Hey all,

I read about people using their sound card to catch transmissions
from dedicated senders such as SAQ by just hooking a roll of wire to the
mic-in and apparently finding some success in this. This got my wondering,
what aside from laws and fines is stopping me from hooking my 80W
stereo amp up to some sort of antenna for global transmission fun?
Somebody must have thought of this before...

--
Nos

Ceriel Nosforit wrote:
I read about people using their sound card to catch transmissions
from dedicated senders such as SAQ by just hooking a roll of wire to the
mic-in and apparently finding some success in this. This got my wondering,
what aside from laws and fines is stopping me from hooking my 80W
stereo amp up to some sort of antenna for global transmission fun?
Somebody must have thought of this before...


It's cheaper to use your car alternator as an LO.
Upconvert by using the transmission as a mixer
and the gear shift knob as a band selector.
FM by riding up or down steep hills in a 2-cylinder Citroen.

On Fri, 29 Sep 2006 14:38:17 +0000, Max Headroom wrote:

Ceriel Nosforit wrote:

snip

It's cheaper to use your car alternator as an LO.
Upconvert by using the transmission as a mixer
and the gear shift knob as a band selector.
FM by riding up or down steep hills in a 2-cylinder Citroen.

Now that would be something. DX licence or driver's licence? Hehe.

Too bad I don't have a car.

--
Nos

ORIGINAL MESSAGE:

On Fri, 29 Sep 2006 16:05:21 +0300, Ceriel Nosforit
wrote:

what aside from laws and fines is stopping me from hooking my 80W
stereo amp up to some sort of antenna for global transmission fun?

------------ REPLY FOLLOWS ------------

What is stopping you?

Well, the laws of physics for one, but you're welcome to give it a
try. You'll find enforcement of those laws is pretty strict. :-)

Bill, W6WRT

On Fri, 29 Sep 2006 08:36:12 -0700, Bill Turner wrote:

ORIGINAL MESSAGE:

On Fri, 29 Sep 2006 16:05:21 +0300, Ceriel Nosforit
wrote:

what aside from laws and fines is stopping me from hooking my 80W
stereo amp up to some sort of antenna for global transmission fun?

------------ REPLY FOLLOWS ------------

What is stopping you?

Well, the laws of physics for one, but you're welcome to give it a
try. You'll find enforcement of those laws is pretty strict. :-)

Bill, W6WRT

Hehe. Well yeah, I figured as much, but why doesn't it work? Too high
impendance? Why is that something the amp can't handle, if I maybe resist
the urge to crank it up to eleven?

I'm approaching the issue from the engineering perspective, but I don't
have much knowledge in this particular field. If you can enlighten me I'd
be much obliged.

--
Nos

Ceriel Nosforit wrote:

Hehe. Well yeah, I figured as much, but why doesn't it work? Too high
impendance? Why is that something the amp can't handle, if I maybe resist
the urge to crank it up to eleven?

I'm approaching the issue from the engineering perspective, but I don't
have much knowledge in this particular field. If you can enlighten me I'd
be much obliged.

Engineering is the application of physics. An "engineering perspective"
is one that starts from knowledge of the basic physical principles
involved, and uses mathematics along with that knowledge to produce a
design or solve a problem. I've seen no evidence of either in your
approach. Whatever you're doing, it's certainly not engineering.

The main problem with what you propose is that the electromagnetic field
you create with the amplifier will be small to begin with, and it will
be attenuated rapidly with distance for a number of physical reasons.
But don't take my word for it. Crank that dude up, and don't stop at 11.
Broadcast your telephone number and wait for the phone to ring.

Roy Lewallen, P.E., W7EL

On Fri, 29 Sep 2006 14:40:26 -0700, Roy Lewallen wrote:

Ceriel Nosforit wrote:

Hehe. Well yeah, I figured as much, but why doesn't it work? Too high
impendance? Why is that something the amp can't handle, if I maybe resist
the urge to crank it up to eleven?

I'm approaching the issue from the engineering perspective, but I don't
have much knowledge in this particular field. If you can enlighten me I'd
be much obliged.

Engineering is the application of physics. An "engineering perspective"
is one that starts from knowledge of the basic physical principles
involved, and uses mathematics along with that knowledge to produce a
design or solve a problem. I've seen no evidence of either in your
approach. Whatever you're doing, it's certainly not engineering.

