August 1, 2000 marked the end of WMAQ after nearly 75 years of broadcasting with those call letters. 670 is now WSCR, The Score. This author was employed by WMAQ from 6-15-92 to May 21, 1999 as a station engineer with the primary duties being the care of the transmitter site, component level troubleshooting of broadcast equipment as well as studio repairs. Many thanks to Scott Childers for providing a link to this website and I am proud to be part of his tribute to WMAQ. If you have any questions about WMAQ's transmitter site, please email me.
When I started this website, I did not have any particular audience in mind. Now I have decided that the audience makeup I'm targeting are people in broadcasting business as well as people with a ham license or similar technical background. If you are a techie of some sort, you will find this website interesting. If some of the information on this webpage goes over your head, not to worry because there is plenty of other information on this site that should suit your interest and curiosity. The contents of this website are totally the responsibility of the author, so if you see a problem here anywhere, blame me and not WMAQ.
This project was started entirely on my own initiative and was done for several resons. First, I wanted experience designing and publishing a webpage. Secondly, I wanted to pick a topic in which I am passionately interested. Third, maybe I can get someone interested in broadcast engineering by showing the kinds of things and systems a broadcast engineer works with. Lastly, we train many operators at WMAQ in a year's time. At the station, we talk about 'the transmitter' often. I thought it would be nice if these trainees could visit my website and see what 'the transmitter' actually is. The studio complex and the transmitter complex are separated by several miles. It is a rarity that anyone from the studio other than engineers, ever visit the transmitter site.
WMAQ began transmitting at 50,000 Watts from this building on September 15, 1935. Our first 50 KW transmitter was a Westinghouse 50B, low level plate modulated and water cooled. The low level plate modulated stage was 5 Kilowatts carrier power followed by a 50 KW linear amplifier, 200 KW PEP. The Westinghouse transmitter was used from 1935 until 1960 when it was replaced by one of the first RCA BTA-50H Ampliphase transmitters. WMAQ was owned by NBC at the time, which was owned by RCA. Below is a photo of our old RCA BTA-50H
The WMAQ auxiliary 50 KW transmitter can be seen in the foreground with the Continental Electronics 317C-3 in the background. The Auxiliary transmitter is a Harris MW-50B and was manufactured in 1978 at the Harris plant in Quincy, Illinois. The MW-50B is used on the air once per week so we can be confident that it will be functional in event of failure of our main transmitter. Both transmitters are built into the wall which simplifies the air conditioning requirements. The transmitter room is air conditioned to about 72 degrees which extends the operational life of the smaller electronic equipments, such as STL receivers, remote control equipment, audio processors, etc. The area behind the transmitter, which is accessable through the double doors seen between the two transmitters, acts as an air plenum and is not air conditioned. It is not uncommon on a hot summer day for this area to reach over 100 degrees!
This is a rear view of WMAQ's auxiliary 50 KW transmitter, the Harris MW-50B. You can see the plate transformer, which is about 4 ft x 4ft x 4ft, in the corner on the left side of the picture. It is a three phase unit with the high voltage rectifier stacks being contained within the transformer enclosure. The rectifiers can be accessed by removing the white cover on the front of the transformer. The DC voltage is 25 Kilovolts at about 4.5 amps. The transformer itself is oil cooled. The plate contactor is in the big white cabinet on the far wall between the transmitter, which is on the right, and the plate transformer. It does not show up very well because the wall is the same color as the contactor cabinet.