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
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 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:
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.
With the spate of ransomware and crypto virus attacks on automation systems, perhaps a quick review of network security is in order:
- 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.
- Use a separate switch for all automation network connections.
- 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.
- Use supported and up to date operating systems.
- 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.
- Install and keep up to date a good antivirus program.
- 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.
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.
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 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…
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
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
There are various models designed to pass POE or even 90 VDC ring voltage.
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.
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:
- 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.
- 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.
- 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.
- Anxiously awaiting this year’s engineering salary survey. For science, of course. Here is last year’s survey.
- 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.
- 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.
- Not too much going on with the AM revitalization. Tom King of Kintronics notes that the fault is in our receivers.
- Government shortwave broadcasters continue to sign off permanently. Radio Exterior de Espana ceases operations.
- 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?
- I am reading Glenn Greenwald’s book, No Place to Hide. I knew this, you should know it too.
At least in some quarters, there appears to be interest in reviving AM Stereo. Perhaps as an unintended consequence of AM HD Radio, it seems. Some people have discovered, quite accidentally, that some AM HD Radios will detect the presence of AM stereo pilot and open up with IF bandwidth automatically, making the analog signal sound much better. AM Stereo being received on an AM HD Radio receiver:
That particular brand of AM HD Receiver only allows 5 KHz audio, which still sounds much better than the typical 2.5 to 3 KHz.
A short video comparing AM HD Radio and AM C-QUAM:
As IBOC and C-QUAM are incompatible, it is an either/or situation. Being that C-QUAM is open source and many new solid state transmitters come with AM stereo cards installed, the financial leap from AM mono to AM stereo is not nearly as steep as it would be to install AM HD Radio. The other nifty thing; C-QUAM is it is completely backwards compatible with existing AM mono receivers, the all digital version of IBOC is not.
It bears repeating; AM is not inherently inferior to FM sound. Wide band AM can sound really, really good. Something that we seemed to have forgotten over the years of listening to crappy receivers. This has caught the attention of Tom King, owner of Kintronics, who penned the following letter to the FCC and all AM broadcasters:
Subject: Meeting with FCC Commissioner Ajit Pai and Mr. Peter Doyle,
Chief of the Audio Division of the FCC Media Bureau
at the offices of the FCC in Washington, DC on Tuesday, September 23, 2014.
To All AM Broadcasters in the USA:
Kintronic Labs is concerned about the declining position of the AM radio service in the United States, which we reflected in our Reply Comments to the FCC NPRM Docket No. 13-249 on the subject of “AM Revitalization,” issued on October 31, 2013. In the interest of preserving this great national resource for local public media, we have scheduled a meeting with FCC Commissioner Ajit Pai and Audio Media Chief, Mr. Peter Doyle, to address what we believe are the critical steps toward putting AM radio on a more competitive basis with FM as follows:
(1) FCC enforcement of regulations relative to the power distribution industry and the consumer electronics industry that are not currently being enforced, resulting in a constantly worsening electromagnetic environment for AM radio service.
(2) The need for parity between AM and FM receivers through the establishment of minimum technical standards for AM receivers that would become effective as soon as January 2016. We plan to demonstrate a comparison of full-bandwidth C-QuAM AM stereo reception with a local FM station and with a typical AM receiver in a popular consumer multi-band receiver. The effects of adjusting the AM bandwidth from 2.5 to 10 kHz in 2.5-kHz steps will also be demonstrated.
(3) The need for FCC authorization of AM synchronous boosters. Unlike FM translators, such on-channel boosters would serve to increase the AM stations’ audiences while concurrently maintaining the future viability of the band. The related technique of wide-area AM synchronization for coverage improvement will also be addressed.
Referring to Step #2, it is absolutely essential that very close to full parity be established for new AM radio receivers versus their FM radio counterparts. This includes all key AM receiver performance attributes, including:
Low internal noise floor, well below the average AM-band atmospheric noise level. This includes all internal synthesizer and DSP circuitry within the receiver (and in the immediate environment for integrated automotive applications).
