Early telephone multiplex systems & Bell Labs

During a recent morning QSO on 3968 we talked about early frequency division multiplex technologies for carrying multiple voice channels on individual metallic circuits. Probably the earliest example was the O-carrier system deployed on open wire routes. A few photos are shown at this web site.

Information about these FDM systems is sparse on the web. The above referenced article on FDM does include a link about L-carrier systems deployed on coaxial cable.

N-carrier systems were used on twisted-pair cables starting about 1950. According to two books in my library, N-carrier was used for routes ranging from 15 to 250 miles. They used two frequency bands: 36 to 140 kHz (low group) and 164 to 268 kHz (high group) in opposite directions, on two cable pairs. At successive repeaters the signals were translated between the low group and high group to promote equalization across the entire route. Depending on the version of the system, either 12 or 24 channels were carried on 2 cable pairs.

Searching the web for more information about these carrier systems also yielded a nice article about Bell Labs. Scroll down to find entries grouped by decades.

The Bell Ringers web site also includes some good historical links on the Links page.

Latest W4BXI System Audio Drawing

Here is a drawing of John's latest audio configuration. It makes use of a second PC to 'mix' a phone line caller via phone patch into a Skype conference call that connects to the transceiver.
Click on the image above for an enlarged view. Drawing is made using the OpenOffice Draw program.

With the drawing produced, one can make copies with overlaid features, such as the one below that illustrates the main flow for a regular phone patch. A series of these can be done to form a slide presentation, if desired.

Larry's Bees

Larry KB0BH sent me some additional photos of his bee keeping and honey production. Outdoor photos were taken by N4OLN. You can view the complete set in this album on the Bell Ringers web site.

Audio Interconnections at W4BXI

Here is a draft drawing based on a sketch from W4BXI, for discussion purposes. Click on the image for a full-sized view.

VoIP HF Radio Bridge in QST

An article on this topic, written by W4UOA with some assistance from W4BXI and WA5MLF, is published in the September 2009 issue of QST, page 40. We welcome your feedback and invite you to also use the vote link for ARRL members.

Huntsville Hamfest Photos

Photos by Gary, N4OLN

These photos are also posted in the Group Photos section. Click on the thumbnail for Huntsville 2009.

Skype under threat

The VoIP technology that we like to use for HF radio interfacing to the Internet is under threat due to E-bay's sloppy acquisition of Skype. See this summary from episode 583 of Leo Laporte's show The Tech Guy. The summary includes a link to an article on the British news site The Guardian.