>>>AA6YQ comments below
--- In digitalradio@yahoogroups.com, Steve Hajducek <[EMAIL PROTECTED]>
wrote:
>snip<
> >I have reviewed enough of the military documentation to understand
> >that they employ dedicated ALE transceivers capable of much faster
> >scanning rates.
Really? Please enlighten me, I was under the impression that the ALE
scan rates of 1, 2 and 5 ch/sec was it at present and that the future
goal as stated in MIL-STD-188-141B was 10 ch/sec. The PC-ALE software
supports 1, 2 and 5 ch/sec with an HF transceiver that is cable of
all selections.
>>>In a previous post, you stated that the scan rate for amateur ALE
was 2 channels per second. Current military equipment supports 5
channels per second. That's 2.5 time faster, is it not?
> > As a result, sounding duration is signficantly
> >reduced,
Sorry, but you will have to explain to me how Sounding duration
decreases with an increase in the Scan Rate.
>>>My understand from www.hflink.org is that a station must sound for
an interval long enough to allow all receivers to scan all channels;
a shorter sounding interval would result in some receivers failing to
hear the sounding. If all receivers scan the same number of channels
at a faster rate, then sounding duration can be decreased. is this
not correct?
> > and channel capacity increases in proportion.
Well not exactly. A 2 ch/sec scan rate allows you to cover the same
number of channels faster than a 1 ch/sec scan rate and thus increase
the odds of hearing a Sounding or a Linking call sooner.
>>>A 2 ch/sec scan rate allows you to use half the sounding interval
required by a 1 ch/sec scan rate. This doubles the number of
supportable simultaneous users, does it not?
Running 2 or 5 ch/sec will also permit the station to be part of more
than one ALE network at the same time, not an issue per see with
Amateur Radio, but if two networks had scan groups of 10 channels
each, you could scan both with excellent results.
>>>We're discussing amateur ALE here.
The number of channels you scan does have an effect on your
Soundings, you sound longer when you have more channels in the mix.
There are variable here as we are now at a stage were you have 3
generations of ALE. The latest ALE technology supports GPS time
synchronization of the Scanning/Sounding which in the future will
radically reduce BER/SNR data transfer for LQA ranking when all
user's can support it.
>>>Yes, that's the sort of approach I was asking about when I asked
if there were techniques for reducing contention among "competing
sounders". PC-ALE would have to be extended to support this, and as
you say its only effective if everyone uses it.
> > But one ham
> >with an amateur transceiver limited to a 2 channel-per-second scan
> >rate would force all ALE participants to sound for 20 seconds, even
> >if their equipment could scan more rapidly. Do I have this right?
The details are to be found in MIL-STD-188-141B Appendix A.
Regardless of the scan rate, if the controller Sounds based on number
of channels in the scan group its less than 1 second per channel. The
minimum redundant sound length (Trs) is equal to the standard
one-word address leading call; that is, Trs = Tlc min = 2 Ta min = 2
Trw = 784 ms. Thus for 12 channels it would be about 9.4 seconds
depending on your address length being sent. The address length is
based on an ALE Word which is 3 ASCII characters, for Amateur Radio
applications we would being using 2 ALE Words as there are no 3
character callsigns, whereas in the Military and Government world
there are 3 character ALE Self Addresses being used. So W1AW, N2CKH
and WB2XYZ are all 2 ALE Words were automatic padding is used to fill
the second word. The least number of ALE Words the more efficient and
reliable is the system. One would now want to use WB2XYZ/W6 to
indicate they are in California. For AQC-ALE where many things were
changed to make things even more efficient, a 2 ALE Word is the
maximum allowed, whereas the original ALE allowed a 5 ALE Word (15
character) Address to support the Military Automatic Digital Network
(AUTODIN) system to directly link a Phone Patch call. Feel free to
double check me with the standards, I am no expert on all this stuff
and I am not perfect either, I make calculation errors often.
>>>I don't see how the sounding duration can be independent of
scanning rate (as discussed above), but using your 9.4 second
sounding duration for 12 channels with each station sounding once per
hour, (60*60)/9.4 yields a capacity of 383 users with 100% pilot
channel utilization. Without synchronization or some other form of
collision avoidance, the realistic number of simultaneous users would
be in the range of 64 to 128.
>>>This is considerably less than Bonnie's claim of 1000 simultaneous
users - so either I'm misunderstanding something, or the claim is
false.
73,
Dave, AA6YQ
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