Re-wired my trucks alarm to use an external NMO antenna

[8K10F1E]

Installed a remote start alarm system in my truck over the weekend. I wanted to hide the send and receive antenna for aesthetic purposes. Since my truck already had a 900mhz antenna mounted in the roof, I decided It would work perfect with my 900mhz alarm system.

All it required was removing the old monopole antenna and soldering on a coax lead. Took me 20 minutes and the results are a huge improvement.


I did cut off the extra coax to as close to the board as possible. It's only about a foot long to the mount. The ground stands are cut as far back as possible so they don't short out. For some reason this setup does not need a ground soldered. The stock antenna was just a straight metal whip.

According to the FCC website this guy transmits at 22db. Using google earth, I determined that I can get about 1,500 feet of distance with this new setup. Not quite the impossible 1 mile that they advertise, but still good enough for me.

 

[mancow]

Cool stuff, but it still needs the coax grounded at the board. Find a ground plane to connect the braid and it will probably work even better.

 

[commscanaus]

Mancow is right....the co-ax shield needs to be soldered to a grounding point on the PCB.

The only issue I can foresee with an external antenna for an alarm/security system is desense.
Park near a strong RF source (particularly in band @ 900Mhz) and you may find yourself locked out of your car or the system behaving erratically.

Had a problem a few years ago when I parked my car below a trunked radio site using 416Mhz.
The car refused to open and had to be unlocked manually which resulted in the alarm sounding.
The key fob transmitter uses 433Mhz (unfortunately) and is susceptible to close RF.

Hopefully your system works well with the antenna fitted.

Commscanaus.

 

[bonez01]

Cool Idea well executed. Thanks for sharing