Rs232 over long distance

[Sneaky-geek]

Hi Everyone,
Not using a pic.
But here is my problem.
A piece of test equipment needs to be located 175 feet from computer. Data rate is 115k baud which is fixed.
Any ideas as to what is needed to make this work?

TNX
Terry K9HA
sneaky-geek

[rmteo]

Look into http://en.wikipedia.org/wiki/EIA-485

EIA-485 (also known as TIA/EIA-485 or RS-485) enables the configuration of inexpensive local networks (http://en.wikipedia.org/wiki/Local_network) and multidrop communications links. It offers data transmission (http://en.wikipedia.org/wiki/Data_transmission) speeds of 35 Mbit/s (http://en.wikipedia.org/wiki/Bitrate) up to 10 m and 100 kbit/s (http://en.wikipedia.org/wiki/Bitrate) at 1200 m. Since it uses a differential (http://en.wikipedia.org/wiki/High-voltage_differential_signalling) balanced line (http://en.wikipedia.org/wiki/Balanced_line) over twisted pair (http://en.wikipedia.org/wiki/Twisted_pair) (like EIA-422 (http://en.wikipedia.org/wiki/EIA-422)), it can span relatively large distances (up to 4000 feet (http://en.wikipedia.org/wiki/Feet_%28unit%29) or just over 1200 meters).

[rmteo]

Get a pair of these http://www.serialcomm.com/serial_rs232_converters/rs232_to_rs485_converters/rs232_to_rs485_converter/rs232_to_rs485.product_general_info.aspx


http://www.serialcomm.com/images/products/rs232_to_rs485/con-485-pe9/CON-485-PE9_big.jpg

[Sneaky-geek]

Rmteo,
Thank you for such a speedy response!
Looks like it might work. The remote device is a Digital-vector watt meter.
It will be located with at the output end of a Harris Platinum I amplifier salvaged from a TV station that switched from analog to digital, These two units are about 35 feet below a pair of 5 element Yagis.
Me, I'm about 175 feet away at the operating location inside a chicken coop.

Before the contest, I guess that all of this has to be assembled and tested to see if there will be any problems caused by all the RF that will be generated.

Just one last question, it looks like that a shielded 2 conductor cable is all that would be needed!

Again, Thank you so much,
Terry K9HA,
Sneaky-geek

[dhouston]

Careful - the RS485 adapter is only half-duplex. You probably need full duplex. The latter is possible but you need different line drivers and more wires in the cable.

[Sneaky-geek]

Thanks Dave,
Will this one work? It appears to offer full duplex and is isolated, which help with all the RF floating around the site.

www.serialcomm.com/serial_rs232_converters/rs232_to_rs485_converters/externally_powered_rs232_to_4_wire_rs485_rs422_con verter/ext_rs232_to_4_wire_rs485_rs422.product_general_in fo.aspx (http://www.serialcomm.com/serial_rs232_converters/rs232_to_rs485_converters/externally_powered_rs232_to_4_wire_rs485_rs422_con verter/ext_rs232_to_4_wire_rs485_rs422.product_general_in fo.aspx)

Thank you again.
Terry K9HA
Sneaky-geek

[dhouston]

That should work but you should consider whether the opto-isolators are adequate if you have a lot of lightning. The datasheet says they offer 2500V isolation but that's not much where lightning is concerned. RS232 to Fiber Optics would offer much better isolation.

[Sneaky-geek]

Dave,
You are correct. That would eliminate both lightning and RF problems.
At the moment, the drawback is the cost. Fiber cable is kinda steep. This is unless there is a low cost (HEY, I'm a HAM and we are noted for being stingy) source for the cable.
This is the method I would love to use.
Maybe on E-day (no copyright infringement here!).

Again, my Thanks to All.

Terry K9HA
Sneaky-geek

[Charlie]

For the distance and frequencies you are talking, cheap plastic fiber optic cables would do fine. A quick search came up with this: http://fiberopticcables.stores.yahoo.net/mmdup625-stst.html You can probably do better by spending more time searching.

[Sneaky-geek]

Charlie,
I will give them a call later today.
Thank you for the link.

Terry K9HA
Sneaky-geek