AGWPE: Baud Rates and Modes

Baud Rates and Modes

Interesting fact: The maximum potential packet baud rate for a sound card is approximately half the sound card's maximum sampling rate. Since most sound cards have a sampling rate of 44100 Hz, the maximum packet baud rate they could support would be 22,050. This is closest to a 19,200 baud rate, a rate not normally used in packet. The maximum baud rate currently provided by AGWPE's sound card feature is 9600 baud and it's not likely that SV2AGW will change this.

The AGWPE sound card modem is capable of both 1200 and 2400 baud AFSK operations.

1200 baud is perhaps the most common rate used on VHF frequencies. It is more common than 2400 baud because of the far greater number of 1200 baud TNCs and radio modems. The 1200 baud sound card modem uses the standard tone pair of 1200 Hz and 2200 Hz.

The 2400 baud AGWPE modem is compatible with a TCM3105 modem chip modified with a 8Mhz crystal for the modem clock and uses a 2165 and 3970 Hz tone pair. Again 2400 baud packet is rarely if ever used.

FSK9600 baud is frequently used on the UHF bands and uses Frequency Shift Keying (FSK) instead of the Audio Frequency Shift keying (AFSK) used for 1200 or 2400 baud mode. Because of this, and because of the very quick TX-to-RX switching times required, you need a radio that will handle 9600 baud packet correctly. Most radios do not! For best results, you can use a radio designed especially for 9600 baud mode, e.g. PacComm's TEKK KS-900 (440 band, 2 watt) or KS-1000 (440 band, 5 watt) radio; or SYMEK's TNC2H. Or you can also use one of the newer multi-mode transceivers labeled as "9600 baud-capable", such as the Kenwood TM-V7/V71 and D700/D710; Yaesu FT-817; or the ICOM IC-275.

The newer 9600-ready radios often have a data jack that has a special pin for 9600 receive and maybe one for 9600 transmit. Consult your User Manual to find out which pins these are and then attach your sound card interface wires -- TX audio and RX audio -- appropriately. The radio will probably also have a special menu selection for a "9600" data mode which may regulate TX audio attenuation/amplification and RX/TX switching times. Typically, the "9600" mode adds attenuation to the TX line so that the radio can accept full sound card LINE OUT voltages, e.g. 500-2000 mV, rather than the approx. 40 mV maximum for "1200".

Note that if you select "9600", your TX audio cable may be better without an attenuation circuit; or if your cable's attenuation circuit has a pot (potentiometer), turn the pot to reduce the attenuation. You may also need to increase the sound card's "playback" volume settings.

Yaesu FT-847 Users: Some interesting notes on 9600 baud mode use can be found at http://www.supercontrol.de/cat/ft847faq/digital.htm#9600bps

Most users report that the RX and TX audio lines in your interface must NOT have audio isolation transformers for 9600 operations. Generally , small audio or power transformers do not have the correct frequency response. For example, Radio Shack's #273-1374 1:1 600 ohm audio line transformer has a 300 Hz to 5 kHz frequency response range which is not low enough. Until someone sends me an isolation circuit with suitable components (please!), take these precautions if you build an interface cable without isolation:

make sure the computer and and the transceiver's power supply are connected to the same AC power circuit (i.e. sharing the same ground).
connect/disconnect the sound card interface to the transceiver or computer only after both devices are unplugged from the AC power circuit.

Older transceivers would need modifications to work properly at 9600 baud. You cannot use the microphone jack to input TX audio on most radios; likewise you cannot use the speaker output for RX audio. For TX audio you must connect directly to the VCO, and for RX audio you must connect directly to the discriminator output. See these web sites for advice on radio modifications:

TAPR: http://www.tapr.org/software_library.php?dir=/general/9600baud
http://www.tapr.org/pub_9600.html (non-ham radio mods)

Report by the ARRL on various radios

AMSAT article that has information about 9600 baud physics

Some notes about 9600 baud use:

