HF APRS Information

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.

Strictly speaking, HF APRS coverage is more of a National issue than a State one, as it is quite possible that the nearest APRS HF IGate is within the skip zone; your HF APRS packets HF might actually be picked up by an IGate in a different state, and relayed into the worldwide APRS network from there! (There was originally very little information on HF APRS in Australia, so I started compiling snippets of information here).

HF Digi Path

The path of "APRS v GATE, WIDE" should get your position to a VHF IGate via an HF Gateway.

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.

I am unaware of any APRS activity on HF using alternative schemes such as 1200bps PSK, or 1200bps AFSK on FM on 29MHz. (Please drop me an email if you are experimenting with anything of note).

Frequencies

Australasian APRS HF Operations Guide.

As HF APRS is becoming more popular in Australasia I have put together a set of guild lines that we all need to adhere to. This will allow the successful long-term use of the ARPS HF 10Mhz network as it’s popularity continues to grow.

The Do’s and Don’ts for APRS HF.

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,WIDE
Do Net (set your frequency) to the Primary Net server VK3MY-4. Or if you can not here VK3MY-4 use a secondary APRS HF Gate server.
Do user a SSID of -4 if your station is an HF to VHF (or IS) Gate. (Refer to the SSID Guide)
Do user a SSID of -15 if your Mobile Station transmitts 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 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

APRS HF NET Servers.

10Mhz

Primary NET Station – VK3MY-4

Secondary Net servers – VK4DMI-4, ZL1GTB

The Primary Net Station will transmit the following messages at the indicated times:

Every 5 Minutes - / APRS 10Mhz Net Station (1)

Every 10 Minutes - APRS HF To VHF Gateway On 10.147.60Mhz USB

The Secondary Net Station will transmit similar messages at 5 minute intervals.

Eg; APRS 10Mhz Net Station (2)

7Mhz

Primary Net Station – ZL3RX - Beacon rate is every 30 minutes approx in compressed format

APRS HF Gates;

10Mhz

VK3MY-4 (Primary Net station)
VK4DMI-4 (Secondary Net station)
VK2KCM-1
VK4KMR-4
VK4AGS
VK5LY-4 (Renmark)
VK7ARN-4
ZL1GTB (Secondary Net station)
ZL3RX
ZL3GR (RX Only)
VK3ECV (Upon Request to ronk at sunlinux.com.au)
VK5AH-4 (Upon Request)

7Mhz

ZL3RX
VK3ECV (Upon Request to ronk at sunlinux.com.au)

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

Band	Prime Net Station	Nominal Frequency	Tone 1	Tone 2	Comment
40m	ZL3RX	7036kHz LSB	7034.2kHz	7034.4kHz	Operational in ZL but not in VK
30m	VK3MY-4	10147.6kHz USB	10149.2kHz	10149.4kHz	This is the 30m Global APRS frequency.
20m	VK6BBS	14109kHz LSB	14106.89kHz ?	14106.69kHz ?	PK-232

	Virtual Carrier 7Mhz	Virtual Carrier 10Mhz	Audio Frequencies
Reference	7034.30	10149.30	Mark	Space
Bell 103 Orig LSB	7035.47	10150.47	1070	1270
Bell 103 Orig USB	7033.13	10148.13	1070	1270
Tiger TM1 LSB	7035.50	10150.50	1100	1300
Tiger TM1 USB	7033.10	10148.10	1100	1300
MFJ1270 LSB	7036.00	10151.00	1600	1800
MFJ1270 USB	7032.60	10147.60	1600	1800
TinyTrack LSB	7036.00	10151.00	1600	1800
TinyTrack USB	7032.60	10147.60	1600	1800
KamPlus LSB	7036.00	10151.00	1600	1800
KamPlus USB	7032.60	10147.60	1600	1800
Bell 103 Answ LSB	7036.43	10151.43	2025	2225
Bell 103 Answ USB	7032.18	10147.18	2025	2225
MFJ1278 LSB	7036.50	10151.50	2100	2300
MFJ1278 USB	7032.10	10147.10	2100	2300
PK232 LSB	7036.51	10151.51	2110	2310
PK232 USB	7032.09	10147.09	2110	2310
DSP-12 LSB	7036.53	10151.53	2125	2325
DSP-12 USB	7032.08	10147.08	2125	2325

HF Digi Path

Modulation

Frequencies

APRS HF Links