How can I boost the signal on my motorcycle's pager alarm?

[matrix02]

I have a Scorpio alarm which has a good range for a 2 way pager alarm, but I need more. I want to cover about 4 residential blocks.

Basically I want to know if my alarm is triggered on my bike or car even if it's parked 4 bloacks away. What will it take to do this?

Also what are the implications of only boosting the transmitter in the vehicle or only boosting the remote transmitter? For example if I boost the remote only, will that mean that the vehicle's weaker transmitter might be picked up anyway since the remote's reciver is very strong? What is more important? Signal transmitter stregth or reciever strength?

 

[MacGyverS2000]

It would take an illegal increase in the power (i.e., no longer FCC Part 15 compliant) as you're not going to get much more sensitivity (no such thing as receiver strength) out of the receive antennas.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Comcokid]

Several issues-
1) FCC - violates the FCC approval the manufacturer has on the unit.
2) Since it is a two way, adding any amplifer in the transmit side also requires additional RF switches so the receiver can still work making any solution more complex.

Suggest you look at improving the antenna. Although still not quite proper on the FCC issue, an antenna change is a more passive and easier approach to improvement.

The rule-of-thumb is every 6db of improvement yields double the range. I would suggest a better antenna on the mototcycle end. Antennas that most items are build with are a compromise for cost and an external antenna will probably get you 6db improvement. If you also added an external antenna to your pager end, you could get additional improvement, but it then wouldn't be as easy to carry. Look for a 1/2 wave rubber duckie antenna at whatever frqeuency the unit uses.

 

[VEBill]

If you only want the alarm signal to reach further, then perhaps you could wire in another (legal) transmitter to the siren circuit so that when the alarm is triggered, in addition to everything else that happens, it also transmits using the additional transmitter.

An inexpensive FRS walkie-talkie comes to mind as the obvious candidate transmitter. There would be a risk of someone else in the area using the same channel and code as you've selected. It might be slightly unlawful to use an FRS transmitter in this manner, depending on the rules in your country.

 

[matrix02]

As far as antenae improvements, I don't want to cut up the existing antenae and end up worst off. Is it a big deal to cut and splice antennas on these kind of devices or is it just like electrical wire splicing? Should I replace the existing antenna completely or do I just splice new antenna onto existing? Thing is these are tiny compact antennas, so I can't just conect to the BNC connector(there is none). I suppose I would need to buy a female BNC/Coax connector to plug the antenna into and then splice wires on the other end of BNC connector?

Thanks guys!

Also considering wireless cameras that could connect to my wireless network and transmit video of bike from car. So my car would basically "watch" my bike.

 

[Comcokid]

What kind of antenna is it now? Some of the possibilities are:
PCB antenna consisting of a trace or pattern on the circuit board?
Wire inside or outside of enclosure soldered to PCB?
Piece of brass soldered on PCB?
Chip antenna - small rectangular ceramic device on PCB?
Seperate PCB antenna connected to main board by coax?
Coax leading to small rubber or spring-wire antenna on outside of enclosure?

Adding an external antenna usually requires using a small coax from where the original antenna attaches to a connector on your enclosure, and then adding an external antenna with matching connector. For small items like this, the choice of connector is a MCX, MMCX or SMA as a BNC is a little large. These smaller connectors are common on computer wireless devices, and a common small coax is RG-178.

Coax and connectors must be connected properly to work well. You just can't cut/splice with electrical tape.

You do not want to splice and have both antennas connected. But, if you add a coax/connector, you can connect either an old or a new to check the range improvement.

Still a question of what frequency your "Scorpio" uses.

 

[matrix02]

Thanks again for your help. The Scorpio uses the 440MHz range. The antenna apears to be a wire coming from within the alarm unit much like a power cord on many electronics devices would be. It's about 13-14" long and directions say to have atleast part of wire exposed(out of bike), so I pushed the tip through hole under tail of bike(rear under and behind passenger seat). The wire is about 22 guage.

 

[Higgler]

Matrix 02

What you can do to improve it is some testing on an open range/field and change the antenna length and location. Right now, your antenna is too long to be an optimal antenna. Should be 0.25*11,803/440 = 6.7 inches if it was a simple monopole antenna (one wire straight up from a metal disk ground plane). I guarantee you that you're using a very crappy antenna.

If I were doing this, and I've been an antenna engineer the past 20 years, I'd try this.
1) Change the wire to a wide wire brade, maybe 2" wide x 10" long. (wider wire/braid gives better bandwidth and is friendlier to mounting near metal objects). Solder your antenna wire to the braid (i.e strip your wire to make it bare,then solder to braid, only need to connect it for and inch or so). Position the unit&braid antenna so the antenna sticks up or down and as far away from another vertically oriented object as possible. Your present location maybe strong backwards and weak frontwards based on your description. That may be ok if you know how to orient your bike when you park.
2) Go to a field or a slight valley with a friend who has a bike too (he'll need to drive around to test at all angles). Test for range. take at least four measurements when doing range, north, south east and west. You'll find one is up to 4x further than the other. It'll help orient your bike if you know which direction you'll be going after you park it.
3) Fold up the braid to make it shorter and duct tape it shorter in one inch increments. Like rolling up a belt. Then retest for range. Hopefully all ranges will be getting larger, some are likely to slightly shorten, so don't worry about that. Both your antenna pattern and it's efficiency will change as you change length. When you find the optimum, you can just cut the braid to that size. I'd tape over the braid so it doesn't short out to your bike's metal, or maybe coat it with some polyurethane.

You could try a different routine, (just use the wire that's on the unit and fold it up) just vary the antenna size and location and test for range. You could also get a multi section rod/pointer to use as a variable antenna. I've purchased them for $3 from a hardware store. The optimum bike location for the antenna is top of fuel tank, braid/antenna standing upward, but that would look pretty ugly. Don't lay the antenna along any metal, it must be by itself, at least 3 inches from metal oriented in the same direction.

Also, describe the unit and how you locate it. i.e. unit is 2"X4" battery operated mounted on tank. Cable from the unit to the antenna, or antenna connected to the unit's housing.

Kevin

 

[VEBill]

If the optimum antenna is too obvious, then the bad guys will simply cut or pull it off and toss it away before they start to disassemble the bike. Perhaps it should be made to look like a normal bike antenna (CB, AM/FM, etc.) so that it can be perfectly hidden in plain sight.

(I once saw a police 'ghost car' where they had 'hidden' the 800 MHz comm antenna on the rear deck just inside the rear window. I spotted the antenna in about 2 seconds. I wonder why they didn't simply use an adjusted cellphone antenna hidden in plain sight?)

Also, it is not uncommon for consumer devices to have a matching circuit for the provided antenna. In other words, if you convert from a Hi-Z half-lambda dangling wire to a Lo-Z quarter-lambda braid, you might also have to adjust the internal antenna matching network if you want things to be optimum.