Brewster Woes

As many of you know, The Brewster station (KPBW 91.9) went off air last week. I have been unable to communicate with the remote control via cell phone.
Two of our brave angels attempted to gain access last Friday but were unable to reach the site, due to the snow conditions.

The next planned assault will be a two-vehicle affair, made possible with the help of Translator District #1. I hope that the fix will be a simple reset, once they reach the site.

We’ll tell you more as the story develops. We are sorry for the disruption in service.

Bonners Ferry Status

I just wanted to let you know that KIBX 92.1 in Bonners Ferry is experiencing very high reflected power (up to 20%.) This is most likely due to severe icing on the antenna but I can’t be certain until the weather clears a bit.
In order to keep the transmitter operating, we’re running it at reduced power. You may not even notice the difference, depending on your location.

Jerry Olson

Latest Plans for 92.1

We’re headed up the mountain early Friday morning (Nov 8) and the plan is to physically isolate the KPBX receiver from the KIBX transmitter. There will be more-than-usual program interruptions while that is occurring but the hope is that this will result in better service.

Jerry Olson

The Ballad of Bonners Ferry

As one of our faithful supporters reminded me, I’ve have been remiss about posting updates on the woes of 92.1 in north Idaho.

As I’m sure you’re aware, the audio has had extremely annoying drop-outs lasting from seconds to minutes. I’m pretty sure the problem is reception of the signal from KPBX in Spokane. The site uses a master antenna system to feed the various signals to all the tenants up there. Some of the difficulty arises because our 92.1 KIBX transmitter at the site interferes with our ability to receive a reliable signal from Spokane. It’s a bit like trying to listen to someone on your cell phone while you’re at a rock concert.
We have tried several methods including signal traps, bandpass filters, and this past trip….replacing all the questionable cables on the master receive system. Each time we “fix” it, it seems to work fine….until the next day. That latest trip was on October 23rd.
My next attempt is going to be physically separating the receiver from the transmitter by about 20 feet. It’s possible that trying to remain within our leased area is just asking too much of the receiver. Why things have changed, I don’t know.
I’ll get this done as soon as I can schedule a trip with the site managers. We’ve probably run out of drive-in capability for the season.
Again, my sincere apologies for the impairment. We are concerned and are working on it.

Jerry Olson
Chief Engineer

Bonners Ferry Upperdate

It appears that the problem was, indeed, a zapped notch filter. We replaced that about 9:30 AM Thursday and all seems to be well.

Yay!

Bonners Ferry Update

We realize that the performance of the 92.1 signal in Bonners Ferry has been poor for the past several weeks. I think that the recent storms have caused damage to several components. My best-guess list of failed parts is on order and I’m planning a field trip for the end of this week.

As I understand it, the audio has been dropping in and out, sometimes for several seconds at a time (most annoying!). At other times, the signal is present but has a lot of static.

What I can tell from our telemetry here is that the transmitter itself remains at full power. Therefore, the issues we are experiencing are most likely due to the master receive antenna system for the site and/or our radio receiver.
To that end, I have ordered a new bandpass filter for our receiver and a bandstop filter for the master antenna. I hope the existing receiver is undamaged, but I will also bring another receiver with me. If I have to use it, we will not be able to receive the HD signal from Spokane which allows the multicasting at Bonners Ferry.

Once again, I’m very sorry for the impaired service. We will get this fixed.

Jerry Olson

How Spokane Public Radio gets from here to hear. Part 4

So, what is the difference between AM, FM, and HD® radio?

AM, or Amplitude Modulation, was the mainstay of radio from its inception on through the 1960s. With AM, the transmitter frequency remains constant. The program audio changes the power output of the transmitter instantaneously. The transmitter is usually set up so that with no audio present, the transmitter puts out a little more than half of its licensed power. It’s done this way so that when the loudest audio is being broadcast, the negative peaks don’t drive the transmitter all the way to zero output when the positive peaks hit 100%. As mentioned in an earlier post, the relatively low frequency of AM allows it to bounce off the ionosphere and be heard at great distances, especially at night. The main disadvantage, though, is that AM is quite susceptible to environmental interference. Any electrical noise sources, such as power lines and especially lightning, are indistinguishable from an AM broadcast to an AM radio. If there is a component of the noise that falls onto the frequency of the station being tuned in, that component will be played along with the desired audio. AM is still going strong even though many of the music formats have moved to FM.

