RS232 Data over STL subcarrier?

Lazy J · Dec 17, 2012

I have a transmitter site that needs an RS232 data link for the remote control. We have a 950mhz STL (Moseley 6010) going to the transmitter and a 950mhz RPU return channel (Moseley 6010) coming back to the studio. I am looking for a simple, affordable solution to send and receive RS232 data via the STL/TSL subcarriers. I'm not really interested in IP-based solutions and there are no copper lines at the site, so phone lines are out. It's STL or nothing. Any ideas?

TomT · Dec 17, 2012

RS232 uses switched voltages to transmit data. Fine if there is a couple wires between the devices (typically transmit, receive, ground reference). Now, if you convert these signals to audio in some form, you can use a pair of 67 khz subcarriers (an uplink on the STL to the transmitter, and a downlink on your 950 return). The data transfer rate will be limited by the response of the subcarrier circuit.

Hmmm--this kind of sounds like a dial-up modem, does it not?

bradgoehl · Dec 17, 2012

If you have or could get the DSP's for your old Mosley units they traffic RS-232 data.

WNTIRadio · Dec 17, 2012

Those DSP units are easy to come by on eBay. Not only will you upgrade your STL in the process, you'll get the RS-232 signal.

Some kind of conversion to "audio frequencies" needs to be done to have a chance at making it work. The voltage swings for RS-232 are very large, doubtful there is anywhere near enough dynamic range to make it work without going digital.

grich · Dec 18, 2012

TomT said:
RS232 uses switched voltages to transmit data. Fine if there is a couple wires between the devices (typically transmit, receive, ground reference). Now, if you convert these signals to audio in some form, you can use a pair of 67 khz subcarriers (an uplink on the STL to the transmitter, and a downlink on your 950 return). The data transfer rate will be limited by the response of the subcarrier circuit.

Hmmm--this kind of sounds like a dial-up modem, does it not?

Actually, this sounds like a job for a pair of Multitech MT2834BL modems...they could be set up for four-wire leased lines, which would essentially be your situation with the subcarrier channels. Our company's modem of choice back in the old days with the Moseley remote controls.

WNTIRadio · Dec 18, 2012

I forgot about those modems!! One of my clients has 4 of them sitting on a shelf that used to be used with the Moseley 1600 remote controls.

local oscillator · Dec 18, 2012

I've used a Moseley Lanlink for the past several years with great results. Uses the 902-928 unlicensed band and diplexes easily into a 950 STL system. Your RPU wouldn't be needed.

Lazy J · Dec 18, 2012

grich said:
Actually, this sounds like a job for a pair of Multitech MT2834BL modems...they could be set up for four-wire leased lines, which would essentially be your situation with the subcarrier channels. Our company's modem of choice back in the old days with the Moseley remote controls.

Ok, you've piqued my interest! How do you get the modem on the the subcarrier frequency?

TomT · Dec 18, 2012

Subcarrier generators. For composite STL's use 67 or 92, for mono STL's Marti makes a subcarrier generator/decoder pair that runs at 39 KHZ.

Another option is a 450 RPU telemetry link--of course, bandwidth limited so slower data rate.

Or, if the path allows, unlicensed data links--up around 5 ghz as I recall--which would give a more reliable and faster data transfer rates.

special ed · Dec 23, 2012

I have seen an Armstrong unit that seems to be a clone of the DSP if you want something new.

or I can make you deal on a set of MRC16's LOL