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Fw: Re: THoughts on minimum ERP...





--------- Forwarded message ----------
From: shorton@juno.com
To: bruninga@nadn.navy.mil
Cc: amsat-bbs@amsat.org
Date: Wed, 28 Jul 1999 22:06:28 -0400
Subject: Re: [amsat-bb] THoughts on minimum ERP...
Message-ID: <19990728.220629.-66303.0.shorton@juno.com>

How long do you have to beat a dead horse...ONE CHANNEL FM BIRDS
WILL NEVER WORK NO MATTER WHAT YOU TRY AND DREAM UP
and forget about telling people to use low power it will never happen...
                              Samuel KD4ESV EL87
On Wed, 28 Jul 1999 18:10:33 -0400 (EDT) Bob Bruninga
<bruninga@nadn.navy.mil> writes:
>> The Minimum Power required to work the Mir 2-meter PMS is a  very
>> elusive calculation....  the most important variable is, How many 
>people
>> are calling at the same time.  If the 2-meter channel is perfectly
>> clear, and there is NO other traffic on the Channel... ... Then you 
>can
>> probably come up with an ERP rating of much less than one (1)  
>watt.
>
>Yes, it calculates to just about 1 watt horizon-to-horizon.  But that 
>does
>tell the user that *in the absence of QRM*, 1 watt is the Link 
>budget.
>
>> Since we are dealing with an FM signal, the signal you need to 
>> transmit needs to be approximately 10 times stronger than the 
>average
>> noise level being  heard at the FM satellite 
>
>[which in most cases is the sum of all the other simultaneous users]
> 
>> I prefer to base my calculation on experience and the term 
>(Reliable
>> Communication).  A one watt HT can ping Mir on a Good day.  However 
>this
>> is mostly luck and should be considered Un-reliable communications.
>> A 45 watt ERP station will have Reliable Communications with the Mir 
>
>> FM system more than 50% of the time.
>
>You have made the point well, that in order for one station (the 
>single
>user logged onto the MIR PMS) must be 10 db over everyone else no 
>matter
>what that power level is.  So if 45 watts is the general 
>recommendation,
>then the user that really needs access should probably run 50W into a 
>10
>dB beam to have 500W ERP.  I think MIR regulars typically run over 
>100W
>into 13 dB antennas or over 2,000 Watts to achieve good reliability.  
>I
>agree that *this is required* for reliable comunications to the 
>single
>user that must get in.  But my only point is that everything over, say 
>the
>5W level is only needed to overcome to QRM (other users).
>
>I am not arguing with the need for these numbers.  THis is what is
>required.  My request for "minimum ERP requirements" is as a benchmark 
>for
>knowing the link budget baseline based on the satellites receiver and
>antenna gain in the absence of QRM.
>
>We used this fact to our advantage in the June MIR-HT tests.  Since
>everyone was running only 5W to a rubber duck, we were all equal 
>players
>and we only got digipeated when we did not collide with anyone else. 
>(and
>we were successful).  If there was no collision, then our 5W was
>just as good as 50 or 500 or 2000.  BUT THE GOOD NEWS IS, that we also 
>did
>not interfere with the PMS user that was logged on and using 50 
>Watts.
>His packets (at 50w or more) would capture the channel and his 
>packets
>were good over us 5w users.  (Of course, he was still competing with 
>all 
>the other 50 watt stations).
>
>THus, in effect, we 5w HT users were using *spare channel capacity* 
>that
>was not being used at that instant.   At the same time we were not
>interfering with any normal activity in progress.  THis in effect is 
>the
>kind of "routine-use" I am suggesting as a possible solution for the
>single user transponders.
>
>Let everyone compete equally at the minimum (QRM-FREE) power level 
>and
>chase grids, ragchew, or just anything they want to do.  They will 
>then be
>the "routine" users.  THen if anyone needs to make an emergency call 
>or to
>give a priority demo, then all they have to do is go to 50 Watts.  The 
>FM
>capture effect is a perfect priority threshold.  If somehow we 
>inculcated
>into the satellite operators psyche that only the minimum published 
>ERP
>was the norm and that everyone was supposed to compete at that level,
>then this would allow those with urgent, or higher priority needs to
>override at any time. 
>
> I think HAMS would do this if it became standard operating practice 
>and
>everyone understood it.  A priority user would just use the word
>"prioirty" so that eveyone would understand that he was using hi 
>power.
>
>By knowing that 1) you could do anything you wanted without criticism 
>if
>you did it at the minimum recommended ERP and 2) that you 
>personnally,
>could get in at ANY time you had to by simply going to 50W, then 
>everyone
>is a winnner.
>
>Will it work?  Possibly...  But only if we work hard to get it 
>accepted
>as the modus operandi.  Conversly, continuing to promote FM 
>satellites
>with no rules, no minimum ERP standards and no operating plan will 
>not.  
>It only leads to escallation to 2,000 watts as the only reliable 
>uplink...
>
>P.S.  THis dual-use worked well on packet, where the objective of the 
>5w
>stations was only to inject their position (grid) and status while 
>the
>main PMS user did his thing.  Being digital, software on the ground
>accumulated everything into good orderly fashion.
>
>On a voice bird, it would be quite disconcerting to have multiple 
>pieces
>of converstaions, grids, and racgchews on such a hit/miss 
>intersperesed
>with "priority" users doing their thing...  But it could work... if
>we changed our expectations.   I donno... just a thought..
>
>bob, WB4APR
>
>
>
>
>
>
>----
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