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

RE: Oscar 0



Let's not forget libation fading as you get higher in frequency.  At
2-meters it isn't very significant but when you get to say 5GHz the Moon
almost sparkles like a disco mirror ball.

73/
Kevin, WB5RUE

> -----Original Message-----
> From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> Behalf Of Scott E. Olitsky
> Sent: Thursday, June 22, 2000 9:44 PM
> To: Tony Langdon; Dan Schultz; amsat-bb@AMSAT.Org
> Subject: Re: [amsat-bb] Oscar 0
>
>
> Bob did raise a good point which I had neglected.
>
>  Although the moon is a very poor reflector, it does capture
> a large amount
> of the signal as it spreads out from earth.  The moon's
> diameter is about
> 3475 km.  If you assume a 100% "reflection" from the
> transponder with a dish
> antenna with a surface area of 2m instead of the moon's diameter, the
> pathloss would  be about -365 dB, much greater than the EME
> pathloss at 144
> mhz.  The improvement in reflection adds about 11dB of gain
> but the decrease
> in size adds about 124 dB of loss from the equations that I have seen.
> Obviously the transponder would have to amplify the signal as well.
>
> An EME station with 20dB (4 x 2.5 wavelength antennas) of
> antenna gain and
> 1500 watts experiences an echo to noise of about  8 dB
> assuming the moon is
> in front of "quiet" sky.  THis is really the bare minimum to
> hear signals
> off the moon often.
>
> A station using a single yagi with  14dB of gain  and running
> 200 watts will
> deliver 10 exp -13 watts to the transponder if the gain of the receive
> antenna is 10dB.  If the transponder then amplifies this to
> 20mW a signal
> will be delivered back to the station with the same signal to
> noise as the
> bigger EME station.
>
> In addition, a one watt transmitter on the moon with a 2dB
> gain antenna will
> deliver a signal to a station with a single yagi with 14 dB
> of gain with a
> signal to noise of about 17 dB.
>
> I am interested if others would come up with similar numbers.
>  What type of
> amplification can a transponder provide?  If it is limited,
> this would make
> this unusable to even large EME stations.  Would a one watt
> beacon be a
> better idea?
>
> Scott
>
> AC3A
> -----Original Message-----
> From: Tony Langdon <tlangdon@atctraining.com.au>
> To: 'Scott E. Olitsky' <solitsky@acsu.buffalo.edu>; Dan Schultz
> <n8fgv@AMSAT.Org>; amsat-bb@AMSAT.Org <amsat-bb@AMSAT.Org>
> Date: Thursday, June 22, 2000 7:40 PM
> Subject: RE: [amsat-bb] Oscar 0
>
>
> >> It would be interesting to do the calculations on this.  The
> >> path loss for
> >> EME is somewhere on the order of -250 dB.  Much of this loss
> >> is related to
> >> the fact that the moon is a very poor reflector and only 6.5%
> >> of the signal
> >> that hits the moon is returned to us.  A transponder should
> >> would return
> >> more than that so the path loss would be significantly less.
> >> I had worked a
> >> couple of very large stations with my satellite antenna and
> >> 300 watts.  With
> >> an extra 11dB of gain in a new amplifier and antenna system I
> >> can hear my
> >> own echos fairly often.  If you assume that the transponder
> >> had the ability
> >> to return 100% of the signal that it hears (i.e. "reflects
> >> 100% rather that
> >> 6.5%) The loss would decrease by that same 11 dB.  A ham
> >> using a single long
> >> boom yagi and a small amplifier, should be able to hear a CW signal
> >> returning from the moon fairly often.  A huge antenna array
> >> like those used
> >> in EME would not be needed.
> >
> >This would seem to match with the guesstimate I put in a
> previous message.
> >I'd estimate 100W and a long Yagi would do the trick.
> >
>
> ----
> 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