This video was shot in DNxHD using the Blackmagic HyperDeck shuttle I showed in another video (https://www.youtube.com/watch?v=cc83-Cc-vtw). After editing in Adobe Premiere and finishing it off in SpeedGrade, I exported it to h.264 at a variable bitrate averaging 35 Mbps. Please let me know if you see an increase in image quality.
In order to provide both lateral and vertical guidance, the ILS consist out of two individual subsystems. The part used for lateral guidance is called the localizer. For the vertical guidance component the term is glide slope. Both localizer and glide slope use a surprisingly simple way of telling on aircraft where to go. The localizer and glide slope each consist out of two independent transmitters with the same frequency and a special antenna array. The antenna arrays each create a radiation pattern with two sidelobes. One sidelobe per transmitter. One sidelobe is fed by a transmitter modulated with a 90 Hz signal and the other sidelobe is fed by carrier modulated with a 150 Hz signal. The antenna pattern is so that the two sidelobes overlap with equal intensity when the aircraft is exactly on the intended path. An AM receiver tuned to the frequency of either the localizer or glide slope will “hear” both the 90 Hz and 150 Hz tones with equal intensity when on the right path. Sounds complicated? Let’s try a picture:
So how does the airplane (and the pilot) know where to go? The ILS receivers simply compare the intensity for the 90 Hz and 150 Hz signals and display the difference. This is done independently for the localizer and the glide slope. If the 90 Hz and 150 Hz tone intensity is exactly the same, the plane is on the right path. But if one signal becomes stronger than the other, the plane is off the desired path. In the case of the localizer for instance, the 90 HZ tone will be stronger if the aircraft is off to the left of the desired course. And accordingly, the airplane is off to the right of the desired course if the 150 Hz tone is stronger. For the glide slope a stronger 90 Hz tone means that the plane is above the intended glide path. For a dominant 150 Hz tone on the glide slope, the plane is below the intended glide path. Simple, isn’t it?
It’s so simple that even some handheld airband radios can decode ILS signals and offer a backup for on board instruments in case of an instrument or electrical failure. An example for such radios are the Yaesu FTA-550 (localizer only) and the FTA-750 (localizer, glide slope and GPS). I recently bought a FTA-550 and when it arrived, I wanted to test it. Unfortunately, I live out of reach of a ILS localizer. But no problem, I’m an engineer.
To generate the 90 Hz and 150 Hz signals, I used by Tektronix AFG3102 signal generator. The two signals were fed into a resistive combiner and from there directly into the external modulation input of my HP8657D. The HP8657D signal generator was set to amplitude modulation and a frequency in the airband, 110 MHz in this case. When you do experiments like this, make sure that you use very low power, a frequency that is not used in your area and abide all communications laws. The last thing you want to do is to interfere with a real aircraft. It is advisable to use a shielded connection to the radio regardless of power.
With equal amplitude of the 90 and 150 Hz signal, the localizer needle of your ILS receiver should be exactly in the center. As you can see on the picture, my FTA-550 passed this test with flying colors. You can test the glide slope portion of your receiver in the same fashion. The glide slope transmitters transmit on UHF. So that the pilot isn’t bothered with entering two frequencies, the VHF localizer and UHF glide slope frequencies are paired so that only the VHF frequency needs to be known. IF you want to test the glide slope portion of the receiver, you need to look up the UHF glide slope frequency corresponding to your VHF localizer. You can look-up ILS frequency pairs on the internet .
If we lower the 90 Hz signal’s amplitude, we expect the receiver to show us to the right of the correct course. As you can see on the following picture, the FTA-550 masters this test as well.
This article is a great example how complex avionics systems can be tested with inexpensive and readily available test equipment. Avionics shops spend tons of money on specialized test equipment. Some are required to be compliant with the law, some aren’t. But on the avionics test market there appears to be a large gap between “super old and cheap” and “brand new but very expensive” when it comes to specialized test sets. Using standard off-the-shelf test equipment may be an alternative to get state of the art test sets for little money.
Links and Sources:
 “Instrument Landing System”, Wikipedia: http://en.wikipedia.org/wiki/Instrument_landing_system
 “Instrument Landing System (ILS) Frequencies”, Radioreference.com: http://wiki.radioreference.com/
So what exactly did I order? I ordered a ten 2cm x 4.8cm boards, red in color, 1.2 mm thick with HASL finish. Technically speaking, I didn’t order 10. I ordered what’s called a Protopack which will give you about 10 PCBs. Could be a bit more, could be a bit less. You’re kind of taking a gamble on the quantity but for $ 14 it is junk cheap either way. If you must have exactly ten, you can of course just order 10 and pay $ 28 instead. But in my case the Protopack actually worked in my favor, more about that later. I paid an additional $ 19 for shipping via DHL China. Free shipping is available but may take a bit longer.
