inductive coupling of UHF

[dz99]

Hello!

I want to couple out the RF power form my small radio (f=446 MHz lamd=67.2 cm=26.48 inch PWR_OUT=26dBm) without opening it, and solder a coax line to the HPA's output. Inductive couping seems to be a good solution (or the conductive coupling better? I haven't got reference.)

The transceivers antenna is a lambda/4 rod ( 80 mm )

1. How can I calculate which coil dimensions would resonate out the maximal power?

2. The coil end will be a differenital (push-pull) output. Thus I can't use coaxial cabel as a transport line. --> a. feed a symetrical dipol directly by the coil or
b. use of a balun transformer?

In case of "instant dipole sticking" I can't transport the signal to (for instance) higher positined antennas.

EDA tools also welcome!
Bye!
Thanks a lot!
Z.

 

[bingjiang99]

1) You have to use EDA software to simulate your antenna. You can use HFSS, which is very accurate.
2) I believe that you have to use a balun to drive your signal. However, if you didn't expect too much, a direct feeding can work OK.
3) If you want to use inductive coupling, you should put a loop antenna pair to do that.

Hello!

I want to couple out the RF power form my small radio (f=446 MHz lamd=67.2 cm=26.48 inch PWR_OUT=26dBm) without opening it, and solder a coax line to the HPA's output. Inductive couping seems to be a good solution (or the conductive coupling better? I haven't got reference.)

The transceivers antenna is a lambda/4 rod ( 80 mm )

1. How can I calculate which coil dimensions would resonate out the maximal power?

2. The coil end will be a differenital (push-pull) output. Thus I can't use coaxial cabel as a transport line. --> a. feed a symetrical dipol directly by the coil or
b. use of a balun transformer?

In case of "instant dipole sticking" I can't transport the signal to (for instance) higher positined antennas.

EDA tools also welcome!
Bye!
Thanks a lot!
Z.

 

[dz99]

OK, but I don't know HFSS yet. Maybe I will.

Any other ideas?

Some guys told me, that forget it! You can't manage that! Losses will be eat up the tiny 0.5W @ 446 MHz. It's true, or can be achived good efficiency with (narrow band) inductive coupling at this freq?

Bye!
Z.

 

[vfone]

In a conducted connection the loss is insignificant, when inductive coupling introduce some loss, and also is bandwidth limited.

 

[dz99]

Than first I have to plan a coil (around the ant) which is resonant @446 MHz.
Planing with, I don't know what. Maybe simple jwL calculations, and then inductance calc. I will see after the formulas!

Then measureing it with a VNA is getting complicated...
Considering that tha VNA's input is assymetrical (let mesure S11), and designed for 50 ohm. So I'm stucked with my differential coil, which has unknow impedance.

:|

 

[bingjiang99]

Inductance calculation will not give you the correct answer for sure, although it will give you some ideas. (This works in low frequency, such as 10 MHz) The truth is simple. The trace also introduces the parasatic capacitance, which may contribute a lot to the impedance.

It is better to simulate it with EM software. VNA will predict how to tune your loop.

Good luck.

Than first I have to plan a coil (around the ant) which is resonant @446 MHz.
Planing with, I don't know what. Maybe simple jwL calculations, and then inductance calc. I will see after the formulas!

Then measureing it with a VNA is getting complicated...
Considering that tha VNA's input is assymetrical (let mesure S11), and designed for 50 ohm. So I'm stucked with my differential coil, which has unknow impedance.

:|