws to attach it. You'll need to drill 3 small holes (about 1/8th of an inch), but those will be invisible if you ever take the mount off to sell the truck. I'd recommend a small star washer to make sure the ground connection to the vehicle body is good. Also, a dab of silicone in the holes before attaching the mount will help reduce the chances of rust. The screws will bite through the silicone when you tighten them down, so that's not an issue.

For the antenna mount, use this one:
https://www.theantennafarm.com/catal...dfme-1126.html
Here's why I recommend this model mount:
The "HF" series mount have a different coaxial entry than the standard mounts. This is a good idea because the underside of the mount will be exposed to the weather, road salts, car washes, etc. Since NMO mounts are intended to be installed through the sheet metal, with the coax inside the warm/dry vehicle, they are not sealed in such a way that will properly protect them when mounted on a fender bracket like this. If you use the standard mounts, the water will eventually get inside the coax and around the conductors and corrode the wire. It will happen, eventually and it'll slowly destroy the cable. That will create long term issues. By using these HF mounts, you can slide a piece of marine grade heat shrink tubing over the coax and where it enters the mount. Heating it up will seal that connection and protect it.

This mount also has the "FME" style connector. While this isn't what your CB uses, it is intended as a "universal" connector that you just screw an adapter onto to match your radio. The benefit to this is that the FME connector is pretty small. Just a bit bigger than the coax itself. That makes routing it to your radio a whole lot easier.
You can go with just bare coax, but unless you have the tools/skills, or pay someone, to install the connector, this is just way easier. There is a benefit to putting your own connector on or getting someone to do it for you, it allows you use just the amount of coax cable you need and cut off the excess. But, without the tools, skills, etc. that might not be the best choice.

So, you'll need this FME adapter to connect to your CB:
FME Male to UHF Male, $4.95 https://www.theantennafarm.com/catal...n-fp-1222.html
That'll connect the coax to your CB.

And as for the antenna. You really cannot do better than the Larsen NMO-27. I've been using those for nearly 30 years without issue. They tune up nice a smooth if you have a good ground plane. Larsen is a well respected company.
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Old 01-03-2018, 9:47 PM
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I've used trunk lip mounts for decades and they work fine but the diamond is way over priced and not built very well.

Larsen trunk lip mounts are half the price and built to last
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Old 01-04-2018, 7:39 AM
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Quote:
Originally Posted by mmckenna View Post
I think that would be a poor choice for a mount.

The Larsen NMO-27 requires a ground plane for it to work properly. That mount will not provide the necessary ground. That will result in likely high SWR and poor performance. If all you were doing is listening or not expecting to transmit very far, it might work "good enough", but you can easily do better.

I understand the reluctance to drill a hole in a truck that new. But the trade off is it will really improve performance and I personally think it looks better than these compromise mounts. The clamp type mount you linked to will have to go on either the top of the door or hood, and both of those are going to be lousy. The mounts can move around a bit and require frequent tightening to keep them stable. The coax still ends up running through the door which will eventually lead to cable damage, high SWR, etc.

If a permanent mount is absolutely out of the question, then go with the fender bracket mounts. They'll at least provide a decent ground connection. Keep in mind that anytime you mount the antenna off to the side edge of a vehicle, the ground plane is not sufficient under the antenna and will result in a lopsided radiation pattern. Also, avoid the temptation to mount these to the bed rail directly behind the cab. If you really need to do a bed mount, put it as far back away from the cab as you can.

Here's what I'd suggest:

For the bracket mount: Larsen TMB34 Chrome, $4.95 https://www.theantennafarm.com/catal...mb34-3847.html
or if you want black, Larsen TMB34B, black, $6.95 https://www.theantennafarm.com/catal...b34b-3848.html
Either of these mounts will work with your truck. You mount the bracket to the inside of the fender by the hood. Use the included screws to attach it. You'll need to drill 3 small holes (about 1/8th of an inch), but those will be invisible if you ever take the mount off to sell the truck. I'd recommend a small star washer to make sure the ground connection to the vehicle body is good. Also, a dab of silicone in the holes before attaching the mount will help reduce the chances of rust. The screws will bite through the silicone when you tighten them down, so that's not an issue.