The order was submitted on a Friday afternoon and I updated the files multiple times. On the following Sunday the files were sent to the manufacturing house and on Thursday they were shipped. That’s a pretty quick turnaround for a super cheap Chinese manufacturing house. Actual pick-up by DHL China was on Saturday. The shipping speed was just incredible, DHL only took 2 days to deliver, despite the first day after pick-up being a Sunday.
So what’s the quality of the board? For $ 33 delivered I naturally didn’t expect much. But I was wrong. First off, I received 12 PCBs. So the Protopack definitely worked in my favor over ordering a guaranteed 10 pack for twice the price. Asides from some minor imperfections on the “J2″ outline, the silk-screen is of very good quality. Even the small text is clearly readable. I’ve often had issues with crappy silk-screen even with “high quality” services so this really impressed me. The vias also look very satisfactory.
After this successful test I sent of a more complex design to Dirty PCB. It has 50 Ohms striplines, a more complex solder stop mask around the striplines, some ground via stitching and Electroless nickel immersion gold (ENIG) finish. I can’t wait to see how well they will turn out.
Links and Sources:
 Dirty PCB: http://dirtypcbs.com/
Having a 10 MHz reference in the lab is a good start. But if you have to feed more than one device with the 10 MHz reference signal, some means of distributing the 10 MHz reference signal is needed. The quickest and cheapest approach is just to daisy chain all instruments using BNC T-connectors. This method can cause rapid signal degradation due to mismatches and reflections rather quickly. The cleaner but still pretty inexpensive approach is to use a simple RF splitter. Unfortunately, this may not work for too many devices as the signal level might dip below the needed value for each instrument. The best approach is to use a professional distribution amplifier to isolate the reference input ports of the instruments and to provide a consistent amplitude.
Buying a professional 10 MHz Distribution Amplifier (DA) is pretty expensive. Luckily, old analog video DAs, such as the Sigma VDA-100, can be bought on eBay for little money. With a bandwidth of ~30 MHz they work just fine for 10 MHz reference distribution. The only real catch is that they are designed for an impedance of 75 Ohms, a common value for video systems. But there are some ways around it, more about that later.
The Sigma VDA-100A offers 6 buffered outputs. Two looped-through inputs allow multiple of these amplifiers to be daisy chained together. The ones I bought of eBay even came with a convenient 19″ tray designed to hold three of these Video Distribution Amplifiers. The gain can be adjusted from the front using a small screwdriver. Some models of the VDA-100 have signal taps on the front-panel to check both the input and output signal for quality.
The PCB inside of the Sigma VDA-100 looks extremely clean and well designed. This comes as no surprise as professional broadcast equipment is usually designed this way. There are 6 x 75 Ohm output resistors, R24 through R31. Since they are responsible for setting the output impedance, simply replacing them with 50 Ohm (or 49.9 Ohm) 1 % resistors should convert this DA for use with 50 Ohm systems.
Please note that the input ports are high-impedance ports, NOT 75 Ohms. One can either leave it as it is and accept an impedance mismatch or – the way I did it – solder a 75 Ohm shunt resistor across the input port. This modification is not pictured as I took the pictures for illustration purposes much later from a second VDA-100A. One important thing to know is that most analog video DAs do not have the bandwidth to carry a 10 MHz square wave signal. Only sine wave signals are suitable for this setup. In case you are using a reference that puts out a square wave, you need to convert it to a sine wave. This can be done by using an inline low pass or band pass filter. Back when I was using a different Jackson Labs GPS-Locked TCXO with square wave output, I used a Mini Circuits BBP-10.7+ to get a clean sine wave.
For my setup I decided to leave the output ports at 75 Ohms impedance. Why? Because I had tons of high quality 75 Ohm impedance cable left over from a former broadcast transmitter side. And from a former project I had a stash of Mini Circuits BMP-5075R+ BNC 75 Ohm to 50 Ohm impedance matching pads left over. But if you are on a tight budget I suggest you replace the output resistors R24 through R31 instead and run 50 Ohm impedance coax to your equipment. In my case I used 75 Ohm impedance cable and plugged it through a Mini Circuits BMP-5075R+ each into my instruments. Note that some instruments have a 10 MHz input and 10 MHz output port. For professional equipment, the 10 MHz output is often a buffered output of the 10 MHz input. Therefore you can use this to daisy chain some equipment that’s physically located close to each other. In my setup I never daisy chained more than 3 devices and I always check the signal quality using my Tektronix MDO4104B-6.
