snipped-for-privacy@aol.com wrote:
This type of party line ringing was called "frequency selective" or "harmonic" ringing.
Most telcos, especially Bell, have used a standard of 20 Hz for ringing a phone line. However, by using up to five different frequencies for ringing each party on the same side of a multi-party line, you could individually ring the desired party without disturbing any of the others.
Also, most party line systems split the line set-up in two "halves". One side of the party line customers have their phones wired "tip to ground", while the other side of the parties have their phones wired "ring to ground".
Regardless of the switching equipment (manual, SXS, Panel, XB, ESS, even digital), you can have fully selective ringing on a 2-party line since one party is the "ring to ground" while the other party is the "tip to ground".
Bell telcos rarely if ever used harmonic or tuned or frequency ringers. Independent telcos have regularly used them, especially on party line systems of more than 2 or 4 parties, since they frequently set up 10 or even 20 parties on a line in rural areas.
It was also possible to have fully selective ringing on a 4-party system by adding "biased" ringing -- i.e., positive bias as well as negative bias, in addition to the tip vs. ring to ground.
Thus, you could also have an 8-party system where only two parties at a time would ever hear their bells ring, since you'd only double the number of parties on a fully selective 4-party system. There would be coded ringing in addition to the "bias" as well as the "tip vs. ring to ground". The most common ringing code sets were single ling rings and double short rings. But there have been others.
Some manual systems had machine controlled ringing. The operator simply plugged into the desired party and the ringing was controlled automatically. But in other manual systems, especially magneto, the operator either pressed a ringing button, or turned a crank (magnet), and thus could produce almost any combination of possible ringing patterns.
Most telcos these days have discontinued party line systems, although some might have grandfathered long time customers under the lower party line rate. However, in today's environment, since telco does not own the customer equipment anymore, it is difficult for telco to make certain that the phones are wired the right way for that particular party. Sometimes the phone company can do the special wiring trick at the demarc box outside the house, thus the customer can have several "standard" wired phones in their house. And with today's plasic electronic phones, it might be impossible for telco to open up that piece of sh** to "re-wire" the phone itself for that particular party line customer.