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Re: AO-40 Link S/N ratios?


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

hasan schiers, N0AN

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,
> 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
> ----
> 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.
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