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RE: Beacon Strength



Hilton,
Bottom line, you are correct. If you can see them turn on the transponder
i.e. the noise floor of the transponder, you can't do much more, at least in
terms of the RF signal to noise ratio.
A couple comments. S Unit equals 6db. 20 to 30 years ago I would say that
was correct. Today, not so. I have an Icom 910H and I have measured the S
Meter units to be 3db. Also remember that the compression of the receiver IF
system can affect the linearity of the S meter.
I monitor the MB with a VU meter on the audio output. I see an Audio S/N
ratio of 25-30db. Occasionally I will see a QSO with the same number, but it
is generally a European running 5kw ERP on L-Band. Most American QSOs are in
the area of 15 - 20db of quieting.
73
Gunther Meisse
W8GSM

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Hilton Meyer
Sent: Thursday, December 13, 2001 12:23 AM
To: AMSAT-BB
Subject: [amsat-bb] Beacon Strength


For some time I have been observing what would appear to be somewhat
extravagant claims for the strength of the AO40 Beacon. It is my
understanding that the best level the Beacon can reach above the noise
floor is perhaps 27 or 28 dB.  Another source measured this as around 21dB.
My question is how can claims be made for S9+ levels when the standard S
point unit is 6dB?   I would suggest that a more realistic level claim
would be dB above the noise floor if this can be determined. With my modest
set-up using an FT847 with attenuator on, pre-amp off and noise floor at
under S1 on the meter, the beacon at best reaches S7.  Signals that don't
upset Leila are around S4 or 5 which in IMHO would equate to 12 or 15 dB
above the noise floor.  The S unit on the FT847 would seem to be 3dB?
Regardless of the size of the antenna if you can detect the noise floor you
have reached the practical limit of signal level?  I would appreciate some
input from more learned persons on this, thank you.
Hilton Meyer  ZL2MN


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