The picture above shows the difference between a 75 Ohm impedance BNC connector (left side) and a 50 Ohm impedance BNC connector (right side). The cable on the right side is a professional 75 Ohm impedance coax cable used in broadcast TV installations. The cable is designed to carry HD SDI (Serial Digital Interface) signals at a data rate of 1.485 Gbit/s. Recycling these high-quality cable leftovers saved me lots of time that I would otherwise have to spend crimping new cables.
The three VDA-100A that I bought of eBay happened to come with a convenient 19″ tray. Installing the Jackson Labs FireFly-IIA proved rather easy. It was a perfect job for 25 mm x M3 standoffs and a bit of epoxy glue.
Of course I could have drilled holes in the bottom of the tray but the epoxy glue is not only pretty stable but it’s also easy to use. To get the dimensions just right, I mounted the FireFly-IIA with M3 nuts on the standoffs, applied epoxy glue very liberally to the standoffs and let it sit overnight. Before I glued everything in place I used some sandpaper to roughen the surface up and provide a better grip for the epoxy glue. It worked very well and the installation was surprisingly tough.
My final setup is pictured above. The FireFly-IIA is sitting on the right. It’s connected to a GPS antenna via MCX to BNC adapter. A serial data port is also available for configuration and NMEA position data output. A 50 Ohm MCX to BNC jumper connects the FireFly-IIA to a 50 Ohm to 75 Ohm minimum loss pad. From there a 75 Ohm jumper takes the reference signal into the amplifier. Of course I could have adjusted the input impedance of the VDA-100 to 50 Ohms and connected the FireFly-IIA directly. But I wanted to make sure that there is at least some isolation between the DA and the FireFly-IIA. And a matching pad provides at least some small amount of isolation. This will become an important fact when several of these DAs are daisy chained. Additionally it is less confusing if all ports of the DA have the same impedance.
The green output cable is connected to my Tektronix MDO4104B-6. Using the gain adjust potentiometer on the front of the VDA- and the MDO4104B-6 I adjusted the output signal to about 1.5 Vpp into a 50 Ohm load via 75 Ohm to 50 Ohm matching pad. This level provided the maximum level without visible signal distortion. A quick test with all my test equipment confirmed that this level was sufficient.
The above picture shows my HP 8657D signal generator and a EIP 548A frequency counter synchronized to the same reference signal. The frequency dialed into the HP 8657D is 1023.456789 MHz. The EIP frequency counter shows this value exactly.
But just accuracy down to the 1 Hz digit wasn’t convincing enough for me. My Tektronix MCA3027 measures down to a 0.1 mHz digit. Synchronized via 10 MHz reference, it shows 3.3 mHz more than the selected frequency on the HP 8657D. Now that’s impressive! So if you’re looking for an inexpensive 10 MHz reference distribution amplifier, an old analog analog video DA may just be the way to go.
This setup works well for me but your requirements and specifications may vary. My primary suggestion would be to not mix 75 Ohm and 50 Ohm systems the way I did unless you have a good reason (e.g. availability of suitable coax) to do otherwise. The best way would probably be to replace the 75 Ohm resistors with 50 or 49.9 Ohm type 1% precision resistors.
Links and Sources:
 Jackson Labs, FireFly-IIA: http://www.jackson-labs.com/
In recent weeks I had to do quite a bit of interference hunting for some government agencies such as a local volunteer fire department with harmful interference on their analog repeater network. When working with government agencies, one of the most important thing is documentation. One can’t just point antennas around ans say “I think it’s coming from that house over there.” This is obvious because this kind of interference will likely kick off some sort of enforcement action or even criminal sanctions if the interference is malicious and intentional. To fulfill this documentation requirement I used my RSA 306 spectrum analyzer, SignalVu-PC and RSA Map.
Since the temperature in the car and outside fluctuates quite a bit, I wanted to make sure that my frequency readouts are as accurate as possible. Especially right now where it’s icy cold outside and the car heater is on full throttle, it was apparent that the reference oscillator frequency would drift each time I would open the door to run a test with a directional antenna. Likely, this drift may not cause all too much trouble but I wanted to be absolutely spot on, especially since this was for government agencies. Since the RSA 306 has a connector for an external 10 MHz reference clock, this was a piece of cake to achieve.
