tech stuff – Page 46 – Engineering Radio

AM radio sucks! It’s horrible, sounds terrible and should be turned off!

This is a youtube video of a Police song from the 1980s received via skywave and recorded off-air on an AM radio.

Video Description:

The classic 1983 #1 smash hit, as received in analog C-Quam AM Stereo… in Japan… via nighttime skywave in the Tokyo area, roughly 500 miles away from Sapporo (ed: where the station is located). The audio quality is among the best I’ve ever heard from analog AM radio, thanks in large part to an excellent wideband receiver, very quiet band conditions, and the Orban Optimod-AM 9100 audio processor being used by HBC Radio to its maximum extent: 12.5 kHz audio bandwidth with stereo enhancement added (above and beyond the amount naturally provided by the matrix processing used by AM Stereo).

Absolute trash, I tell you. Just awful.

Of course, I know several FM stations around here that wished they sounded as good. Naturally, Japan, they have sought to minimize night-time interference problems by limiting the number of stations on the air and enforcing the rules and regulations in place to protect those stations on the air. They also seem to allow greater bandwidth, out to 12.5 KHz in spite of the narrower channel allocations (9 KHz in ITU regions I and III, vs 10 KHz here in the US, ITU region II). One other thing to note, there is no digital buzz saw occupying several channels of the broadcast spectrum. Keep in mind, this was received in Tokyo, likely a very high noise environment.

I was trying to find out the power level of the transmitter, the call sign is JOHR in Sapporo Japan, frequency is 1287 KHz. HBC is the Hokkaido Broadcasting Company, a privately held company. The state-run radio outlets in Japan are NHK, which has several radio and TV stations throughout the islands.

Anyway, AM is dead. Killed by the very owners of the broadcasting companies themselves with help from the NAB. They are the ones that petitioned the FCC to loosen up the allocations and allow more and more stations to be crammed into the band. That is old news. The new news is same forces that killed AM radio are diligently working their magic on the FM band as well. More stations, translators, digital IBOC nonsense that doesn’t work, more of everything. After all, more is better. Until it is not. Then it’s too late.

Secretly, I like it when things break, sort of

Not that I am a glutton for punishment or anything, but I enjoy troubleshooting. There is a certain satisfaction in the analytical aspect of tracking down a problem and fixing it, hopefully in a permanent fashion. Figuring out where a problem is requires a good bit of detective work;

Examining the clues; what happened before the failure, what are the fault indications, are there any external factors
Round up the usual suspects; a good maintenance log is helpful here to track re-occurring failures. If the failure cannot be attributed to an external source (such as a power surge or lightning storm), what was the last thing that was changed or worked on?
Following the trail back to the origin; Often the first failed part found is a symptom, not the actual problem. It takes some skill in reading schematics and making sense of a failure to trace it back to the real problem.

It can sometimes be exciting, like turning on the 25 KV high voltage supply and having big blue flashes issue forth from the top of the transmitter. Sometimes it can be quite frustrating, like when the station owners refuse to spend money to fix a problem. Sometimes it can be dull, like fixing the same problem over and over again because of the previously stated money problem. It’s also disheartening when the problem was caused by the stupid DJ spilling soda in the console. Not that all DJs are stupid, just the ones that spill things into consoles.

The challenge of finding the root cause can often be enlightening. I have often discovered unrelated problems waiting in the wings while investigating the why of an outage. It is great to fix those things before they burn the house down, but this approach often goes unnoticed by the ownership or management. Lately, for some reason, an ounce of prevention goes unnoticed or unappreciated.

There is quite a bit of science to troubleshooting, but there is some combination of personal traits that make a good troubleshooter. These are:

Inquiring or curious disposition. It is fairly easy to get to the first failed module or part. Discovering the reasons behind the failure and or getting down to the component level takes a good deal more effort.
Patience. This goes with the second part above, it takes some stick-to-it-tive-ness to trace out the not readily apparent problem.
Good analytical skills. Often failures generate a cause-and-effect scenario. The effects can be startlingly distractive and mask the causes and the underlying problem.
Ability to view the large picture. This is critical to discover outside influences and other issues that are indirectly connected to the system or issue at hand.
Ability to analyze the system design. This requires background training and experience to look at a circuit diagram and discover non-error-tolerant systems. Sometimes these systems can be modified for better fault tolerance.

Poorly designed equipment is the bane of the broadcast engineer. Equipment manufacturers can sometimes fail to follow two key principles: KISS and maintainability. KISS stands for Keep It Simple, Stupid. There is no better design criteria than the KISS principle. Adding layers of complexity increases the failure expectations. Maintenance can be something as simple as cleaning or changing air filters. Making maintenance tasks difficult almost ensures that they will not be done.

Eventually, all things wear out. It also takes some large-picture skills to know when it is time to replace equipment and that can vary greatly from situation to situation.

