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Tom Johnson and I were talking about pests.

Fig. 1: Eaves and overhangs at unmanned transmitter buildings can attract stinging insects.

We met at the Alabama Broadcasters Association and Larry Wilkins’ Engineering Day seminar; and as we talked about bugs infesting transmitter sites, Tom shared the picture in Fig. 1.

I don’t know many engineers who care for wasps, hornets or other flying, stinging insects. Tom’s photo is a great reminder to spray under eaves, and around door and window frames — any place that’s protected from the weather.

Unfortunately, with cold weather approaching, it’s not just vermin that seek shelter from the cold. An unoccupied transmitter building or AM antenna tuning unit is an ideal home for insects and rodents. Make sure it is sealed.

ATUs in particular can attract unwanted guests. If your ATU has a light fixture inside, wait til it’s dark and then  turn it on, then walk around the ATU looking for any escaping light (remember to look underneath, too; and also watch out for the “hot” tower). Any holes you spot, perhaps where bolts once held coils or other components, are “welcome signs” for insects, and usually the proper diameter for these insects to squeeze through. Plug those holes with RTV or caulk.

Remember also that before opening the ATU door, pause to watch whether stinging insects are flying around. They may have infested your enclosure already.

Check that entry panels or doors to the ATU also fit tight; again look for light leakage. Remember that field mice can squeeze through amazingly small crevices.

Tom waited till dark, then sprayed that nest and its occupants.

When I did contract work, a client was losing their satellite signal every day at dusk. I stood on a ladder and unscrewed the LNB. A swarm of angry wasps escaped the nest they built inside. How we didn’t get stung —  or break a leg, frantically jumping off the ladder — still amazes me.

As I mention in my Workbench sessions, a one-liter clear plastic water bottle fits nicely in the throat of a satellite feed horn and will prevent infestation. As for your building, a good spritz of wasp and hornet spray applied under all the overhangs on your building is good preventive maintenance.

 

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San Francisco contract and project engineer Bill Ruck writes, “Been there, done that.” He was referring to the electrolytic capacitor woes we described recently.

Back around 1967, Bill learned about electrolytic capacitors working at a hi-fi store. Rule of thumb in those days was (1) if they’ve “puked their guts” by exploding, replace them; (2) if not, replace them anyway.

Since then, Bill’s experience is only worse. Many times he has traced spurious outputs of an FM exciter to the power supply oscillating and modulating the carrier.

Recently, Bill had two BE FX-30 exciters with that problem. The issue was traced to the FMO module. The problem was that the FMO is potted and to dig out the potting compound to replace the capacitors would take a lot of time and was no longer cost-effective. The group owning the exciter preferred to purchase a new exciter rather than put a lot of money into reconditioning something that was over 30 years old.

Bill adds a few more nuggets to consider:

1. Although high ESR (equivalent series resistance) doesn’t cause “ringing,” it does let an unstable amplifier oscillate. Furthermore, most three-terminal regulators can be defined as an “unstable amplifier” and will oscillate. Bill learned in his own home-built power supplies to put a 1 uF tantalum bead capacitor and a 0.1 uF ceramic disc capacitor as close to the regulator IC input pins as possible.

2. Always put in 105 degree C electrolytic capacitors. They’re slightly larger and slightly more expensive but they last a lot longer.

3. It takes the same effort to remove capacitors from a printed circuit board to measure them, than to just replace them. Yes, Bill can measure ESR and capacitance, but he does that only to confirm his suspicions, after putting in new low ESR 105 C replacement capacitors.

In summary, Bill writes that these days, component level repair is less cost-effective than during his misguided youth; but if you do make these repairs, replace!

 

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Fig. 2: Find this DIY rat trap at the YouTube link in the text.

Our Workbench Malaysian connection, broadcast engineer Paul Sagi, found an interesting YouTube video that we’ll call “Curiosity Killed the Rat!” Here’s the link: https://m.youtube.com/watch?v=T-KJMM55A9A

Paul comments that it appears that clear box sealing tape was used to hold the grain, and the “ramps” appear to be floor tiles, placed so the underside faces up. Placing two ramps on opposing sides permit some rats to balance out each other, a single ramp may be better. Finally, for remote locations, Paul suggests affixing the ramp to the bucket, so it doesn’t fall.

