About Alarm antenna wire

[thedag]

Hi,
The antenna of my Alarm in my car is simple short thin wire,
I tried to add more wire to this wire and the range of the remote is little changed,
The Thickness of the wire is important for the range?
And if i add e-tape to the center of the antenna wire, the length of the wavelength should be counted from the point of the etape??

Sorry for my bad english,

Thanks in advance.

 

[Syncopator]

Hi,The Thickness of the wire is important for the range?

No, the thickness of an antenna's wire or elements affects only the antenna's bandwidth.

... if i add e-tape to the center of the antenna wire, the length of the wavelength should be counted from the point of the etape?

What is e-tape? What type of antenna is it?

 

[thedag]

I mean black tape, to insulate the connection between the new wire I Added to it.
and its just wire antenna, for car alarm. the frequency is 325MHz

 

[biff44]

The length of the antenna is important. Just adding more wire length may hurt rather than help.

Try re-routing so that the antenna is not so close to anything metal.

 

[thedag]

i tried it, still not work, i tried make the wire 23cm length for 325MHz
but the range not that good, not satisfied from the range.

what can i do ?

 

[Syncopator]

I mean black tape, to insulate the connection between the new wire I Added to it.
and its just wire antenna, for car alarm. the frequency is 325MHz

It's probably a 1/4λ (quarter wave) antenna. If you try to extend it to, say, 5/8λ, you will have to experiment with loading.

It would mean a lot of trial and error, and, unless you are well experienced in adjusting antennas, it's hardly worth your effort in view of the small advantage you might achieve.

 

[thedag]

i also tried 1/2 wavelength, and the same results,
Help pleasee, maybe i can know what the frequency of the antenna by alternative way?

 

[vfone]

Basically here is about radiation resistance of the antenna. Higher the radiation resistance greater the antenna efficiency.
In your case parameters that affect the monopole antenna radiation resistance, are the antenna shape, objects near the antenna, and the ground losses.
Ideally, to get the best radiation, the antenna should be perpendicular to a solid ground plane (which can be the car in your case).

 

[thedag]

Hi,
Im sorry, but im not that good at english,
please try to explain me that in easy way, please...

Thanks a lot, Thedag

 

[vfone]

Google Translate

 

[WimRFP]

Hello,

As others said, a quarter wave is the simplest option with good probability of success (so that is about 21 cm, including correction for fringing). Wire thickness is not of importance; use whatever you have and what is easy to work with.

A half wave antenna has too high impedance for direct connection to 50 Ohm output and 5/8 wave requires series inductance.

If there is a cable in between the antenna and the unit, make sure you connect the screen (braid, shield) of the coaxial cable (at the antenna side) to a large metal part (metal chassis). Keep the connection between cable's braid (shield) and ground short (< 1 cm).

Best is to have the antenna perpendicular to the surface. Worst case is when the antenna is parallel to a metal surface. If there is no other option, keep it away from parallel metallic structures for at least 10 cm (more is better).

 

[thedag]

Hi,
I Dont have coax shield in the cable
the cable is only regular cable without any coax or shield.
and the unit place is near the engine of the car, So, i think the antenna is parallel to metall, and 21cm is short to make it not parallel to metal.
what can i do?

BTW, Do you have MSN Address or Skype to contact you ?
Thanks, Thedag

 

[WimRFP]

Hello Thedag,

For the antenna itself, you just need wire (so no coaxial cable).

If the antenna wire is connected directly to the unit, there is no coaxial cable. If this is the case you can:

1. check the length of the wire and reorient it for best performance, using the guidelines in this thread, or

2. You need to relocate the complete unit (probably time consuming), or

3. you need to modify the unit.

For the last option, you may need to open the unit and connect a coaxial cable to the RF output. Then you run that cable to a place where the antenna (21 cm of wire soldered to the center conductor of the coaxial cable) will perform better. If you think you don't have the knowledge to do this, try to get local advise, as you damage your alarm permanently.

 

[thedag]

Hello,
This is will work? :
Add long extra wire, Add e-tape (black tape) (for insulate) in some point, And from this point, The length of the antenna will be counted? (In this case, 23cm).
This is the only way i could make it away from metal (Metal Blocks the signals).

Thanks.

 

[WimRFP]

Hello,

If you want a certain distance between the unit and the antenna, you need (50 Ohms) coaxial cable in between (at the unit, the braid must be connect to the ground on the PCB inside the unit).

The antenna length counts from the point where the coaxial screen (braid) stops. Don't forget to connect the braid to some metal (chassis part for example).

If you don't have metal parts available, you may connect same 21 cm wire to the braid (so you get I dipole). this will work better then connecting nothing to the braid (at the antenna side).

 

[thedag]

Hi
the cables that connected to the unit (the antenna included) is like this connector:
**broken link removed** arezone.com/img/data/articles/2004/1215/tutorial-24pin_atx_power_co.jpg
(disable spaces)
kinda like this...

Can i make the Coax cable without opening the whole unit ?
there is a video or picture'd tutorial how to add the coaxial cable to the antenna ?

thanks

 

[WimRFP]

Hello,

Strange connector for HF.... If the antenna wire is on one of the pins, you have to find the ground pin. The center conductor goes to where the antenna is/was connected, and the braid goes to the ground pin. Make sure you keep the connections as short as possible, especially the connection between coax braid and the ground pin.

If you you are ready, best is to post a picture so we can see what you did (picture before you apply sealing compound or sealing tape).

 

[thedag]

the antenna is on one of the pins,
can i just keep something like 10cm of the old antenna, and solder to it the center of the Coax cable ?
and how can i solder the braid to the ground pin?

Please tell me if you have MSN Address or Skype, its can be much faster, please.

 

[WimRFP]

Hello,

For best results, you should make all connection as short as possible, 10 cm (that is almost 0.1*lambda) is too long. Sorry, I don't have MSN or Skype.

Do you know a radio amateur? If so, he can help you with the connections, and antenna positioning (for sure).

 

[thedag]

Sorry but i dont know radio amateur,
2 cm is ok?
and how solder the braid? make it like wire and solder it ?