DX-50 Transmitter Installation
(DX-50 Goes On the Air!)
Posted By Steve Blodgett
This is Page 6
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At 12:04 am on Saturday, August 11th, KNX's Chief Engineer and Transmitter Supervisor, Larry Wichman, pushed the button and started the automatic sequence that turned off KNX's main transmitter, the Continental 317C, and switched over to the new main transmitter, the Harris DX-50. By all indications, we were on the air and all was well. The meter reading below was good news. |
| This is an actual photo of the Power output meter on the DX-50 just moments after the transmitter was switched into tower 1 at KNX for the first time. The changeover from the old to the new transmitter went smoothly, bringing much happiness to the transmitter site. |
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Tests during the week into the "dummy load" had shown that the DX-50 operates quietly and efficiently with a minimum of heat released into this, the "back" transmitter room previously occupied by the G.E. BT50. New air filtering systems will easily be able to handle the heat from this transmitter. This is the first photo of the DX-50 while it is actually on the air for the first time at KNX. |
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The Continental 317C, now the auxiliary transmitter for KNX, is
idle while Larry Wichman (right) and Joel Saxberg discuss the way that
slight differences between towers 1 and 2 were shown on the transmitter.
During the 1 a.m. to 2 a.m. hour, KNX was to be off the air so that we
could do tests of the "base impedance" of each tower. Small variations
between the two towers and the "dummy load" will show up as differences
in the transmitter readings and on test equipment. Our test
measurements on the tower revealed information that we'll need to precisely
compute KNX's 50,000 Watt operating power.
All tests went well and were completed on time so that KNX could be back on the air at 2 a.m. for the very popular "drama hour" program. We knew from past experience that if we missed broadcasting that program, we'd disappoint listeners from all over Western America, so we planned our work in order to finish on time and avoid a flood of email inquiries from listeners. |
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At the base of a typical AM station tower is a tuning network like
this one (left) for KNX's tower 1. The network shown in this ATU (Antenna Tuning Unit) is housed in the left
hand cabinet shown in the photo to the right. Coils and Capacitors in
these networks tune the tower so that the energy from the transmitter's signal
is transferred efficiently to the tower, and out over the air. Each
component is carefully tuned and checked with specialized technical equipment to
insure that the system will work properly. The photo on the right shows a 10,000 Watt Continental 316, KNX's 3rd transmitter, next to the ATU. The 316 is extra insurance against the unlikely failure of the two existing 50,000 watt transmitters now in service, and is our last remaining link with some impressive older, serious heavy-duty, iron based hardware. Best of all, it still works! |
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Here's just one more reason to do regular equipment
inspections. The photo on the left shows high voltage damage to a tuning
capacitor. A close look shows a hole blown through an interior plate of
this "vacuum capacitor". Fortunately, the glass isn't broken, although the
photo does give that impression. We considered that the problem probably
occurred during a lightning storm, but could also have happened during some
other high voltage condition during regular transmission. This expensive
device has been replaced, but points out the reason why regular equipment
inspections are vital at high power stations such as KNX. Tests and maintenance of equipment such as that shown here, keep KNX's signal reliably available to the millions of listeners who tune in throughout Southern California and Western America. |
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Some final notes on KNX's transmitter site and this project What you see here is only a small portion of the complex technical requirements involved in the transmission of radio signals from a large broadcast station like KNX. There's more, much more high tech and industrial equipment required to produce the signal we tend to take for granted every day at 1070 AM. History reveals that the old-school broadcasting operation at CBS intentionally maintained a technical staff that understood the intensive requirements of a high power AM transmission facility, and who were able to carefully maintain and operate it so that there was virtually no downtime from technical failures. Installation, tests and maintenance of equipment such as that shown on these web pages, are no small matter at a station like this one. KNX's signal reliability over the years has been directly attributable to the training and dedication of broadcast engineers from KNX's past who have contributed to the art, the science, and the business success that we call radio broadcasting. KNX, in spite of industry trends, managed to maintain its own experienced and skilled engineers for quite some years. Predictably however, corporate mandates finally took their toll, and with few engineers on staff, the site now sees little maintenance or inspections compared to the scheduled maintenance that once insured reliable operation. Although today's equipment is more reliable than previously, only time will reveal the effects of little or no regular inspection of this transmitter plant. Special thanks to Larry Wichman, KNX's former Chief Engineer and long time Transmitter Supervisor, now retired, for his on-site supervision of this project. His know-how insured that this job went smoothly and on schedule. Thanks to Bob Conger for making himself available when we needed him most, to Barry Mishkind and Michael Smith for sending along historical notes about KNX, and to Eric Disen for contributing pre-project information and personal notes on the DX-50. - Steve Blodgett,
former Director of Technical Operations, KNX, Los Angeles, Aug 11, 2001.
(text updated January, 2005) |
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