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Re: Re: was TS-2000X, now AO-40 lids



At 02:13 PM 2/4/03 -0500, RogerKola@aol.com wrote:
>Instead off using the RST system of reporting your contact's signal strength 
>on AO-40, why not use a different system which includes the Beacon as the 
>reference?
>
>"you are two S-units under the beacon OM"
>
>"about 10 dB above the beacon Bob"
>
>"you and the beacon are neck and neck"
>
>"your signal is in the mud"
>
>I have too many oak trees to deal with to put up my dish, but maybe I will 
>get that BBQ dish mobile in the Summer.  But if I am told I am louder than 
>the Beacon, I can lower my power and operate essentially "simplex."  Other 
>then finding myself in the band why do I have to hear me?
>
>Roger
>WA1KAT

Roger, James, Jon and others that have responded on this topic:

First, Roger that is a very good idea.  RST is meaningless on the
satellite.  Probably dB as well, because I would guess not many stations
have actually calibrated their receiver S-meters with an accurate signal
generator (or step attenuator).  I did do this a couple years ago to better
understand what my s-meter readings were telling me.  Now this is from
memory but my FT-847 (at 144 MHz):
s-0 to s-1 is about 5 dB
s-1 to S-2 is about 3 dB
s-2 to s-3 is about 4 dB
s-3 to s-4 is about 3 dB
s-4 to s-5 is about 4 dB

Not not only does it not conform to the 6 dB/s-unit convention but is
non-linear.  I showed this for a reason:

My on-satellite noise floor is s-0.5 and the beacon is usually about s-5.5,
so I am seeing the beacon about 18 dB over the noise!  You can add/subtract
a dB or so but that is about as accurate as I want to state it.  If I
off-point my dish the noise floor falls to S-0, so that tells me I am
seeing the satellite receivers noise floor (you can't improve over that).
{you might chose a larger dish so that you get this performance are greater
squint angles, though}

Last Sunday I observed two stations (calls to be unsaid..not wanting to
criticize...just educate) at S-4.  They were loud (arm-chair copy in the
next room on my speakers).  This means they were "around" 6 dB below the
beacon!  

At the same time I uplinked on mode-U and produced an ssb signal at S-1
(about 2 to 3 dB above the noise floor)...it was a weak signal but clear
enough for me to understand without too much trouble.  That would
correspond to being about 16-dB below the beacon.  I am guessing (haven't
verified power measurements for over a year) that was with about 12w to my
16.5 dBic UHF antenna.  Being that it was my first time on AO-40 in a long
time, I experimented with pointing and found my UHF x-yagi is about
5-degrees off alignment with the S-band dish.  When I peaked on my own
signal, the MB read S-3.5 (got to correct this).

So when I get my 60w PA re-mounted close to the UHF antenna (50w-max at the
driven element) and the antenna re-aligned, I expect to see about 8 dB
stronger signal.  On last Sunday that would have resulted in my signal
running (about) S-3.5!  I should have good reserve power for high squint
angles and be able to lower power to say S-3 most of the time, yet
producing an sufficiently copyable signal for most.

I would like to point out that Amsat (I believe) is recommending you keep 8
to 10 dB below the MB.  This is so more stations can operate at the same
time and yet share sufficient downlink power to be heard.  If a few
stations persist is operating an s-unit or less below the MB they "steal"
power away from other QSO's making operation at -10 dB (MB) difficult.
What we end up with is a power "contest"!  ...and everyone loses!

I have heard that the L-band stations don't steal the downlink power budget
(I haven't a clue how that could be).  But there is no reason for them to
operate so high either.  If your receiving system can hear well (can you
detect the noise floor?  If not there is room for improvement) then there
is no good reason to operate with too much uplink signal power
(translation: ERP).

Why some stations persist in running too close to the MB level is hard to
say (maybe they can't hear well, maybe they don't care, maybe it hasn't
been sufficiently explained to them).  I would say (even though individual
s-meters will vary) that a good rule is to stay two s-units below the MB.
Then more folks can get on AO-40 and enjoy it.

So, in closing, Roger I like your reporting suggestion...but I would just
use s-meter readings, e.g. "you are 'x' s-units below the MB".  If you wish
to clarify your report more, hey great!  The more we compare with others
the better we understand how well we are doing.  Let's keep an open mind!

73, see you on AO-40!

Ed - AL7EB

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