Power Line Carrier Tx/Rx

Are the frequencies radiated as RF out put or transmitted over wire? What is the distance between substations?

For your guidance:

[PDF] Powerline Carrier (PLC) Communication Systems - KTH

That reference explores PLC for metro data carriage not for grid control telemetry. It specifically discounts the viability of FSK modulation in section 4.9 on page 45. (OP did say that it was an FSK system.)

Sorry mate, although it is an interesting dissertation I'll have to OT you on that one.

It is a signal transmitted via an overhead transmission line. The distance is 10-20 miles.

What is the bandwidth of your FSK TX signal ?

Distinguishing frequencies at a fraction of 1% difference? No problem at all!

If we take for a rough comparison channelized communications widely used in commercial, fire, police, radioamateur bands with 25kHz channel separation (not even the latest and greatest spec.) at 1000 MHz, that is 2,5x10^-5 separation. A common resonant quartz is markedly better than that, as a frequency establishing element. Better stabilized forms reach 10^-7 to 10^-8 in a stable fashion.

Taking 10^-7 quartz stability to 100kHz means, that with its help 0,01Hz frequency difference can be separated. Obviously, the circuit's realization has something to do with it too. That subiect is the whole area of frequency synthesizers.

They aren't close at all.

500Hz is loads of channel separation giving 250Hz channel bandwidth (without guard band) for each.

This is FSK telemetry not broadband data.

I found this ancient publication that explains the basics and details reasonably well.

I found something a little more contemporary where it states ( on page 2-8)that the channel separation can be as low as 500Hz providing 200Hz bandwidth for 100Hz shift on a unidirectional system.

There will be no issues with reflections if the line tuners are properly setup. That's why they are called tuners.

That's about all I can help you with unless you pony up with more specific information.

Thanks Wal; the RFL instruction manual had some of the values I was asking directly about.

On pages 2-7 and 2-8 it talks about the "minimal channel spacings". We have three transmitting devices all connected on one line operating at guard frequencies of 115.125, 115.250, and 114.875 kHz. The receive devices are programed at 115kHz, giving a 125Hz separation between signals. on 2-8 of the RFL manual it says that the nominal bandwidth is 200 Hz. Does this mean that each of those three signals should be at least 200 Hz apart? I just can't wrap my head around the resolution these terminals are capable of in regards to distinguishing what signal means what.

I just can't wrap my head around the resolution these terminals are capable of in regards to distinguishing what signal means what.

...and yet they are perfectly capable.

Sharp filtering is all it takes. This was sorted out way back in the days of analogue circuit multiplexing equipment. All packed in and very close and yet it worked.