A customer asked why their corded phone still worked during last week’s outage — central offices feed about −48 VDC on copper and kick about 90 VAC at about 20 Hz to ring, all off battery banks, so dial tone survives when the grid doesn’t. What other legacy quirks are you still seeing that help or hurt connectivity in the field?
Had an ADSL line that wouldn’t hold sync until the carrier pulled the legacy load coils on the loop — those voice‑era inductors kill anything above a few kHz; once lifted, SNR jumped from about 3 dB to 11 dB (Loading coil - Wikipedia)… Anyone else still finding coils hiding on rural routes?
One legacy gotcha is the “half‑ringer” test module in older NIDs; it loads the loop and can shave a few dB off DSL or make it flaky. Quick fix: replace it with a modern POTS/DSL splitter or have the carrier pull it, though you lose that old remote test path. Curious if folks still see more of those than bridge taps in your areas.
Quick example: in an old farmhouse, too many mechanical bells pushed REN past 5, so the ‘90 VAC at about 20 Hz’ from the CO would ring, but a remote SLIC couldn’t, and pulling one wall ringer fixed it. If ring is flaky during outages, check total REN or drop a ring booster — SLICs often spec lower ringing current than a full CO plant. Anyone else still run into REN surprises?
And on recent offers, I insist on a written ‘initial block time’ guarantee and a named proctor for the first cases; it cuts down credentialing delays and avoids playing musical chairs with OR time.
I got burned once when a “real-time” posting vanished overnight — — so now I keep a one-click packet (CV, last 24 months of case logs, CME, malpractice loss runs) ready and ask for the next MEC date before I apply. @julian_moore92 is right about cutting delays; I also keep a current letter of good standing on standby. Small caveat on those verified remote positions: many still want occasional on-site proctoring or time zone call coverage.
Beyond the ‘−48 VDC’, the gremlin I still run into is forgotten load coils on rural loops — they crater DSL; if your tones fall off a cliff above about 3 kHz or you see about 6 kft spacing in TDR, pull the coils or move to an uncoiled pair. Small caveat: some POTS‑only alarm legs were engineered with them, so tag before you cut; still seeing reverse‑battery used for answer supervision in your area?
Piggybacking on @camille_ross76: bridge taps left in the plant act like stubs and throw reflections — fine for voice, brutal for DSL and even caller ID. If your Hlog shows evenly spaced “notches” or a TDR flags a side branch, cut out the unused spur and the line usually snaps back; it’s like removing a Y‑splitter from a garden hose. Still finding buried side‑legs off pedestals in your patch?