Most Popular Articles
111C Coils: A Golden Find
Program distribution. You can use each winding separately of course; if you were to feed one winding with a 300 ohms source you would see that program repeated on each of the other three windings. It's a good idea to make sure each winding is terminated in 300 ohms (Figure 3), otherwise the frequency response of the system may be aberrant. You could call this a poor man's distribution amp (DA), but the fact of the matter is it works great, and it's passive.
Mono-Summing. You can mono sum with two of the windings, but make sure that you have the source impedance correct. Each winding needs to be fed with a 300 ohms source impedance. You may need to add build-out resistors in series with any DA or other output amps, otherwise the windings could compromise the peak output level of said output amps, creating a headroom problem. In addition, you need to make sure the phase relationship is correct between the left and right channel (unless maybe you want an L-R source?). See Figure 4. The two remaining windings will have L+R on them.
RF isolation. One of the neatest things about the 111C coils is the built-in faraday shield between the line side and the drop side (see Figure 1 again). If you have a long line bringing analog audio to some location, say near an AM transmitter site, you can isolate that line from any amplifiers connected to the line side by connecting the S terminal to your local ground.
In this day and age of balanced AES digital circuits, Ethernet and fiber, the functionality given by the old trustworthy 111C coil isn't nearly as important as it once was; however, one day it may save your bacon. Keep a couple on hand just in case.
Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at firstname.lastname@example.org.
Acceptable Use Policy blog comments powered by Disqus
[an error occurred while processing this directive]
Today in Radio History
The history of radio broadcasting extends beyond the work of a few famous inventors.
Read each issue online in our Digital Edition Format in your Web browser.
EAS Information More on EAS
The feed provides feeds for all US states and territories.
Need a calendar for your computer desktop? Use one of ours.
Information from manufacturers and associations about industry news, products, technology and business announcements.
When building its new broadcast production vehicle, MRN applied lessons learned from the past.
Browse Back Issues[an error occurred while processing this directive]
Also in the April Issue
- Update on Transmitters
- On-air Missteps to Avoid
- Tower Lease Renegotiation
- New Products
- Applied Technology: Streaming with the MPEG HE-AAC Audio Codec
- Side by Side: Studio Furniture
- Practical Use: Circulators and Isolators