A perfect solution for supplying both the 10 MHz reference signal and GPS position information that was the GPS-Locked TCXO evaluation board from Jackson Labs that I reviewed about two years ago. This board served me very well as timing reference for my lab until it was recently replaced by a Jackson Labs Chip Scale Atomic Clock and an Analog devices PLL. The GPS-Locked TCXO board was perfect in many ways for this job. It’s small, USB-powered and inexpensive. The latter is important since items used in the field tend to get broken or lost.
CAUTION: The RSA 306 expects the level of the reference signal to be no greater than 10 dBm. That's 2 Vpp max. The GPSTCXO's output level is, however, 5 V CMOS level.
Despite the level difference, setting up the 10 MHz reference is a piece of cake; Simply connect the 10 MHz out from the GPSTCXO Evaluation board to the 10 MHz reference input on the RSA 306 through a 10 dB attenuator. The attenuator I used is a Mini Circuits HAT-10+.
By default the GPS-Disciplined TCXO Eval board uses a baud rate of 115200 bps. For some reason the RSA Map software only supports speeds up to 38400 bps. Also, by default, the board doesn’t put out NMEA (=position information) data over the serial port. So we have to change the baud rate and set up the GPSTCXO board to spit out NMEA sentences periodically. These settings are modified by sending SCPI (Standard Commands for Programmable Instrumentation) commands to the board. To do this, you will have to use a terminal program to talk to the board and send commands. I used the freely available software Putty. Set the Terminal program to 115200 baud, 8 data bits, N parity bit, 1 stop bit. To verify that you are successfully connected, type the SCPI command “help?” or “syst:stat” (or any other valid command) and see if you get a reply. If everything went right, type the following SCPI commands, one after another and press enter after each line.
The first two commands enable GPRMC and GPGGA NMEA sentences. The ‘2’ is the interval in which the system will provide us with updates, in this case 2 seconds. We don’t really need a high update rate at all. Even while driving around the county I don’t usually take snapshots more often than every minute or so. But if the NMEA sentence interval is set to anything less than 3, the RSA Map keeps switching back and forth between “GPS locked” and “GPS unlocked.” That’s why I left it at 2 to keep the software happy. After typing the first or second command, you should see NMEA messages being outputted into the terminal you are using to send commands. The last command obviously sets the baud rate. The Jackson Labs GPSTCXO Evaluation Board supports the following baud rates: 9600, 19200, 38400, 57600 and 115200 bps. I was somewhat surprised that it doesn’t support 4800 – a fairly standard speed for navigational receivers. But that doesn’t matter to us, pick any rate you please between 9600, 19200 and 38400 for compatibility with RSA Map. Remember to adjust your terminal’s baudrate to the new rate. Else you won’t be able to communicate with the board.
For an overview of all possible SCPI commands and setting I recommend you review the comprehensive user manual .
Now that we have the GPS receiver functionality of the GPSTCXO set up, we need to tell RSA Map where to find the navigation data. In order to do this you need to know the COM Port number and the baud rate you just set via SCPI command. Just enter it into the GPS Setup dialog, check “Enable” and hit “Apply”. If everything went right, valid GPS data should be displayed in the “status” section of the dialog. If so, click “okay” and start hunting interference
Just as a side note: This set-up of course also works with different Tektronix instruments such as the MDO4000(B) or the higher level RSA5000 / RSA6000 and SPECMON product line. While they are less portable, they do the job just as fine. And before the RSA306 was released to the market I would actually use my MDO4104B-6 in the car for interference hunting. When you power these instruments through an inverter, make sure it’s of high-quality. The last thing you want is a cheap power inverter to kill these sensitive instruments.
If you use Tektronix SignalVu, odds are that you also have the RSA Map option installed. SignalVu comes installed on some instrument (e.g. RSA5000, RSA6000 or SPECMON) or as SignalVu-PC for use with entry-level instruments (e.g. RSA 306, MDO3000 or MDO4000) on a PC. RSA Map is a mapping tool for SignalVu. RSA Map makes it easy to map different measurements, such as spectrum, spectrogram and amplitude over time measurements. The measurement locations can me either set manually or automatically via GPS synchronized location information. It is even possible to add directional information (=azimuth) if a directional antenna is used. Therefore, this is a perfect tool to hunt down interference issues or to create coverage maps.
