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#1
March 9th 06, 02:46 PM
posted to rec.radio.amateur.homebrew
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how to wind 10mH inductor for AF diplexer?
"Tim Shoppa" wrote in message oups.com... wrote: My question is: how on earth should I wind those 10mH inductors? In years past I would pick up 88mH/22mH and like "phone company" toroids at hamfests etc. My understanding is that these were used to compensate for line loading in long phone wire runs. Windings were either used as-is (if 88 mH or 22mH was appropriate) or were removed and rewound. =========================================== 88 mH loading coils were used on 300-3,600 Hz phone circuits ever since around the years 1900 to 1910. Spaced every 2000 yards in 542-pair underground, long distance cables between phone exchanges and towns and cities, they were an international standard of loading. Countless millions were manufactured. 88 mH coils must have outnumbered all coils of all other values of inductance put together. Originally the core was a bundle of soft iron wires but in the 1950's after 50 years they changed to ferrites. 22 mH coils were another popular value. They were used on "music" circuits. Spaced every 500 yards the frequency range was 100-15,000 Hz. At one time used on a network between radio broadcast studios and transmitters. Coils had to be removed to make cables suitable for carrier telephony and then digital transmission. But there must be millions still in use around the World. ---- Reg. |
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