WA8LMF Home Page | Main Ham Radio Page | Main Links Page | Updated 10 Nov 2006

TNC Test CD

The file linked below is an image file that can be used to re-create a compact disk containing files to test and compare the performance of standard 1200 baud VHF packet radio TNCs under various conditions.

This disk is a "CD-Plus" combination disk that contains CD-ROM data files (including a readme file similar to this page) viewable on a computer, and standard CD audio files playable on any normal home or car audio CD player, boombox or DiskMan. The audio files could also be played on an old CD-ROM drive standalone, without a computer, by connecting the TNC under test to the drive's front panel earphone jack, or to the 4-pin analog audio jack on the drive's rear panel. (A CD-ROM drive normally doesn't need computer support to play audio CDs. A drive with a front panel volume control and track-select button is preferred.)

Playing back standard CD audio rather than CD-ROM .wav data files avoids the timing errors and incorrect playback sample rates that often accompany low-cost software-based PC sound systems (i.e. motherboard AC97-based systems). Note that some recent PC CD and DVD drives now extract audio digitally rather than using the digital-to-analog converters inside the CD drive for audio playback. With this kind of drive, there is no separate analog audio output and cable from the CD drive to the PC motherboard. In this case, take the audio directly from the front panel earphone jack of the drive rather than from the computer sound system.

You may have to disable the the digital audio extraction mode to do this. Go to the Windows Device Manager, bring up the properties panel for the CD drive, and under the "Properties" tab uncheck the box "Enable digital CD audio for this CD-ROM device".

The CD-ROM data area may be seen by some audio players as an un-playable first audio track. Use the hardware track select button on an audio player or computer CD-ROM drive's front panel to jump to the second track (first audio track) if the disk doesn't play automatically.

On a laptop CD drive that doesn't a hardware track select button, start the Windows CD Player (not Media Player !) to create a software control panel with track selects, play, stop, etc. Normally this is accessible from "Start, Programs, Accessories, Entertainment, CD Player".

To aid in selecting the cuts on a CD-ROM drive that lacks a front-panel track-number indicator, voice announcements and cue tones have been added to the beginning and end of each track.

Track 1 has a DTMF digit "1" at the beginning and a DTMF digit "6" at the end.

Track 2 has a DTMF digit "2" at the beginning and a DTMF digit "7" at the end.

Track 3 has a DTMF digit "3" at the beginning and a DTMF digit "8" at the end.

Track 4 has a DTMF digit "4" at the beginning and a DTMF digit "9" at the end.

Track 5 has a DTMF digit "5" at the beginning and a DTMF digit "0" at the end

The differing digit values could possibly be used with a DTMF decoder to automatically start or stop data acquisition devices.

Note that all these recordings are taken directly from the discriminator. Tracks 1, 3 and 4 are not de-emphasized. Track 2 is de-emphasized (see below). If you wish to evaluate how various TNCs behave when connected to a radio's speaker or headphone output (rather than directly to the discriminator such as from a 6-pin mini-DIN "data" jack.), you will have to insert an RC de-emphasis network between the CD player and the device under test.

NOTE: A very useful APRS program for this kind of testing is KH2Z's APRS+SA a.k.a "APRSplus" because it keeps a running count of the number of times each station has been heard. Thus one can easily compare the number of successful decodes different TNCs produce. Both track 3 and track 4 are recordings exclusively of a single callsign (WA8LMF), making this comparison of number of decodes very simple.

The Tracks

Track 1 is an off-the-air recording of 40 minutes of activity on 144.39 MHz in Los Angeles, California, during the afternoon rush hour at about 5:00 PM when the channel is totally saturated to several hundred percent of the Aloha threshold. This recording was taken from the non-de-emphasized direct discriminator output of a Yaesu FT-1500 via the 6-pin mini-din data connector. It contains a variety of over- and under- deviated signals, packet collisions, rapid-fire packets with practically no pause between them, raw NMEA string trackers, TinyTraks, clueless idiots using CW ID on packet, etc. All periods of dead air over about 1 second have been edited out so that 40 minutes of real-life activity have been compressed to 25 minutes on the CD.

This track is intended to be played back directly into TNCs to compare the performance of various TNCs "under fire" in the real world . The rapid pace of the packets should be a good test of the ability of buffers in TNCs and associated applications to hand a rapid flow of data without overrunning.
Track 2 is identical to Track 3 except that a precise 6db-per-octave/20db-per-decade de-emphasis between 300 and 3000 Hz has been applied to simulate the typical de-emphasis found at the volume control or speaker output of the typical land-mobile receiver. This can used to evaluate the relative performance of TNCs in handling raw non-deemphasized discriminator audio vs de-emphasized speaker audio. The effectiveness of jumper-selected equalization networks available inside some TNCs can also be tested. This track was created by applying the graphic equalizer filter in Adobe Audition set to simulate the standard EIA land-mobile radio de-emphasis curve.

Note that a roll-off was also applied below about 200 Hz to simulate the typical highpass filtering used to keep CTCSS ("PL") tones out of the speaker of mobile radios.

