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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
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 
>> 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 
>> probably come up with an ERP rating of much less than one (1)  
>Yes, it calculates to just about 1 watt horizon-to-horizon.  But that 
>tell the user that *in the absence of QRM*, 1 watt is the Link 
>> Since we are dealing with an FM signal, the signal you need to 
>> transmit needs to be approximately 10 times stronger than the 
>> 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 
>> Communication).  A one watt HT can ping Mir on a Good day.  However 
>> 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 
>user logged onto the MIR PMS) must be 10 db over everyone else no 
>what that power level is.  So if 45 watts is the general 
>then the user that really needs access should probably run 50W into a 
>dB beam to have 500W ERP.  I think MIR regulars typically run over 
>into 13 dB antennas or over 2,000 Watts to achieve good reliability.  
>agree that *this is required* for reliable comunications to the 
>user that must get in.  But my only point is that everything over, say 
>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 
>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 
>and we only got digipeated when we did not collide with anyone else. 
>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 
>not interfere with the PMS user that was logged on and using 50 
>His packets (at 50w or more) would capture the channel and his 
>were good over us 5w users.  (Of course, he was still competing with 
>the other 50 watt stations).
>THus, in effect, we 5w HT users were using *spare channel capacity* 
>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 
>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 
>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 
>capture effect is a perfect priority threshold.  If somehow we 
>into the satellite operators psyche that only the minimum published 
>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 
>everyone understood it.  A priority user would just use the word
>"prioirty" so that eveyone would understand that he was using hi 
>By knowing that 1) you could do anything you wanted without criticism 
>you did it at the minimum recommended ERP and 2) that you 
>could get in at ANY time you had to by simply going to 50W, then 
>is a winnner.
>Will it work?  Possibly...  But only if we work hard to get it 
>as the modus operandi.  Conversly, continuing to promote FM 
>with no rules, no minimum ERP standards and no operating plan will 
>It only leads to escallation to 2,000 watts as the only reliable 
>P.S.  THis dual-use worked well on packet, where the objective of the 
>stations was only to inject their position (grid) and status while 
>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 
>of converstaions, grids, and racgchews on such a hit/miss 
>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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