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Current APRS Satellite Status

The page embedded below is provided by Andrew, VK4TEC, and can be viewed as a standalone page here.


Stations heard via satellite

The raw data below is provided by Andrew, VK4TEC, who has created some scripts to collect all Satellite beacons from the APRS-IS.
Andrew's site can be accessed here.

The following sites can also be used to view the latest APRS data:

HF Operation Guidelines

Australasian APRS HF Operations Guide.

As HF APRS is becoming more popular in Australasia, we have put together a set of guidelines that we should all adhere to. This will allow the successful long-term use of the ARPS HF network as it’s popularity continues to grow.

The Do’s and Don’ts for HF APRS.

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 Net (set your frequency) to the Primary Net server for the band you are operating on. If you can not hear the Primary NET server, use a secondary NET server.
  • Do use a SSID of -4 if your station is a HF to VHF or HF to Internet Gate. (Refer to the SSID Guide)
  • Do use a SSID of -15 if your Mobile Station transmits on HF. (Refer to the SSID Guide)
  • 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. (The primary and secondary net stations are the Only station that will beacon at more frequent intervals)
  • 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, SLOTtime 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

NOTES:

Remember that an average length APRS Posit packet takes 3 to 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. At a transmission rate of one posit per 10 minutes the maximum number of stations that can be in a single APRS Gate’s coverage area is 70 stations. This will be less as the Net stations transmit frequently and messages and/or tuning may be under way on the channel. HF Propagation is also an important factor in limiting station numbers

APRS on HF

Why use HF?

APRS operation on HF is highly attractive for people traveling "off the beaten track", as it provides a low cost way of keeping the rest of the world advised of their location, without relying on extensive VHF or UHF "hilltop" infrastructure.

HF APRS coverage is a National (actually Global) issue, as it is quite possible that the nearest APRS HF Gateway is outside the skip zone - your HF APRS packets might actually be picked up by a Gateway in a different state or country, and relayed into the worldwide APRS network from there!

HF Path Settings

The path of APRS v GATE, WIDE2-1 should get your position to a VHF IGate via a HF Gateway.

Although most HF Gateways are connected to the Internet, there are some gateways that offer a traditional RF gateway from HF to VHF.

Any HF to VHF Gateway the hears a beacon with GATE in the path will gate that beacon to VHF. The path that follows the GATE is the path the beacon will take on VHF, and must be adequate for the beacon to reach an IGate.

Modulation

The dominant modulation scheme for HF APRS, is Frequency Shift Keying (FSK) with a frequency shift of 200Hz, and at the rate of 300 bits per second. (The same as ye olde HF Packet)

Note that, due to the NRZI nature of AX.25 packet radio, it doesn't matter which tone is the mark and which is the space; it's the transitions that matter. Importantly, this means that you can use an old ex-commercial HF transceiver which is only capable of USB operation, and still successfully operate on HF APRS. All you have to do is ensure your transmitted tones fall on the right frequencies (ie the suppressed carrier frequency for an USB transceiver will be lower than the displayed suppressed carrier frequency on an amateur LSB transceiver).

The exact two frequencies that you will transmit on are a function of your suppressed carrier frequency, whether you are running USB or LSB, and the audio tones generated by your TNC or modem.

Bell 103 based HF modems (such as the AM7910 used on VK6ZTN's Flash TNC) use two different sets of tones, depending on whether the modem is configured for "Originate" or "Answer" mode. The PK-232, and the Tigertronics TM-1, use different audio tones again. Overall, the dominant tone set seems to be 1600Hz & 1800Hz, followed by the 2110Hz & 2310Hz tones of the PK-232.

 

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