Successful 9600 packet operations may require a near full-scale S-meter reading. 9600 signals are far more susceptible than 1200 baud to multi-path conflicts, phase distortion, and noise. As a result, you may need 5 to 10 times the signal strength for 9600 baud to work reliably compared to 1200 baud. Another way to look at it is that the usable range for 9600 will be far less than 1200 for the same antenna and transmit power. Note that if your 9600 packet exchange is slowed by signal problems and data repeat requests, 9600 operations won't be any faster than 1200 operations.
Likewise, unless your radio has fairly fast RX-to-TX switching time (less than 50 ms) you won't gain much from 9600 use. The increase in baud rate will not make much difference if the radio has lengthy RX-to-TX switching delays.
You will probably need to set the AGWPE volume controls almost to the maximum for 9600 operation.
Some soundcards do not have an adequate audio response range for 9600.
What can you expect for an approximate maximum operating distance for 9600 baud at 440 MHz? Approx. 15 km / 10 miles @ 10 watts in urban areas with a good antenna and radio.

For more on 9600 baud operations, see:

300 baud (HF)

300 baud HF packet operations are quite different from 1200 baud VHF/UHF operations:

Tuning is more difficult - the incoming audio tones from the receiver have to match the frequencies AGWPE is expecting within 20 or 30 Hz in order to be reliably decoded (that is within 10-15% or so of the 200 Hz shift). Since the receiver tuning directly affects the frequency of the recovered audio, this requires very precise manipulation of the receiver tuning knob. Since most modern HF rigs tune in synthesized steps of 10 Hz, this means that nudging the knob barely one or two clicks from center is enough to completely kill reception. [Many hams still have problems tuning in an SSB signal so that voice sounds reasonably natural, and that requires "only" a tuning accuracy of 50-100 Hz, not 20-30 Hz!].

Note: this extreme sensitivity to frequency error means that any traditional analog VFO rig will be virtually unusable on a fixed HF frequency (such as for APRS), since they are unlikely to stay within 10 Hz for very long. For this reason, your radio should have a very stable VFO if you hope to stay exactly on frequency.
Signals are more easily affected by interference and propagation conditions and by low signal-to-noise ratios and spurious noise
The tone shift is 200 Hz rather than the 1000 Hz used in 1200 baud packet
Digipeating is not generally used (3rd party traffic concerns)

Configuring AGWPE for 300 baud HF packet isn't much different than for 1200 or 9600. On the AGWPE Properties for Port 1 window, push the Options button to call up a Sound Card Modem/TNC Setup window with baud choices for the left channel (port 1/radio1) and right channel (port 2/radio 2). Just select 300 baud for the left channel (see also the AGWPE setup page).

Processor Tip: George SV2AGW suggests that to save some processor resources, it's best to operate 300 baud in Single Port mode (see the AGWPE setup page.)

For example, if you have selected dual port, the Sound Card Tuning Aid window (see below) will show 2 active tuning windows and the program may run slow. To close (gray out) the lower window, change the AGWPE port properties to Single Port. (Note: If you've messed around a lot with the AGWPE port configuration, it is a good idea to delete the AGWPE.INI file and all PORTx.INI files from the AGWPE directory and start again.)

To aid tuning, AGWPE includes a Sound Card Tuning Aid. You can find it on the AGWPE pop-up menu accessible by clicking on the AGWPE tower icon in the System Tray. For HF tuning, select the Waterfall Spectrum style. Signals are represented by blues, greens, yellows, and reds (weaker to stronger) on a black background (black =no signal).

Tune your transceiver so that the colorful portion of the screen scrolls down between the two vertical lines. To get good copy, the tone must be precisely centered between the two lines.The sound volume (represented by the colors) in the Waterfall Spectrum can be adjusted by the TX audio volume. But it's better to use the SineWave style to see the volume of the incoming signals. The wave heights should only be 1/3 to 1/2 the screen. If necessary, adjust the Line In or Mic slider in the Recording window of the Volume Control program.Note: AGWPE emulates a PK-232 HF modem and uses tones of 2110Hz and 2310Hz for a center frequency of 2210 Hz (and the standard HF packet tone shift of 200 Hz). If you are accustomed to KAM tones of 1600Hz and 1800Hz, you'll need to adjust your radio tuning an additional 510 Hz (+510 Hz for Lower Side Band and -- 510 Hz for Upper Side Band).

The Packet Engine Pro version offers both the PK-232 tones and the KAM tones.