High overall RF sensitivity, selectivity, and dynamic range, to provide adequate amplification of weak signals, even in the presence of significant adjacent- and/or alternate-channel signals, especially in strong-signal environments. This would incorporate typical advanced, multi-stage AGC action, with appropriate interaction between the RF and IF AGC control mechanisms to maximize overall receiver dynamic range, including adaptive front-end attenuation for signal-overload protection in very strong-signal areas. Useful typical specs include: sensitivity – 1 mV for 10-dB SNR; selectivity (adjacent-channel) – 25-50 dB (adaptive).
Highly effective noise (EMI) rejection, including staged RF and IF noise blanking, accompanied by appropriate audio blanking and/or expansion when required. Such features were developed and included in Motorola chip sets in the 1990’s in the AMAX program, and are easily integrated into modern, high-density AM/FM receiver chips.
Full 10-kHz audio bandwidth capability with low detector distortion. This would obviously incorporate dynamic, signal-controlled bandwidth control (including AMAX-style adaptive 10-kHz notch filtering) as dictated by noise and adjacent-channel interference.
Stereo capability. If the receiver has FM stereo capability, it must have corresponding C-QuAM decoding for AM.
Without fulfillment of the first three requirements (this also includes the associated AM antennas both for vehicles and for home use), basic AM reception will suffer significantly compared with FM. Without the last two, the output sound quality cannot be closely competitive with FM (i.e., 10-kHz full bandwidth on AM versus 15-kHz nominal for FM).
We therefore petition the FCC to mandate the following minimum allowable performance specifications for all AM receivers that will be manufactured and installed in new automobiles as of January 1, 2016:
Audio Bandwidth: 10 kHz typical, adaptive, with a minimum nominal bandwidth of 7.5 kHz
Signal-to-Noise Ratio: minimum 55 dB, preferably 60 dB
Sensitivity: -120 dBm for a signal-to-noise ratio (SNR) of 10 dB
Selectivity: 25-50 dB (adaptive filtering, using co-, adjacent-, and alternate-channel detection)
Dynamic Range: 100 dB
Noise Figure: 1 – 3 dB
Image Rejection: -50 dB
Intermod: IP2 , IP3 intercepts +10 to +40 dBm
IF: low with image-rejecting down-conversion, or double-conversion
Stereo Separation: minimum 25 dB
Tom F. King
All of those technical specifications are doable with modifications to the current receiver chipset. Currently there are very few if any AM Stereo receivers being manufactured. One might ask, how can a typical AM mono receiver be modified to receive AM Stereo. A great question. For a small sum, an outboard circuit board can be purchased and installed in a typical AM mono receiver. For most non-car radios, this modification would be fairly easy. Car radios, on the other hand, will be very difficult to modify since most new radios will be bricked if tampered with (thanks a lot, crackhead radio thieves of New York).
And for those interested, there are also lists of radio stations broadcasting in AM stereo:
According to the Wikipedia source, there are 90 some odd station using C-QUAM AM stereo. Using iBquity math, that is nearly the same number as are broadcasting AM HD Radio.
If you are an AM station owner, you can start by transmitting good programming.
Many articles have been written on the topic and it is still a black art to some. Making a Medium Frequency (MF) antenna that has enough bandwidth to pass 10 KHz audio can be challenging, to say the least. The VSWR out to +/- 15 KHz carrier needs to be kept at a minimum and the power needs to be evenly distributed between the two sidebands. This can become problematic with complex Directional Arrays or towers that are tall or short for their operating frequency.
