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Re: iss packet, collisons




Hi all:

Packet Split frequency.

I have been studying the packet frequency issues for a few years, with
Mir and ISS.  On Mir we used simplex for both voice and data.
There are advantages to keeping the voice and data channels separate.
There is also the slight advantage of keeping voice uplinks and down
links
separate for public channels.  The theory is, that if the crew used
simplex,
then some people would not hear the ISS down link, if a Local station
began calling
at the same time.

For packet, Monitoring the down link is not as critical as on voice.
Running Split frequency, will actually increased the number of
Collisions vers running Simplex.

Theory:
When Running Split,  your TNC can never hear any of the local stations
calling ISS.
Your TNC will only hear the ISS packet down link and will use the
collision avoidance
features of Slot/Persist settings of your TNC to determine when Your TNC
will start transmitting.
Your packets will collide with other stations transmitting within a 1500
mile radius circle
around ISS, including Stations in your local receiving range.

Simplex:
With simplex you will still collide with stations transmitting within a
1500 mile radius circle 
around ISS.
Except for stations within you local hearing Range.
Most terrestrial 2-meter stations have a hearing range of 25 -50 miles
(your actual mileage may vary).
Since your TNC has a built in collision avoidance software
(Slot/Persist), you can take advantage of
this software if you run simplex.
The way simplex works, is if you live in an area, where you are not the
only one trying to 
access the ISS.  Then you TNC will hear the other local stations pining
packet on the simplex channel.
The collision avoidance settings of your TNC will help you avoid
colliding with the local station and
thus reduce the amount of collisions you experience from LOCAL stations.
It is difficult to calculate how much better it would be to run simplex
vers Split.
Mathematically Simplex will reduce collisions.
With Simplex Packet, you will still collide with stations beyond your
hearing range.
However you will be able to reduce local collisions significantly.

So if you are limited to "Mono band Half duplex" operations, then
Simplex is more
efficient for this type of satellite operation.

IMHO  Miles WF1F

www.marexmg.org



"Christensen, Eric" wrote:
> 
> Yeah, but it isn't full duplex.  When it is transmitting, it isn't listening
> on the up freq.  So it might as well have been a collision because the radio
> didn't hear it.
> 
> 73s,
> Eric KF4OTN
> 
> -----Original Message-----
> From: Paul M Dunphy - VE1DX [mailto:sarex_list@ve1dx.net]
> Sent: Friday, December 26, 2003 08:46
> To: 'sarex@AMSAT.Org'
> Subject: RE: [sarex] iss packet
> 
> At 02:31 AM 26/12/2003, Christensen, Eric wrote:
> >Why go with the frequency pair?  I am hoping for more time on the
> >digipeater
> >(-4) and I think the duplex is just added "stuff" to have to deal with.  Is
> >there a bonus for having the split?
> >
> >Eric KF4OTN
> 
>      Cuts the traffic (and hence the probability of colliding packets) in
> half.  I would think the "hidden transmitter syndrome" is greatly enhanced
> when trying to work a moving target with just a 12-15 minute window.  Split
> operation helps this.
> 
> 73/DX Paul VE1DX (QSL via VE1YX)
> 
> http://www.ve1dx.net/index.html
> 
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