The main problem with what you propose is that the electromagnetic field
you create with the amplifier will be small to begin with, and it will
be attenuated rapidly with distance for a number of physical reasons.
But don't take my word for it. Crank that dude up, and don't stop at 11.
Broadcast your telephone number and wait for the phone to ring.

Roy Lewallen, P.E., W7EL

Hm. I was a student of IT on a polytechnic... The basic state of mind one
needed there was that we don't need to know all the facts by heart, but we
must know where to find them.
In this case through a few degrees of separation I had specs which say
that it doesn't need to be efficient; it only needs to work. Then when I
have it working I can begin identifying bottlenecks and come up with ways
to widen them.

Good info on magnetic field strength there, thank you. It gives me a good
idea of where to start looking and comparing.

I'm not going to experiment just yet since I'm not a radio amateur, though
I'm vying for a licence. The radio-regulatory authorities here in
Finland don't have much to do, so I'm not going to give them a reason to
hunt me down. )

--
Nos

"Ceriel Nosforit" wrote in message
news
Hehe. Well yeah, I figured as much, but why doesn't it work? Too high
impendance? Why is that something the amp can't handle, if I maybe resist
the urge to crank it up to eleven?

No. The problem is that wavelength of a, say, 10kHz signal is 3km in free
space. You need to have an antenna that's a decent fraction of that length
for the antenna to look "distributed" enough (that is, the phase of your 10kHz
signal at the far end of the wire is significantly different than that at the
near end) in your to start getting any radiation. You can go through the math
for all this -- look up the input impedance of a short dipole on Google -- and
you'll find that the radiation resistance of a reasonable length speaker wire
is probably going to be in the milliohms, yet the finite (real) resistance of
the wire is going to be 10-1000 times as much, and the reactance will be as
well. Hence, all three parameters are against you: The high reactance will
keep the amps from being able to put much power into the cable in the first
place, and of what does get there, the vast majority will be eaten up as heat
rather than radiating.

To make matching tenable (so that you can actually get power into the cable),
you need a *very* long wire. To make things efficient, you need low loss
conductors -- nice, thick metal rods. Hence, doing a good job becomes rather
spendy, and thus you don't see that many people outside of the military
building VLF systems.

I think I'd almost suggest trying something like a 1.3GHz moonbounce system
prior to building your own VLF transmitter...

On Fri, 29 Sep 2006 16:05:21 +0300, Ceriel Nosforit
wrote:

Hey all,

I read about people using their sound card to catch transmissions
from dedicated senders such as SAQ by just hooking a roll of wire to the
mic-in and apparently finding some success in this. This got my wondering,
what aside from laws and fines is stopping me from hooking my 80W
stereo amp up to some sort of antenna for global transmission fun?
Somebody must have thought of this before...

At least previously, the frequency tables started at 9 kHz, so
anything below that would not cause any interference to any other
service.

However, the problem with VLF is that any practical antenna is going
to be very short compared to wavelength and since the radiation
resistance is proportional to the square of frequency for antennas
well below 1/4 wavelength, most of the power injected into an antenna
is going to be dissipated in resistive losses.

At the LF aeronautical beacon band with 90 m antennas, the antenna
efficiency based on measurements flown around these beacons seems to
be about 1 %. In Europe, the maximum _radiated_ power limit on the 135
kHz amateur radio band is 1 W, but generating that kind of radiated
power with reasonable sized antennas (30 m) would require at least 1
kW of transmitter power, indicating that the practical antenna
efficiency is about 0.1 %. At 13 kHz, the efficiency would be about
0.001 %.

The near field distance for a simple antenna extends to about 1/6
wavelength, so at VLF, the practical communication range for amateur
communication systems would be well within the near field.

Since you are apparently from Finland and since the Finnish
telecommunication law only grants the jurisdiction to the
telecommunication authorities for "freely propagating" electromagnetic
radiation, my interpretation of the law is that it does not cover any
near field i.e. magnetic or electrostatic communication systems, in
which the near field communication systems work.

Of course, if you are able to generate huge magnetic or electric
fields that cause interference to other systems, this may cause
problems to you.

But otherwise, go ahead with your experiments, but unfortunately the
laws of physics will hit you sooner or later :-).

Paul OH3LWR

On Fri, 29 Sep 2006 17:13:28 -0700, "Joel Kolstad"
wrote:

No. The problem is that wavelength of a, say, 10kHz signal is 3km in free
space.

This must be a typo, since the free space wavelength at 10 kHz is 30
km.

Paul OH3LWR