For some radios, the KAM tones may be a better choice since the PK232 tones (2110/2310) land right on the upper edge of the passband of the typical SSB filter, where they could experience differential phase shift and unequal amplitude output; i.e. severe distortion. In fact, the tones may not make it through the passband of many HF transceivers with sharp cutoff SSB filters. (For example, many "contest grade" SSB filters have a cutoff at 2100 or 2200 Hz.) On the other hand, the KAM 1600/1800 Hz tones land in the flat part of the pass band of any SSB rig and will be unaffected by the filter.

Note that on some HF rigs the passband tuning provided on RECEIVE allows you to shift the pass band to a higher band of audio frequencies, but it may not effect the TRANSMIT side. If so, your transmitted tones will still be affected by the filter and may be distorted or may not even be transmitted.

Another option for HF packet is the UZ7HO modem (free) or the MixW program ($50 shareware). They may have a few advantages over AGWPE, including improved decoding, easier tuning and more user-selectable tone pairs. MixW can also link to AGWPE, where the UZ7HO modem is used instead of AGWPE.

PTT: If you are able to use your VOX key up on your HF rig, you will not need a separate PTT cable, although many users find VOX troublesome and prefer a hardwired PTT circuit and cable. If you use VOX, set the AGWPE PTT port (COM or LPT) to some unused port (e.g. LPT3) so you don't conflict or tie up a real port. Also remember that VOX is subject to other noises that it hears, such as Windows sounds, program sounds, etc. It is probably best to turn those off if you run with VOX. Also, depending on your microphone setup, watch out for room noise, talking, etc.

HF Packet - LSB
Band	Suggested Frequencies* (channel centers = RF between the 2 tones)
80	3580-3635, priority at 3620-3635
40	7035-7050, priority at 7040-7050 and 7100-7120 with Americas
30	10.130-10.150, priority at 10.140-10.150
20	14.070-14.112, except 14.100 (beacons); priority at 14.095-14.0995
17	18.100-18.110, priority 18.104-18.110
15	21.070-21.125, priority 21.090-21.125
12	24.920-24.930, priority 24.925-24.930
* AGWPE tones have a center frequency of 2210 Hz, so for LSB you would set your radio dial + 2210 Hz higher than the frequencies listed above. (For LSB, remember that the higher the frequency shift, the lower the resulting LSB frequency.)

20 Meters is the most active HF packet band.

Interested in HF APRS? Stephen WA8LMF has some great pages at: http://wa8lmf.net/aprs/HF_APRS_Notes.htm http://wa8lmf.net/APRS_PSK63/index.htm

Look for APRS beacons at:

7.035.5

10.151.51 MHz LSB (North America)

14.105.51 MHz LSB (Regions 1 & 2 only)

18.102.5

21.103.5 (Africa)

29.250.5

The frequencies above are the suppressed-carrier (radio dial) frequencies for AGWPE (and PK-232 TNCs) with a +2210 Hz center frequency. Users of other TNCs may refer to these APRS dial frequencies as 510 Hz less than AGWPE's tones, for example 14.105.0 instead of 14.105.5.

Example for 30 Meters APRS

Using LSB, set the radio to 10.151.51
The radio dial frequency is listed first in blue. The actual transmit RF frequencies for the AGWPE Mark and Space tones are in red:
10.151.51 - 2.310 = 10.149.200
10.151.51 - 2.110 = 10.149.400

Using USB, set the radio to 10.147.09:
10.147.09 + 2.110 = 10.149.200
10.147.09 + 2.310 = 10.149.400

Note that some HF radios with "DATA" or "FSK" modes automatically offset the indicated dial frequency to account for the difference between the suppressed carrier freq and the actual mark or space frequency, but they typically assume tones different than 2310/2100 tones used by AGWPE. You'll need to get the data mode offset from your user manual and then calculate the an adjustment offset for AGWPE.

Super fast packet

The highest baud rate that AGWPE's sound card can emulate is 9600 baud, but hams have experimented with much faster baud rates using special equipment. At the bottom of this page by Symek, there is some discussion about these higher rates.

Sound Card Packet with AGWPE

Baud Rates and Modes

1200 and 2400 Baud AFSK

9600 Baud FSK Operations

300 baud (HF)

HF Packet - LSB

Super fast packet