Range versus frequency for a transmitting ferrite loopstick ?

[Externet]

Hi.
What performance difference is to expect using a ferrite rod or an iron rod as wound transmitting antenna under 100 KHz ?

Would ranges be way different at a given -say 1 Watt- TX power, or not of major concern to reach 100 m distance?

 

[Externet]

Rephrasing... Would a <100KHz transmitting ferrite loopstick antenna reach farther if the core is replaced with soft iron ?

The permeability is much higher for pure laminated soft annealed iron :

----> https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

 

[FvM]

Increasing the permeability over a certain value (e.g. 500) doesn't effectively increase the sensitivity. On the other hand, a soft iron core must have very fine lamination (e.g. < 50 µm) to work at 100 kHz.

 

[schmitt trigger]

What the table does not show are the core losses.
Which I believe would be more significant than the relative perm.

 

[Externet]

A ferrite transmitting loopstick antenna will have a bigger or smaller range if the signal uses a 100KHz carrier frequency or if the modulation only is applied to the coil ?
In other words; which same power signal will propagate farther; feeding only audio range to the loopstick versus feeding audio modulated 100KHz carrier ?
I suppose also depends on the attenuation of the propagation medium. Is that right ?

 

[BradtheRad]

I've looked at articles telling how to receive EM waves in the audio spectrum. The atmosphere produces interesting sounds (eg., whistlers). These can be detected at long distances. The antenna needs to be large, such as a length of wire wrapping around an entire room.

In view of that I imagine it implies a transmitting antenna needs to be large. It sounds as though your transmitting antenna is a few inches long, so it's an advantage for the frequency to be high.

 

[Externet]

Thanks, BradtheRad for responding to this apparently weird unusual topic and perhaps poorly worded.

The plain ferrite loopstick would be as you may imagine, about 10cm long, 1cm diam. The planned transmitting power around only 1 Watt. The expected range hopefully over 10 metres, ideally 50 metres, to be received by another loopstick. It is not about distant communication. And ferrite saturation at 1 W will have to be watched.

With these humble specifications, I wonder if a 1 Watt 100KHz carrier modulated with voice audio fed to the loopstick coil is needed,
or if direct 1 Watt voice audio -no carrier- fed to the loopstick coil would produce a not-too-different transmission range.
Weird question, agreed, but am not crazy... yet. 8-O

Like asking if 100KHz will have much more propagation range than a 1KHz signal, both at same 1 W transmission power, or would not be 'that' much.

 

[FvM]

Using modulated 100 kHz carrier gives a certain chance to achieve 10 to 50 m range, it's about to impossible for non-modulated audio signal.

The problem is related to "transmitting power". Actually, a small coil, with or without ferrite core transmits only an infinitesimal fraction of the 1 W 100 kHz generator power to the far field (guess < 1 µW), most of it will be dissipated in the coil. At audio frequencies, transmitted power is much smaller.

 

[Warpspeed]

I've looked at articles telling how to receive EM waves in the audio spectrum. The atmosphere produces interesting sounds (eg., whistlers). These can be detected at long distances. The antenna needs to be large, such as a length of wire wrapping around an entire room.

In view of that I imagine it implies a transmitting antenna needs to be large. It sounds as though your transmitting antenna is a few inches long, so it's an advantage for the frequency to be high.

Yes I agree, this is the way to go. Its only near field magnetic coupling, not electromagnetic propagation.
The larger your coil physically, the better it will both transmit and receive.

The problem with using a ferrite or iron rod as a transmitter is that the magnetic field will not want to leave the rod.

A concentrating rod will work much better as a receiver, because it will concentrate the surrounding flux through the coil.

Probably the optimum arrangement would be to surround a very large area with a multi turn loop. Then use a flux concentrating rod in the receive coil that works pretty much within the area enclosed by the large loop.

 

[FvM]

AM systems in the LF band (e.g. 50 to 130 kHz) have been used for multi channel speech transmission at times when UHF systems weren't available, e.g. in simultaneous interpreting equipment. A single loop around the room was pretty sufficient, or single or multiple eight shape to cover a large area. Voice quality was telephone-like due to small bandwidth.