Fender vs roof mount.

[78k10]

I currently have a radio shack analog scanner in my truck, and recently put an NMO antenna on a fender mount for the bands I monitor, all between 150-160 megahertz. Reception is really good since I used an antenna cut for that frequency range. But what would I gain by moving the mount and antenna to the roof? I’m contemplating drilling my roof for the NMO but would it make any real world difference in reception quality?

 

[Hit_Factor]

A couple feet in elevation and better omnidirectional RX pattern.

 

[mmckenna]

Compared to installing a permanent mount NMO dead center in the roof of the vehicle, you are losing somewhere between 2 and 3dB. That could be half your signal, compared to putting in on the roof.

If it works where it is, and you are happy with it, then leave it. If you want to get better performance out of it, then absolutely, an NMO mount in the center of the roof will help.

 

[bharvey2]

You'd also gain a little less temptation to errant kids who come by your vehicle and grab antennas. Again, depending upon location, YMMV.

 

[n5ims]

Anyone that wants to compare the differences in locations for an antenna on their car should consult this from Larsen -->
http://www.repeater-builder.com/antenna/pdf/larsen-mobile-antennas.pdf <-- that has some good advice in text for what kind and what location may provide the best performance. It also has a picture with various locations and how much worse one location has vs. the reference location where an equivalent antenna would have at another location and/or type of mount. They include magnetic mounts, trunk lip mounts, glass mounts, and permanent (read drilled and correctly mounted NMO) mounts.

 

[bharvey2]

Anyone that wants to compare the differences in locations for an antenna on their car should consult this from Larsen -->
http://www.repeater-builder.com/antenna/pdf/larsen-mobile-antennas.pdf <-- that has some good advice in text for what kind and what location may provide the best performance. It also has a picture with various locations and how much worse one location has vs. the reference location where an equivalent antenna would have at another location and/or type of mount. They include magnetic mounts, trunk lip mounts, glass mounts, and permanent (read drilled and correctly mounted NMO) mounts.

Very informative. The loss in dB on the aerial view was at 800mhz. It'd be interesting to see the same at other bands too. Showing mag mount vs. through hole NMO would be good as well and might encourage some to more seriously consider the benefits of a proper NMO installation.

 

[78k10]

Thank you for the input. Let me ask you this. My truck is a 78 Chevy, with a double layered roof. What’s the best way to get the mount in between the layers? From my understanding, there are two different size mounts. The 3/4” one goes in from below, while the 3/8” size drops in from the top. Is that correct? So I would need to use the 3/8”?

 

[mmckenna]

Backwards.
The 3/4" mounts will go in from the top.
The 3/8" mounts need to go in from the underside.

As for where, center is obviously best, but you need to make sure there is room. Start looking up by the dome light.

 

[MisterLongwire]

Ok,,,,wait a second, This is for receiving, regarding scanners, right? I don't think it is such a big deal for the receiving end. Understandable for transmitting. You can even use the scanner antennas that clip on the window. Or, if you want to go hard core, get the "mini discone" that looks like a full sized discone just reduced to mini-me size and put it on a trunk mount.. For a scanner (receiving) I wouldn't waste the time, energy, or hole in my roof for one minute. Ham radio...transmitting...is another story. Just my opinion....

 

[78k10]

Ok,,,,wait a second, This is for receiving, regarding scanners, right? I don't think it is such a big deal for the receiving end. Understandable for transmitting. You can even use the scanner antennas that clip on the window. Or, if you want to go hard core, get the "mini discone" that looks like a full sized discone just reduced to mini-me size and put it on a trunk mount.. For a scanner (receiving) I wouldn't waste the time, energy, or hole in my roof for one minute. Ham radio...transmitting...is another story. Just my opinion....

Correct, for a scanner. I know the roof is the absolute best for transmission, but I wasn’t sure if it was worth the effort for a scanner. I’m also putting a cb in for hunting purposes, and am considering utilizing the roof for a Larsen NMO27. Was thinking about putting the scanner antenna up there as well.

 

[mmckenna]

Correct, for a scanner. I know the roof is the absolute best for transmission, but I wasn’t sure if it was worth the effort for a scanner. I’m also putting a cb in for hunting purposes, and am considering utilizing the roof for a Larsen NMO27. Was thinking about putting the scanner antenna up there as well.

It works both ways for transmitting and receiving. A scanner antenna mounted dead center of the roof will outperform clip on, brackets, any other compromise mount.

Just make sure you space the antennas out a bit. CB antenna should go dead center. Mount the scanner antenna off to the side/rear if needed.

 

[78k10]

It works both ways for transmitting and receiving. A scanner antenna mounted dead center of the roof will outperform clip on, brackets, any other compromise mount.

Just make sure you space the antennas out a bit. CB antenna should go dead center. Mount the scanner antenna off to the side/rear if needed.

I’ve decided against using a permanent cb antenna so the scanner antenna would be the only one up top. I almost punched the hole today but I chickened out. I’m not sure I have enough to room between the roof layers to fish my BNC connector through there. It came with the connector already attached and I don’t have the tools or know how to cut it off and put another one on.