# Extreme Low Frequency Project

#### fsoender

Joined Dec 10, 2015
26
Hi,

I'm looking into to start a low frequency transmitter project. I'm not an expert in electronic circuits, but I do get most
I need help with how a transceiver with H-bridge and coil work or show examples. There is not much on the net to find.
Transmitting distance would be approx. 4-5 meters.
I want it to send "1" at 12Hz and "0" at 9 Hz.

I will use FSK with a ATmega microprocessor.

Can anyone help me out with ideas or samples?

#### GopherT

Joined Nov 23, 2012
8,009
Hi,

I'm looking into to start a low frequency transmitter project. I'm not an expert in electronic circuits, but I do get most
I need help with how a transceiver with H-bridge and coil work or show examples. There is not much on the net to find.
Transmitting distance would be approx. 4-5 meters.
I want it to send "1" at 12Hz and "0" at 9 Hz.

I will use FSK with a ATmega microprocessor.

Can anyone help me out with ideas or samples?
Ha! What size antenna do you plan to use?

If something like this was practical, it would be done on a regular basis. Since it is not, why don't you explain your end goal - something like: how could I transmit a logical 1 and logical 0 over a distance of 4 to 5 meters.

Also, you could tell us something about why 9 and 12 Hz are important to your design.

Note: sending a frequency 5x higher is very difficult. Even when an antenna is twisted through your house at 50 or 60Hz with huge currents as your stove turns on or off results in only a fairly modest signal - try to build an battery powered amplifier for the 60 Hz emitted by the mains power in your house.

#### kubeek

Joined Sep 20, 2005
5,795
What made you choose the extremely low frequencies?

#### fsoender

Joined Dec 10, 2015
26
Ha! What size antenna do you plan to use?

If something like this was practical, it would be done on a regular basis. Since it is not, why don't you explain your end goal - something like: how could I transmit a logical 1 and logical 0 over a distance of 4 to 5 meters.

Also, you could tell us something about why 9 and 12 Hz are important to your design.

Note: sending a frequency 5x higher is very difficult. Even when an antenna is twisted through your house at 50 or 60Hz with huge currents as your stove turns on or off results in only a fairly modest signal - try to build an battery powered amplifier for the 60 Hz emitted by the mains power in your house.

I just picked the frequencies, can be anything low. It have to be low frequency since I want to penetrate 30mm steel.
Ive seen it been done, coils are not that big, approx. 40cm long and 5cm dia.

#### fsoender

Joined Dec 10, 2015
26
What made you choose the extremely low frequencies?

To be able to penetrate steel

#### #12

Joined Nov 30, 2010
18,224
Ive seen it been done,
I think you should tell us where you saw somebody transmit 10 Hz through 30 mm of steel with coils smaller than a fist.

#### GopherT

Joined Nov 23, 2012
8,009
I think you should tell us where you saw somebody transmit 10 Hz through 30 mm of steel with coils smaller than a fist.
If it were possible, many issues with a submarine' inherent Faraday cage could be overcome and many advantages of a submarine's inherent Faraday cage could be defeated. There is a guy at the Navy Research lab named Joe, he will want to talk to the OP if he can do this.

#### Lestraveled

Joined May 19, 2014
1,946
I think you should tell us where you saw somebody transmit 10 Hz through 30 mm of steel with coils smaller than a fist.
Sub woofer??

#### GopherT

Joined Nov 23, 2012
8,009

#### Papabravo

Joined Feb 24, 2006
21,225
Am efficient half-wave dipole antenna at 12 Hz would be about 7,767 miles in length. That would not be possible in the continental US, but maybe you could interest Mr. Putin in the project. OOPS -- it is only 6,600 miles from Europe to the Asian Pacific, so I guess that won't work either. What do you suppose will be the IR losses in such an antenna? Hmm...10 AWG is about 1 Ohm per 1000 feet, so that's only 41 KΩ. As you can probably surmise there are technical challenges that just may be out of reach.

#### fsoender

Joined Dec 10, 2015
26
I think you should tell us where you saw somebody transmit 10 Hz through 30 mm of steel with coils smaller than a fist.
There is many applications where this is used, but it's not a fist size. I said approx 40cm long and 5cm dia.

#### #12

Joined Nov 30, 2010
18,224
There is many applications where this is used, but it's not a fist size. I said approx 40cm long and 5cm dia.
Ah yes. Much better to point out my mistake than to answer the question.

#### Papabravo

Joined Feb 24, 2006
21,225
I'm curious about why you would want to use an H-bridge to drive your coil. I don't think I've ever seen an RF design do that.

#### GopherT

Joined Nov 23, 2012
8,009
There is many applications where this is used, but it's not a fist size. I said approx 40cm long and 5cm dia.
Ok, I believe a coil that size will work. But, it would have to be more of a solenoid instead of a transmitter. A 16" x 2" solenoid should be able to ring a plate of 1 1/4" steel like a bell.

#### Papabravo

Joined Feb 24, 2006
21,225
Ah yes. Much better to point out my mistake than to answer the question.
Hope you're not losing your sharp edge there, my friend.

#12

#### GopherT

Joined Nov 23, 2012
8,009
I'm curious about why you would want to use an H-bridge to drive your coil. I don't think I've ever seen an RF design do that.
At 9 Hz, he could get a monkey to turn a potentiometer back and forth to generate his signal.

#### #12

Joined Nov 30, 2010
18,224
Hope you're not losing your sharp edge there, my friend.
Meh. I make misteaks. Metric measurement is a second language to me.

#### Alec_t

Joined Sep 17, 2013
14,317
There is many applications where this is used
Can you post links to a few?

#### Kermit2

Joined Feb 5, 2010
4,162