Track 3 is a recording of a Kenwood D700 transceiver sending a Mic-E position report, taken from the wideband low-distortion discriminator output of an IFR1500 service monitor. The receiver was unsquelched and no de-emphasis was used. This recording of a single packet was then copied and pasted repeatedly in the Adobe Audition audio editor. The result is 20 bursts each minute, for 5 minutes, for a total of 100 absolutely identical packets.

This track is intended to modulate an RF signal generator, or the generator mode of a service monitor. Connect the CD player to the external modulation input of a generator, and set the playback level so that the data bursts deviate the generator about 3.5 KHz. Connect a radio's receive audio output to the TNC under test. Connect the RF generator to the radio's antenna input. While the recording is playing, gradually decrease the generator RF output level until the TNC starts failing to decode. Since the recording contains exactly 100 bursts, counting the number of successful decodes can directly indicate the percent success rate at various RF carrier levels.

Possible uses of this track:
1)     Compare different TNCs connected to the same radio.

2)     Connect the same TNC to different radios to compare the weak-signal data performance of various receivers.

3)     Evaluate the relative receive performance of audio taken from the radio's speaker versus audio taken from dedicated "data" or "packet" jacks or outputs. (De-emphasis and audio bandwidth may be different at these two sources.)
Track 4 is an off-air recording of 25 minutes of a single mobile D700 beaconing every 12 seconds (maximum beacon rate) on a quiet channel (no other stations) while driving around the San Gabriel Valley area of Los Angeles. The signals were monitored in Pasadena, California. Most of the drive test course was 8-10 miles from the fixed station, far enough away from the monitoring fixed station to create some mobile flutter, multipath and loss of quieting. In several stretches, several successive packets are audible on the recording but failed to decode with the AGW packet engine.

Again, this recording was taken from the non-de-emphasized direct discriminator output of a Yaesu FT-1500b via the 6-pin mini-din data connector. Click Here for a map of the route driven, produced with UIview32, Precision Mapping 7.1 and UI-HeightTrack (opens in new window).

This track is intended to be played back directly into TNCs under test. An APRS application running on a computer attached to the TNC should create a realistic moving object.

The three following tracks are for TNC alignment rather than testing. They are intended to evaluate TNC demodulator tolerance to tone "skew" (unequal levels of the 1200 and 2200 Hz tones).

Track 5 is a direct recording of one minute of a KPC3+ TNC in the CAL mode sending the alternating 1/0 test pattern (i.e. alternating between 1200 and 2200 Hz tones) with both tones at the same amplitude.
Track 6 is the same recording with a precise 6 dB/octave 20 dB/decade de-emphasis applied as in Track 3 above.
Track 7 is the same recording with a mirror-image precise 6 dB/octave 20 dB/decade pre-emphasis applied.

File Download

READ THIS FIRST !!!

The image file you download produces a MIXED MODE disk that combines CD-ROM data and audio CD tracks.

This is not a normal CD_ROM.
This is not a normal audio CD.
It is a combination of the two. When you place this disk in a computer CD drive, you will only see the CD-ROM data part of the disk. The audio tracks will NOT show, and will NOT automatically start playing.

Go to the Windows Start menu and do Start -- Programs -- Accessories -- Entertainment, and select the "CD Player" applet. You will get an on-screen display that looks like a car stereo CD player with start, stop and track select buttons and a volume control. Use this software "device" to play the audio tracks.

NOTE: This player applet was supplied with Windows 95, 98 and 2000, but was apparently not provided with Windows XP. The Windows 2000 version of this player works just fine with Windows XP. Copy the player (which is a single file CDPLAYER.EXE) located in the \WINNT\SYSTEM32 of a Windows 2000 setup to a WinXP installation. The program is a single ready-to-run .EXE that doesn't require SETUP or mysterious hooks to the Windows registry to function. Just copy the file to any convenient place in the Windows XP setup, and double-click CDPLAYER.EXE to run it.

In a non-computer audio player such as a boombox or DiskMan (or a CD-ROM drive being used stand-alone outside of a computer), the drive may mistakenly see the first (data) track as a defective unplayable audio track and do nothing. If so, use the track selector button to jump to the next (first actual audio) track.

The downloadable file is an image file in Adaptec/Roxio "Easy CD Creator" .CIF format. This file, like the more common .ISO file type, is a "snapshot" of an entire CD, sector by sector, captured into a single file. [Unfortunately, the industry-standard .ISO CD-image-file format doesn't support the mixed-mode (part-CD-ROM/part-audio-CD) format of this disk.]

Adaptec/Roxio Easy CD Creator and some other CD-recording applications can re-create a disk from this type of file. You do not place the .CIF file in a list of files to be recorded as you typically do. Instead, pull down "File" from the menu bar, and look for something like "Record Disk From Image ..." or "Make CD From File..." .

WARNING! This is a very large download (over 530 megabytes). It may take several hours even on a broadband connection, and days on a 56K dialup connection.

If you would rather avoid the huge download, you can purchase a recorded CD and have it mailed to you. The recorded CDs are being distributed by Argent Data, the online store of N1VG of OpenTracker fame. Scott has also graciously offered to host the large CD image files, downloadable for free if you wish to make your own, on his Argentdata server.

Click Here for ordering information.

Click Here to go to the file downloading page.

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