In Part 3, we talked quite a bit about FM Radio, so we’ll only touch on it here. Since FM radios are only sensitive to a frequency change within a specific range, most environmental noise is ignored. That’s the main reason that FM can be so quiet, even with a thunderstorm going on. As an aside, FM transmitter sites are often vulnerable to lightning. Since FM relies on line-of-sight transmission, FM transmit antennas are mounted on tall towers or atop mountains…sometimes both. Being high enough up to “see” a long way, makes the tower a great lightning rod. KPBX is located on a relatively short tower (less than 100 feet), but located on a tall mountain (Mica Peak, almost a mile above sea level.)

The newest kid on the block is HD® Radio. HD® Radio is the trademark of iBiquity Digital Corporation for their method of encoding digital data in what’s called the In-Band, On-Channel (IBOC) method. This is a fairly recent addition to the industry. HD® Radio technology can be applied to both AM and FM stations but so far, very few AM stations have adopted it. I think there’s only one in Spokane (KQNT). All three of Spokane Public Radio’s stations are transmitting in HD. We also are broadcasting in HD from KIBX in Bonners Ferry, ID.
For FM IBOC transmission, two identical sets of digital information are transmitted, one on either edge of the FM analog envelope. You’ve probably heard this digital data buzz when you tune your radio slightly off dead center. This digital information is transmitted at either 1/100th or 1/25th the power of the analog, depending on the transmitter and how it’s set up. Having the twin sets of data allows some error correction to be done in the receiver.

The main advantages of HD® Radio are improved audio quality and, most importantly, the ability to multicast. KPBX makes great use of this by broadcasting KSFC’s program as KPBX-HD2 and KPBZ’s program as KPBX-HD3. Licensing requirements state that HD1 must always mirror the program of the parent analog station.

There are a few disadvantages of IBOC transmission.

• IBOC requires higher cost transmitters and lowered efficiency if the same transmitter broadcasts both the analog and digital signals. KPBX and KSFC both use separate transmitters and antennas for analog and digital transmission. KPBZ, being relatively low power, uses a single transmitter and antenna to broadcast both signals.

• The digital encoding takes a long time, somewhere between 8 to 10 seconds, depending on how old and slow the equipment is. This requires us to delay our analog signal so that it matches up perfectly with the digital signal. This is done so that your program doesn’t jump back and forth in time when you’re listening near the edge of the digital signal’s effective range. Your radio will be “blending” back and forth between the digital and analog signals. Since there’s no backup analog for the HD2 and HD3 channels, they just drop out when the digital signal is too low.

• A third disadvantage is that transmitting the digital carriers adds some noise (buzz) that is detectable by some older analog radios that have a wide IF bandwidth. Most of the newer radios don’t have this problem.

So, we’re doing the experiment. More and more cars are offering HD® Radio as standard equipment. We’re hoping that more and more listeners will enjoy it in the car, at home, and at work.

Next time….Getting the signal from the studio to the transmitter.

Mid-July Update

It’s been quite a while since I’ve posted about station engineering events, so I thought I’d comment on a few of the happenings.

Amidst all the other excitement of the Independence Day weekend, we lost the connection for all three of our online streams. We tried the usual fixes (several times) to no avail. My thanks to Brian Coburn at Argia North America who got our streaming re-routed around the offending equipment.

The high temperatures of the prior week caused a bit of concern about the transmitter sites but the only outages were caused by power bumps and not by overheating. This year’s Antoine Creek fire knocked KPBW off the air in Brewster for a day or so, due to a power outage.

Some exciting news…we were approached by the Thompson Falls (Montana) TV District with a request to carry KPBX’s program on their local translator. We, of course, gave them the go-ahead. As of today, the translator is still on the previous source, but listen for KPBX on 103.9 in Thompson Falls in the not-too-distant future.

Another project that we’re considering is changing the program feed for KXJO in Saint Maries, Idaho from KPBX to KSFC. The reason for this is that most, if not all, listeners in Saint Maries already get a great KPBX signal on 91.1. If we can make this switch, the KSFC programs will also be available in Saint Maries on 92.1.

I traveled to Omak a few weeks back and, with the help of Mike Peterson of KSPS, we hardened up the support structure for the KOMQ transmit antenna. Even though it survived last winter, it was knocked out of alignment. Ironically, a falling piece of ice did manage to take that station down for several days by breaking the LNB off the indoor satellite dish.

So, that’s just a summary of what we’re doing. This is the season to repair last winter’s damage and try to get ahead of what next winter is planning for us.

Jerry Olson
Chief Engineer

How Spokane Public Radio gets from here to hear. Part 3

Last time we left off, we had our audio stream ready for signal processing. Processing involves not only regulating the volume and tone quality of the signal; it also prepares the audio for FM broadcast.

