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ranging experiment: Measure different snr's. Re: AO-40 Link S/N ratios?



Followup to the radar thing, written as much for my notes as anything else,
on 9 16 01...

I noticed when I was pointing the antenna with a fast motor that:
The impulse noise I hear comes from the transponder not from some local
source, as if there is a strong radar or something on the uplink or some
mechanism
that causes impulses to come down..
I get a squelch break and the s meter rises 1 unit (3db) when I point to the
satellite. So I am after all seeing the transponder noise, at squint 177,
just about as good as it gets from what I've seen here.
Uplink TX 7 watts at antenna 7t helix est gain 13db
see http://www.seaveyantenna.com/catalog/p50/pg50.htm various gains and
turns.
Transponder base noise 1 s units above offpoint ~3db
Max uplink 7 watts to 13 db eirp 139 watts 6db power above noise bw 2.5k.
Min detectable uplink .175 watts to antenna 3.5W eirp
Beacon is 12 db above noise level measured in 3k bw with spectrum analyzer.

The guys I work that use the 7-10 foot downlink antennas can always hear
every peep on the satellite, some guys uplink fine that cant hear you, they
lose
you pretty easy even with a few db fade on the uplink, you can find em
pretty
easy cause leila gets em alot and they are just as strong as the beacon is
sometimes.
I found 8 watts just about never draws in the leila but its not enough power
if
the agc starts riding up to 10db on the uhf.

Ranging: Transmit a 1.5 khz tone of 9 cycles.
Record with a mixer the uplink audio and the downlink recieve.
Measure the delay with sound editor.
Elset 115 Time 9/15/2001 22:44:10 cst
Orbit elements: 37272mi
Range delay:.383sec 35671mi.
Repeat measurements multiple times:
35577
35671
35577
35671
35671
35671
Hm seems my resolution is quite large.. +-94 miles I will try this with
an FM repeater at known distance and see how I can do.
It really disagrees with that elset ....



I measure the signal power, I think using an attenuator to find this out
adds
in a lot of variables such as interpretation and how the ear works, if thats
what you are doing. Are you using an audio program and measuring sound power
or going by ear or what?

with no signal
 Mono
Min Sample Value: -10240
Max Sample Value: 9984
Peak Amplitude: -10.17 dB
Possibly Clipped: 0
DC Offset: .225
Minimum RMS Power: -21.07 dB
Maximum RMS Power: -19.09 dB
Average RMS Power: -20.05 dB<<<<<<<<<<<
Total RMS Power: -20.16 dB

Using RMS Window of 50 ms

Uplink a carrier at: 1200 hz audio freq in passband
 Mono
Min Sample Value: -18944
Max Sample Value: 19968
Peak Amplitude: -4.34 dB
Possibly Clipped: 0
DC Offset: .252
Minimum RMS Power: -10.95 dB
Maximum RMS Power: -10.12 dB
Average RMS Power: -10.46 dB with sig< --20.05 db without>
Total RMS Power: -10.54 dB

Using RMS Window of 50 ms







----- Original Message -----
From: "hasan schiers" <schiers@netins.net>
To: "Leland C. Scott" <lscott@inductoheat.com>; <amsat-bb@AMSAT.Org>
Sent: Sunday, September 16, 2001 7:20 AM
Subject: Re: [amsat-bb] AO-40 Link S/N ratios?


> Leland,
>
> It depends on the portion of the pass, but when squint is < 20 deg, I see
> the beacon S/N > 30 dB most of the time. Most stations I copy with "good"
> signals are running 20 to 25 dB S/N. These are measurements with a
> calibrated attenuator. What I have found on my FT-847:
>
> Noise level S-1
> Beacon S5 to S6
> Signal near to triggering Leila: S3 to S5.
>
> I take a measurement on neary every station I work on AO-40. It is not lab
> grade, by any means, but this is what I do:
>
> Turn the volume up a bit, start cranking in attenuation...starting wtih 20
> dB. Keep increasing attenuation until I can still hear, but can no longer
> understand the station talking. If they don't have a 20 dB or better "fade
> margin", they don't have a "really good signal".  I copy stations with
> signals 6 to 9 dB out of the noise with some attention...in other words, I
> have to listen very carefully. For comfortable copy, I would say that 12
dB
> SNR for SSB is comfortable satellite copy. 20 dB is armchair.
>
> Rx Ant: HyperLink Tech 39" BBQ, 24 dB Linear Horizontal Polarization
> D/C: SSB Electronics UEK-3000
> Rx Feed: 80' LMR-400 1 dB loss or so
> Radio: FT-847, preamp OFF. Noise level S1 to 1.5.
>
> Tx Ant: M2 CP-30 14.2 dBc
> Amp: TE Systems 100W (used sparingly, see notes below)
> Tx Feed: 80' LMR-400, 2.x dB loss
> Radio: FT-847
>
> My view of the bird is obscured by trees. I only get a clean look at AO-40
> from Azimuth 120 to 210, at elevations greater than 10 degrees.
>
> When I'm shooting through the edge of trees, I need all 100w out and am
> still well below the beacon in strength. This happens because the TX
antenna
> is going through a MUCH thicker portion of the trees than my RX antenna is
> looking at. In fact, there are many times, early in the pass when my TX
> antenna is in the thick of trees and my RX antenna is pointing at open
sky.
>
> Once the tree line is cleared the following applies:
>
> (This is approximate power to the antenna)
>
> Squint > 28 deg, 60w out and have to watch Leila carefully for spin mod.
> Squint > 20, <28, 40w out, most prone to get dope slapped by Leila.
> Squint > 15, < 20, 35w out, Leila almost never a problem.
> Squint < 15, > 10 20w out. No Leila
> Squint < 10 deg, 5 to 10 w out , Great Signals, No Leila.
>
> hope this helps you and anyone else trying to figure out "how loud should
I
> be"
>
> 73
> hasan schiers, N0AN
>
> schiers@netins.net
> or use amsat.org or arrl.net remailer
> ----- Original Message -----
> From: "Leland C. Scott" <lscott@inductoheat.com>
> To: <amsat-bb@AMSAT.Org>
> Sent: Wednesday, September 12, 2001 2:19 PM
> Subject: [amsat-bb] AO-40 Link S/N ratios?
>
>
> > What kind of S/N ratios are people getting on their AO-40 mode U/S
links?
> > What would be considered the minimum comfortable S/N ratio, 6db, 9db,
> 12db,
> > or what? It looks like the best I can do with linear feed on both up and
> > down links is around 6db to 9db, depending on coax loss.
> >
> > Leland C. Scott
> > KC8LDO
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