My comment? I sure hope this isn’t someone’s transmitter site! That’s a lot of rats.

I also hope you’ll contribute to Workbench. You’ll help your fellow engineers and qualify for SBE recertification credit. Send Workbench tips and high-resolution photos to johnpbisset@gmail.com.

John Bisset has spent 50 years in the broadcasting industry and is still learning. He handles western U.S. radio sales for the Telos Alliance. He holds CPBE certification with the Society of Broadcast Engineers and is a past recipient of the SBE’s Educator of the Year Award.

The post Deter Stinging Insects at the Transmitter Site appeared first on Radio World.

The author is membership program director of the National Federation of Community Broadcasters. NFCB commentaries are featured regularly at www.radioworld.com.

This week’s big news in community radio was all about layoffs at Pacifica radio station WBAI(FM) in New York and termination of its existing programming. The seriousness of the situation is a bellwether to conversations community media must have about relevance.

WBAI is certainly an iconic noncommercial radio station. It has hosted a veritable who’s who of cultural vanguards, especially in the 1960s. From Bob Dylan to Malcolm X, WBAI has been fondly remembered by fans for such history. Unfortunately, those glory days are long gone.

When I wrote for Radio World about the Empire State Realty Trust $3 million judgment against WBAI and Pacifica in 2017, matters were already quite dire. Pacifica audits noted a listener support decline between 2007 and 2017 in the millions. The California Attorney General’s Office and the Corporation for Public Broadcasting Inspector General launched probes in 2015 and 2011 respectively over management issues. WBAI had seen crashes in 2009 and 2013, and its internal strife, inability to make payroll and subsidization by other Pacifica outlets had been in public circulation for years. WBAI folks, a smart and interesting bunch to be sure, have long contended what may seem to be farfetched theories, from essentially embezzlement by its licensee to its owner kneecapping the station staff and volunteers for their liberal orientation and willingness to host marginal programming under the free speech banner.

[Read: Community Broadcaster: Changemakers]

Indeed, any publication that termed this week’s action stunning or a shock clearly must be excused for not paying attention to a crisis decades in the making.

Pushback to Pacifica’s decision was swift, including a state court intervening in the situation. However, it may be unclear how influential a New York court injunction to prevent layoffs and program changes will be. After all, Pacifica is a California nonprofit organization. The network’s payroll and WBAI’s federally assigned license (and thus programming placed on it) are both based far from said court’s jurisdiction. This story is developing.

Regardless of what happens to WBAI, the health of community radio as a whole is always a concern. What can stations learn from this issue?

As I conveyed to radio station WORT this week, community radio stations should always ask themselves about how they are truly listening to and serving local listeners with content they are passionate about and rely on. It is not difficult to figure out why WBAI, at 99.5 FM and in a city of eight million people and with one of the nation’s top median household incomes, could muster only 78,500 weekly listeners (according to Nielsen Audio) and not cover basic expenses. An old friend at Radio Research Consortium, noncommercial media’s data clearinghouse, once shared, listeners tell you what they think of your programming with their ears and wallets. Every station should track what their local fans think, and be responsive to area needs. That can be hard, given the many perspectives that are part of a station, but centering listener experiences with our stations must always be a priority.

Careful financial monitoring and adopting an approach to problems that sees them as a shared responsibility should also be a part of any station’s ethos. When tensions arise, the easy way out is to cast blame on others. Difficulties such as those experienced by the community radio space this week might have been averted with more swift, productive actions, and buy-in from everyone. All community stations might be wise to unify in times like these.

And finally, every station would be well served to take the lead in telling its story. In times of trouble, explaining one’s vision and where one hopes to be reassures listeners and tells donors you have a solution. Once a station loses control of its narrative, it is hard to regain credibility. Pacifica’s message posted on WBAI’s website is a start, in this instance.

