[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: S-band receiving requirements



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.
> >
>
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home