[OZAPRS] Igate to RF

[Gary Stern]

Unfortunately "Local" is still a relatively small area.

I just drove from Cairns to Sydney, via Townsville, Charters Towers,
Emerald, Surat, St.George, Moree, Narrabri, Gunnedah, Singleton.

Didn't have aprs, but in honesty what coverage would there have been.

Ok, HF, but I would like to be able to track "near" travellers as well ?

(sorry for the intrusion)
Gary
vk2zbb

Richard Hoskin wrote:
> The AIM of APRS is to have one National 2mtr frequency that will allow a
> mobile station when ever it is in range to access the network.
> 
> The operator of the station does not need or want to constantly change
> frequencies to 'get in' when travelling out of his / her local area. This is
> why 145.175 Mhz was established as the primary ARPS channel.
> 
> The UHF APRS frequency of 439.100 MHz was established to provide an APRS RF
> channel for Home stations with additional services that are not suitable for
> the VHF channel due to band wide limitations. This will leave the VHF
> channel available for Mobile & Country station.
> 
> To accommodate the requirements of all and fulfil the primary objective of
> the National 2mtr frequency for APRS the following strategies where adopted
> by VK3
> 
> Victorian APRS Network Design
> 
> I thought this may be helpful for others who are building up APRS networks.
> 
> Here is what we did to plan the APRS network here in VK3.
> 
> First asked ourselves the following questions and came up with the listed
> answers;
> 
> 1) Q: What APRS stations are most important for a local station to see on
> his map?
> 
>     A: Local stations. They have more meaning for us than stations in other
> states, Europe or the USA.
> 
> 2) Q: What APRS stations are next in importance for a local station to see
> on his map?
> 
>     A: Neighbouring local stations, other Australian stations followed by
> New Zealand station followed by the rest of the world.
> 
> 3) Q: What is the biggest single limitation in an APRS network?
> 
>     A: RF Bandwidth.
> 
> 4) Q: What volume of traffic do the local station generate on RF over a 10
> minute period?
> 
>     A: In VK3 over 10 minutes it is measured at approx. 30 to 40 packets.
> 
> 5) Q: What is a reasonable volume of traffic that will not overload the RF
> channel and allow mobile stations access to the RF network when required.
> 
>     A: Approx 100 packets per 10 minutes on average. Exceeding this average
> greatly reduces the chances of a mobile station from accessing the RF
> network especially if it is in a poor coverage area.
> 
> 6) Q: How much additional traffic can we let onto the RF network?
> 
>     A: Approx. 60 packets per 10 min.
> 
> 7) Q: Where do we get these packets from?
> 
>     A: The next priority the local stations want to see.
> 
> We found that the total volume of traffic that came through the IGate from
> 500km radius of Seymour was about right to keep the local channel running on
> average at 100 packets per 10 min. If the traffic volume on the RF network
> increases we can reduce the amount of traffic coming through the IGate by
> reducing this radius.
> 
> The rate of 100 packets per min assumes that each packet is approx. 80 bytes
> in length with a TXDelay of the digipeaters set to 35 mS and a TXTail of
> 4mS. If the size of the average packet increases then you will need to
> decrease your networks packet rate. If the packet size decreases (enable
> compression in UI-View, reduce status text etc.) you can increase your
> packet rate.
> 
>  One of the biggest generators of traffic on a local RF network is
> digipeatered packets. Each time a packet is digipeated it reduced the
> available RF bandwidth by half. If an IGate is sending 5 packets per minute
> on to the RF network through 2 digipeaters the IGate is in effect creating a
> traffic level of 15 packets per minute. (IGateTx + Digi1Tx + Digi2Tx) * 5
> 
>  In VK3 the APRS network has been designed with the following
> considerations.
> 
> 1) All Home station will be a maximum of 1 digipeater hop from the centre of
> the RF network.
> 
> 2) The TX/TX IGate be placed as close to the centre of the network as
> practical.
> 
> 3) All home station will have a maximum of 2 digipeater hops to access an RX
> IGate.
> 
> 4) Home stations will have a maximum of 3 digipeater hops to get from one
> side of the RF network to the other.
> 
> 5) If greater RF coverage is required a new RF network is to be used with a
> new RX IGate.
> 
> 6) Beacon transmission times: Home, Stationary stations & Objects 30 min,
> Weather stations 15 min, mobile station 2 min.
> 