Noncommercial radio observers may recall the WBAI move is not without precedent. In May, Humboldt State University shuttered its volunteer-based programming and laid off staff at KHSU in a bid to reorganize. A Humboldt State University advisory review identified a need for financial review of university investments, a realignment of the station’s operations and other issues for the licensee. One can hope WBAI’s reorganization is successful, and that all of community radio takes a cue from what’s happened to make the best media possible.

 

The post Community Broadcaster: A Cautionary Tale appeared first on Radio World.

The author is the head of technical and infrastructure department at German national public broadcaster Deutschlandradio.

The reception of radio programs with smartphones is becoming increasingly important for radio makers, particularly due to young people’s tendency to use their hand-held devices for a wide range of purposes — information and entertainment, social media networks, smart home and smart speakers, amongst others.

Chris Weck

There is no doubt that broadcasters have to be present on that platform with both linear and non-linear audio, with social media and the various functions of the internet.

At first glance, 5G broadcasts seem to be a promising solution for the future of broadcasting, and a viable solution to bring radio to the smartphone — one device and one transmission standard on one transmitter network. But who will benefit from this — the user, the mobile network operators, radio broadcasters or the industry as a whole?

Physical laws for radio communication are still valid for 5G as for DAB and all the other broadcasting and telecommunication schemes. From the well-known Shannon limit of 1948 we know that a minimum of energy per bit is necessary in order to provide an error-free transmission over a channel with a certain bandwidth (Eb/N0 = −1.6 dB in AWGN-Channel).

New and very efficient transmission systems like 5G are able to transmit very high data rates in a channel of a certain bandwidth, however, the energy per bit will never fall under the minimum defined by the Shannon law. With other words, the higher the data rate of a transmission system, the higher the signal-to-noise ratio required. This means in practice for a certain transmitting power the size of the transmitter cell will be reduced for higher data rates accordingly.

Now, from a theoretical point of view with respect to the energy per transmitted useful bit (including all the overhead), there is no significant difference in performance between 5G modulation schemes compared to the still very robust system of DAB+.

The 5G broadcast mode provides also a robust QPSK modulation to make use of bigger cell sizes. However, the expected performance compared to DAB especially in a single frequency network is rather the same. In fact, there are no results of a system comparison in the field available and therefore it is reasonable to focus on other basic differences between the idea of 5G broadcast and conventional DAB+ broadcasting.

Today, DAB radio receivers have an external antenna as well as car receivers. In comparison to a smartphone with a less sensitive built-in antenna, the link budget for the required field strength differs at minimum of 15 dB or even 20 dB and more.

This means that in order to achieve the same coverage for radio reception by smartphones, 10 dB more transmitting power is required. This is also true for 5G broadcast networks, so that 5G broadcast networks for smartphone reception have to aim for 10 dB more transmitting power compared to a conventional DAB+ network. In practice, this means that a significantly denser transmitter network is required for 5G broadcast to smartphones than for conventional DAB+.

Radio reception differs for smartphones compared to conventional radio receivers.  The field strength required depends on the effective antenna size, and has to be higher for smartphone reception.

The reduction of the transmitter distance can be anticipated easily from the CCIR propagation curves. For example for VHF propagation a loss of field strength of 20 dB corresponds to a reduction of the distance to the transmitter from 30 km to 10 km.

With the basic transmitter distance of about 60 km for DAB+ networks, the average transmitter distance for 5G broadcasting to smartphones has to be around 20 km. In fact this means that the transmitter distance has to be reduced by a factor of three in order to overcome a loss of 20-dB field strength. This means nine times more transmitters in the area are required in order to achieve the same coverage as a conventionally planned DAB+ network. Can radio broadcasters really afford this? In fact round about 10 dB more transmitting power results in 10 dB more money.

For the time being, the national DAB multiplex in Germany comprises of 130 transmitters in a nationwide SFN. Today, coverage stands at around 95% for mobile reception, but in order to reach 99% coverage, the number of transmitters has to be increased to 250 at least and may be around 400 (including small gap fillers) in the long term.

