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Zmog!

The quick disconnect LNB:

C-Band LNB

C-Band LNB

Umm…

No food or drink in the studio

This is a rule that I always find difficult to enforce.  Since switching into contracting mode, I am often at any particular studio once per week or less.  It seems to me, no matter what signs are posted or what words are spoken, the DJ seems to hear; “It is okay to eat and drink in the studio.”

Of course, with that attitude, the inevitable is bound to happen:

RS-18 Millenium console on/off button membrane

RS-18 Millenium console on/off button membrane

To make things worse, this was spilled on the main mic on/off buttons.  These button membranes come in groups of six and are not inexpensive.  The complaint was “The main mic will not turn off.”  Ah well, I am paid to fix things after all.  The DJ’s are only inconveniencing themselves at this point.

Vote

Here in the good ole’ US of A, today is election day. I try to stay away from politics, that is not what this blog is about.  However, once in a while, a good public service announcement is required.  So, this year, if you are a citizen and eligible to, go vote.  People say, “Oh but it is a midterm election, it does not matter.”  Horse hockey, every election matters.  Think of it this way; for 364 days out of the year, the politicians are fucking you.  You get one day to return the favor.  I suggest you use it wisely.

Whatever happened to the CFA?

Remember way back when, perhaps in high school or college, you met this really cool person who seemed to be wonderful in every way? Yeah, then you got to know them a little better and, well, those first impressions changed a little bit.

Crossed Field Antenna, Courtesy of Wikipedia

Crossed Field Antenna, Courtesy of Wikipedia

The Crossed Field Antenna (CFA) sort of reminds me of my first prom date.  There was a lot of promise there, but plans fell through.

From a 1999 Radio World article:

Imagine an AM antenna one–fiftieth of a wavelength long, that needs no radial ground system, occupies a small parcel of land, produces little or no RFI (Radio Frequency Interference), has great bandwidth and performs better than a full–sized vertical radiator.

This potential new antenna was all the rage during the early 00’s or whatever you call that decade.  I remember thinking to myself; I will believe it when I see the test results.  At one point, there was a battery of tests run in the installation in Egypt and China.  The test results are spotty at best, however, none of these installation performed up to expectations.  While it looks like a cool idea, and it would have been great to see it succeed, it seems that sheer will power alone will not make a particular system work outside of the laws of physics.  There are a few of these still in operation out in the wild, mostly in Egypt.

Fixing small problems

This happened recently at an AM station we were doing work for. It seems the modulation monitor was not working when connected to the backup transmitter. A quick check of the RG-58 coax showed that I had the correct cable plugged into the monitor selector relay.  Another check with an ohm meter showed the cable was okay.  Then I looked at the connector on the monitor port of the transmitter and saw this:

BNC connector pin  improperly located

BNC connector pin improperly located

Looks like the pin is too far back in the connector. This is an old style BNC connector with a solder in center pin:

BNC connector center pin

BNC connector solder type center pin

The center pin has a blob of solder on it, preventing it from seating properly in the connector body. I could have lopped it off and applied a new crimp on connector, but my crimp tool was in the car. I didn’t feel like walking all the way through the studio building, out into the parking lot and getting it. Therefore, I used a file and filed off the solder blob then reassembled the connector:

BNC connector

BNC connector

The transmitter was installed in 1986, I think the connector had been like that for a long time.

It may seem like a small detail to have the modulation monitor working on the backup transmitter, however, the modulation monitor is also the air monitor for the studio.  Switching to the backup transmitter but not having a working air monitor would likely have caused confusion and the staff might think they are still off the air.  I know in this day and age, a lot of station do not even have backup transmitters, but when something is available, it should work correctly.

I like my cool network analyzer and all that, but sometimes it is the Mark 1, Mod 0 eyeball that gets the job done.

Network Security, part II

With the spate of ransomware and crypto virus attacks on automation systems, perhaps a quick review of network security is in order:

  1. Isolate the automation system on a separate network from the general office network and do not allow internet access on the automation system’s work stations or servers.
  2. Use a separate switch for all automation network connections.
  3. install a small router between the automation network and the office network.  On the router, the WAN port faces outward toward the office network, make the WAN port non-pingable.  Grant access from the office network for certain users; e.g. traffic, music director, etc via access lists.  Open up a few ports for VNC or RDP on the router so technicians can remotely access machines to do maintenance and troubleshooting.
  4. Use supported and up to date operating systems.
  5. Use separate admin and user accounts, make sure that admin rights are removed from user accounts and keep machines logged in as users.  This ensures that some errant DJ or other person does not install any unauthorized programs.
  6. Install and keep up to date a good antivirus program.
  7. Back up the data and test the backups.