Wireless LAN bridges and STLs

Wireless LAN technology has been around for quite a while. Point-to-point 2.4 and 5.8 GHz spread spectrum hardware has also been around for some time. These systems operate in the ISM bands at relatively low power levels and are license free. There are several different makes and models, however, they all have some similar specifications. Most have DS-1 (T-1) or ethernet 10 base T or 100 base T 802.3 architecture. Some are field configurable for either format.

The advantage of using 802.3 ethernet is the availability of ethernet sound cards and the possibility of making inexpensive audio to ethernet A/D converter. However, if a station is currently using telephone company DS-1 service, then they likely have the audio to DS-1 multiplexers on hand.

I have used the Axxcelera point to point system as an inter-city relay for a satellite downlink. Axxcelera is owned by Moseley, which has a long history in the STL business. The point-to-point system has an indoor unit, which has the RJ-45 ports, and an outdoor unit, which has the RF section and an integrated antenna. The two units are connected via Cat 5 cable (be sure to use UV resistant cable) through a power injection port. The newer units do not need the power injection port. The system gain is about +46 dBm and the claimed effective range is 20 miles. I’d suspect it to be somewhat less than that with the integrated antenna. There is also an N connector for an external antenna, making the outdoor unit a MMA (Mast Mounted Amplifier).

The indoor unit came configured with four 10 base T ports, which we reconfigured for DS-1 service. We connected a QEI CATLINK T-1 mux with several 7.5 KHz audio channels and one control channel connected to a broadcast tool DSC 3264 (Starguide satellite receiver channel controller) that allowed the station to change channels on the fly. It took some doing, but in the end, the system worked well. The path was about 1/2 mile through downtown buildings, it was line of sight but did not have full Fresnel clearance. I never heard of any dropouts.

The other system that I have used is the ADTRAN TRACER. This system is different in that it does not have an integrated antenna, an external antenna is required. We installed this over an eight-mile path using two six-foot grid parabolic dishes (Radio Waves G6-2.4NF) on 2.4 GHz. The primary configuration is a rack-mounted indoor unit with either four or eight 802.3, E-1, or T-1 ports. These ports are not field configurable. The antenna connector is a type N. There is also a split configuration available; an indoor unit with the T-1 ports and an outdoor MMA. This setup is best used where transmission line lengths would create prohibitive losses. MMA’s are not my first choice in these systems, there are too many things that can go wrong when active components are mounted high above ground level.

This system replaced two Telephone company T-1 lines and is used as an STL for two stations and an inter-city relay for a satellite downlink site. It also extends the office LAN (802.3 ethernet) to the transmitter site where a backup audiovault server lives. This is accomplished through a T-1 port using an ethernet to T-1 bridge.

ADTRAN Tracer 6000 series microwave radio

ADTRAN also created a path analyser spreadsheet.

The license-free aspect of these system makes them easy to deploy. There are several frequency plans available and the paths are fairly robust. In highly congested areas, however, interference may become an issue. Of course, because they are unlicensed, frequency coordination would be a real problem. Axxcelera has the ExcelFlex which is a unit requiring a license that can run in any frequency band from 6-38 GHz

Temperature Sensor for Burk Remote Control

As a part of the re-wiring of a transmitter site, I realized that the site needed a temperature sensor. I believe it is important for any remote transmitter site to have a temperature sensor, too many things can go wrong at a transmitter site.

I recall one incident at WGNA-FM in Albany, NY where a ventilation fan failed on a hot summer day. The Harris HT-10 transmitter stayed on the air while the temperature climbed through 160 degrees inside the building, finally shutting down when the solid-state driver module failed. This site had a temperature sensor and a live operator taking transmitter readings every three hours. They faithfully logged the temperature increase in three-hour increments but didn’t call anyone until the station went off. When I arrived there, it was so hot inside the building that I couldn’t touch a metal surface.

For the present-day project, I looked at the Burk BTU-4, which seemed a little pricey. After doing a bit of quick research, I found the National Semiconductor LM34 a good alternative. This unit puts out 10 mv/degree F, which can be directly calibrated to a metering input of an ACR-16 using the Lin scale. I checked the accuracy by using a piece of melting ice, it was right on. The design and implementation are very simple:

The LM34 is available in TO-46 or TO-92 case. I bypassed the V+ with a 0.01uf capacitor. It should be mounted in a small box with the case of the LM34 mounted on a metal cover or heat sink. The TO-46 version, the case is ground. It can be run on any voltage from +5 to +30 VDC, I used +5 because I had a little wall wart with the right voltage. The wire is any type of balanced audio wire like Belden 8459, etc. The LM34 cost 4 dollars, the rest of the parts were laying around. It took about 15 minutes to create.

The site is air-conditioned, therefore I set the remote control to alarm if the temperature goes above 85 degrees F inside the building.