With 5G Broadcast round about 10 times more transmitters will be required which might sum up to 2,500 or even 4,000 transmitters in Germany. The mobile network in Germany comprises already 40,000 transmitters today and everybody experiences that this is rather not enough. Concerning 5G mobile networks, experts anticipate that future high data rate networks will be based on a cell size of less than 1 square kilometre, which would sum-up to around 400,000 transmitters in Germany for nationwide area coverage.

CCIR 370 Propagation Curves

What can we learn from these facts?

1. The DAB+ network with its low number of transmitters is the most efficient network to realize a full area coverage
2. The 5G broadcast networks, the mobile network and future 5G mobile networks require far too much transmitters for a full area coverage that nobody can expect the same area coverage as for DAB radio services

Assume e.g. transmitting costs for a full area DAB network in Germany of about €25 million per year. In order to gain 10 dB more transmitting power for smartphone reception, the network will cost a nationwide broadcaster approximately €250 million per year, as opposed to €25 million a year for conventional DAB. In Germany, no broadcaster is in a position to afford this amount of money — the price for this purpose to reach smartphones with radio is incredible high, and quite frankly, out of reach for any public broadcaster.

If one says that 5G would only be applied in cities as opposed to rural areas, the additional costs would indeed be lower. However, setting aside a budget of €10 million a year for this purpose is also unrealistic for a broadcaster and, should this sum even be available, it would certainly make more sense to spend it on the DAB network, where coverage gaps could be closed, and where broadcasters and consumers could benefit from it.

What’s more, it wouldn’t make sense for a broadcaster to give up nationwide DAB coverage. In order to supply 10% of the area with 5G broadcast to mobile phones for the same amount of money.

So, if broadcasters are far from being able to afford 5G broadcasting, who would pay for this? Mobile network operators will never provide a 5G-radio service for free, and broadcasters will not pay for 5G broadcasting either, so there really is no business model for either.

The one and only solution is that the user pays for the broadcasting service to his smartphone — this could be done by a contract with the broadcaster or with the mobile network operator, something that is already being done today with 3G/4G.

The smartphone user has a mobile contract and pays for the data volume on an individual basis. This enables the mobile network operator to set up very dense mobile networks that have enough power to be received by small smartphones. This works perfectly for radio with LTE and even UMTS, so why wait for 5G broadcasts?

Users already have radio services available on smartphones today, and it works well, so long as the user has enough high-speed volume on his contract.

Today, hybrid radio with DAB+ and Internet via mobile networks or via Wi-Fi at home provides the most suitable solution. Hybrid radio is the perfect fit for all broadcaster and user requirements, as with DAB+ it allows broadcasters the proven and most efficient radio network at an affordable price for area-wide coverage. It allows for free access of the users to radio and information, regardless of whether they live in cities or in rural areas, and whether or not they can afford a high-volume data contract for their mobile phones.

Hybrid DAB radio provides broadcasters with a content distribution platform directly linked to the customers, and independent of the commercially driven infrastructure of mobile network operators. This may be an advantage for emergency warnings, too.

On the other hand, users already have audio streaming and additional non-linear services available on their smartphone via the Internet. So, the only need for radio broadcasters today is to think about attractive hybrid radio services, and an impactful marketing strategy for their brand.

I cannot comprehend why broadcasters and politicians would want to switch a system running with DAB and IP with the more expensive, and in practical terms less efficient system that is 5G. Instead, why not use and extend the existing and approved technology? Hybrid radio is the best approach both economically and in terms of efficiency, and this is unlikely to change in the future.

Diversity between broadcaster networks and mobile phone networks will result in better efficiency and will offer more advantages than disadvantages for broadcasters as well as for users — so proceed with Hybrid DAB and IP. There is no need for 5G for radio broadcast.

[Read: Using Digital Radio to Boost Listening Figures and Revenues]

 

The post Does 5G Make Sense for Radio? appeared first on Radio World.

Six industry professionals have already made their plans to attend the 2020 edition of Radiodays Europe in Lisbon, Portugal, as the conference has announced the first batch of its planned speakers.

Those confirmed to speak at next year’s conference are Cilla Benkö, director general and CEO for Swedish Radio; Cathrine Gyldensted, co-founder and director at the Constructive Journalism Network in the Netherlands; Yagmur Özberkan, journalist and presenter for YLE, Finland; Torben Brandt, Danish radio legend; Ole Hedemann, content developer and head of formats at NRK in Norway; and Susani Mahadura, journalist for YLE, Finland.