A quick explanation of FM is in order. FM stands for Frequency Modulation. The program audio actually instantaneously changes the frequency of the carrier that the transmitter is putting out. KPBX only transmits at exactly 91.1 MHz when there’s no audio. The louder the signal is, the farther we move away from 91.1 MHz. The FCC has strict guidelines as to how far we can deviate from the center frequency. With complex audio, especially music with loud high frequencies, we need to be very careful about the harmonics produced. High energy, high frequency sound can very easily drive our modulation past the legal limits.

Much of the enjoyment of music is due to the difference between the soft parts and the loud parts. This is referred to as dynamic range. At Spokane Public Radio, we strive to provide a good balance between not-too-quiet and not-loud-all-the-time. If we didn’t compress the dynamic range somewhat, it would be nearly impossible to hear softer passages while in your car. This also means we need to put the brakes on the really loud passages in order to stay legal. But that’s only part of the job of processing; it does much more.

Until very recently, the FCC had mandated that enhancements to broadcast technologies had to be backward compatible with existing equipment. The effect of this is that a person listening to a stereo program on a monaural radio must be able to hear the entire program. This is all done by the audio processor.

The processor receives the Left Channel and Right Channel audio signals from the mixing board. After adjusting the volume levels and the tone color, etc, the processor combines the two signals together to produce both a Left+Right signal and a Left–Right signal. The L+R part contains all the audio information and thereby becomes the monaural signal which occupies the center of the spectrum from –15 KHz to +15 kHz around the center frequency. That’s the only part of the signal that a monaural radio needs to receive.

When the station is in stereo mode, the processor produces a very precise 19,000 Hz sine wave (+/– 1 Hz !) This stereo pilot tells your radio that it’s receiving a stereo program and turns on the “Stereo” light. Your radio has a filter to keep this pilot tone out of the audio you hear (15 kHz “brick wall”.) The processor then uses this pilot to produce a second signal at twice that frequency (38 kHz) which is combined with the L-R information. This resultant carrier is parked out at +/–38 kHz from the center frequency.

Out beyond the 38 kHz L–R information, there are SCA (Subsidiary Communications Authority) channels. The Radio Data Service (RDS) at 57 kHz provides station information to radios that are equipped to use it. KPBX uses a 67 kHz SCA to transmit the Evergreen Radio Reading Service for the Blind. It takes a special radio to be able to listen to this service. There’s even a 92 kHz SCA that we can turn on as a backup return telemetry path for the remote control equipment at the transmitter site.

In a previous installment, I promised a discussion of digital audio, so let’s go back to some sound fundamentals. When we hear sound, it is because all the objects producing sound are vibrating and producing tiny variations in the air pressure right around them. These pressure variations travel away from the source and combine with all the other sound producers. All of their pressure waves mix, adding here and subtracting there, which results in a single (but very complex) pressure wave that arrives at your eardrum (or a microphone) and causes it to vibrate in accordance.

We talked earlier about protecting this signal from outside interference with shielding and balanced wire techniques. An alternate way of reducing noise is to convert the sound information into code. After the voltage signal is received, it goes through an analog-to-digital (AD) conversion. This consists of taking thousands of measurements each second and assigning a number to the instantaneous voltage of each measurement. The beauty of this is that these numbers are very interference-resistant. They’re all encoded in binary form with each bit being either a “one” or a “zero”. These numbers can then be transported between computers and “reassembled” at the final destination using a digital-to-analog (DA) conversion. As you might surmise, the more measurements (samples) you take per second and the finer degree of voltage variation you can detect, the closer you can get back to the original sound…..which is analog. As an example, the standard digital coding used for CDs is 44,100 samples per second. Each sample can have a value of between 0 and 65536 (16 bits).

Okay. So what’s the difference between AM, FM, and HD® radio?
Watch for Part 4.

Twisp Update

As it turns out, the audio problem at Twisp appears to be a satellite system problem rather than a receive problem. We now have information that shows that Omak (and consequently, Oroville) have had the same drops in the audio.
The Toronto office of the satellite company confirmed that they are having intermittent failures with all the programs from Spokane but they don’t yet know what is the problem.
So, there’s little we can do to fix the satellite issue.
The immediate plan is to get working on an alternate delivery system. We will be testing to see if we can get an adequate over-the-air signal from Brewster to feed both Twisp and Omak. The Brewster transmitter was not in place when the Twisp and Omak units were commissioned.
We’ll have to buy some more gear to make this happen but, over the long run, the system will be more reliable if we have two ways of getting the KPBX signal to those transmitters.
In the short term, let’s hope the satellite issue gets resolved sooner rather than later.