Friday, October 9, 2009

Critical Directional Antenna Patterns: Dave M. Replies To Bob Nelson

From the very early days, all AM transmitters over a certain power were required to have an on-duty engineer. The 50kW transmitters were the top o' the technical heap, and therefore had to have an on-site First Class Radiotelephone licensed engineer on duty whenever they were in normal operation.

The duty engineer was required to make readings at least once per hour.  That explains why, for example, Beaker Street originated from the transmitter rather than from downtown - Dale Seidenschwarz (aka Clyde
Clifford) had a "first phone" and he served double duty - as the overnight transmitter engineer - and as the host of Beaker Street. The subsequent Beaker Street announcers also had to have a First Class Radiotelephone license until the rules were relaxed allowing a Third Class license to be a "meter reader" by remote control. By that time, Beaker Street had been retired, and all operations were out of the Cottondale Lane studios.

An engineer on site could read the meters, make a reasoned determination whether things were running within the norm, and continue operations or pull the plug. If you remember, at night time, you had to make three separate antenna base current readings and log them, as well as the other readings - Plate Current, Plate voltage, and transmitter output current. The KAAY power divider and antenna phasors were very robust and stable, and I don't ever remember a shutdown due to a breakdown of one of these elements.

KAAY had a full time staff of First Class Radiotelephone engineers on duty when I started in the late '60's. The deejays worked from downtown studios, from West 7th street and later from the Cottondale Lane studios. All the while there was someone at the transmitter site reading meters, making the directional/non directional switches, and generally tending to the place. Felix kept them busy.

Roughly in the mid 70's (not exactly sure of the date ???) there was a relaxation of the rules allowing 50kW directionals to be remote controlled. A major task was to convert the transmitter to remote control. The RCA-BTA50F transmitter was originally designed to be operated strictly in "local" or manual mode, so all the remote control interface had to be custom designed and installed. Felix and Tom Rusk (and others) worked many long hours on this project, and "mission accomplished".

There was a transition period as I recall, between on site control and remote control of the transmitter. The last couple of KAAY transmitter engineers were verging on retirement, and Felix kept them around to watch things after the remote control was made operational. Dual transmitter logs were kept (1 at the studio and 1 at the transmitter) and were compared with each other. The downtown people had to be trained how to make the antenna change and keep the down-time to a minimum (and on-time) without burning up the antenna relays.

Eventually, the last of the KAAY engineers retired, and the transmitter was then run on full remote control from downtown.

Do you remember the plate voltage and current readings? Or the antenna base current? I seem to remember the RCA ran about 10,700 VDC @ about 5.7A. Calculated out this would be about 61kW+ "input power".

Here's another trivia bit - We ran two separate transmission lines from the transmitter building to the center doghouse, where the power divider and phasor units were located. One transmission line was used daytime, and the other was used nighttime.

There was an RF contactor (relay) at each end of the transmission line that "switched" the transmitter between the tuning units. There was an additional contactor at the antenna tuning unit for the East and West tower, used to detune the towers in the daytime, and connect them to their transmission lines during nighttime operation. There were a lot of moving parts, and almost anything could go wrong. But it seldom did.

It was a well known problem that if you switched transmission lines while the transmitter was "hot" you could burn the relay contacts, and cause VSWR to "spike" and take the transmitter truly and solidly off the air instead of remaining in "hot standby". So Felix developed a procedure to keep this from happening.

At antenna change (happened twice a day) you would:

1) Kill the plate HV (transmitter off)

2) Press the CHANGE button.


3) Apply the plate HV (transmitter back on)

If you were fast enough, you could do the whole thing by counting "ONE-MISSISSIPPI" and be back on the air on less than 2 seconds.

But if you EVER switched "hot", or too fast, you ran the risk of having the transmitter shut down and then you had to explain yourself first to the Program Director (why the &#%*@&# were you off the air???) and then explain again to Felix (son, I thought you knew better than that...).


Fixing the contactor could only be done with the transmitter off the air. The main contactor was on top of the P.A. cabinet and you had to use a ladder to get to it.
KAAY's pattern protects WBAL Baltimore and vice-versa. The major northeast null is oriented toward B'more and if you look at a map, you can see it clearly. In broader terms, we also protected the 1090 XEPRS out of San Diego, but that was much farther away to the southwest and not generally an interference problem.


  1. When I kid, I used to think people who held a first class license were really something special. Then I discovered there were schools which specialized in teaching nothing but exam questions and answers. They would guarantee one could eventually pass the exam as long as he or she kept attending the classes. There were some students who made numerous trips to the FCC to sit for the exam, and most finally passed. I tutored briefly at a school like this in Chicago. There were a bunch of licensed people who didn't really know the first thing about electronics. The cellular phone industry put the nail in the coffin because there weren't enough licensed people to work on the cellular phones and infrastructure. The law had to be changed to fit the circumstances. Money talks! If one has a commercial FCC license now, it looks good as something to put on a resume, but there aren't many circumstances which require it anymore. I'm a certified examiner, but there aren't too many people interested in earning a license now. The first class license was downgraded and combined with the second class; It is commonly referred to as a GROL or General Radiotelephone Operators License. The license term is lifetime now. Does this mean I need to take another test in the afterlife?

    Ron Henselman

  2. Actually, KAAY, WBAL, and XEPRS were all upgraded at the same time and are mutually exclusive. Consulting Engineer A. Earl Cullum of Dallas designed all three stations and optimized the coverage of each one.

    Multimedia hired Consulting Engineer Ron Rackley in 1983 to study an increase in nighttime radiation toward Benton and he found that the WBAL-KAAY-XEPRS protections were fixed and could not be increased.

    The XEPRS null accounts for KAAY's poor coverage toward Benton at night. As an aside, both KLRA and KXLR were much stronger to the Southwest than KAAY. KLRA could be reguarly heard in Dallas at night.