Engineering Radio

We have a few stations that are currently encoded with the Arbitron PPM encoders.  I did a little research on the encoding method, since it is not immediately apparent how they are transmitting their data.

Arbitron PPM encoders

According to Wikipedia, which can sometimes be relied upon, Arbitron used Martin Marietta to help develop the technology.  Martin Marietta (now Lockheed Martin) is mostly known as  a defense contractor, they have helped develop several complex military communications systems over the years.

There are no fewer than 39 US patents that cover the technology used in the PPM.  The most significant of these appears to be 7,316,025 which describes the psychoacoustic masking technique employed.

It really is pretty slick, using a sample rate of 8.192 kHz, it transmits 4 bits per second in the 300-3000 Hz range by hitting specific frequencies in that range at varying intervals, adapting to the audio levels to keep the encoding below the programming content.  4 BPS is very slow and thus very robust.  After all, I believe the only formation transmitted is a six digit encoder serial number.   I did not read all 39 patents to see if anything else was changed in the encoding method, so it may be slightly different.

This type of system would have fairly low overhead, not adding to the station’s bandwidth which is a consideration for FM stations, and in the correct frequency range for most AM receivers on the market today.  Some people have said they have heard the encoding on one of our stations, most notably during silence or very quite programming.  Perhaps, especially in a dead air situation, one might hear in nearly imperceptible  low frequency slow fluttering sound.

If anything, the encoding is perhaps too robust.

Now for the deployment of the monitor technology, which has so many up in arms.  As with other Arbitron ratings methods, the main bone of contention seems to be the size and distribution of the sampling hardware.  Minority groups feel they are under represented because the PPM is unevenly distributed.

Ratings samples always seem to skew one way or another.  The data samples themselves seem to be too small to accurately predict a station’s listenership.  One anomaly and the entire month or quarter can be thrown off.  The PPM seems to correct some if the issues with keeping an accurate written diary.  One problem with the PPM however, it can also pick up incidental background noise and count it as time spent listening (TSL).

Think of the cubical environment where somebody several cubes away might be listening to a radio station.  To the PPM wearer, it is unintelligible background noise, however, because of the perceptual encoding, the PPM picks it up and it counts as several hours of TSL.

A broader sample would dilute this with other more accurate representations of radio listening.  A broader sample would also alleviate some of the complaints from the Minority Media and Telecommunications Council (MMTC).  First year physics students would recognize that not enough sample data can make results wildly inaccurate.  Or, as one emergency room doctor stated while washing my knee out with a liter of sterile water after a dirt bike accident, the solution to pollution is dilution.

In case you have wondered it yourself:

4CX3500A

This is an EIMAC 4CX3500A which came out of a Harris HT5 transmitter. As you can see it the ceramic cracked in half. When I arrived at the transmitter site, the unit was on, full plate voltage, no plate current, no overload lights. I figured it might be something with the tube, so I tried to pull it out, but only the top half came. One of those “Ah ha” moments.

Fortunately, there was a working spare at the transmitter site and we got back on the air relatively quickly.  That, in and of itself is amazing considering the building that this transmitter lived in.  One of those abandond former studio sites with the transmitter jammed into a back room somewhere.  To get to it, one has to dodge pigons, beware of rats and wade through piles of garbage.

It is a little bit hard to tell in this photograph, but there are to “cages” which are the Screen and Grid.  The post in the center is the filament/cathode and the top detached part is the plate/anode.  In an FM transmitter, the exciter is coupled to the grid, the screen accelerates electrons toward the plate and therefore controls the power, the plate collects the electrons and is coupled to the output stages and the antenna.  Good stuff.

Behold, I do not work for Clear Channel.  I do not work for Cumulus, or Citadel.  The company I work for is not about to go bankrupt, in fact, we have purchased a brand new FM transmitter for the wretched mountain top transmitter site featured here.

Nautel V 7.5 FM transmitter

Am I happy?  Oh yes I am. New transmitter = fewer midnight phone calls thus better quality of life for me and my family.  A solid state Nautel transmitter means fewer unscheduled trips to the transmitter site and better reliability.

