VK APRS Network

HF Guidelines

In Australia, APRS on HF sees occasional use. While the following conventions exist, be prepared to experiment, and be aware of limitations compared to VHF:

BandFrequencyModeDigipeater Path
30 metres10147.6 kHz (USB)SSB
300 bps AFSK		WIDE2-1
40 metres7045.2 kHz (USB)SSB
300 bps AFSK		WIDE2-1

For VHF, see VHF Setup & Guidelines.

There are some important differences for using APRS on HF, so keep the following Do’s and Don’ts in mind:

Do’s

  • Do consider all other users of the HF network. Remember you are sharing this single frequency with hundreds of other operators.
  • Do use only a path of GATE,WIDE2-1
  • Do use a SSID of -4 if your station is a HF-to-VHF or HF-to-IGate.
  • Do use a SSID of -15 if your Mobile Station transmits on HF.
  • Do keep your packet size to a minimum. Use the Mic-E or APRS compressed format and no or minimal information in your status text.
  • Do set your beacon time to 10 minutes or more to minimise the chance of collissions.
  • Do use the path of ECHO or TUNE Only for tuning your radio into the Net.
  • Do use the following TNC settings for your success:
    • TXDelay: 400ms
    • Packet Length: 128
    • Slot Time: 300ms
    • Persistance: 64ms

Don’ts

  • Don’t Digipeat any packets on HF (the only exception is for tuning your radio).
  • Don’t transmit Home station positions on HF. Only Gates and Mobile stations need to transmit position information.
  • Don’t feed VHF or IGate data to HF
  • Don’t allow your station to operate as a digipeater

Remember that an average length APRS position report takes 3–4 seconds to transmit on HF. Assuming a channel efficiency of 30% for AX25, this results in a maximum of 7 stations being able to transmit per minute.

Assuming a transmission rate of one position report per 10 minutes, this means the maximum number of HF APRS stations that can be in a single coverage area is 70 stations.

With overhead such as tuning, misconfigurations, interference, or propagation changes, this may further limit the number of stations that can operate.

Keeping all of this in mind, configuring your equipment appropriately, and using APRS on HF thoughtfully, will allow the successful long-term use of the network as it continues to grow.