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'RF transceivers'
1999\09\14@042540 by Bill Kichman

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I need to transmit small bursts of repetetive digital data via RF (or
otherwise wireless)  in an automotive type environment and receive same via
a separate receiver approximately 6 feet away.  The method must be very
reliable and made so as not to cause or receive interference from sources
external  to the circuit.
Can anybody provide some feedback as  to how one might (as simply as
possible) design such a connection?
Any and all help is greatly appreciated.

Bill Kichman
Cornwall, PA USA

1999\09\14@084551 by Art Allen, KY1K

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At 04:22 AM 09/14/1999 -0400, you wrote:
>I need to transmit small bursts of repetetive digital data via RF (or
>otherwise wireless)  in an automotive type environment and receive same via
>a separate receiver approximately 6 feet away.  The method must be very
>reliable and made so as not to cause or receive interference from sources
>external  to the circuit.
>Can anybody provide some feedback as  to how one might (as simply as
>possible) design such a connection?
>Any and all help is greatly appreciated.


For short range (less than 10 or 12 feet), you can use poor mans fiber
optic cable. It sounds bad at first, but it DOES WORK, and the best part is
that you don't need special RF chips, antennas, it's interference free and
can be contained in the existing enclosures. It's also RUGGED as Hell,
easily concealed and cheap!

Transmitters are simple LED's and receivers are photodiodes. The fiber
optic cable is 20 to 40 pound test fish line, make sure you get the clear
kind and make the ends with a razor sharp blade in a singe cut.

I am currently using this for communication between my keyer and my ham
rig. This Fall, I hope to convert my wall mounted t-stat to a similar
system to avoid an rfi problem when we transmit on the ham radio at high
power.

If you need more range or a higher data rate, use a laser diode, find the
focal point of the collimating optics and put your fiber optic cable there.
I don't know the range of this setup, but would guess it to be 1km for
narrowband and 100 feet or more for medium bandwidth. I HAVE NOT tried the
laser transmitter myself, but the sub mini surface mount (RED) LED's work
like a champ.

Snag an LED out of a late model piece of consumer electronic scrap gear and
look for the sub mini smt type led's (the kind with the flat leads coming
out of the sides of the package 180 degrees apart). While it's still
mounted on the pcb, file down till you almost hit the die--making a flat
face on the front of the led package. Now, use some Comet or abrasive
containing toothpaste and polish the front surface on a piece of glass.
When the LED has a flat and smooth face, you can attach the fiber at point
blank range. I like to attach the cable to a small chunk of plastic with a
pin hole in it, the plastic needs to be .25 inches thick and snug when the
line is forced into the hole. The plastic is the only thing that keeps the
cable at right angles to the LED's active area. Glue the led so that it
shines through the pin hole. After the glue sets, you can slide the fiber
optic cable into the hole until it butts up against the flat surface of the
LED. After the assy is glued and tested, be sure to coat the entire assy
with something that doesn't let stray light in (any stray light that gets
into either end of the cable is interference and degrages the signal to
noise ratio).

Before hanging the messenger or having him committed, try sighting down a
piece of fish line with the the far end close to a light and you will
easily observe the light transmission capability of the poor mans fiber
optic cable.

OK, got my shields up-

Regards,

Art



PS: Note that if you only need 6 feet, and IF you can arrange for line of
sight between the RX and TX, you can use an IR LED and transmit through the
air.

1999\09\14@141540 by William K. Borsum

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At 08:45 AM 9/14/99 -0400, you wrote:
{Quote hidden}

Motorolla used to make a really nice, inexpensive pair of
transmitter.receivers with the connector built in--used CHEAP plastic fiber
cable.
Mouse and digikey both are selling experimenters kits using these parts.
Great way to experiment.  What they don't tell you is the Motorolla sold
off the business to someone else (Harris I think) and they are still being
made, but hard to find.  Contact me off list if you need a current source
and I'll see what I can dig up.
Suggest getting one of the kits first though.

Kelly


William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>

1999\09\14@203458 by Bill Kichman

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That's a great idea and the cost cannot be beat, but won't suit my
application.  My need is for anti-tampering of the receiver, that is, I
don't want an average user to "follow the wires" to detect its location.  I
will research some of the transceiver module leads to hopefully find a cost
effective solution.  Thanks again, this list is just amazing in the breadth
and availability of help.
Bill Kichman
Cornwall, PA USA
{Original Message removed}

1999\09\15@094904 by Art Allen, KY1K

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>What they don't tell you is the Motorolla sold
>off the business to someone else (Harris I think) and they are still being
>made, but hard to find.

