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Video Transmitter/Receiver question - radio license question

Hello,
I am installing a video security system at the business where I work.
The cameras are mounted in enclosures recessed into the ceiling. I
have minimal access to the video output cable on the camera when the
camera is mounted in the enclosure.

This makes it sort of difficult to position the camera, set the zoom,
and adjust the focus--I can't connect a local video monitor to allow me
to see what the camera is actually viewing. In order to solve this
problem, I have decided to buy a video transmitter and connect this to
the output of my video switcher in the electronics room (quite a
distance from the many cameras). I would then mount the transmitter
out in the main building amid the cameras. I would then carry a
receiver and portable video monitor to use for camera adjustments. I
wouldn't use it very much--maybe a few hours every few months. There
are walls inside the building that the signal would need to penetrate
plus it would need to penetrate the roof for adjustment of outdoor
parking lot cameras.

The question I have relates to the video transmitter/receiver link: I
have found on eBay, and Froogle transmitter/receiver pairs that appear
to be made in China. I have read that these units are probably illegal
(too much power) to use in the US without a license. I have also read
that they are cheaply made and that they may stray outside their
frequency bands. I don't know anything about these items-maybe
someone has had some direct experience with them. Maybe someone has
another suggestion for a transmitter/receiver pair.

I really don't know how much transmitter power I would need to access
all the areas of my building. The building is 150 ft by 150 ft with
concrete tilt up walls on the four sides. The internal walls are
constructed using 2x4s with sheet rock covering. There is lots of
fluorescent lighting throughout the building.

I have been thinking about using a 1.2 GHz transmitter/receiver pair.
This seems like a good frequency since it won't conflict with 2.4 GHz
portable phones, and WiFi. Does this seem like a good choice?

My intent here is to be legal though not fanatical. I do understand
that amateur licenses are not too difficult to get (I do have an EE
degree but I never studied radio transmission-though I am
interested). If I did get a license, I could operate more powerful
transmitters-though it is hard for me to know if this is overkill.

Some suggestions from knowledgeable individuals would be appreciated.

Thanks,
Greg Laird
 
My suggestion would be for you to investigate spread spectrum wireless
technology, where no license is required, and it can bounce a video
signal clear across Boston where it is extensively used on television
monitoring of the traffic flow on our Central Artery and Tunnel system.

When we built the CA&T, spread spectrum equipment was quite expensive,
but today that same technology is available dirt cheap.

Harry C.
 
Hi Harry,
Thanks for your suggestion--which I think is a good one. I have looked
around on the web and found lots of spread spectrum
transmitter/receiver devices. I can't seem to find any that are
designed for ntsc video--they do rs232, ethernet, various other serial
formats. I have looked around for a ntsc to serial converter and then
a serial to ntsc for the other end. I haven't been able to find such
an item--though I would imagine it would be common.

Do you have any pointers to spread spectrum video tranceivers, or video
to serial encoders/decoders?

Thanks again for your help,
Greg Laird
 
J

JANA

Jan 1, 1970
0
I myself have never seen spread spectrum video transmitter devices. Real
time video needs a lot of bandwidth and power dispersion.

You will not really know if the system you want will do the job without
testing it. High frequencies can easily be blocked by walls, depending on
their thickness and required distance. If the unit has high enough power, is
should be able to penetrate a near by wall.

As for license requirements, anything that can transmit a signal through the
air, and has a rating over the legal limit, is subject to have an operation
permit. For any device that can transmit an RF signal through the air,
requires to meet very strict standards. If the signal interferes with
emergency or essential services in the area, the user will be held
responsible.

In your case, if your building is in an industrial area, and if you are
going to only use it for a short period of time once in a while, there is
probably very little chance of having any type of problem to use a small RF
transmission device. As for the FCC or DOC, depending where you are, they
usually will only respond if there is a complaint.


--

JANA
_____


Hi Harry,
Thanks for your suggestion--which I think is a good one. I have looked
around on the web and found lots of spread spectrum
transmitter/receiver devices. I can't seem to find any that are
designed for ntsc video--they do rs232, ethernet, various other serial
formats. I have looked around for a ntsc to serial converter and then
a serial to ntsc for the other end. I haven't been able to find such
an item--though I would imagine it would be common.

Do you have any pointers to spread spectrum video tranceivers, or video
to serial encoders/decoders?

Thanks again for your help,
Greg Laird
 
Jason, I was simply posting what my experience is, and not why spread
spectrum is now being widely uses for video transmissions.

I really am not very interested in where and how the video originates,
only in its transmission. The advantages of spread spectrum include
virtual elimination of multipath effects (which was a real problem in
the early 420-Mhz amateur TV days), and license free communication.

It's honestly a hard concept for a non-engineer to grasp, since it
depends on spectral dispersion of the signal in a pre-assigned
statistical manner, which makes for great communication at high
bandwiths, and is virtually undetectable unless you have receiving
equipment that has the same frequency shifting key and algorithm as the
transmitter. On top of this, a 5-mile link range is relatively easy to
achive, and inexpensively. This makes it the choice of most new highway
surveilance video systems and many remote control applications.

Harry C.
 
Hello,
I am installing a video security system at the business where I work.
[...]

These are all good suggestions. I did spend some time looking around
for a spread-spectrum wireless video transmitter/receiver and had no
luck. As JANA said these sorts of items are hard to find so I have
given up on this approach. I do like the idea though.

Jansen's suggestion is also interesting. I do have a wireless network
in the building. I looked at PC video capture cards and have found
quite a few. Some issues with this approach--it was not clear to me
what sort of software I would have to run on my Linux sytem to source
the video frames over the wireless network. Then, what would I have to
run on my laptop to view the frames.

Also, I am sort of uncomfortable about taking my laptop to the top of a
ladder for camera adjustments--I imagine that I would drop it for sure!
I did think about finding some little cheap PDA to view images with,
but I don't know exactly what to look for.

So, now I am back to my origional idea of using a simple
transmitter/receiver comination like the ones sold on eBay. I have a
small NTSC LCD video monitor to use for viewing. JANA is correct, my
building is in an industrial area and I will be using the transmitter
for short periods of time infrequently. If I put the antenna indoors,
there probably won't be that much radiation outside the building--so I
probably won't be bothering anyone.

The question I now have is what frequency would be a good choice? I
have been thinking about a 1.2 GHz frequency so I won't bother portable
phones or WiFi. Is this a good choice? How about power--1 Watt, 1.5
Watts?

Best to you,
Greg Laird
 
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