The office network is more vulnerable because of the human element.  Internet access is require, of course.  Click on a pop up, sure!  Hey, that photograph has a funny file extension, lets open it and see what it is.  I never heard of this person before, but look, they sent me an executable!

Much of the office network security will rely on the quality of the router connected to the internet and the antivirus software installed.  Of course, the network users have a good deal of responsibility also.

O Canada

In light of recent events…

You know, in this day and age, one can subscribe to certain ideas or religious viewpoints and pull some pretty serious shit.  You might even get away with it.   That being said, here is a bit of advice: Do not fuck with Canada.

Brother, can you spare a theorem?

A theorem is not, indeed, a fact.  It is rather, an idea which is deduced and supported by other proven facts.  Thus, a theorem is generally believed a truth.  It should be of interest to the “All Digital” AM (AKA Medium Wave) proponents that noise on the digital channel will reduce data throughput as a function of channel bandwidth and Signal to Noise Ratio.  This is known as the Shannon-Hartley theorem:

 C =  B \log_2 \left( 1+\frac{S}{N} \right)

Where:
C is the channel capacity in bits per second;
B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);
S is the average received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watts (or volts squared);
N is the average noise or interference power over the bandwidth, measured in watts (or volts squared); and
S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels).

With this equation, one can discern a fundamental flaw in the all digital logic.  One of the main issues with AM Medium Wave broadcasting is the ever increasing noise floor.  Our society has changed drastically in the last one hundred years or so since AM was invented.  Electrical noise generators; computers, plasma screen monitors, mobile phones, appliances, energy efficient lighting, data over power line, street lights, poor utility line maintenance, even electric cars, it seems, generate a cacophony of noise in the Medium Wave frequency band. A digital modulation scheme, be it HD Radio or DRM, will mask the noise to a certain extent, that is true.  However, once the SNR exceeds the ability of the receiver to decode the necessary bits, the receiver will mute.  While it is true, the listener will not hear noise, they may not hear anything at all.

I will also note; none of the current “AM improvement” schemes under consideration by the FCC addresses the noise issue on the AM band.  Without addressing the noise issue, any digital modulation scheme will be a temporary fix at the very best.  The noise floor will continue to rise and after it gets high enough, the all digital modulation will simply not work.

It will be interesting to see the data from the all digital HD Radio testing that is being done in various locations.  That is, if the NAB, et al. does not decide to treat that data like some kind of state secret; they have become reticent of late.  When somebody acts like they have something to hide, it makes me think they have something to hide…

Lightning protection for WLAN links

More and more wireless LAN links are being installed between the transmitter and studio.  Often these links are used for network extension, remote control, site security, VIOP telephony, and sometimes even as a main STL.  These systems come in several flavors:

  • Moseley LAN link or similar system.  Operates on unlicensed 920 MHz (902-928 MHz) band.  Advantages: can use existing 900 MHz STL antennas, can work reliably over longer distances, transmitter and receiver located indoors.  Disadvantages: slow, expensive
  • ADTRAN TRACER or similar system with indoor tranceivers and coax fed antenna systems.  Operates on unlicensed or licensed WLAN frequencies.  Advantages: fast, transmitter and receiver located indoors, can be configured for Ethernet or T-1/E-1 ports.  Disadvantages; expensive
  • Ubiquiti Nano bridge or similar system where tranceiver is located in the antenna, the system is connected via category 5/6 cable with POE.  Operates on unlicensed or licensed WLAN frequencies.  Advantages; fast, relatively inexpensive.  Disadvantages; equipment located on tower, difficult to transition base insulator of series fed AM tower.
  • Ubiquiti Rocket or similar system where the antenna and tranceiver are separate, but the transciever is often located on the tower behind the antenna and fed with category 5/6 cable with POE.  Operates on unlicensed and licensed WLAN frequencies.

For the first two categories of WLAN equipment, standard lightning protection measures are usually adequate:

  • Good common point ground techniques
  • Ground the coaxial cable shield at the tower base and at the entrance to the building
  • Appropriate coaxial type transmission line surge suppressors
  • Ferrite toroids on ethernet and power connections

For the second two types of WLAN equipment, special attention is need with the ethernet cable goes between the tower and POE injector or switch.  Shielded, UV resistant cable is a requirement.  On an AM tower, the shielded cable must also be run inside a metal conduit.  Due to the skin effect, the metal conduit will keep most of the RF away from the ethernet cable.  Crossing a base insulator of a series excited tower presents a special problem.