As a result of consolidation and smaller engineering departments, almost my entire work day is now scheduled weeks in advance.  One little hiccup in the schedule can throw things off for days, resulting in many apologies, phone calls to reschedule, and general wasted time.

This is a V 7.5 FM transmitter, very likely the last V series transmitter Nautel ever makes.  They have moved on to the NV series.

It is replacing the Broadcast Electronics FM5A, which is 24 years old.  The BE has been a good transmitter, we lost a few rectifier stacks due to lightning over the years, but over all, it has been reliable and easy to repair when problems did arise.  This transmitter will be going into standby service.

The new transmitter, it sounds awesome.

Very similar to a TiVo, only works  with radios.   There are some very good radio shows out there, the kind that make you sit in the car long after you have reached your destination.  The kind that you might schedule your day around if possible.

A few of them are syndicated on NPR a few are locally produced, some are interesting talk, some are perspective, some are new music, etc.

Radio Shark Digital Audio Recording Device

Wouldn’t it be great if you could time shift those shows and listen to them when you wanted to?  Imagine this, you know that “This American Life” is airs on Saturday afternoon and it is a favorite.  However, this  Saturday you are busy working or what ever.  Go to the Radio Shark and program it to record your show, then listen to it later.  What a concept.

What this unit does:

1. Plugs into PC or Mac USB port.
2. Has AM and FM receivers built in.
3. Can record programming and play back later, or pause programming and resume playback while recording.

What this unit does not do:

1. Not very portable, unless the user want to lug a lap top around.
2. Does not integrate into cars or other playback devices, such as I-pods, etc.
3. Does not record internet sources directly, although there are a few links to shareware on the Radio Shark website that will do this.

This is a start, but what is really needed is something that is factory installed in cars.  Say the Digital Audio Recording Device (DARD) can be in installed in the car, or in the house, or both.  Then  each DARD has a flash drive that can be moved from one unit to another, but only played back in DARD units (to thwart pirating music). It can even be an I-pod app.

This is the type of new technology that will bring listeners to radio and make radio stations create good quality local content, stuff you can’t get anyplace else.

Why aren’t these being marketed?  Heck, radio stations should be giving them to listeners, I bet you could even get them manufactured with station logos.  Seems like an opportunity lost to embrace some meaningful, understandable, young technology.

Update: Okay, there are others out there as well.  What needs to happen is all these features tied together and offered in stock car radios.

Another picture from my collection, this one is the back side of a power supply module from a Broadcast Electronics AM6A transmitter:

Bang!

It happened during power up from 1 KW to 5 KW and it was quite loud, as I was standing right next to the transmitter.  The exploded part is a 0.1 uf capacitor that looks like an add on.  In fact, some of the other power supplies don’t have it.  It also took out the 20 amp slow blow fuse.

I like the exploded look of the board, kind of like on The Road Runner, when Wyle E. Coyote looks into a box and something explodes.

This is the only problem I have had with this particular transmitter.

Another example from my blown up shit collection, pictures archive:

Burned out harmonic filter, BE FM-30T transmitter

The harmonic filter from a Broadcast Electronics FM-30T.  This actually started in the bullet connector to the 3 inch hardline on the output side of the filter.

Burned out 3 inch hard line section

Again, I did not install this myself, someone else did.  Cutting 3 inch hard line is pretty straight forward.  When using a field flange, the outer and inner conductors are cut flush.  Both conductors should be de-burred and filed smooth.  It only takes a little thing to start an arc with 30 KW of FM power, so once again, attention to detail is key to avoiding these things.

Fortunately, BE sent along replacement parts for the harmonic filter and the line section was replaced.

As promised, here is the AM transmitter site maintenance check list.  This is for a generic directional AM station with a backup transmitter, generator and an RF STL.

Broadcast Electronics AM6A transmitter

Usual disclaimers apply.

