Packet Engine Pro Help

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Tips, Tricks, & Trouble
   Tips and Tricks
Sound Card Use
     . Sound Card Interface
     . HF Operations
     . 9600 Operations
     . Receive Problems
     . Transmit Problems


Help Date: 21 June 2004



Sound Card HF Packet Operations (300 Baud)

HF vs VHF/UHF Packet
Setting the HF Baud Rate
Tuning HF Packet Signals

HF vs VHF/UHF Packet
HF packet operations are different from VHF/HF operations in several ways:

* signals more easily affected by interference and propagation conditions
* signals adversely affected by low signal-to-noise ratios and spurious noise
* the maximum data rate is less -- 300 baud compared to 1200 baud or more on UHF/VHF
* the tone shift is 200 Hz rather than the 1000 Hz used on UHF/VHF
* frequency shift keying (FSK) on SSB (Single Side Band) is used instead of audio frequency shift keying (AFSK) on FM (Frequency Modulation)
* digipeating not generally used (because of 3rd party traffic concerns)
* precise tuning can be much more difficult!

Setting the HF Baud Rate 

You can set the baud rate for HF (High Frequency) operations from the Radio Port Properties screen. Use the drop down list to select an "On Air Baud Rate" of 300 for the radio port/radio you plan to use for HF operations. You will have two choices for 300 baud:

  • 300 KAM - uses 1600/1800 mark/space tones as a KAM TNC does; center of tones is 1700 Hz

  • 300 PK232 - uses 2110/2310 mark/space tones as a PK-232 TNC does; center of tones is 2210 Hz

The best choice is probably the 300 KAM tones. The 300 PK232 tones are an option for hams who are accustomed to working with this tone pair.

Warning: The PK232 tones (2110/2310) land right on the upper edge of the passband of the typical SSB filter and they very likely will 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 on many HF rigs the passband tuning provided on RECEIVE allows you to shift the pass band to a higher band of audio frequencies, but it has no effect on the TRANSMIT side, so your transmitted tones will still be affected by the filter and may be distorted or may not even be transmitted.

if you pick the KAM tones, the key point to remember is that your transmitted signal will be 1600-1800 Hz from the dialed frequency. If you operate Lower Side Band (LSB), as is common, your packet tones will be lower than the dialed frequency by that much; if you operate Upper Side Band (USB), they will be higher by that much. The same is true if you pick the PK232 tones; your transmitted signal will be 2110-2310 Hz from the dialed frequency.

PTT Option: Many HF radios have a VOX (voice activated transmission) feature. If your radio does, you can use it instead of a PTT cable, although VOX can be troublesome. Depending on your microphone setup, VOX can also transmit room noise on your packet signal (not good). In addition, any sounds from Windows or your programs can trigger a transmission (so you might want to switch them to off). If you do use VOX, then in the Packet Engine Pro port setup, choose an unused or non-existent RS-232 port for PTT control. You won't "waste" a port or invite a port conflict with another device.

Tuning HF Packet Signals

To aid tuning, Packet Engine Pro includes a Sound Card Tuning Aid. You can access it from the Radio Port Manager screen. Highlight the radio port/frequency to analyze and then from the Edit menu, select Tuning Aid; or click on the Tuning Aid icon

Note: If you have configured the sound card for single port use, you will see only one oscilloscope. You will see two scopes only if you configure the card for dual port use.

For HF tuning, use the Waterfall Spectrum oscilloscope display. Signals are represented by the blues (weakest), greens, yellows, and reds (strongest) on the 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.

Here's some samples:

       ^ Radio Needs Tuning -- signal is outside the two white marker lines.

        ^ Radio tuned correctly

       ^ No signal present, just the band noise.

Dial Frequency - the suggested frequencies in the list below are the channel centers between the 2 transmitted tones. They are not the dial frequencies. To get the dial frequency, take the frequency you want your packet tones to center on and then add (for LSB) 2210 Hz (if you selected the PK232 tones) or 1700 Hz (if you selected the KAM tones).

Example for 30 meters using LSB with KAM tones: 

Channel Center = 10.140.000
KAM Tones              + 1.700
Dial Frequency  = 10.141.700

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 an assumed mark or space frequency. In other words, the frequency shown on the radio's display will not be the true dial frequency.  If your radio does this and it uses an offset that matches either the KAM or PK232 tone center, then if would be advantageous to choose that tone pair -- either the KAM or PK232 -- when you select the baud rate in Packet Engine Pro. Your radio's User Manual will have the data mode offset. If the offset does not match the KAM or PK232 tones, then you must calculate a dial adjustment that factors in the radio's offset and the tone pair used by Packet Engine Pro, i.e. (Actual Tone Center minus Radio Offset) = Dial Adjustment needed to put tones on correct frequency. Example:
Actual Tone Center  1700
Radio Offset           -2210
Dial Adjustment        -510

Suggested HF Packet Frequencies - LSB Band

BAND                 CHANNEL CENTER
80 Meters       3.580- 3.635, priority at 3.620-3.635
40 Meters       7.035- 7.050, priority at 7.040-7.050 and 7.100-7.120 in the Americas
30 Meters     10.130-10.150, priority at 10.140-10.150
20 Meters     14.070-14.112, except 14.100 (beacons); priority at 14.095-14.0995
17 Meters     18.100-18.110, priority 18.104-18.110
15 Meters     21.070-21.125, priority 21.090-21.125
12 Meters     24.920-24.930, priority 24.925-24.930
10 Meters     28.070-28.189, priority 28.120-28.189

20 Meters is the most active HF packet band.

Look for APRS beacons at these center channel frequencies:
10.149.30 (North America)  
14.103.30 (Regions 1 & 2 only)
21.101.29 (Africa)

Signal Volume - The signal volume (as seen by the colors in the Waterfall Spectrum) can best be adjusted by using the Sine Wave oscilloscope display. The sine wave heights should only fill 1/4 to 1/3 of the screen. To adjust the volume, press the Set Volume button on the Sound Card Tuning Aid screen. This brings up the Sound Card Volume Settings screen. Select the appropriate RX Input Line from the drop down list -- either LINE IN or MIC -- and then move the slider under the RX header. Use the left slider to adjust the volume of the first sound card port (left channel). Use the right slider to adjust the second sound card port (right channel), if you are using it.