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5
Oct07: Been busy over the passed few week with new digital
radios in the form of the type :P25 .
This has been a very interesting time to test the mixed
mode operation and in my mind is the way of the future .When comparing
what these radios are capable of ,
the D-Star functionality regarding voice is somewhat lacking.
We have very few ham activity on the digital audio modes
in S.A .
Listen to an audio test: Analog /Digital C4FM test
On the left is the HT1250 and on
the right is the ASRTO Saber III.
I have my own yahoo group
relating to the Astro radio parameters , by invitation only .
Brief History : Public Trunking
South
Africa
brought trunking to the public
sector in and around 1993.
Two major players invested in
the networks .
Q-Trunk owned and maintained to this day by the state owned telecoms
company called Telkom SA.Q-Trunk
website
Fleetcall at the timed was owned and maintained by the State Railways offspring called
Transtel.http://www.fleetcall.co.za/
The third regional operator only
rolled out in KZN region , this being One2One
The frequency allocation was the
254-000 Mhz starting block at 12,5 khz with an offset of 8Mhz(Mobile Tx at 262-000.)
The block allocation was intermediate where the
total of 432 channels were sub-divided into rows and colums .A-R across
and 1-24 down )
Click on this link to see how the channels are
defined in order to allow greater separation between the channels which
allow for better spectral usage.
South African 250_Mhz Tunking_block.xls
Systems:
Q-Trunk : Marconi RNC and TSC’s where the RF hardware was locally
produced Q&D transmitter/Receivers .Use mpt1343 numbering scheme
.Q-Trunk offers the ACT NOW Voting
which is extremely effective and allows the on-the-move mobiles to
keep in the best RSSI and BER from the control channels .
Fleetcall : Fylde TSC and Key RF hardware .MPT1327 numbering scheme.
Fleetcall seem to use voting more for load sharing in busy urban areas.
One2One :Nokia Controllers with Key and other RF .
Having worked in the environment
each system had its own unique advantages.
Current Systems : Q-Trunk and Fleetcall still operate but One2One folded where the
equipment was bought by Fleetcall/Transnet.
Systems are slowly being deployed in small confined
areas such as the petrochemical
companies but non in the way of private commercial ventures to
superceded the old community repeaters .Our railways are currently using a UHF system BASE
TX
:455-000 that superceded the old allocation for the C-450 mobile
telephone system. Their system is well used together with PSTN and PABX
connections.
Trunking AFFSK : The data one hears on the Control
Channel (CC ) and traffic channel (TC ) is 1200 bps 1200 hz and 1800 hz making up the
binary 1’sm and 0’s .
Here are some explanations to the control channel
and voice messages
Trunking\Control_Channel.WAV
(App 1 min of downlink contol data on
the given CC)
Trunking\Control.txt
Trunking\Voice_call_TC.WAV
Trunking\Simple_Voice_call.txt
(note the BCAST Act now vote message)
Trunking\Simple_Voice_call_a.txt
(Simple voice call setup over CC )
Future :I would like to see our government force the original Sabre
migration from owners who have more than one community repeater on a site
, over to a trunked system in order to make better use of the channels
.Currently there are no private radio trunking systems in the greater KZN
region.
I have in the past looked at a
single channelled site linked into our current UHF system and that
interest has been renewed.
I have read of other countries
looking at a similar venture for disaster type scenarios in the field of
emergency communications .This type of system together with its rich
data/status messaging could be vital in disaster recovery exercises .
Our country does not have a
variety of trunked systems and the growth has been somewhat stunted with
the advanced cellular rollout .
Amateur Project: I have been trying to get a TSC in order to run an experiment for
my own interest on perhaps UHF . (So if you have one such as a Zetron
827 of Fylde TSC – I would
appreciate any donations towards this idea. )
A great idea could be that of
some of the now redundant One2One allocation possibly being used for amateur experimental
purposes.
Perhaps those that use trunking
commercially could use simplex into their respective area repeaters .
At the moment these frequencies
have been idle for some years now and they could be very interesting .
For mobile communications the 250
Mhz band works very well as it is not uhf and seems better than the
amateur VHF allocation .
MPT 1327 /LTR and other trunking
could be beneficial to the South African market but unfortunately some of
the radio companies are less informed so they are hesitant to approach
any form of trunking .
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