For the antenna mount, use this one:
https://www.theantennafarm.com/catal...dfme-1126.html
Here's why I recommend this model mount:
The "HF" series mount have a different coaxial entry than the standard mounts. This is a good idea because the underside of the mount will be exposed to the weather, road salts, car washes, etc. Since NMO mounts are intended to be installed through the sheet metal, with the coax inside the warm/dry vehicle, they are not sealed in such a way that will properly protect them when mounted on a fender bracket like this. If you use the standard mounts, the water will eventually get inside the coax and around the conductors and corrode the wire. It will happen, eventually and it'll slowly destroy the cable. That will create long term issues. By using these HF mounts, you can slide a piece of marine grade heat shrink tubing over the coax and where it enters the mount. Heating it up will seal that connection and protect it.

This mount also has the "FME" style connector. While this isn't what your CB uses, it is intended as a "universal" connector that you just screw an adapter onto to match your radio. The benefit to this is that the FME connector is pretty small. Just a bit bigger than the coax itself. That makes routing it to your radio a whole lot easier.
You can go with just bare coax, but unless you have the tools/skills, or pay someone, to install the connector, this is just way easier. There is a benefit to putting your own connector on or getting someone to do it for you, it allows you use just the amount of coax cable you need and cut off the excess. But, without the tools, skills, etc. that might not be the best choice.

So, you'll need this FME adapter to connect to your CB:
FME Male to UHF Male, $4.95 https://www.theantennafarm.com/catal...n-fp-1222.html
That'll connect the coax to your CB.

And as for the antenna. You really cannot do better than the Larsen NMO-27. I've been using those for nearly 30 years without issue. They tune up nice a smooth if you have a good ground plane. Larsen is a well respected company.

mmckenna, Thank you VERY much for the detailed response.
**Question however, could you add a small ground strap from the Diamond Mount to improve the ground plane?**

Last edited by rbomba; 01-04-2018 at 7:43 AM.. Reason: adding to comment
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Old 01-04-2018, 7:42 AM
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Default Larsen Mount ?

Quote:
Originally Posted by MOTEX View Post
I've used trunk lip mounts for decades and they work fine but the diamond is way over priced and not built very well.

Larsen trunk lip mounts are half the price and built to last

Thanks, I searched (quickly) the Antenna Farm site and couldn't find a Larsen mount. Do you have a link to a mount you would suggest ?
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  #6 (permalink)  
Old 01-04-2018, 8:59 AM
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Quote:
Originally Posted by rbomba View Post
mmckenna, Thank you VERY much for the detailed response.
**Question however, could you add a small ground strap from the Diamond Mount to improve the ground plane?**
Yes, you could.
There is a difference between a DC ground and an RF ground plane. Running a ground strap might help a little bit, but it's not going to fix a lopsided ground plane.
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Old 01-04-2018, 9:02 AM
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Quote:
Originally Posted by rbomba View Post
Thanks, I searched (quickly) the Antenna Farm site and couldn't find a Larsen mount. Do you have a link to a mount you would suggest ?
https://www.theantennafarm.com/catal...otlp-1171.html

I agree with Motex. The hammy grade Diamond stuff is overpriced and not built as well. I'd still recommend the bracket mount, but if a trunk lip mount is what you want to use, then get a decent one. You won't have an issue with the Larsen products.
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Old 01-04-2018, 3:34 PM
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I use this mount and have had no issues with it. No SWR problems at all. When you tighten down the hex screws make sure that one is contacting the body . As I said no issues with swr on 2 mtrs or 70 cm.
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Old 01-04-2018, 3:46 PM
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Take a look at the LBT8 made by Laird. Have used these on many commercial accounts for many year with no problems
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