Using power or signal cable as antenna at 2.4GHz

[BusyEng]

Hi all,

I would like to know how I can use a multi-wire cable (including battery and wires that carry audio signals) as a 2.4GHz antenna. The cable has no shielding and all wires go in parallel with each other in the cable. The cable is about one foot long, however, I can change the cable length if necessary.

I understand that I can use some small capacitors (in pF range) to inject the RF signal to the cable. However, I am not sure on how to choose the length of the cable, how to select the capacitor values, and also how to select the wire in the cable as the antenna (should I inject the RF signal to all of them?). I am also not sure how this will affect the antenna impedance seen by the RF source.

Any practical advice or sample schematic will be very helpful.

Thanks.

 

[goldsmith]

I would like to know how I can use a multi-wire cable (including battery and wires that carry audio signals) as a 2.4GHz antenna.

Hi
What you're attempting to do exactly ? using a cable to handle DC voltage and audio signal and Rf wave together ? am i right ?

I understand that I can use some small capacitors (in pF range) to inject the RF signal to the cable. However, I am not sure on how to choose the length of the cable, how to select the capacitor values, and also how to select the wire in the cable as the antenna

What you mean by inject into the cable ? i really confused can you draw a schematic about what you are about to do please ? perhaps i can guide ?

Best Luck
Goldsmith

 

[vfone]

While ago I read in a magazine that: "Antennas are like blondes. There are only two types: good and better."
Myself I am not totally in agreement with this statement, because I've seen very nice looking and shinning antennas working poorly, and ugly and rusted antennas working incredible well.
Can use as an antenna a lot of things from the nature. The only problem is that most of things will radiate the energy very poorly, and will work much worse than a simple wire tuned on the desired frequency.

 

[biff44]

sure, as long as you do NOT care too much about how good the antenna is, you can run a series capacitor to the DC line, and a shunt inductor to ground (to snub any DC spikes) and then hook it up to your RF circuit.

 

[BusyEng]

Hi
What you're attempting to do exactly ? using a cable to handle DC voltage and audio signal and Rf wave together ? am i right ?


What you mean by inject into the cable ? i really confused can you draw a schematic about what you are about to do please ? perhaps i can guide ?

Best Luck
Goldsmith

Hi GoldSmith,

Here is a drawing that shows what I have in my mind:



Obviously, getting the best performance for the antenna is what I am looking for. I would like to know if this scheme works. If not then what the right approach is and if yes then how should I calculate the length of the cable, values of the capacitors, and values of the inductors.

Thanks

 

[FvM]

A λ/4 monpole (3 cm piece of wire) with some ground plane or a λ/2 dipole are the first candidates for a good 2.4 GHz antenna. A long wire/cable as imagined will primarly involve an unwanted directional characteristic. In other words, a rather small antenna integrated with the transmitter will probably give better performance than any solution connecting the cable.

You didn't tell anything about device size.

 

[BusyEng]

Although I have some control on the cable length, but it is within a limited range. The cable length could be anything between 35mm and 45mm. Therefore, a λ/4 monpole (3 cm piece of wire) is not possible in this design. The length of the board is about 8mmx35mm (WxL). Please let me know if any other information is needed.

Thanks

 

[goldsmith]

Hi GoldSmith,

Here is a drawing that shows what I have in my mind:



Obviously, getting the best performance for the antenna is what I am looking for. I would like to know if this scheme works. If not then what the right approach is and if yes then how should I calculate the length of the cable, values of the capacitors, and values of the inductors.

Thanks

Hi again
Sorry i can't help you in this case so i leave it into capable hands of the other ones and just read the result to learn

Best Wishes
Goldsmith

 

[FvM]

The cable length could be anything between 35mm and 45mm.

The length of the board is about 8mmx35mm (WxL).

That's nearer to a λ/2 dipole than I thought.

For the coupler L and C, any value with XL >> 50 ohm and XC << 50 ohm should work. An additional matching network can be designed for optimal power transfer, usually an LC pi filter.