WISN 1130 AM has been on the air since 1922, although not always with those call letters. In an interesting twist, the license was granted to the local newspaper, the Wisconsin News and the Milwaukee School of Engineering. Initially, both entities were programming the station, however, by about 1925, the newspaper was responsible for programming and the engineering school was responsible for technical operations.
In 1941, the station increased power from 1,000 watts to 5,000 watts and added night time service. This is a series of pictures from that time period.
Back in 1941, night time interference was taken seriously. The night time allocation study (on 1150 KHz, WISN’s former frequency) includes co-channel stations in the US, Canada, Cuba and Mexico.
The array consisted of four Blaw-Knox self supporting towers in a rectangle. Notice the lack of fencing, warning signs and the like around the towers.
From the front of the transmitter building
The site looks well designed, no doubt manned during operation, which at the time would likely be 6 am to midnight except under special circumstances. Most of these old transmitter sites had full kitchens, bathrooms, and occasionally a bunk room. The transmitter operators where required to have 1st telephone licenses from the FCC. There is only one manned transmitter site in the US that I know about; Mount Mansfield, VT. There, WCAX, WPTZ, WETK, and VPR have their transmitters.
The WISN RCA BT5E transmitter looks huge for that power level. Back in the day when AM was king, these units were designed to stay on the air, no matter what. I don’t know too much about this model transmitter, but if it is like other RCA/GE models from the same era, it has redundant everything.
Old school antenna monitor. I have never seen one of these in operation, however, as I understand it, the scope was used to compare the phase relationship of each tower against the reference tower.
These pictures are of the WISN 1150 array was it was in 1941. Since then, the station has changed frequencies to 1130 KHz and increased power to 50,000 watts daytime/10,000 watts night time. The daytime array consists of six towers and the night time array has nine towers, all of which are 90 degrees.
Special thanks to John A. for sending these pictures along.
Update: What? Nothing Happened! Something I think any radio engineer can appreciate, the incoming magnetic field from the flare was not polarized for maximum effect. According to NOAA Space Weather Prediction Center, the incoming particles were parallel to the earth’s magnetic field, and thus blocked. In order for storms to have major effects, they need to be cross polarized with the earth’s magnetic field. Learn something new everyday.
On February 15 at 01:50 UTC, a massive flare erupted from the sun. Classified as a X2.2 storm, it is the largest since December 2006. The 2006 storm disrupted GPS, some satellite signals and caused 950 mHz STLs to burp occasionally. With all of the cellphone systems synced to GPS, not to mention things like HD Radio exciters, it could be an interesting day. Or not. Already, some reports are trickling in from southern China of communications disruptions.
According to NOAA Space Weather, there is a 45% chance of geomagnetic activity starting on Thursday, February 17th. It is noted that Geomagnetic storms reaching the G1 level and radio blackouts reaching the R1 level are to be expected. Mid to high level latitudes may see extensive aurora borealis, which will be visible in spite of the full moon.
All of the programming elements, all of the engineering equipment and practices, all of the creative process, the music, the talk, the commercials, everything that goes out over the air should reach as many ears as possible. That is the business of radio. The quality of the sound and the listening experience is often lost in the process.
Unfortunately, a large segment of the population has been conditioned to accept the relatively low quality of .mp3 and other digital files delivered via computers and smart phones. There is some hope however; when exposed to good sounding audio, most people respond favorably, or are in fact, amazed that music can sound that good.
There are few fundamentals as important as sounding good. Buying the latest Frank Foti creation and hitting preset #10 is all well and good, but what is it that you are really doing?
Time was when the FCC required a full audio proof every years. That meant dragging the audio test equipment out and running a full sweep of tones through the entire transmission system, usually late at night. It was a great pain, however, it was also a good exercise in basic physics. Understanding pre-emphasis and de-emphasis curves, how an STL system can add distortion and overshoot, how clean (distortion wise) the output of the console is, how clean the transmitter modulator is, how to correct for base frequency tilt and high frequency ringing, all of those are basic tenants of broadcast engineering. Mostly today, those things are taken for granted or ignored.
Every ear is different and responds to sound slightly differently. The frequencies and SPL’s given here are averages, some people have hearing that can go far above or below average, however, they are an anomaly.
An understanding audio is a good start. Audio is also known as sound pressure waves. A speaker system generates areas or waves of lower and high pressure in the atmosphere. The size of these waves depends on the frequency of vibration and the energy behind the vibrations. Like radio, audio travels in a wave outward from it’s source, decreasing in density as a function of area covered. It is a logarithmic decay.
The human ear is optimized for hearing in the mid range band around 3 KHz, slightly higher for women and lower for men. This is because the ear canal is a 1/4 wave length resonant at those frequencies. Mid range is most associated with the human voice and the perceived loudness of program material.
