Recommendations

Beaconing Rate

These values were agreed to at the 2008 NZART Conference (Dunedin).

Note that the times below are approximate, you should use the stated value as a guide and in fact use a value a few minutes either side. This is to avoid constant collisions with others who might otherwise beacon at the exact same time as your station.

  • Homes: 60 minutes approximately.
  • Weather Stations: 15 minutes approximately.
  • Trackers: usually defined by the tracker itself. As a rough guide, often enough to give a reasonable track, but not so often as to hog the channel.
  • Objects: This depends on the Object. A repeater or hamfest venue could be once an hour, whereas something related to an urgent situation (washed out bridge, crashed aircraft, AREC/SAR event) should be a lot quicker.

Deviation

As with voice transmission, too much or too little deviation is not ideal. AX.25 packet using AFSK at 1200 baud (i.e. APRS on VHF or UHF) needs pre-emphasis at the transmitter and de-emphasis at the receiver just like voice mode does, and for the same reason (triangular noise spectrum of raw demodulated FM).

More details.

Digipeaters

RX ONLY DIGI

All digi-peaters should be bi-directional and there should be No MAJOR digi-peater with RX only attached on 144.575 (National APRS Freq) this Frequecy should be bi-directional it is the National APRS Freq . Placing an RX ONLY on 144.575 will KILL messaging back to the originator

The better solution would be to install a bi directional 144.575 digi and then hang your altrenative RX Freq on that this way the National Freq is working as it should.

DWAIT
This is a parameter hidden away in the TNC (or equivalent) configuration. It might be alternatively be referred to by the combination of PPERSISTENCE and SLOTTIME. With traditional BBS oriented packet, the idea is for users to politely share the channel, however with APRS being a one-to-many scheme it is to our advantage for beacons to spread out rapidly through the network and it uses up less timeslots overall if digis immediately repeat what they hear, and FM Capture Effect is used to overcome what one might think would have been interference.

For an APRS digipeater, DWAIT=0 is the correct value, alternatively SLOTTIME=1 and PPERSISTENCE=255 are correct values where those parameters are used instead.

Frequencies

At the 2009 NZART Annual Conference it was confirmed that 144.575 MHz would remain as the 2m APRS frequency. 432.575 MHz is the assigned 70cm frequency.

iGates

Filter Settings

It is reccommended that all Igates connect to port 14580 and set their own Filter

All Igates should set their Filter to cover their immediate RF Foot Print Only, eg: m/50 will give a radius of 50 Kms of the " Igate " or such a distance that it will include any digi that hears mobiles that hasn't a direct path to an Igate.
There should be no Igates pumping out all of NZ to RF !

To set your Igate filter follow this link
http://www.aprs2.net/wiki/pmwiki.php/Main/FilterGuide

Transmitter Power
What power does an iGate transmitter need to be using when it is gating beacons of all NZ from the internet to RF? Perhaps it only needs enough to be only just heard by the nearest hilltop digipeater, so that RF users including distant trackers are still able to be heard by the digi and not frequently denied access due to their weaker signals being overwhelmed by very strong and very frequent signals from the iGate.

RX Only Igates

Receive only Igates are NOT ENCOURAGED for general use. These RX Igates will KILL messaging within their RF coverage area !

This comes about by the RX Igate posting a message to the APRS-IS , the return path /answer will be sent to the RX only Igate by default hence the message sender will NOT get a reply.

As more bi directional message trackers / radios become available the use of RX only Igates will degrade this capability and users will be discouraged and start to complain that the APRS network is broken, when it is not.

If you really need to run an Igate run it bi directional but set a filter just for your immediate area M/50 this will give message users in your area a fighting chance of getting a reply.

Bi-directional Igate : An Igate that will Receive and Transmit Data

RX Igate : One that Receives only ( Not recommended on National Freq )

TX Igate: Only Transmits no Receiver ( Should never be used )

Paths

Home Stations

See the New Paradigm.
A home station path should be WIDE2-2 normally, however you may wish to tailor this for your particular situation and you might even use a directed path such as DIGI1,DIGI2 or DIGI1,DIGI2,DIGI3 to cover a specific area or to avoid a specific area.

Mobile Stations

See the New Paradigm.
Mobile stations should use a path of WIDE1-1,WIDE2-2 and the reason for this is that WIDE1-1 is a special case, an exception to the norm, in that there are certain home stations ( fillin ) which digipeat only WIDE1-1 to assist nearby mobiles in what would otherwise be a very poor coverage area. Hilltop digipeaters handle WIDE1-1 through to WIDE2-2.

SSn-N

See the New Paradigm.
This is a technique that may be useful in covering specific regions without propagating into unwanted regions.

Txdelay

This is the time delay needed between the PTT line being asserted, and the transmitter to have developed power on the desired frequency, adequate for others to receive you properly. Some handheld radios need around 300 milliseconds, some radios designed for data use might need only 10 or 20 milliseconds.

Note that the units used in the configuration program might not be milliseconds, often they are 10's of milliseconds, so a value of "20" might correspond to 200 milliseconds. In the case of a tracker, the units might be some weird number related to a microcontroller's timer.

In practice it is wise to determine the best value of Txdelay. Too short and you won't be received properly by other stations, and too long will be wasteful of precious on-air time.

To find the right value, start with a small value, say 50mS, and gradually increase it in 50mS steps until you are just being heard, then add another 50mS to cater for receivers with a slow squelch. That is the basic idea anyway.

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