The BAD NEWS is that HARRIS has been sold too-for now the old link to them
still works, it just connects you to the new owners site.

Bill, if you really need a stealthy wireless link, you can use free air
laser as long as you have line of sight. VCSEL laser diodes in plastic LED
type packages collimated to 2 degrees beamwidth are simple to drive
(constant current, no monitor diode needed), and best of all--VCSEL laser
diodes begin lasing at 4 ma. IR beams can be 'hidden' on the tx and rx ends
of the link by dark plastic (as your VCR has on it's front panel)-when you
scrap a junk vcr, ALWAYS SAVE the black plastic in front of the IR
recveiver module, same with some hand held remote control transmitters.
VCSEL laser diodes are ideal for moderate range free space laser comm ap
becasue the drivers are simple!

Second choice is the MICREL wireless chips, 300 mhz AM only and you only
need a ceramic resonator and a few outboard parts-they are cheap, use low
power and run at 3v Vcc. They are made for data transmission at up to 300
feet. Since you do not need 300 feet range, I'd use a smaller antenna on
each end to aid in the stealth factor.

If you need stealth, I strongly suggest encrypting data and making 'dummy'
transmissions for the purpose of concealing the legitimate data
transmissions. You don't need complicated encryption to keep the average
hacker type out:>:

Regards,

Art

1999\09\15@101358 by Harrison Cooper

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If Andy Warren was still on this list...he could offer plenty of advice.
Wonder where he is these days?

Anyway, there are still some rules from the FCC about what kind of data can
be transmitted without a license. Most of these modules are designed as
telemetry types, or remote controls. I've used the DVP modules and had
pretty good success, but I did have to add my own external dipole antenna.

There has been allot of activity on the list about RF links.  Take a look at
the archives and do a search on RF and see what you find.

1999\09\15@175804 by William K. Borsum

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At 09:05 AM 9/15/99 -0300, you wrote:
>Hello William,
>
>
>
>> Motorolla used to make a really nice, inexpensive pair of
>> transmitter.receivers with the connector built in--used CHEAP plastic
>fiber
>> cable.
>> Mouse and digikey both are selling experimenters kits using these parts.
>> Great way to experiment.  What they don't tell you is the Motorolla sold
>> off the business to someone else (Harris I think) and they are still being
>> made, but hard to find.  Contact me off list if you need a current source
>> and I'll see what I can dig up.
>> Suggest getting one of the kits first though.
>
>    I'm interested in this.

OK--first thing to do is order a demo kit from
       Mouser electronics <http://www.mouser.com>  Just went through the NEW mouser
catalog, and could not find the kits
                                               They may have discontinued them
       DIGIKEY <http://www.digikey.com>               FB104   $10  (simple--digital li
nk, 1 meter or
so--optic parts only No PCB)
                                               FB105   $17  (complete kit, all
parts including PCB, you assemble)

       I got the FB105--has everything I needed to experiment with.
       Digikey also has course kits, and other stuff up into the $100's.

The parts in the Kits were made by Motorola, and have been out of
production for many years.
The same parts are made now by SIEMENS, and you would want the SFH756 and
SFH551 transmitter / receiver pairs.

What I have NOT been able to find is a cheap source for the jacketed
PLASTIC fiber cable they use.

The nice thing about the POF (Plastic Optical Fiber) is that no special
treatment must be done to the ends of the cable--just cut with a good,
SHARP razor blade.

Please let me know if you find a source for the POF.  I am particularly
interested in PAIRS--two fibers together--sort of like ribbon cable.

kelly



William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<.....borsumKILLspamspam@spam@dascor.com> & <http://www.dascor.com>

1999\09\15@181119 by TIM

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if such cable was made in pairs how does one  measurue cross talk to verify
that the cables maintain signal integrity say ........one to one and not
somewhere they  happen to "be not so " .......just wondering?
{Original Message removed}

1999\09\15@234137 by William K. Borsum

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As with electrical  ribbon cable, the actual conductors were jacketed with
an "insulator"--in the case of optical fiber (of the plastic variety
anyway), the jacket was loaded with carbon black to make it opaque.  The
individual cables were either extruded as pairs inside a common opaque
jacket, or two separate cables were glued together somehow.
Kelly

At 06:09 PM 9/15/99 -0000, you wrote:
>if such cable was made in pairs how does one  measurue cross talk to verify
>that the cables maintain signal integrity say ........one to one and not
>somewhere they  happen to "be not so " .......just wondering?
>{Original Message removed}

1999\09\16@085515 by Harrison Cooper

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Check circuit specialists or Jameco as well for these kits.

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