Monday Morning Coffee and Technical Notes

January 6, 2025 View as Webpage

January Engineering Webinar

Over the last several months there has been a lot of discussion in the trades and social media about the need to move EAS origination and distribution into the IP world. The driving force seems to be centered around allowing EAS information to be inserted in a more seamless manner for stations that are operating entirely in the IP arena.

The January ABA Engineering Webinar will feature Bill Robertson with Digital Alerting Systems. Bill has been involved in the development of an IP EAS system and will talk about the future of EAS distribution and how it can be implemented in the IP world.



The webinar is scheduled for Tuesday January 21^st, 2025, starting at 10:00 AM central time.  Register online for this important webinar.

  Annual AM Occupied Bandwidth Measurements

AM stations are reminded of the requirement to conduct their annual occupied bandwidth and harmonic measurements. Formerly called NRSC measurements, these tests must be made annually not to exceed 14 months between tests.

FCC Rules 73.44 indicate that measurements made of the emissions of an operating station are to be made at ground level approximately 1 kilometer from the center of the antenna system. These measurements ensure that the emissions from the transmission system do not exceed their bandwidth, which could possibly cause interference to other stations.

Most AM stations do not have the necessary test equipment to perform these measurements and should contact a qualified engineer to make the measurements and create the necessary documentation. This documentation is to be retained by the station for a period of two (2) years.



Should these measurements indicate an out of tolerance based on 73.44, the station must take steps to correct the issues.

Authorization Notebook

We have written before about the importance of maintaining an “Authorization Notebook”. As we start a new year it is a good idea to review the notebook to ensure all the authorizations are current. At a minimum the notebook should include the following:

1.   Main Station authorization (license)

2.   Translator authorization (if applicable)

3.   Renewal authorization

4.   IBOC Notification (if applicable)

5.   Equipment Performance Measurements

6.   Documentation to determine how FM and TV TPO are determined.

7.   Antenna Structure Registration (ASR)

8.   STL, TSL, RPU, Satellite authorizations (if applicable)

9.   ABIP Certification (if applicable)

10. Chief Operator Documentation  

Reviewing FCC Rules

73.1740 covers the rules concerning silent operations

Once a station has ceased operations for 10 days, a notice must be filed with the FCC providing notification that the station is not operational. 

If the station remains silent for 30 days, specific permission, in the form of a request for Special Temporary Authority (STA) to remain silent, must be sought from the FCC.

The rules refer to reasons beyond the control of the licensee as providing justification for the station being off the air.  Traditionally, the FCC has wanted a licensee to demonstrate that there has been a technical issue that has kept the station off the air. 

The Commission is reluctant to accept financial concerns as providing justification for the station being silent – especially if there was no clear plan to sell the station or to promptly return it to the air.  

If a station is off the air for 12 consecutive months, then the station’s license will automatically expire. 

While that statute has since been amended to give the Commission the authority to reinstate such an expired license "to promote equity and fairness," it still provides a powerful deterrent against stations staying silent, as the Commission is reluctant to find that this exception is met. 

Even if there are technical reasons for the station being silent, if the conditions persist for a full year and no operation (even at a limited power) is restored, the license may well be forfeited. 



So, if you want to preserve the license, don’t allow a station to remain silent for a full year.

AM Directional Arrays

If you have ever been involved in the designing and installation of a directional antenna array, I am sure that you are aware that the FCC rules require alignment of the array based on true North and not magnetic North.

The reason is simple, the north pole is not a stationary point. This point on Earth, where the magnetic field points vertically downwards, is constantly changing due to the dynamic movement of iron and nickel within our planet's core. Experts around the world collaborate every five years to update the World Magnetic Model (or WMM), a crucial tool that maps this shifting magnetic landscape. Historically, the magnetic North Pole has drifted slowly around Canada since the 1500s, but recent decades have seen an unprecedented acceleration towards Siberia, followed by a sudden deceleration in the past five years.

The procedure to locate true North is by locating the Big Dipper constellation. This constellation, also known as Ursa Major, is the key to finding the North Star (Polaris), the star that shows you where true north is in the Northern Hemisphere. This is a large constellation and finding it on a clear night is easy.

Then find the outer edge of the Big Dipper. The outer edge, what looks like the end of a spoon, is made up of 2 stars. These 2 stars are known as “pointers,” because they literally point towards the North Star.

Draw an imaginary line outward from the pointer stars. This line should extend through the top of the spoon of the Little Dipper. The North Star sits at the end of this line.

The North Star forms the end of the handle on the Little Dipper and is the brightest star in that constellation. Mark the direction to true north on the ground starting at the reference tower. Mark the true north direction. This will give you a true north reference line. Based on the azimuth for the towers (as determined by the consultant and listed on the construction permit), you can plot the angle off the true north reference line.



We can’t stress enough the need to hire a professional survey company to come out to conduct the layout of towers. Make sure they are qualified to conduct a Polaris survey to determine layout referenced to true north. To satisfy my curiosity, I once laid out a simple two tower array using magnetic north, then had a surveyor come out (on a clear night) and lay it out using true north. As I suspected there was about a 2-degree difference.

Thanks to Chris Alexander, Crawford Broadcasting for his input with this article

Pro Audio - Polar Patterns

Pro audio engineers as well as broadcast engineers understand microphones have polar patterns or pickup patterns. A polar pattern defines how a microphone captures sound, specifically indicating the microphone’s sensitivity to sound waves arriving from various directions.

There are four basic types of polar patterns. The first is omnidirectional. This mic pattern picks up sound in a 360° sphere around the microphone capsule—all directions equally.

The next polar pattern is Cardioid. This pattern looks a little bit like a heart, hence the name cardioid. Cardioid microphones are highly popular in live sound settings due to their directional pickup pattern, which captures sound primarily from the front while rejecting noise from the sides and rear.

The super-cardioid pattern is very similar to a Cardioid pattern but features a narrower pickup pattern in front of the microphone, rejecting more sound from the sides of the mic. However, there is a larger rear lobe in the back of the mic that can be slightly more susceptible to sound coming from directly behind the mic.

The fourth pattern is bi-directional. A bidirectional microphone has a figure-8 polar/pickup pattern. It is equally sensitive to sounds from the front and back while rejecting sounds from its sides (ring of silence). The sound captured from the front side capture is opposite in polarity to the sound captured to the rear side.

Knowing your microphone’s polar pattern in a live sound reinforcement scenario is essential for managing feedback, isolating specific sound sources, and capturing ambient sounds effectively. Different polar patterns offer unique advantages in controlling unwanted noise and enhancing sound quality. This knowledge allows sound engineers to select the right microphone for each application, ensuring a clear and focused audio experience for both performers and the audience.



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Wonder if there are any engineering jobs open in Miami!