AM site Maintenance checklist

Weekly Maintenance:

A.  Visit site, Check following:

1. Check critical transmitter values against last logged value
2. Check forward/reflected power on main transmitter
3. Check and reset any overloads
4. Check signal strength on STL against last logged value
5. Check generator fuel level
6. General check of building, look in all rooms, inspect for damage from vandalism, Leaking roofs, obvious signs of trouble, take steps to correct.

Monthly Maintenance:

B.  Visit site, Check following:

1. Do a full multi-meter log, (includes tower phase angles, loop currents), run backup transmitter into dummy load.
2. Start and run generator for 5 minutes, check block heater, hoses, belts, oil and antifreeze levels
3. Calibrate remote control meters with transmitter meters, log it*
4. Check all tower fences for integrity and locked gates*
5. Complete Items 3, 4 and 5 under weekly maintenance.

Quarterly Maintenance:

C.  Visit site, Check following:

1. Complete 1 through 5 under monthly maintenance.
2. Check all air filters, clean or replace as needed.
3. Check frequencies of all transmitters, STL receiver, and log.
4. Complete quarterly tower lighting and painting inspection*

Bi-yearly Maintenance:

D.  Visit site, Check Following:

1. Complete 1 through 5 under quarterly maintenance.
2. Conduct monitor point readings for all directional antenna patterns*
3. Check base current readings for day/night towers.  Ratio.*
4. Clean backup transmitter
5. Place backup transmitter on air and clean main transmitter.

Yearly Maintenance:

E.  Check all licenses and authorizations for accuracy. Make sure that all renewal cards etc are in public file and are posted at control point.*

F.  Visit site, Check following

1. Complete 1 through 5 under Bi-yearly maintenance
2. Equipment performance measurements (NRSC, Harmonics, frequency)*
3. Complete service of generator
4. Complete Inspection of towers, check for vertical and plumb, check guy wire tensions, retension as needed.
5. Check property for anything out of the ordinary
6. Repair driveway as needed

General maintenance that is completed on an as needed basis

1. Re-fill fuel generator fuel tank when drops below 50 percent
2. Empty trash, sweep floors, dust.
3. Cut/remove vegetation inside tower fences, spray herbicide as needed
4. Water proof tower fences every 2 years
5. Paint exterior of building
6. Replace tower lights*
7. Paint towers*

*These are FCC inspection items, pay close attention if you do not want a fine.

That is it, a .pdf version of this file can be downloaded here.

I developed these check lists for FM transmitter site based on experience and what needs to be checked, how often it needs to be checked and what else can go wrong.  This checklist is for a generic FM transmitter site with a back up transmitter and an RF STL.  Every site is different, so some things on this would likely need to be changed or adapted depending on equipment and other facilities.

BE FM20T transmitter

Enjoy!

Weekly Maintenance:

A.  Visit site, Check following:

1. Check critical transmitter values against last logged value
2. Check forward/reflected power on main transmitter
3. Check and reset any overloads
4. Check generator fuel level
5. Check the STL signal strength level against last logged value.
6. General check of building, look in all rooms, inspect for damage from vandalism, Leaking roofs, obvious signs of trouble, take steps to correct.

Monthly Maintenance:
B.  Visit site, Check following:

1. Do a full multi-meter log, run backup transmitter into dummy load.
2. Check line pressure, Check tank pressure and/or desiccant for water
3. Start and run generator for 5 minutes, check block heater, hoses, belts, oil and antifreeze levels
4. Calibrate remote control meters with transmitter meters, log it*
5. Check the tower fence, be sure it is secure and locked.*
6. Complete Items 3, 4, and 6 under weekly maintenance.
7. During summer months, be sure the vegetation is cut around building and tower.

Quarterly Maintenance:

C.  Visit site, Check following:

1. Complete 1 through 7 under monthly maintenance.
2. Check all air filters, clean or replace as needed.
3. Check frequencies of all exciters, STL receivers, TSL transmitters and log.*
4. Complete quarterly tower lighting and painting inspection

Bi-yearly Maintenance:

D.  Visit site, Check Following:

1. Complete 1 through 4 under quarterly maintenance.
2. Clean backup transmitter
3. Place backup transmitter on air and clean main transmitter.