The best way to get across the base insulator of a series excited tower is to use fiber.  This precludes the use of POE which means that AC power will be needed up on the tower to power the radio and fiber converter.  This my not be a huge problem if the tower is lit and the incandescent lighting system can be upgraded to LEDs.  A small NEMA 4 enclosure can house the fiber converter and POE injector to run the WLAN radio.  Some shorter AM towers are no longer lit.

Another possible method would be to fabricate an RF choke out of copper tubing.  This is the same idea as a tower lighting choke or a sample system that uses tower mounted loops.  I would not recommend this for power levels over 10 KW or on towers that are over 160 electrical degrees tall.  Basically, some 3/8 or 1/2 inch copper tubing can be wound into a coil through which a shielded ethernet cable can be run.  Twenty to twenty five turns, 12 inches in diameter will work for the upper part of the band.  For the lower part, the coil diameter should be 24 inches.

In all cases where CAT 5 or 6 cable is used on a tower, it must be shielded and the proper shielded connectors must be used.  In addition, whatever is injecting power into the cable, ether POE injector or POE switch must be very well grounded.  The connector on the shielded Cat5 or 6 cable must be properly applied to ensure the shield is grounded.  A good video from Ubiquiti, which makes TOUGHCable, on application of connectors to shielded Cat5 cable is here:

In addition to that, some type of surge suppressor at the base of the tower is also needed. Tramstector makes several products to protect low voltage data circuits.

Transtector APLU 1101 series dataline protector

Transtector APLU 1101 series dataline protector

These units are very well made and designed to mount to a tower leg. They come with clamps and ground conductor designed to bolt to a standard copper ground buss bar.

Transtector APLU 1101 series dataline protector

Transtector APLU 1101 series dataline protector

There are various models designed to pass POE or even 90 VDC ring voltage.

Transtector APLU 1101 series dataline protector

Transtector APLU 1101 series dataline protector

This model is for POE. The circuit seems to consist mostly of TVS diodes clamping the various data conductors.

As more and more of these systems are installed and become a part of critical infrastructure, more thought needs to be given to lightning protection, redundancy and disaster recovery in the event of equipment failure.

Trends in Terrestrial Broadcasting, II

Things seem to be relatively quite these days, no earth shattering developments, no big news stories, etc.  My work load consists of mostly driving to one location and cleaning things up, then driving to another location and cleaning more things up.  Nothing really new to write about.  However, industry wide, there have been some developments of note:

  1. More AM HD radio only testing out in Seattle.  We hear that these tests are phenomenal but have yet to see any data.  The HD Radio proponents keep pushing for an all digital transition.  To that I say good, let those stations (AM and FM) that want to transition to all digital do so, provided they conform to the analog channel bandwidths and do not cause interference to analog stations.  It should also be an either/or decision: Either transmit in all digital format or revert to analog only format, no more interference causing hybrid analog digital.
  2. BMW depreciates AM radio in some models.  It seems the all electric car generates too much electric noise to facilitate AM reception.  My question; are these mobile noise generators going to cause reception problems for other vehicles too?  What if I want to hear the traffic on 880 or 1010 and one of these things roles by?  There are larger implications here and the FCC should be concerned with this.
  3. General Motors pauses the HD Radio uptake in some models.  No real reasons given, but more emphasis on LTE in the dashboard is noted.  We are reassured by iBquity that this trend is only temporary.
  4. Anxiously awaiting this year’s engineering salary survey.  For science, of course.  Here is last year’s survey.
  5. Clear Channel is no more!  They have gone out of business and a new company, iHeart Media, has taken over.  Things will be much better now, I can feel it.
  6. John Anderson finds a chilly reception at the last NAB confab: An Unwelcome Guest at the NAB radio show. This is not surprising but kind of sad. John has been a reasonable critic of IBOC and wrote a book titled: Radio’s Digital Dilemma.
  7. Not too much going on with the AM revitalization.  Tom King of Kintronics notes that the fault is in our receivers.
  8. Government shortwave broadcasters continue to sign off permanently.  Radio Exterior de Espana ceases operations.
  9. European long wave and medium wave stations are also throwing the big switch; Atlantic 252 (long wave), as well as German long wave stations on 153, 177,  and 207 KHz, medium wave stations 549, 756, 1269, and 1422 KHz also are signing off.  Those 9 KHz channel spacings look strange don’t they.  What fate awaits US AM radio stations?
  10. I am reading Glenn Greenwald’s book, No Place to Hide.  I knew this, you should know it too.