NMO mount antennas

[FPR1981]

If I possessed the talent to cut a clean hole into a vehicle and run the coax neatly, you bet your back side that my vehicles would have Larsen NMO 30's with the appropriate mast size. But I don't, so magnet mounts rule the day.

 

[mmckenna]

If I possessed the talent to cut a clean hole into a vehicle and run the coax neatly, you bet your back side that my vehicles would have Larsen NMO 30's with the appropriate mast size. But I don't, so magnet mounts rule the day.

Nothing at all wrong with that.
Having the right tools and skills takes money and time. Not everyone wants to invest in that stuff. If the magnetic mounts allow you to talk to who you want, then it's working 100%.

On the other hand, keep your eyes open, and you may run across someone local to you that would be happy to assist. Many ham operators have the right tools. 3/4" hole saw, coax crimpers and a simple antenna analyzer isn't uncommon.

 

[krokus]

On the other hand, keep your eyes open, and you may run across someone local to you that would be happy to assist. Many ham operators have the right tools. 3/4" hole saw, coax crimpers and a simple antenna analyzer isn't uncommon.

Quick note: See some of mmckenna's previous posts, to see the correct type of hole saw. (Not the one you get at your favorite home improvement store.)

 

[laidback]

Greenlee knockouts are better than hole saws.

 

[prcguy]

I know for a fact you could make a nice hole and do a good install with maybe 2 minutes of instruction, don't think you can't do it.

If I possessed the talent to cut a clean hole into a vehicle and run the coax neatly, you bet your back side that my vehicles would have Larsen NMO 30's with the appropriate mast size. But I don't, so magnet mounts rule the day.

 

[prcguy]

Maybe if you have all day to do an install but a professional installer would never use one. A Home Depot 3/4" hole saw makes a perfectly good hole for an NMO and you can put in 20 or more roof mount antennas a day with that compared to maybe 10 with a punch because you have to remove so much stuff to get the hole punch up inside the headliner. I think I tried a hole punch once in the 1970s and moved on.

Greenlee knockouts are better than hole saws.

 

[ForestRunner98]

I used a HF step bit and it worked great! It’s kinda scary at first but after the pilot hole is done just keep going forward. Can’t turn back.

I was actually surprised how easy it was!!! Besides the small gain I would get from a permanent mount would be the appearance and most importantly safety. I didn’t want a huge magmount to take flight in case of an accident or hard brake. Those are my reasons.





Hmm..not sure why ^ that pic is sideways.

 

[mmckenna]

Greenlee knockouts are better than hole saws.

I have a 3/4" knock out punch, and it's been handy on a few occasions.
But as prcguy said, it can take longer to do the work since you need access to both sides of the sheet metal. Not always possible on a mobile install.

The DeWalt brand 3/4" hole saw designed for steel works really well. Got in a pinch once and left my hole saw in the office. A quick trip by Home Depot got me what I needed and finished the job just fine.

The step bits (aka Christmas Tree bits) are sketchy. They can grab if you are not careful. Not something an inexperienced person should be trying. The nice benefit to the true NMO hole saws is that they have a depth limitation design, so no risk of going to deep and damaging the headliner.

 

[prcguy]

With some minor experience you learn to adjust the pilot bit to only stick beyond the hole saw about 1/8" and you develop a method of pushing down on the pistol grip of the drill with one hand while holding the pistol grip hand back with the other hand with the elbow resting on the roof so the saw doesn't jump through the finished hole. You can saw holes all day long in car roofs and only penetrate a fraction of an inch and not grab anything.

The other trick is to only pull down the rubber door seal from roughly even front to back with the hole to be cut in the roof and down the front or rear pillar where the coax will run. Then slide a chunk of long thin plastic maybe 1/16 to 1/8" thick and a foot wide up between the headliner and roof to catch debris and to prevent the saw from touching the headliner. With that you can cut the hole, put in an NMO mount center of roof and run the coax under the dash and have the car back together in about 5min. Add another 2min to strip the coax, put on a crimp connector and seal up with some heat shrink. 7 minutes after you started your on the air mobile.

