tech stuff – Page 52 – Engineering Radio

Audio over IP, what is it, why should I care?

IP networks are the largest standardized data transfer networks worldwide. These networks can be found in almost every business and home and are used for file transfer, storage, printing, etc. The Internet Protocol over Ethernet (802.x) networks is widely understood and supported. It is robust, inexpensive, well-documented, readily deployed, and nearly universal. Many equipment manufacturers such as Comrex, Telos, and Wheatstone have developed audio equipment that uses IP networks to transfer and route audio within and between facilities.

Audio enters the system via an analog-to-digital converter (A/D converter), often a sound card, at which point a computer program stores it as a file. These files can be .wav, .mp3, .mp4, apt-X, or some other format. Once the audio is converted to a digital data format, it is handled much the same way as any other digital data.

IP stands for “Internet Protocol,” which is a communications protocol for transmitting data between computers connected to area networks. In conjunction with a transmission protocol, either TCP (Transmission Control Protocol) or UDP (User Datagram Protocol) IP forms what is known as the Internet Protocol Suit known as TCP/IP. The Internet Protocol Suit contains four layers:

Application layer – This is the protocol that contains the end-use data. Examples of these would be HTTP, FTP, DCHP, SMTP, POP3, etc. Telos Systems uses its own application called “Livewire” for its equipment. Wheatstone uses “WHEATNET.” Digigram uses “Ethersound.” This is an important distinction.
Transfer layer – This contains the TCP or UDP header information that contains such things as transmitting, and receiving ports, checksum value for error checking, etc. It is responsible for establishing a pathway through multiple IP networks, flow control, congestion routing, error checking, and retransmission. TCP allows for multiple IP packets to be strung together for transmission, increasing transfer rate and efficiency.
Internet layer – This is responsible for transporting data packets across networks using unique addresses (IP addresses).
Link Layer – This can also be called the physical layer, using Ethernet (802.x), DSL, ISDN, and other methods. The physical layer also means things like network cards, sound cards, wiring, switches, and routers.

Advantages:

An IP network can be established to transmit data over almost any path length and across multiple link layer protocols. Audio, converted to data can thus be transmitted around the world, reassembled, and listened to with no degradation. Broadband internet connections using a cable, DSL, ISDN, or T-1 circuits can be pressed into service as STL’s, ICR’s, and TSL’s. This translates to fast deployment; no STL coordination or licensing issues, no antennas to install if on a wired network. Cost reductions are also realized when considering this technology over dedicated point-to-point TELCO T-1’s. Additionally, license-free spread spectrum radios that have either DS-1 or 10baseT Ethernet ports can be used, provided an interference-free path is available.

IP audio within facilities can also be employed with some brands of consoles and soundcards, thus greatly reducing audio wiring and distribution systems and corresponding expenses. As network speeds increase, file transfer speeds and capacity also increase.

Disadvantages:

Dissimilar protocols in the application layer mean a facility can’t plug a Barix box into a Telos Xtream IP and make it work. There are likely hundreds of application layer protocols, most of which do not speak to each other. At some point in the future, an IP audio standard, like the digital audio AES/EBU may appear, which will allow equipment cross-connections.

Additionally, the quality of the physical layer can degrade performance over congested networks. The installations must be carefully completed to realize the full bandwidth capacities of cables, patch panels, patch cords, etc. Even something as little as stepping on a Category 6 cable during installation can degrade its high-end performance curve. The cable should be adequately supported, not kinked, and not stretched (excessive pulling force) during installation.

TCP/IP reliability is another disadvantage over formats like ATM. In a TCP/IP network, no central monitoring or performance check system is available. TCP/IP is what could be called a “broadcast” protocol. That is to say, it is sent out with a best-effort delivery and no delivery confirmation. Therefore, it is referred to as a connection-less protocol and in network architecture parlance, an unreliable network. Lack of reliability allows any of these faults to occur; data corruption, lost data packets, duplicate arrival, out of order data packets. That is not to say that is does not work, merely that there is no alarm generated if an IP network begins to lose data. Of course, the loss of data will affect the reconstruction of the audio.

Finally, latency can become an issue over longer paths. Every A/D converter, Network Interface Card (NIC), cable, patch panel, router, etc has some latency in its circuitry. These delays are additive and dependent on the length of the path and the number of devices in it.

Provided care is taken during design and installation, AOIP networks can work flawlessly. Stocking adequate spare parts, things like ethernet switches, NICs, patch cables and a means to test wiring and network components is a requirement for AOIP facilities.

Denon DN-950 FA Cart CD player

These were all the rage when they came out some 23 years ago or so. They were specifically made for DJs who were used to shuffling carts in and out of cart machines. The idea was to use familiar motions and procedures so DJs could easily perform their shifts using CDs without relearning studio dynamics. The only downside, a DJ could remove the CD that was playing by accident whereas pulling a playing cart out of a cart machine is difficult to do. Later Denon versions made it more difficult to remove playing CDs.

This is a promotions photo circa 1987.

This machine is still in use 22 years after its manufacture date. Over the years the top cover has been removed countless times, no doubt to replace the KSS-210A optics and bearings or to periodically clean them. The Phillips head screws are so worn a screw extractor is nearly required.

They are located under a circuit board, which has to be removed. Again, the DN-951 series CD players did away with this, making maintenance easier. These CD players could and often were affected by RF especially when the studios were co-located with an AM transmitter site. One such symptom was randomly speeding up and slowing down while playing. It made for some interesting-sounding songs and even more interesting commentary by the morning show.