Radiodays Europe Lisbon 2020 is going to take place from March 29–31, 2020. For more information or to register for the event, click here.

 

 

The post Radiodays Europe Announces First Group of Speakers appeared first on Radio World.

Over the years I’ve become a student of mic preamp design, building and modifying several along the way and learning a little more each time. Usually, I worked from a kit or published set of plans. Recently, I’ve tried some designs from “scratch,” researching various components, studying earlier designs, and incorporating them into raw schematics, followed by circuit layout, design tweaks and final fabrication.

Since my last two builds were vacuum tube devices, I wanted to do a simple, solid-state design this time. I came across some old preamp ICs in a parts box and almost used them but discovered they had been obsolete for years.

Was there a viable updated replacement? Enter THAT Corp., a relatively small IC manufacturer that specializes in chips for audio applications. THAT makes a few chips that are direct replacements of some popular preamp ICs like the Analog Devices SSM2019 or Texas Instruments INA163. If you’ve ever cracked open a broadcast console, you may have seen one. THAT’s website is a treasure trove of design notes and white papers on mic preamp design, with plenty of ideas to get a project going.

This project uses two ICs from THAT: the 1512 Low-Noise Audio Preamp, and the 1646 Balanced Line Driver. Using design notes from THAT and other sources, including advice from several more experienced DIYers, I was able to come up with a relatively low-cost design that has plenty of gain and good performance numbers for most applications.

The mic preamp can make or break a recording. Aside from the microphone, it’s the first stage in the signal chain before the recorder, and in some cases the only stage. It has to be clean and have ample headroom (unless noise and distortion are your thing), yet have sufficient gain to handle a wide variety of microphones.

Professional microphones have a balanced output, so the preamp will have a balanced input. Normally this is accomplished either with transformer balancing, which is expensive, or by using a standard op-amp as a differential amplifier, usually involving two op-amp stages with their attendant gain feedback loops, etc. The THAT 1512 takes care of this within the chip, providing its own balanced input. All that’s needed is a pretty standard input stage that can provide phantom power. The phantom power is sent to Pins 2 and 3 of the input XLR jack through a matched pair of 6.81K resistors, R1 and R2. These limit the current of the phantom supply.

The phantom power section

In order to preserve common mode noise rejection, any components that are mirrored between positive and negative signal paths must be matched in value as closely as possible. SW1 [switch] allows for turning off phantom power when it is not needed, and LED1 illuminates to show the actual presence of phantom voltage. R9 limits current through the LED to keep it from going “poof!” Capacitor C13 is there to smooth out any ripples from the 48 V supply. Between Pins 2 and 3 of the input jack and ground, ceramic capacitors C1 and C2 shunt any RF noise that might hitch a ride on the mic cable. Bad mic cables make good radio antennas!

Keeping stray static at bay is the job of the diodes.

Obviously, we need to keep 48 VDC out of our audio circuit. In a transformer-based design, the transformer would handle this, as transformers only pass AC. Likewise with capacitors, which are much cheaper and take up less space. This is why inexpensive designs use them. The problem is that inexpensive designs tend to skimp on these coupling capacitors. Years ago, I hot-rodded a mic preamp that originally had 4.7µF tantalum capacitors in the coupling stage. I replaced them with nonpolar electrolytics of a much higher value, and performance was improved.

Here, for C3 and C4, I use the same ones. At 100µF it’s overkill, I’ll freely admit, but the higher value reduces low-frequency phase shift (the LF response here is in the single-digit Hz range). Anything around 22µF or greater will work. Besides, it’s very difficult to match capacitors to such tight tolerances.

The high-pass filter is engaged by a switch — SW2.

Here’s where R5, R6, and R7 come in. They form what THAT calls a “T-bias” circuit, which boosts low-frequency common mode impedance. C14 is another ceramic capacitor across the inputs to clean up any remaining RF noise. By the way, R3 and R4 are there to limit any fault currents that might sneak by the capacitors. Their low value prevents input impedance issues.

