70kHZ transmitter

[WM6]

Originally Posted by Geo

Hi WM6. I am interesting for the second case. Frequency will be 100Khz so not so good for audio transformer. Ferrite core maybe is a solution!!!!. I want to have a strong signal at distance of 10...30m far from antenna so i believe that there is not need for high power.
2...3 watts maybe is enough

Regards

Agree. Ferrite toroid can be proper solution. As proposed, depend on amplifier output impedance (usually between 4-8 Ohms) you wind primary first with resistance equal (or a little more) to tech. spec. for speaker driven by amplifier, then test secondary first by 10 turns and measure peek-to-peak voltage at about 50% of amplifier power. Out of results you can calculate total secondary turns to about 50 - 60V pp no more.

As I say, I prefer air cored coil antenna (unshielded of course), but for distances of 10-30m ferrite cored antenna can be usable too.

Proper distance from detecting place is achieved when antenna polarization (changing orientation of antenna in different directions) can give you very clear differences in signal strength on field strength meter (receiver).