Base frequencies contain a lot of energy due to the longer wave lengths. This energy is often transmitted into structural members without adding too much to the listening experience due to a sharp roll off starting around 100 Hz. Too much base energy in radio programming can sap loudness by reducing the midrange and high frequency energy from the modulated product.
High frequencies offer directivity, as in left right stereo separation. Too much high frequency sounds shrill and can adversely effect female listeners, as they are more sensitive to high end audio because of smaller ear canals and tympanic membranes.
Processing programming material is a highly subjective matter. I am a minimalist, I think that too much processing is self defeating. I have listened to a few radio stations that have given me a headache after 10 minutes or so. Overly processed audio sounds splashy, contrived and fake with unnatural sounds and separation. A good idea is to understand each station’s processing goals. A hip-hop or CHR stations obviously is looking for something different than a clasical music station.
For the non-engineer, there are three main effects of processing; equalization, compression (AKA gain reduction), expansion. Then there are other things like phase rotation, pre-emphasis or de-emphasis, limiting, clipping and harmonics.
EQ is a matter of taste, although it can be used to overcome some non-uniformity in STL paths. Compression is a way to bring up quite passages and increase the sound density or loudness. Multi band compression is all the rage, it allows each of the four bands to react differently to program material, which can really make things sound differently then they were recorded. Miss adjusting a multi band compressor can make audio really sound bad. Compression is dictated not only by the amount of gain reduction, but also by the ratio, attack and release times. Limiting is a relative to compression, but acts only on the highest peaks. A certain amount of limiting is good as it acts to keep programming levels constant. Clipping is a last resort method for keeping errant peaks from effecting modulations levels. Expansion is often used on microphones and is a poor substitute for a well built quite studio. Expansion often adds swishing effects to microphones.
I may break down the effects of compression and EQ in a separate post. The effects of odd and even order audio harmonics could easily fill a book.
Not to take anything away from Gary Breed, K9AY, who makes and sells these things under the corporate name AYTechnologies, I decided to make my own K9AY antenna system and controller. Basically, after looking at the currently available commercial version, I figured I could make a better unit for less money and be happy.
The basis for the K9AY antenna is that it has a steerable null. The gain around the antenna is close to unity, except for the terminated side of the loop, which has a deep null. This can be switched around using a combination of relays that change the loops and termination. This comes in very handy for MW and SW listening, when co-channel stations can create annoying interference and hetrodynes. I have had good success pulling many stations out of the muck, especially in the AM band using this antenna.
This antenna requires a good ground to work against. For optimum installations, I would recommend placing two radials under each side of the loops. This will keep the ground conductivity below the antenna fairly constant, thus the value of Rterm will remain consistent for each band.
My other idea is to add a preamp right at the antenna to overcome transmission line loss and the loss from a 4 port passive receiver coupler. Something around 10 dB, low noise (obviously), low parts count and rugged. I decided that a Norton preamp was a good design, with only one active device, a common 2N5109 BJT. Most of the time, this preamp is switched off and out of the circuit. There have been several occasions, however, where an extra 10 dB made the difference between no copy and good copy.
This is the schematic of the relay board and preamp combined:
The parts list is as follows:
C1 – C5
Ceramic 0.1 uf capacitor
2 Kohm ¼ watt
Ferrite bead, Amidon FB-43-101
8.2 Kohm ¼ watt
K1 – K3
Omron G6K-2F-Y small signal relay
100 ohm ¼ watt
22 uH ¼ watt
51 ohm ¼ watt
100 uH ¼ watt
2N5109 w/heat sink
Norton feedback trans
The 2N5109 transistor is a CATV unit and it has a 50 input and output, that reduces the number of impedance transformers required. The value of Rterm is determined by which band one wants to operate on. I used Omron G6K series low signal relays. Again, because this is a receive only antenna, those relays will work well.
Terminal board connections, TB1:
Wire loops go between Terminals 1-4 and 2-3.
Control terminal board connections, TB2:
To create a low noise preamp, I decided to use surface mount devices and to try and make all the traces as close to 50 ohm impedance as possible. I created this SMT printed circuit board:
From this, I ordered 6 boards from PCB express:
This is the board with all passive components installed:
This is the board completed:
My current K9AY is an amalgamation of parts removed from various equipment. The relays are large, 12 VDC units which do not have the best contacts. It works well enough, but I’d love to get one of these units into the control box at the base of the antenna. Unfortunately, my antenna field is still in about 18 inches of snow, so it will have to wait until some of the snow melts off.
I would position this antenna as far away from transmit antennas as possible to avoid overloading the preamp and or causing problems with the switching relays. For the average amateur set up, 75 to 100 feet separation should be more than enough.