External NMO Mobile antenna performance

[gamewarden3006]

Ok So I have a Panasonic tough book cf-31 along with a Gamber Johnson docking station in the vehicle. The toughbook has a built in Verizon LTE card in it. I recently installed a NMO mount external antenna on the top of my truck to increase reception. Past vehicles I have had had this set-up with the same antenna and it did increase reception noticeably. Especially in fringe areas. However this is not the case with this one. With the built in antenna on the PC inside the vehicle, I am getting around -71db. as soon as I plug it into the dock and connect the external antenna, it drops to -85db. I have tried two different antennas that I have used in the past. (one browning and one Pctel). both yield the same results between -83 and -85db. Signal jumps back to -71 as soon as I disconnect it. Same results with both rf ports on the docking station.

last night while in town with great coverage I did a download test and was getting 23 megs down on the internal antenna. as soon as I connected the external one, the speeds dropped to around 10 megs. I tried this twice to verify...same results.

I tested the antenna cable and it seems great. .02 ohm.. on both wires.. going to try to probe the docking station next. going to also try to test my PC in a different vehicle next week when I get a chance.

Any other thoughts or suggestions??

 

[chief21]

With some NMO mounts and NMO antennas, they don't exactly match and the center conductor of the antenna does not quite touch the center conductor of the mount. They could be *just* close enough that there is some inductive coupling but not full electrical contact.

 

[KK6ZTE]

Which particular antenna setup did you use?

LTE and other higher frequencies applications often use a specialized mount with larger diameter coax for less loss than the typical LMR antenna cable.

 

[gamewarden3006]

Checked the nmo alignment and it seems to be spot on... As for the wiring, I used standard antenna with that the radio tech gave me. Same wire that I have used for several other antennas from vhf to uhf and even other mobile antennas on other vehicles.

 

[Project25_MASTR]

Checked the nmo alignment and it seems to be spot on... As for the wiring, I used standard antenna with that the radio tech gave me. Same wire that I have used for several other antennas from vhf to uhf and even other mobile antennas on other vehicles.

But how long of coax? Especially if you are in an area where bands were recently switched and your external antenna setup doesn't quite cover it.

 

[gamewarden3006]

I believe the cable is around 12- 15 ft or so. The antenna is mounted on top of can above passenger rear seat on an F-250. It runs to the passenger front side then down the Piller to the floorboard-under the floor mat and up to the docking station.

As for the bands. I am unsure ofexactly which band. Verizon 4g lte...

 

[lmrtek]

Verizon 4G LTE uses 747-787 Mhz so you need to be sure your antenna is built for that frequency range.
........
You can also just trim any 1\4 wave vhf or uhf whip to 3 inches length and get good results.

 

[alcahuete]

Verizon 4G LTE uses 747-787 Mhz so you need to be sure your antenna is built for that frequency range.
........
You can also just trim any 1\4 wave vhf or uhf whip to 3 inches length and get good results.

They use way more than that. They use band 2, 4, and 13. Band 2 is 1900 MHz, Band 4 is 1700/2100 MHz, Band 13 is 700 MHz.

If your LTE card utilizes more than one of those bands and your antenna only covers one of those bands, it's no wonder there is a problem.

 

[speedway_navigator]

I installed 2 identical lip mounts yesterday, one has a return loss of 42dB, the other half that. They are on opposite sides of the hood about as symmetrical as I can get them. I used the same antenna on each, the 20 dB RL was worse until I removed the rubber gasket at the base and got the antenna to seat further down.

The 42 dB mount has the rubber gasket. I suspect the coax is the culprit since one had a deeper U in it to go around the hood lid. I don't recall which one it was.

 

[n5ims]

There are also different types of NMO mounts available now from Larsen. They make the normal one that has a flat disk for the antenna to rest on to make contact and is designed for lower frequencies (below 800 MHz generally) and most of the NMO mount antennas. They also now have a newer "HF" model that uses a similar design for the older style antennas but allow the disk to be removed and allow the antennas specifically designed to use the HF mount to slide into a pin hole in the mount so a better contact is made. The new HF mount antennas require the new HF mount, but using the disk, the older style antennas will work as well. Since the OP is wanting an antenna designed for cellular use, they may want to check into an HF style antenna and use the new HF style mount to improve the contact between the antenna and mount.