Yearly Maintenance:

E.  Check all licenses and authorizations for accuracy, make sure all license renewal cards are posted and placed in the public inspection file.*

F.  Visit site, Check following

1. Complete 1 through 3 under Bi-yearly maintenance
2. Complete service of generator
3. Complete Inspection of tower and antennas, check concrete tower bases, check guy wire anchors, (grounding, turnbuckle safety cable) check property for anything out of the ordinary
4. Repair driveway as needed

General maintenance that is completed on an as needed basis:

1. Tube changes on main/backup transmitter.
2. Sweep antenna with a spectrum analyzer/return loss bridge to make sure it is on frequency and has sufficient bandwidth to pass FM signal.
3. Look at FM RF mask with spectrum analyzer, check harmonics for proper attenuation.
4. Sweep transmission line with a spectrum analyzer/return loss generator.
5. Re-fill fuel generator fuel tank when drops below 1/2
6. Empty trash, sweep floors, dust.
7. Paint exterior of building
8. Replace tower lights*
9. Paint towers*

*These are FCC inspection items, pay close attention if you do not want a fine.

The .pdf version can be downloaded here. I’ll to an AM directional check list next week.

Yesterday, I threw out a transmitter.  I know there is probably some radio station out there that may have been able to use a 5 KW FM transmitter, but believe me, not that one.  There are limits to how much you can help out a fellow broadcaster.  Donating an FM transmitter that never really worked right in the first place is counter productive.

Anyway, to demostrate that I am not a total heel, here is my favorite brand of transmitter, Nautel:

Nautel V-40 transmitter (4 V-10 transmitters combined)

I like Nautel because they are rugged, reliable and good looking.  Okay, good looking is low on the list of transmitter attributes, however, you have to admit, it is good looking.  It is also good sounding.  The night we switched over from the long in the tooth BE FM30A to the Nautel V-40 I noticed a marked improvement in the station’s sound.  It was like somebody switched off the background noise generator.

As the caption states, this is 4 V-10 transmitters combined with a ERI magic T combiner.  It is set up so that if any one transmitter fails or reduces power, the magic T combiner automatically adjusts for minimum rejected power, then the SC-1 controller turns up the other three transmitters to maintain the stations Transmitter Power Output (TPO).

TPO 28 KW

In this case the TPO  is 28 KW, which is getting into the semi serious range for an FM station.   Nautel has updated their transmitter line, which now consists of the NV series transmitter.  The differences mainly have to do with the IPA module/PA module interchangeability (not interchangeable in the V series, fully interchangeable in the NV series) and the “Advanced User Interface.”  I don’t know, fancy touch screens are optional on FM transmitters as far as I am concerned.  It’s the underlying RF generating sections that I am most concerned about.

Nautel V-40 transmitter

Another view.  Just for the useless trivia that is in it, the “V” in these transmitter names stands for “Virtuoso.”

Takes its rightful place in the world today, the scrap heap:

Gates FM5G carcass

As EDWARD I of ENGLAND once said, “A man does good business to rid himself of a turd.”

Of course, he was speaking about Scottsman John Balliol and not some old cranky FM transmitter, but I understand that feeling.  The Gates and later Harris transmitters always seemed to be somewhat less than top notch. The 5G was no exception to this rule.  The final step for tuning the transmitter was to turn off the lights in the room and look down through the screen on top to make sure there were no little arcs in the PA tuning section.  It also had a way of self oscillating, which could make for some exciting tuning.

Gates FM-5G transmitter prior to disassembly

Good bye, I will not miss you.

In one of my past jobs, I worked in a RCA town.  I worked there long after the broadcast arm of that company went out of business, however, all of the broadcast transmitters, AM, FM, TV were made by RCA.   I had an RCA FM-20ES1 which was 22 years old, built like a tank and just kept going along.  I think that transmitter was finally destroyed in a fire, caused by it’s replacement transmitter.

Old Collins, Contenental, RCA and even Broadcast Electronics transmitters had some heft to them.  Of course, not every RCA transmitter was well thought out, the amplifuze series of AM transmitters were a maintenance nightmare.