Additional protection from stray static charges and other voltage transients is provided by diodes D1 through D4. This is a simplified version of a number of protection circuits I’ve seen. Anything ugly gets shunted to ground.

Now, it’s on to the preamp IC, which does the heavy lifting in terms of gain: up to 60 dB of gain, in fact. While a lot of designs will set the chip at a fixed gain level and introduce level controls somewhere between subsequent stages, ours is a simple mic preamp. It would be a simple matter of just inserting a potentiometer (VR1) across the gain setting pins of the chip, right? Not that easy!

Rapid changes in that resistance can introduce DC offset in the chip, which translates to thumping and popping on the output. This is where C5 comes in; a very large capacitor to kill DC offset. Why so large? Because VR1, R8, and C5 comprise a high-pass filter, so the capacitance has to be large enough to bring the low-frequency response down. In this case, it puts it around 5 Hz at maximum gain, keeping any rolloff well below 20 Hz. VR1 is a reverse-log pot, which provides the correct gain vs. position curve.

Capacitors C7 through C10 filter RF gunk out of the power rails to each chip.

Speaking of high-pass filters, I included one here to roll-off any mic or room rumble. C6 and SW2 provide a HPF, but this one has a twist. (Special thanks to the folks at www.groupdiy.com for this idea.) Because the changing resistance of VR1 naturally changes the characteristics of the HPF, this filter’s rolloff actually increases somewhat at higher gain settings. At first, this may seem undesirable, but think about it — low frequency artifacts are more likely to be a problem at higher gains than at lower gains. At any rate, C6 is small enough to rolloff the low end, but not to the point of sounding thin.

Now on to the output stage, handled by the THAT 1646. It’s one of the simplest I’ve ever seen. One IC and a couple of nonpolar capacitors. Caution must be used if inserting any other stages or components before the 1646, as it is very sensitive with regard to impedance. C11 and C12 are there to address any common-mode DC offset on the outputs. From there, it’s on to the output XLR jack, passing through a simple polarity switch, SW3, to reverse phase if needed.

Finally, capacitors C7 through C10 filter RF gunk out of the power rails to each chip, a very important consideration in any design. Clean audio has to have clean power.

Since this whole thing is built around THAT ICs, I decided to simply call it “THAT Thing.” Tune in next time, and we’ll talk about the power supply, breadboarding the prototype, and putting it all together.

More information about the THAT 1512 and 1646 ICs, as well as design notes and other information can be found at:

• www.thatcorp.com/Design_Notes.shtml
• www.thatcorp.com/datashts/THAT_1510-1512_Datasheet.pdf
• www.thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf

Curt Yengst, CSRE, is a contributor to Radio World and an assistant engineer with WAWZ(FM) in Zarephath, N.J.

Email us with your own DIY ideas at radioworld@futurenet.com.

The post “THAT Thing” — A Solid-State Mic Preamp Project appeared first on Radio World.

First Meeting and Chairs of Advisory Committee on Diversity and Digital Empowerment

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Petition for Declaratory Ruling and connected assignment applications granted

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The Media Bureau Announces a Freeze, effective immediately, on the following Filings (collectively, Filings)

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First I’ll tell what you already know. Back in the day, AM broadcasting was king and FM was commercial-free. Things changed in the 1970s as FM grew in popularity. Here we are 40+ years later with many AMs struggling. Some have gone away because they were no longer financially viable. To make matters worse, AM directional stations are more time-intensive and costly to maintain, especially when compared to FM stations.

On the positive side, I know a number of smaller AM/FM combination and stand-alone AM stations in Minnesota that are doing well. One town has a 1 kW AM with a 100 kW FM. The AM brings in 40% of the sales revenue because it has always been locally programmed with live announcers until 1 p.m., then is live again during afternoon drive.

AM radio isn’t supposed to sound bad. It can be a clean and pleasurable listening experience, even when there is only 3 kHz of audio bandwidth. On the other hand, AM can be ugly to the ear when there are maladjustments.