Obviously, no mapping software is very useful if it doesn’t have a good map. Out of the box RSA Map only comes with a very coarse world map. While it has the ability to zoom in, no features other than the continental outlines are shown in the default map. So unless you intent to fly around the world with an RSA306 in your carry on luggage maybe, this is not very useful. In case you wonder why Tektronix doesn’t include better maps, just imagine how expensive it would be to gather fully licensed maps for the whole world. Also, the file size would be ridiculously huge. It’s just unrealistic for Tektronix to do. So bottom line, we need to acquire our own maps if we want to use RSA Map. Luckily, there are some free online resources available to source some free maps.
One of those free resources is OpenStreetMaps .
Downloading a map is rather simple. Simply adjust your map view to the area you would like to be covered in RSA Map and click the “Export” button. But there’s one more step needed to make the map compatible with the RSA Map software. RSA Map requires files in the MapInfo Interchange Format (*.mif) but OpenStreetMap exports the files in its own format, *.osm. But no need to worry, there’s a free online tool called GeoConverter .
Converting the file is super simple, just select the *.OSM file you downloaded from OpenStreetView and select “Map Info interchange Format (MIF/MID)” as export format. To import the map into RSA Map, simply click on “File -> Load Map…” and select the *.MIF file you downloaded from GeoConverter. That’s it.
The only issue I have with this map source is that it appears to only map houses, not the streets or street names. But since it’s free I won’t complain. The maps are more than useful for my purposes the way they are. However, if you know of a better map source, please let us know. The above image shows a real measurement that I have performed and documented with RSA Map. With just two directional measurements I was able to track down a leaky cable TV distribution amplifier. It caused severe noise on portions of the VHF aviation and amateur radio bands.
Links and Sources:
DirtyPCBs.com offers super cheap PCBs for up to 10 cm x 10c m through Chinese fabrication houses . Despite their dirt cheap approach, the options are still plentiful for the average hobbyist. All PCBs, 2-layer or 4-layer, are of FR4 material with selectable thickness, color and finish. Even electroless nickel immersion gold (ENIG) finish is offered. Also available super cheap are solder paste stencils. Dirty PCBs stresses that you shouldn’t expect much and that this is a real “as cheap as it gets” approach. It’s a great service for prototyping inexpensive prototyping and hobbyist use though.
Dirty PCB differentiates between the different layers by the file extension of the Gerber files. The following extensions are used for each layer:
Extension – Layer
GTO – Top Silkscreen (text)
GTS – Top Soldermask (the ‘green’ stuff)
GTL – Top Copper (conducting layer)
GBL – Bottom Copper
GBS – Bottom Soldermask
GBO – Bottom Silkscreen
GML/GKO/GBR* – Board Outline*
TXT – Routing and Drill (the holes and slots)
This is different from the default DipTrace setup. By default, DipTrace uses the .gbr extension for all Gerber files and differentiates between layers by file name. So before exporting one needs to click on the “Files” button in the Gerber export menu and enter the above nomenclature. Furthermore, please deselect layers that are unnecessary. The following picture shows the correct setup:
The most important file is the board outline. According to Dirty PCBs, forgetting to include this file is a common error that leads to designs being rejected. Technically speaking, a board outline is the only required file. However, this would be an extremely boring board. But it might be useful if you need someone to cut some FR4 material to size for some strange reason.
The next common problem Dirty PCBs mentions is missing drill files. They require an Excellon drill file (also called NC drill file) with either a .TXT or .DRI file extension and embedded tooling information. DipTrace accomplishes this as follows:
All the files generated by the Gerber and Excellon export need to be combined in a .zip archive. That is really all of the magic behind exporting a layout for Dirty PCBs. Just upload the .zip archive to Dirty PCBs, select a package size and send off the order. Dirty PCBs will offer you a preview of your uploaded design. They stress that this feature is experimental, however, it is probably a useful tool to see if something went horribly wrong.
One really cool feature of Dirty PCBs is the ability to share one’s design with the whole wide world. For instance, my design from a previous article on how to use DipTrace can be ordered here. Perfect for Open Source Hardware (OSHW). You can even collect $1 every time somebody orders your design. But don’t be greedy; Dirty PCBs doesn’t make much money of orders. If you intent to get rich with your design, I suggest you order a larger quantity and sell it at a profit yourself.
Another feature is the fact that you can upload new design files at all times until Dirty PCBs sends them off to the fabrication house. Seems like no big deal but every design engineer knows that almost always at least one improvement comes to mind just after submitting the design files. As you can see from the previous image, I actually revised the uploaded design files 3 times. It’s a real life saver.
That’s it. Assuming that your design is abiding their design rules, not much can go wrong from here. Enjoy!
Links and Sources:
 Dirty PCBs: http://dirtypcbs.com//