> From these considerations we came up with a star configured network that
> covered roughly a 500km radius depending on local terrain.
> 
> The design we used for VK3 may not work in other locations as the local
> terrain and conditions has a large part to play in the RF network design.
> 
> It takes a lot of hard work, good will, unselfish cooperation and a bit of
> luck to develop a fantastic APRS network that provides are reliable service
> to all its customers.
> 
> Cheers
> Richard
> VK3JFK
> 
> 
>> -----Original Message-----
>> From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
>> Behalf Of Jack Chomley
>> Sent: Monday, 30 August 2010 8:47 AM
>> To: Australian APRS Users
>> Subject: Re: [OZAPRS] Igate to RF
>>
>> FWIW
>> There must be gating to RF for stations with D700, D710, D7, VX-8 and like
>> radios for 2 way messaging etc, but sending beacons by Igates on RF from
>> hundreds of kilometres away, over digis of which many are solar powered
>> does not make sense. The operations of an Igate rests with its operator,
>> he/she knows what the network load is and should tailor it's operation to
>> cater for all users.  Given we are now seeing an increase in the use of
>> APRS ready low power portable radios, maybe we need to think of the
>> network load a little more carefully, when it comes to gating onto RF.
>> A simple solution IF the traffic level on the national frequency is too
>> high for what ever reason, is to simply set up a local digi on a secondary
>> 2m frequency and Igate it to the Internet, the secondary freq local Igate
>> can then have control over what they send out on RF etc.
>> Traffic levels on the secondary freq will be far less and give local
>> operators on it, a far better chance of access. It's something I am going
>> to do here in my local area and experiment with.
>> I don't see a published secondary 2m freq, so I guess I will just have to
>> pick one!
>> maybe 145.150 or close to it.
>>
>> 73,
>>
>> Jack. VK4JRC
>>
>> Sent from my Apple iPad Tablet PC
>>
>>
>> On Aug 30, 2010, at 7:54 AM, Ray Wells <vk2tv at exemail.com.au> wrote:
>>
>>> Howard,
>>>
>>> aprs usage and traffic density varies greatly across this vast country
>>> and, a one size fits all just doesn't fit.
>>>
>>> I'm in Kempsey and run both the hf/vhf igate and the local digi. Apart
>>> from the digi beacons and my occasional igate beacon there is just one
>>> other fixed station (vk2cvr) and my "seldom on" mobile signal. There is
>>> the occasional traveller passing through but there is no constant local
>>> mobile activity to maintain user interest in aprs.
>>>
>>> The nearest "next" digi to here is 115km away.
>>>
>>> To provide a bit more interest involving a wider geographic area I
>>> permit a select few out-of-area stations to be broadcast on RF. This is
>>> being constantly reviewed with regard to channel traffic, which is very
>>> light, even at the busiest of times.
>>>
>>> It's safe to say that most traffic via the local digi is weather related
>>> - warnings and current wx at 9 regional wx stations.
>>>
>>> If you live in a densely populated area the concept of wanting to know
>>> about things hundreds of km away is probably foreign to you. For someone
>>> in a lightly populated region those other towns are as local as someone
>>> in the next suburb in Sydney or Brisbane.
>>>
>>> Armidale, for example, is 125km away from Kempsey, as the radio travels.
>>> Kempsey has considerable interest in the wx (rainfall) at Armidale
>>> because the Gara River, north of Armidale, flows into the Macleay River.
>>> It was melting snow in the Gara River that was largely responsible for
>>> the devastating 1949 Kempsey flood. We definitely consider Armidale to
>>> be "local".
>>>
>>> It's all very well having guidelines but they don't provide for every
>>> situation, nor can they ever. Having "guidelines" permits things to be
>>> done a little differently, provided "different" doesn't impact the wider
>>> network; the impact of different must be purely local.
>>>
>>> And having guidelines doesn't stop individuals completely misconfiguring
>>> in an ad hoc way to cause havoc in densely populated areas.
>>>
>>> It should be more about common sense than strict adherence to rules. If
>>> we bend the rules to suit the local environment we should also be
>>> prepared to bend them back when circumstances change. One day I will
>>> have another digi in range of vk2rmc-1. When that happens I will review
>>> my settings. Until that time there is no need and, I suspect Warren
>>> feels the same way.
>>>
>>> Ray vk2tv
>>>
>>>
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