When we were working on the WFAS-AM tower in White Plains, NY, it became apparent to me that something was not right. The tower is skirted and now holds the antenna for W232AL, a 250 watt translator broadcasting the WPLJ HD-2 channel. After installing the FM antenna, some tuning of the AM antenna was required and this is the graph of the resistance and reactance curves:
WFAS 1230 KHZ, ATU output resistance and reactance
This looked very similar to the resistance and reactance curves before the FM antenna work was done. Red line is resistance, the blue line is reactance. I think it had been like this for a long time. While it is not terrible, it is not that good either. As alluded to in a previous post, some re-working of the ATU was needed. After some trial and error, this is the circuit that we ended up with:
WFAS 1230 KHZ White Plains, NY ATU schematic
Not quite what I expected, however, it was designed with the parts on hand, excepting the vacuum variable output capacitor, which was donated by me. That part was key in making the proper adjustments.
After my redesign and tune up of the ATU, this the resistance and reactance curves at the input terminal of the ATU:
WFAS 1230 KHz resistance and reactance after ATU modification
The graphs have a slightly different format, but you get the idea. The red line is resistance, the blue line is reactance and the green line is overall impedance. The resistance is symmetrical about the carrier as is the reactance. Truth be told, I think there is a little more that can be had here, but for now, there is no reason to go any further. I made the initial measurements at the input of the ATU and confirmed them again at the output terminals of the transmitter. When we turned the transmitter back on, I noticed that the modulation index had dropped by about 15 percent. I think the reflected power was getting back into the RF sample and fooling the mod monitor. I also noticed that the high end in particular sounded much nicer.
WFAS 1230 KHz, White Plains, NY ATU
The ATU building is a little cramped and it is hard to get a good picture. The vacuum variable capacitors were salvaged from a scrapped AM transmitter years ago. The tower is 202 degrees tall, which is also a factor. It will be interesting to see what seasonal changes there are with snow cover, mud, etc.
Overall, this was a fun project.
It seems branding and programming issues are a long running problem for radio stations. This is a copy of something that was made at WALL in 1974. It has been circulated extensively in the NY metro market, but perhaps some of you from other areas or countries have not heard it yet. There is no WVWA 900 in Pound Ridge, it is a fictitious station:
What is hilarious is that the same exact this is still going on forty years later. How many times have programming consultants, program directors, corporate programming guru’s sat around and said “What we really need is a catchy name, like The Buzz or something.” I don’t know how many times I have heard “The X” or “The Eagle” or “fill in stupid name here.” Do the listeners really think “Oh wow, they changed their name, I will listen to this station now!” No, not likely.
The funniest part; “After more than 100 hours of extensive research… (the programming consultant) developed, refined, molded, polished, honed, shaped and pulled out of left field a revolutions new formatic programing concept…” Play music, say nothing, and scream “NINE!” between each song.
Most ordinary field engineers will not need to design an ATU in the course of their normal duties. However, knowing the theory behind it can be very helpful when trouble shooting problems. Also, fewer and fewer people understand RF these days, especially when it comes to AM. Knowing a little bit can be an advantage.
We were working on an AM tower recently when several discrepancies were noted in the ATU:
WFAS ATU, 1230 KHz, 1 KW, N-DA
This was connected to a 202° tower. There were several complaints about seasonal shifts and narrow bandwidth. The VSWR meter would deflect slightly on high frequency audio peaks, always a bad sign. A little bit of back story is in order. WFAS signed on in 1930 using a four legged self supporting tower. This tower was used until about 1986, when it was replaced with a series excited, guyed tower. The ATU in use was initially designed for the replacement tower, which was likely had a good bit of capacitive reactance. I am speculating on that, as I cannot find the original paper work for the replacement tower project. At some point, somebody decided to ground the tower and put a skirt on it, likely to facilitate tower leasing. The skirt was installed, but the ATU was never properly reconfigured for the high inductive reactance from the skirted tower. The truth is, the Collins 820-D2 or Gates BC-1G tube type transmitters probably didn’t care. They were probably like; bad load, meh, WHATEVER! Although the audio quality likely suffered. That all changed when the Broadcast Electronics AM1A was installed. To fix the bad load problem, a BE 1 KW tuning unit was installed next to the transmitter.
