{"id":3276,"date":"2017-07-24T06:11:41","date_gmt":"2017-07-24T12:11:41","guid":{"rendered":"http:\/\/play.fallows.ca\/wp\/?p=3276"},"modified":"2017-07-21T14:09:17","modified_gmt":"2017-07-21T20:09:17","slug":"wired-wireless-ssb-phone-lines","status":"publish","type":"post","link":"https:\/\/play.fallows.ca\/wp\/radio\/ham-radio\/wired-wireless-ssb-phone-lines\/","title":{"rendered":"Wired Wireless – SSB Over Phone Lines"},"content":{"rendered":"

\"wired<\/a><\/p>\n

Wired wireless was the original name for carrier telephony. Single sideband transmission first made its name over phone lines a century ago.\u00a0<\/p>\n

Most people associate single sideband with ham radio voice communications on the HF bands. However,\u00a0single sideband got its start at the telephone companies. SSB was popular over long distance phone lines long before its adoption for ham and commercial radio. Starting around 1910, telco’s learned how to send modulated radio carriers over pairs of wires. Here’s how it came about.<\/p>\n

Sending a single baseband audio signal over a single phone line is not very efficient.\u00a0As use of telephony grew, phone companies had to figure out how to send multiple voices over single lines at the same time. This was especially important when considering the high cost of long distance cables.<\/p>\n

So, engineers learned how to do carrier multiplexing<\/a>, which at first allowed the transmission of two signals over one cable. The inventor was a major in the US\u00a0Signals Corps, who coined the term “wired wireless”. Soon after, telephone carriers began using single sideband modulation to send multiple signals over phone lines. They called the technique Frequency Division Multiplexing.<\/p>\n

Multiple voice signals were frequency shifted and then combined into a band between between 60 to 108 kHz. Each voice signal was single sideband superimposed on a carrier signal. Soon, sending 12 SSB voice channels simultaneously became common. By the 1930’s this increased to 24, and so on.<\/p>\n

Simply put, voice signals in the 300-3400 Hz range were multiplexed onto various channels within a low frequency radio signal, which was then transmitted over long distance phone lines and undersea cables. Many amplifiers were placed in the circuit to maintain the signals. Post-war, the carrier signals increased in frequency and were able to carry 600 or more SSB signals concurrently.<\/p>\n

Wired Wireless – Analog FDM of SSB<\/h2>\n

More recently, with the shift to digital transmission, analog FDM has become obsolete. But it had a long life, boosted by the switch to coaxial cables (more bandwidth) and transistor amplifiers (more reliability).<\/p>\n

High frequency wired telephony first entered service in 1918 at Western Electric. Single sideband was established as the standard for these systems. Application of SSB for wireless radio signaling did not emerge until the 1920’s.<\/p>\n","protected":false},"excerpt":{"rendered":"

Wired wireless was the original name for carrier telephony. Single sideband transmission first made its name over phone lines a century ago.\u00a0<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","_share_on_mastodon":"0"},"categories":[5],"tags":[246,239],"series":[281],"class_list":["post-3276","post","type-post","status-publish","format-standard","hentry","category-ham-radio","tag-hamr","tag-hamradio","series-single-sideband-era"],"yoast_head":"\nWired Wireless - SSB Over Phone Lines - Making It Up<\/title>\n<meta name=\"description\" content=\"Wired wireless was the original name for carrier telephony. 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