SCIENCE

Modulation is the process of adding audio to a transmitted signal. Amplitude modulation is aptly named. A station’s carrier (transmitter power) is varied by the station’s audio. Carrier power is depressed to zero watts to achieve 100% negative modulation. It increases to 1.5 times carrier power when 100% positive modulation is reached. That is why a thermocouple antenna ammeter reading rises with modulation. You read it during a programming pause to get an accurate measurement.

METERING

AM modulation monitors have –100% and +125% lights indicating overmodulation. You really don’t want those lights to come on. More is not better.

First, be sure to set the monitor’s RF carrier level control so the carrier meter needle is in the right spot, as per manufacturer’s instructions. A carrier meter misadjustment will result in inaccurate modulation monitor readings.

Fig. 1 shows an AM modulation monitor. The –100% and +125% lights are on and yet the analog modulation meter reads only 94%. It is normal for an analog meter to read lower than actual modulation. In fact, 85 to 90% is a more realistic meter display, because it cannot track peaks as lights do.

Fig. 1: AM modulation monitor showing overmodulation.

A monitor’s audio output will sound excessively bright or harsh if a de-emphasis audio circuit is not included. Monitors traditionally do not have this, but often a simple capacitor and resistor modification will do the trick. The idea is to undo the high-frequency boost that is a part of the audio processing, per the National Radio Systems Committee (NRSC) standard. As you probably know, the transmitted audio has increased high-frequency response to overcome high-frequency rolloff in most receivers. The goal is to restore flat frequency response to the listener. Some audio processor manufacturers are using non-standard pre-emphasis curves to suit their taste. That complicates getting a realistic feel for frequency response. At least they are trying to make the best of receiver frequency response roll-off.

ON A SCOPE

An article I wrote regarding the operation of oscilloscopes, “Your Scope Is a Tool for all Seasons,” appeared in the Jan. 13, 2013, edition of Radio World.

To refresh your memory, a scope has a display where a dot that travels from left to right is deflected up and down with voltage. In this case, we will look at a transmitter’s RF output.

Fig. 2: An AM RF carrier wave on an oscilloscope.

I’ll begin with Fig. 2. It shows an oscilloscope with a view of the transmitter’s carrier with the scope sweeping at high speed (0.2 microsends per horizontal screen division) to see the actual carrier wave of an AM radio station. By carrier, I mean the transmitter’s power output. What you see is an almost perfect sine wave at the station’s operating frequency.

 

Fig. 3: A carrier with no modulation.

Let’s zoom in to the scope’s screen. Fig. 3 shows the carrier when the oscilloscope is slowed down to view audio (0.2 milliseconds per division). No modulation was present at that instant. Fig. 4 shows a 1 kHz sine wave modulating the carrier 100% positive and negative. The positive parts are the top and bottom peaks. They are mirror images of each other. The negative modulation part is where the carrier is just pinched-off at zero power in the center of the screen. This sine wave is relatively clean/undistorted, with less than 0.5% audio harmonic distortion.

Fig. 4: A carrier modulated 100% with a 1 kHz sine wave.

Many receivers do not reproduce it that way. The last 5 or 10% of negative modulation, between 90 and 100%, is where receiver detectors have trouble faithfully reproducing what the transmitter is sending. The result is audio distortion. We all know that unwanted audio artifacts are a listener turnoff.

Fig. 5: 100% modulation with receiver detector output.

In Fig. 5, I’ve switched the oscilloscope to dual trace mode. It shows the transmitter at 100% modulation on the top trace. The bottom trace was sampled at the receiver’s detector. I made the measurement there so it rules out additional audio harmonic distortion, which might be added in the output stage. By definition, harmonic distortion is where this 1 kHz audio tone will have unwanted audio products at 2 kHz, 3 kHz, 4 kHz etc. because of non-linear system performance. In this case, distortion from transmitter through the receiver detector measured 5.1%. It was only 3.1% at 90% modulation.

Fig. 6: 125% positive modulation, 100% negative modulation with receiver detector.

Fig. 6: Traditional analog audio processing used diodes to clip the negative side of audio before it went to the transmitter so it would not attempt to overmodulate the negative modulation while allowing positive modulation to go to 125%. The downside is that it added as much as 6.5% harmonic distortion in the process. Add the receiver’s problems to the mix and you have a whopping 10.2% distortion. Ouch! You’d never allow that on FM.