I have a 3/4" knock out punch, and it's been handy on a few occasions.
But as prcguy said, it can take longer to do the work since you need access to both sides of the sheet metal. Not always possible on a mobile install.

The DeWalt brand 3/4" hole saw designed for steel works really well. Got in a pinch once and left my hole saw in the office. A quick trip by Home Depot got me what I needed and finished the job just fine.

The step bits (aka Christmas Tree bits) are sketchy. They can grab if you are not careful. Not something an inexperienced person should be trying. The nice benefit to the true NMO hole saws is that they have a depth limitation design, so no risk of going to deep and damaging the headliner.

 

[slowmover]

What meets “needs”:

Needs are not desires
Confusion abounds with this.

CB performance will have been a function of experienced use at some early point.

Mag Mount susceptibility to damage will render it unusable, forgoing long term experience AND what was needed the very next day. (Spares must be carried).

When it matters, the antenna system will have mattered most.

One does not want the family Conestoga with all aboard . . and ratty coax draped loose.

.

 

[spikestabber]

Thanks all, loved reading this thread as it gave me some great ideas.
Loved CB since I was a kid a good 30 years ago, still enjoy having one in my car hearing whats going on around the highways. Getting the urge to want one again was because of this forum. Here's my setup, hope it inspires others.

 

[KA0XR]

Just discovered this thread. I am intrigued with the idea of pairing the Larsen NMO30 with the W640 whip but I would be wanting to use it mainly for 10 meters instead (but also wanting to have the option to at least monitor CB). This would be a way to "resurrect' the Laird CW27 antenna with its 67" long whip which has been discontinued.

Any thoughts on whether the Larsen NMO34 would actually be the better coil for 10 meters vs. the NMO30? I figure that to achieve resonance at a center frequency of ~28.8 MHz using the NMO30, a good portion of the 65" whip would need to cut off vs. using the NMO34, reducing overall efficiency.

I don't see why the W640 whip couldn't be paired with a non-loaded spring base coil for VHF high band like the one made by PC-Tel/Maxrad, cut to ~56" or so, and then be a resonant quarter wave on 6 meters.

 

[krokus]

Just looking at this thread again. Has anyone tried the longer (W640) whip with the NMO27? Based on the comments with cut charts, it sounds like it would be much too long, and have to be trimmed to the point of the shorter whip.

 

[prcguy]

Just looking at this thread again. Has anyone tried the longer (W640) whip with the NMO27? Based on the comments with cut charts, it sounds like it would be much too long, and have to be trimmed to the point of the shorter whip.

A longer whip would have to be trimmed to the same length as a stock whip so I don’t see any advantage unless the new whip is thicker. If you get a higher freq coil like 30 or 34MHz as mentioned in post 52 then you can make use of a longer whip and improve efficiency.

 

[steve9570]

I just had to buy a new bedroom A/C and had to remove the 2 NMO mag mounts to reinstall on the new A/C. Those NMOs have been on that A/C for over 30 years and still work like new!

They have seen LOT Mass snow storms and summer heat and keep on working,

Steve

 

[smittie]

Is there a recommended spring that can be used with the Larson NMO30 and the 64" whip?

 

[mmckenna]

Is there a recommended spring that can be used with the Larson NMO30 and the 64" whip?

Springs - Pulse / Larsen Antennas - Antenna Accessories

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You can insert one of those between the base and the coil. You will have to shorten the whip by an appropriate amount since the spring becomes part of the radiating element. The antenna whip cut charts usually include a measurement for "without spring" and "with spring".

 

[smittie]

@mmckenna assuming I use my soon to arrive nanoVNA to properly tune the system, is there a downside to having the spring in the system?

 

[mmckenna]

@mmckenna assuming I use my soon to arrive nanoVNA to properly tune the system, is there a downside to having the spring in the system?

No, not really. Might allow a bit more flex that without it, which can result in some flutter in the signal if you are driving along well above highway speeds.

I have a spring on the base of a 1/2 wave VHF antenna on a Polaris Ranger, and it's taken some healthy tree branches without any issues. It's a good option to have.

 

[mrweather]

Theoretically, adding a spring will make the antenna a little more broad banded, but in practice I don't know if the effect is noticeable.