10 HSM100s How much power?

[mwaite]

Eliminate the power source as the problem: Does this unit work on batteries correctly? The voltage is fine, so if it works on batteries then as suggested it's likely noise. You could run a coax cable to power this unit, just ground both ends, that should eliminate the noise.

[reidfo]

Noise can cause problems in either AC or DC circuits. If you were to look at a "clean" DC source on a scope it would appear as a straight line. A noisy source would be spiky and look distorted. Clean AC power looks like a perfect sine wave.

In many DC circuits (especially those designed to run off of batteries) there is little to no filtering being done on the power. Many (most?) designers assume battery power will always be clean. Same goes for devices designed to be USB powered since the USB power supply presumably does the filtering.

[Koviak]

In case of noise, previously mentioned, you guys could consider an electrolytic capacitor inside the battery compartment of each unit. 100 microfarad should be enough.

I just wanted to report that it looks as if this trick has fixed my problems. Thanks to everyone who has contributed. - Josh

[Wadenut]

I just wanted to report that it looks as if this trick has fixed my problems. Thanks to everyone who has contributed. - Josh

I suspect with that long run there would be a lot of 60Hz induced onto the power supply from the A/C wiring in the house.
Reid is right; these devices are designed to be supplied with a battery and probably don't have any built in filtering, which is what you've just added.
Using a twisted pair cable next time would help too, but that's another chapter.
Glad the cap worked for you though.

[Koviak]

All my alarm wires are 4 conductor twisted pairs, but the lines are laying across several AC lines. That is why when you mentioned "interference" my ears immediately perked. It just made sense. When my network finishes re-optimizing I will have a complete picture. - Josh