Newer digital processors reduce but may not eliminate the problem. Yes, the station can be a bit (about 0.9 dB) louder on the dial, but it is irritating to many listeners. They don’t know how to describe it, but oops, there goes another tune-out! Again, some people hear it and some don’t. Best not to penalize the station with high modulation.

Fig. 7: The transmitter is being badly over-driven at 100% negative modulation.

Fig. 7 shows the transmitter being modulated at over 100% negative modulation. I’ve moved the scope’s trace up a bit so you can see detail. Negative peaks go flat to the center, which is no carrier at that instant. Modulation like this will not pass the required NRSC occupied bandwidth nor will it pass my ear test for listenability. It is tiring to hear.

Fig. 8 is where you want to be. No more than 95% negative modulation, the sweet spot between loudness and listenability.

Fig. 8: 95% program modulation of the carrier.

It is a shame to lose listeners for that last 5% (about 0.5 dB) of modulation. Few if any will hear the loudness difference. Likely most will hear grit in the audio of transmitters modulated to the max. You can make up much of the modulation percentage difference with careful adjustments of the audio processing, before it goes to the transmitter. Software-defined receivers eventually will solve much of this problem, but we need to deal with today’s radios.

When I was installing AM stereo years ago, negative modulation was usually set at 95% and positive modulation at 95% for stations to sound clean. It was positive +125% if the client preferred it. That extra positive modulation comes as “forced asymmetry” where the negative audio peaks are soft clipped so the positive peaks can go higher. Ouch!

Surprisingly, bad-sounding audio with less than 100% modulation will usually fit into the NRSC occupied bandwidth mask, in the FCC required annual measurement. That is because of the required 9.5 kHz low-pass filter in audio processing.

AM stations competed in loudness wars to beat the other guy years ago. Now it is time to give listeners a pleasant experience with natural-sounding audio. Don’t drive them away.

I grew up in a broadcasting family that owned two AM stations and no FM. Success was dependent on keeping listeners. Loudness was not the answer.

Comment on this or any article. Write to radioworld@futurenet.com.

Mark Persons, WØMH, is an SBE Certified Professional Broadcast Engineer. He recently retired after more than 40 years in business. His website is www.mwpersons.com.

The post Find Your Modulation Sweet Spot appeared first on Radio World.

The BBC has announced that its two flagship radio programs for Afghan audiences will now be carried live by Radio Television Afghanistan, the country’s national broadcaster.

BBC News Dari

“Majale Shamgahi,” which is broadcast in Dari, and “BBC Naray Da Wakht,” broadcast in Pashto, will have the first half of its hour-long evening news programs every day on RTA’s FM networks in all 34 provinces of Afghanistan, as well as on medium wave.

The BBC programs examine key local and international issues with daily reports, interviews and analysis.

“A partnership with the BBC further reinforces RTA’s mission of informing the Afghan nation,” said RTA Director General Ismail Miakhail.

Pictured from left to right are Diva Patang, RTA presenter based in London; Ismail Miakhail, RTA director general; Jamie Angus, BBC World Service director; and Ismael Saadat, planning and commissioning editor, BBC News Afghan.

“Adding BBC programming to our output will contribute to the provision of trusted and impartial news about Afghanistan and the wider world.”

[Read: Radio TechCon Opens Registration]

BBC News Pashto

“We are delighted that the new partnership with RTA will allow our content to reach more people in Afghanistan, on channels they already know,” added Jamie Angus, BBC World Service director.

Miakhail also said that the RTA Academy would use the BBC as an example as it looks to train its country’s journalists on ethical journalism.

“Majale Shamgahi” will air from 6:30–9:30 p.m. Kabul Time, and “BBC Naray Da Wakht” will air from 3–4 p.m. Kabul Time.

 

 

The post Radio Television Afghanistan Rebroadcasting BBC Radio Programs appeared first on Radio World.

Announces auction of FM broadcast construction permits and seeks comment on auction procedures

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