Every time the optics and bearing were replaced, there was a pretty involved alignment procedure that took some time to get right. I remember some funny Japanese-to-English translations in the service manual.

Of course, nowadays if there are any issues, you just chuck the computer and get a new one.

Great Circle Map Generator

For those of you who are interested in radio listening, particularly over long distances (AKA DXing) with even a moderately directional antenna, having a great circle map projection for your location is a necessity. Looking at a Mercator Projection, the normal “flat” map most are familiar with, one might come to the conclusion that due west from upstate NY lies the Washington/Oregon state border. Appearances can be deceptive, bearing away at 270 degrees true (due west) from upstate NY is the California/Mexico border.

This is because we live in a big sphere. In this regard, the only place the Mercator Projection is accurate is around the equator unless one is going due north (0 degrees) or due south (180 degrees). The further north or south from the equator, the less accurate a flat map is. Therefore, having a Great Circle map projection based on your location is handy for choosing the right azimuth to listen along.

As with many things, the internet provides the required tools to generate a great circle map for any location in the world. The first thing needed is an accurate fix of your location. This can be obtained via GPS, or, if you know how to look at a map and or satellite picture, itouchmap can be very useful. Once you know where you are, you can plug that information into this Great Circle Map Generator.

I saved the image as a bit map and used it as the wallpaper on my computer. That way, I just need to minimize any running programs and I can see what the correct azimuth is to any place in the world. This is for upstate NY:

great circle projection — Great Circle Projection

Working with Surface Mount Technology (SMT)

A quick glance at almost any circuit board these days will show that almost all of the components are surface-mounted. They are small rectangles or squares that sit on top of the circuit board. This is different from the through-hole components that were used for many years and are still found in older equipment. There are radio engineers who feel that surface mount components are too hard to work on, thus the boards are not repairable.

California Amplifiers C band block down converter

As with anything in the engineering field, there needs to be a cost/benefit analysis. Most computer component boards, things like NICs, modems, sound cards, VGA cards are very inexpensive, and often times it would be more expensive to repair the board than it would to buy a new one. In other situations, however, local repair of circuit boards makes good sense and can be a good learning tool.

Consoles and transmitters offer some good opportunities for local repair, provided the schematics are available. SMT component troubleshooting is the same as through-hole troubleshoots, except the components are smaller. That is where a magnifying glass comes in handy. I purchased a magnifying glass/light to work on SMT boards.

Soldering and unsoldering techniques are also different. A temperature controlled soldering iron with a small tip is important. I find the easiest way to unsolder a component is with solder wick. Once most of the solder has been wicked up, a brief touch of the iron and the component will come off. Small resistors and capacitors are fairly rugged, but should not be overheated. Semiconductor components such as diodes, transistors and ICs are susceptible to heat damage and Electro Static Discharge (EDS). A grounding wrist strap should always be used when handling semiconductor components. Soldering iron temperature should be enough to quickly melt the solder and heat the connection surface without overheating the SMT component. Lead free solder requires slightly higher temperatures than the traditional 60/40 rosin core.

Weller WD1 temperature controlled soldering station — Weller WD1 temperature-controlled soldering station

A temperature-controlled soldering station is a must. Too much heat will damage components and boards, too little will make soldering SMT an arduous task.

Other soldering supplies include liquid flux, desoldering wick, flux remover and 55/40/5 solder. The desoldering wick makes it easy to clean up an errant solder deposits and is the best way to desolder surface mount components. I have had limited success using a solder pump on surface mount boards. They do come in handy for RF MOSFETS, which have large tabs, often with liberal amounts of solder applied at the factory.

Soldering new components:

A typical 0.1 uf capacitor is placed on the surface mount board and ready to be soldered. These components are all small, but I would characterize this as a medium sized one. There are some very small diodes, ICs and other devices that require the magnifying glass to identify pins and polarity.

The best way that I have found to solder components onto a surface mount board is to use a little bit of liquid flux on the board.

Using tweezers or small needle nose pliers, place the component.

Soldering 0.1 uf bypass cap on SMT board

Wet the end of the soldering iron with a little bit of solder.

Using the placing tool, hold the component in place and touch one of the pads with the soldering iron. This should tack the component in place. Solder the component to the other pad using the soldering iron and solder. Then come back and touch up the tacked side. I have found that 600 degrees F is a good temperature to quickly melt the solder, while not heating up the component too much.

HF receiver preamp with bypass capacitor soldered

Sorry I could not get pictures of the actually process, I don’t have enough hands to hold the soldering iron, hold the component down and take a picture.

The completed preamplifier. I have been calling this an HF preamp, because that is its intended use. In practice, this preamp should work well from 50 KHz up to about 75 MHz, with 3dB points at 30 KHz and 100 MHz.

Norton HF preamp schematic — Norton HF preamp Schematic

The Norton design is an inverse feed back and using the 1N5109 transistor, which has input and output impedance of 50 ohms, makes it simple to implement. In testing, I found this unit has about 10-11 dB of gain with about 4 dB of noise. The use of SMT makes the design stable and I didn’t see any evidence of oscillations when testing it. More on the preamp here. I installed it out at the base of my K9AY antenna and it can be remotely turned on and off as needed. My main reason for wanting it is to overcome the 6.5 dB signal loss in the four port hybrid receiver coupler and transmission line I use. Truth be told, most of the time it is off.