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[aprssig] Local Event using RELAY?

Robert Bruninga bruninga at usna.edu
Wed Mar 30 00:50:37 UTC 2005


>>> mwrobertson at comcast.net 3/29/05 12:49:48 PM >>>
>Why do you twist things around to favor your side, ...
>The gentleman only stated that his tracker could not 
>reach a digipeater and wanted to set up his D-700 to 
>do a simple RELAY for the tracker. ...There was 
>absolutely nothing said about operating in the boonies 
>and that the RELAY could only hear a "Distant Digi". 
>That was your twisting things around to justify transmitting 
>in the blind with complete disrespect for any possible 
>traffic from other users on 144.390.

Sorry, but those were the FACTS from the beginning though
maybe not clear to the APRSSIG readers.

1) The digi he was referring to was W1CAR-1 which is over 
70 miles and 3 hops from Washington DC and is about as 
far into the boonies as you can get and just on the edge with 
West Virginia.  

2)The digi is on a hill and hears for about 50 miles or so.   
Other than the digi owner, the only other stations heard in 
the last 6 hours within 40 miles are 1 WX station, 1 Home 
station, and one mobile. and 7 other digis.

3)Thus, in an area of about 5000 square miles there were
3 other stations.  And since  his mobile can only hear another
station direct within about 5 miles, the probability that he
could hear those other stations are about 1%.

4) Yet the digi hears almost constant packets from the other
7 digis it hears, thus a flea-power bike tracker would never
get in.  Thus he wants to use his car as a digi...

5)  Now the probability that his tracker packet is only
transmitted once a minute, and lets allow for a second
tracker if he can arrange for one.  Then that is one packet
per 30 seconds or a channel load of 3%.

Now then the probability of his operation to impact any
other of the nearby users by collision with one of those 
other 3 stations would be about 1% times 3% or about 
0.0003 or one chance in about 3000.

In my mind it is OK for him to use his mobile as a digi without
any impact on his fellow ham...or the network, even though 
his mobile digi cannot hear nor avoid a collision with them.

>> The fact that the 50W mobile wont hear any other local
>> traffic in the first place...
>Where did you get this fact?   Who said that the mobile 
>was not going to  hear anything except a far off digi?

I did, in stating the situation I was analyzing.

>> Yet the richeous will condem  your use of the mobile as a 
>> digi for your tracker which -isnt listening- while saying it is 
>> just fine to use the  mobile (which -is- listening but -cant- 
>> hear any other users).  Though the impact on the network 
>> is identical... 
>>
>> Let common sense prevail in each case...
>
>Common sense helped make ham radio what it is today.. 
>I am proud I am richeous and try to abide by common 
>sense.  I don't transmit period if the channel is not clear, 
>on any mode! and I don't advocate others do it...

Sorry, you dont see the difference between intentional
interference and 0.0003 probability of an unavoidable
collision.  Each time you key up the PTT on  your voice rig,
I bet you have a greater than that probbabilty of
doubling with someone.  Yet you seem to do that
without guilt... or condemnation...

>I am out of this thread, so twist it any way you want, 
>and I hope common  sense will prevail!

Its not twisting it.  The situation was as I describe
from the begninning.  Sorry if I did not make that
clear.

Bob, Wb4APR

> --- Robbie Robertson <mwrobertson at comcast.net> wrote:
> 
>>Bob,
>>
>>That then makes the TMD-700 to transmit on 144.390
>>without listening first and thus qrm'ing anything else on 
>>144.390.  That is not the right way to operate period.
>>
>>We have had this discussion before.... If there is no 
>>other transmission being heard by a station, it is
>>assumed ok to transmit, but just to turn on without 
>>listening for a signal is wrong.
>>To suggest that others do this is not correct.
>>
>>Robbie
>>
>>Robert Bruninga wrote:
>>
>>>>>>Boyd D Garrett Sr <N5CTI at texasnative.com> >>
>>>>
>>>> I plan to support a public service event from my
>>>> bicycle. (TH-D7)... [and]...have >>
>>>> virtually no chance of getting into a WIDE digi
>>>> ...so I plan to have my truck in the vicinity with my
>>>> TM-D700 set for RELAY digipeating.
>>>
>>>
>>>Then I would set your mobile DIGI to RELAY but set
>>>it  to listen on 144.99 and TX on 144.39.  Then
>>>operate all trackers at the event on 144.99.  That way
>>>they get a 100% clear channel and yet the event and
>>>everything else shows up on 144.39
>>>
>>>Bob





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