anybody know of any VLF (3-30Khz) transcievers?

[Michael]

Hi - does anybody know of any VLF (3-30Khz, "Very Low Frequency")
transcievers? I would much prefer not to have to make one from scratch!
Thanks alot!

-Michael

 

[Michael]

Hi - does anybody know of any VLF (3-30Khz, "Very Low Frequency")
transcievers? I would much prefer not to have to make one from scratch!
Thanks alot!

-Michael

Oh I forgot to mention that this would be for underwater digital
communication. And size is *very* important - I need something as small as
possible. Thanks,

Michael

 

[Tim Wescott]

Oh I forgot to mention that this would be for underwater digital
communication. And size is *very* important - I need something as small as
possible. Thanks,

Michael

One 16-bit fixed point DSP with a built-in stereo CODEC should be pretty
small and simple.

Oh, but you'll need algorithms, too.

 

[John Popelish]

Oh I forgot to mention that this would be for underwater digital
communication. And size is *very* important - I need something as small as
possible. Thanks,

Why is size such an issue, since an effective antenna is going to need
to be at least as big as Rhode Island?

 

[Ken Smith]

Why is size such an issue, since an effective antenna is going to need
to be at least as big as Rhode Island?

It only needs to be a core about the size of a loaf of bread. A coil on a
core about 2 inches in diameter and 3 feet long will get you down to the
environmental noise.

 

[Michael]

Why is size such an issue, since an effective antenna is going to need
to be at least as big as Rhode Island?

Hrmm - I wasn't aware of this. I'm working on a fairly small underwater
mobile robotics platform - about a meter in length - and I'm trying to
design a backup communication system for it. VLF is what military
submarines use - so that seemed like the logical choice for me. Was I
mistaken?

-Michael

 

[Michael]

It only needs to be a core about the size of a loaf of bread. A coil
on a core about 2 inches in diameter and 3 feet long will get you down
to the environmental noise.

Could you possibly show me a picture of what this antenna design looks
like? I'm not exactly sure from your description - and I'd just like to see
if it would work with my current design. I hadn't really thought that the
antenna would be a problem!

-Michael

 

[Activ8]

^ transmitting

Hrmm - I wasn't aware of this. I'm working on a fairly small underwater
mobile robotics platform - about a meter in length - and I'm trying to
design a backup communication system for it. VLF is what military
submarines use - so that seemed like the logical choice for me. Was I
mistaken?

-Michael

No, not at all as long as that 1 m submersible can haul a big reel
of wire and a winch. Those rigs are used to alert a sub to do
something or come up for sat comm, in case ya didn't know.

 

[John Woodgate]

I read in sci.electronics.design that Michael <nleahcimathotmaildotcom@n

Hrmm - I wasn't aware of this. I'm working on a fairly small underwater
mobile robotics platform - about a meter in length - and I'm trying to
design a backup communication system for it. VLF is what military
submarines use - so that seemed like the logical choice for me. Was I
mistaken?

For ELF transmission, especially under water, you use **magnetic**
antennas for sending and receiving. Magnetic antennas are inductors -
coils, maybe with ferrite cores. A single coil makes a directional
antenna, with a figure-8 response. If you need omnidirectional sending
and receiving (as you probably do), you need to overcome the directional
effect. There are several ways of doing that, with varying complexity.

 

[Ken Smith]

Could you possibly show me a picture of what this antenna design looks
like? I'm not exactly sure from your description - and I'd just like to see
if it would work with my current design. I hadn't really thought that the
antenna would be a problem!

Try searching on Magnetotellurics. I can find a picture in electronic
form.

Basically, the core is a stack of sheets of Metglass with a very thin
plastic between sheets. Each sheet is about 3" by 36". Don't cut
yourself!

Onto this core many turns of finish wire are wound. Over this a insulator
layer is placed and then many-many-many turns of fine wire is wound. The
huge number of turns converts even lowish frequencies to modest impedances
for the input to an amplifier. The coil with merely many turns is a
feedback winding. The output of the amplifier drives this with a
current. This way the frequency responce of the whole thing is made
fairly flat. Modern systems like this outperform high temp. SQUIDs above
about 1Hz.

 

[Ken Smith]

For ELF transmission, especially under water, you use **magnetic**
antennas for sending and receiving. Magnetic antennas are inductors -
coils, maybe with ferrite cores. A single coil makes a directional

Metglass is claimed to work better than ferrite. Both have Barkhousen
noise. Since, we can assume the sub isn't turning quickly in a magnetic
field, the Barkhousen shouldn't be too bad for either core. Just remember
to let you coil age like fine wine for a day or so after you make
it. Mechanical stresses make Barkhousen worse.

antenna, with a figure-8 response. If you need omnidirectional sending
and receiving (as you probably do), you need to overcome the directional

I disagree.

I think we can safely assume the submarine is more down than anything else
from the control transmitter. In this case a vertical core is good
enough.

 

[Ken Smith]

Try searching on Magnetotellurics. I can find a picture in electronic

.........................................^^^
Make that "can't"
Opps

 

[Kevin R]

Hi - does anybody know of any VLF (3-30Khz, "Very Low Frequency")
transcievers? I would much prefer not to have to make one from scratch!
Thanks alot!

-Michael

There is a radio set designed for cavers/pot holers which is vlf
There was an article about it in New Electronics a few months back

maybe have a look around some caving web sites.
and here's a PDF about it
http://www.sat.dundee.ac.uk/~arb/heyphone/radcom-january-2002.pdf

 

[John Woodgate]

I read in sci.electronics.design that Ken Smith <[email protected]>

Basically, the core is a stack of sheets of Metglass with a very thin
plastic between sheets. Each sheet is about 3" by 36". Don't cut
yourself!

Onto this core many turns of finish wire are wound. Over this a insulator
layer is placed and then many-many-many turns of fine wire is wound. The
huge number of turns converts even lowish frequencies to modest impedances
for the input to an amplifier. The coil with merely many turns is a
feedback winding. The output of the amplifier drives this with a
current. This way the frequency responce of the whole thing is made
fairly flat. Modern systems like this outperform high temp. SQUIDs above
about 1Hz.

This is a cost-no-object solution. And you make the frequency response
flat by equalization at the receiver, where it's rather easy.

What range do you want?