Technically, there are several problems with the above circuit, starting with the capacitor on the wrong side of the base current meter. This capacitor was installed outside of the ATU between the tower and ATU output. Was the base current meter really measuring base current? I don’t know, maybe? The shunt leg was lifted but both of the inductors of the former T network were left in the circuit.
We reconnected the shunt leg and moved the capacitor inside the ATU and on the correct side of the base current meter. After several hours of tuning and fooling around with it, the ATU is still narrow banded, although now at least the input is 50Ω j0. I believe the current design has too much series inductance to be effective.
Thus, a redesign is needed. I think, because of the inductive reactance of a skirted tower, a phase advance T network will lead to best bandwidth performance. The basic design for a +90 degree phase advance looks like this:
WFAS +90 phase advance ATU, 1230 KHz, 1 KW, N-DA
To calculate the component values for the ATU, some basic arithmetic is required. The impedance value for each leg in a +/- 90 degree T network can be calculated with the following formula:
Z = √(inputZ × outputZ)
Where Z = impedance per leg
Input Z = the ATU input impedance, 50Ω
Output Z = the antenna resistance, 58Ω
Thus: Z =√ (50Ω × 58Ω)
Z = 53.85Ω
Formula for Capacitance: C = 1/(2Π × freq × XC)
Thus for the input leg: C = 1/(6.28 × 1.23MHz × 53.85Ω)
C (input) = 0.0024 μF
Formula for Inductance: L = XL/(2Π × freq)
Thus for the shut leg: L = 53.85Ω /(6.28 × 1.23 MHz)
L (shunt) = 6.97 μH
For the output leg, we must also consider the inductive reactance from the tower which needs to be cancelled out with capacitance. Thus, the output capacitor needs to have a value of 53.85Ω + 580Ω = 633.85Ω
Thus for the output leg: C = 1/(6.28 × 1.23MHz × 633.85Ω)
C (output) = 0.000204 μF
The amazing thing is, all of these components are available in the current ATU, they just needed to be rearranged. The exception is the vacuum variable capacitor, which I salvaged from an MW-5 transmitter many years ago. I donated that to the project, as I am tired of looking at it in my basement. The reason for the vacuum variable capacitor will become evident in a moment. The input capacitor will be slightly over value, which will require the inductor to tune out the excess capacitance. A good design rule is to use minimum inductance to adjust the value of a fixed capacitor, thus the capacitor should be not more than 130% of the required value.
About the Vacuum variable output capacitor; in the existing ATU had a 0.0002 μF capacitor already. With a +90° phase shift, this capacitor is likely adequate for the job. The vacuum variable may be pressed into service if something other than a +90° phase shift is needed for optimum bandwidth. That will be the topic of my next post.
Final consideration is the current and voltage ratings of the component. As this is a re-build using existing components, chances are that they already meet the requirements. On a new build or for replacing parts, one must consider the carrier power and modulation as well as any asymmetrical component to the modulation index. For current and voltage each, the value is multiplied by 1.25 and then added to itself. For a 1,000 watt carrier the input voltage on a 50 ohm line will be approximately 525 volts at 10 amps with 125% modulation. A good design calls for a safety factor of two, thus the minimum rating for component in this ATU should be 1050 volts at 20 amps, rounded up to the next standard rating. The capacitor on the output leg should be extra beefy to handle any lightning related surges.
The current rating for a capacitor is usually specified at 1 MHz. To convert to the carrier frequency, the rating needs to be adjusted using the following equation:
IO = IR√ FO
IO: current rating on operating frequency
IR: current rating at 1 MHz (given)
FO: operating frequency in MHz
The vacuum variable output capacitor is rated for 15,000 volts, 42 amps. Adjusted for frequency, that changes to 46 amps. The calculated base current is 4.18 amps carrier, 9.41 amps peak modulation. Thus, the capacitor on hand is more than adequate for the application.