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Re: S-band receiving requirements



Hasan, and...

Gene Marcus' spreadsheet is very useful for this process.  Much better than
my spreadsheet in that he calculates the entire path-link and predicts
signal level.  I'm curious about how he performs the squint math, what he
uses for Tsky, Tant, etc.  But this program is easy for anyone to check his
system numbers.  Then when you listen see how it measures up to the
predicted performance!  Obviously the beacon is the frame of reference for
this.

I have seen several numbers thrown around regarding the average signal
level thru the transponder [so many dB down from the beacon].  I've seen
anywhere from -8 dB to -13 db quoted.  I wonder what the correct factor is.
 My understanding of this is that it is based on x number of stations on
the input at the same level sharing the total output.  So would -12 dB mean
the signal is being shared by roughly 16 stations?  {-3dB = two stations,
-6 dB = 4 stations, -9 dB = 8 stations, -12 dB = 16 stations}.

Of course in reality each station will have a different input level and get
a proportional share of the output [up to the level limit of LEILA].  On
lightly operated days more down-link power is available per QSO.  On
heavily operated days, less.  Squint lowers the total signal level at a
given station.

Arguments have been given that it is too early to decide the 2.4 GHz
requirements.  OK then wait for afew more months until the "dust
settles"...or use what you got, try it out, improve it if needs it.  I ran
my planned set up on Gene's program and got this:

Coax loss at antenna 0.1 dB
Preamp NF 0.7 dB
Preamp Gain 32 dB  {-3 dB for splitting the signal to two Drakes} 
Coax jumper loss to Drake 3 dB
Drake NF 6 dB
Drake Gain 15 dB
Coax loss to Reciever 3 dB
Reciever NF 14 dB
Receiver BW 2200 Hz
Antenna Gain = 19 dB {18 inch dish with 60% efficiency}
Range = 65,000 km

So my system S/N:
Beacon = 22.1 dB for squint = 0
Beacon = 20.8 dB for squint = 10
Beacon = 10.5 dB for squint = 29
Beacon = 9.6 dB for squint = 30
Beacon = 0.2 dB for squint = 39

So this will limit my use of the transponder to squints < 29 degrees at
apogee.  I begin to hear the beacon at squint 39.

If I upgrade to a 33 inch dish [34 dB gain] then I can operate at squints <
34 degrees at apogee.

Now of course if you use CW or PSK-31 you can run BW ~ 200 Hz and it gets
much better.  No surprize here.

This is a nice design tool.  Plug in your system and it will tell you how
you will do.  Enjoy!

Ed
BTW my DEM 144/1268 Tx Conv. arrived today...mode-LS very soon.
Unfortunately no sign of the preamp from SSB; I'll probably have to wait
until after Dayton and hope he doesn't sell out {I placed my order 9 days
ago by phone}.  Sure takes long for UPS these days...hmm!


>From: "hasan schiers" <schiers@netins.net>
>Based on the info you provided, the Excel program written by the gentlemen
>below predicts the following:
>
>
>                                                 Groundstation Receiver
>Performance (AO-40 S2 Transponder)  - Gene Marcus w3pm gm4yre
>
>  System NF (dB) 0.8
>  System Temp (oK) 58
>  MDS (dBm) -147.0
>  MDS uV RMS 0.010
>  Path Loss (dBm) 196.3
>  Beacon S/N (dB) 25.7
>  Beacon S/N ("S-units") 5.1
>
>I used 65,000 km and squint of 0 for the program. I put in 10 dB of coax
>loss between your downconverter output and the radio, and used a 15 dB NF
>for your radio and an IF bandwidth of 2500 Hz.
>
>The graph of signals in the passband (that I can't put into text), shows
>that you will be able to hear signals as weak as 26 dB below the Beacon. The
>strongest signals are supposed to be no louder than 8 dB below the beacon,
>so you have an 18 dB "fade margin" for other signals in the passband. That
>looks like pretty darn good performance to me.
>
>The important thing you have done: ANTENNA MOUNTED PREAMP! Low noise figure,
>and I approximated it's gain at 25 dB. If that is too generous, your
>performance may suffer a bit. I strongly suggest you get a copy of the the
>Excel program and run your best estimates through it and you should find
>that it corresponds very well with your actual experience.
>
>   http://home.hiwaay.net/~mmarcus/download/ao40_s2.xls
>
>
>Let us know what you find out. 73
>
>...hasan
>
>----- Original Message -----
>From: "Vince R." <vincesr@ij.net>
>To: "Estes Wayne-W10191" <W10191@motorola.com>; <amsat-bb@AMSAT.Org>
>Sent: Friday, May 18, 2001 9:40 AM
>Subject: Re: [amsat-bb] S-band receiving requirements
>
>
>> I disagree that these setups won't be "good enough." Good enough for
>> what? My subjective tests have shown the ability to clearly copy
>> relatively strong SSB QSO's on the S2 transponder when the U-Rx AGC is
>> driven to only about 2-3db. What that corresponds to in EIRP I do not
>> know but it is WAY below the present LEILA threshold. My last telem
>> graph of U-AGC still showed AGC being pushed to almost 20db suppression
>> on one occassion.
>>
>> My S2 downlink consists of:
>> Unobscured line of site to the satellite & good squint ---->
>> ARMSTRONG Pointing system ---->
>> 2x3 foot BBQ dish, long axis horizontal ---->
>> Standard dish dipole feed and splash plate ---->
>> Standard dish coax to DEM 0.7db LNA ---->
>> IF only modified Drake 2880 directly (M/M N coupling) on LNA output --->
>> 75' of ancient, cheap RG-58 ---->
>> Well used TS790A---->
>> A pair of not so young ears/AO40RCV
>>
>> With this I can hear the sun vs the sky at 2.5khz ssb bandwith. It
>> doesn't budge the s-meter but I can definately hear old sol! I copy the
>> MB telem 100% for any reasonable squint. The final test will be to see
>> if I can copy my uplink of 20w into my "shorty" LEO 70cm CP antenna.
>>
>> Maybe my setup isn't "Good Enough" to hear a 5w uplink on an arrow
>> antenna... but I have a feeling that it will suffice as long as the
>> gators stay submerged. See you on the bird as soon as I can get my
>> uplink on line.
>>
>> Vince Risalvato
>> KD7AI
>>
>> ----- Original Message -----
>> From: "Estes Wayne-W10191" <W10191@motorola.com>
>> To: <amsat-bb@AMSAT.Org>
>> Sent: Thursday, May 17, 2001 11:04 AM
>> Subject: [amsat-bb] S-band receiving requirements
>>
>> much snipped...
>> > In retrospect, the only thing that mystifies me is why today's
>> "alligator critics" were SILENT when months of amsat-bb traffic was
>> dominated by discussions about building helixes, modifying surplus
>> converters, etc.  One or more of these silent experts should have spoken
>> up to explain why those setups won't be good enough.  Then for the last
>> few weeks the experts remained silent when several people reported
>> modest success hearing the Middle Beacon.  Again, the experts should
>> have pointed out that we need to hear much weaker signals than the
>> Middle Beacon.  The "alligator critics" are vocal now, but they were
>> strangely silent when their advice would have been most helpful.
>> >
>>
>>
>> ----
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>> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>>
>
>----
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