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

Re: Is my AO40 beacon strength average ?

At 12:57 PM 12/10/2002 +0000, darren.rainer@btinternet.com wrote:
>Hi all, I am wondering if my received signal from AO40 is average for my
>I am using the following :
>20 metres of RG213
>DB6NT MKU24 pre-amp
>G3RUH 60cm dish and patch feed.
>AO40s beacon never peaks above S3. My noise floor < S1.
>I can hear my signal coming back about S2 using 50 watts into a 8 9 ele
vert beam on 70cm. I tried a 1m prime focus dish last night and got the
beacon to S5. Is there anyone out there using a 60cm dish and patch getting
S9 signals ? or are some of the reports a bit on the keen side.
>I have painted the dish with plasticote paint which is non metalic, but
wondering if this could be having some effect.
>Darren Rainer G4VTQ


I suspect that your system is working OK in receive.  I only get around
S-5.5 on the beacon using a db6nt MKU-232A2 preamp, but this is very loud.
Satellite reception will not produce S-9 or 40 over nine type of signals on
most equipment.  Those that report S-9 readings probably also have S-3 to
S-5 noise levels without any signal.  So its the difference you are looking
for not the absolute S-meter reading.  Do you hear the beacon loud and
clear?  If so then its working fine.  One very important thing is that the
MKU-24 needs to be attached directly to the patch-feed.  Any coax between
the feed and preamp/downconvertor at 2.4 GHz will seriously degrade the
performance of your preamp/down convertor.

Going from a 60cm dish to a 100cm dish (1m) is going to give you approx. 5
dB more signal if the feed is the same.  If the patch is linear
polarization and the 1m dish has circular polarization then you get another
3 dB.  My FT-847 shows about 4 dB per S-unit so the numbers you are seeing
are about right.  A 1-meter dish will out perform a 60cm dish on AO-40.  I
use a 85cm offset feed dish with a helix-feed (so it is circular pol) and
my guess it performs as well as a 1m center-fed dish.

Hasan's comments are right on.  To adequately analyze a microwave satellite
system you must take into consideration every component.  The spreadsheet
does this very nicely.  All you need is the specs for each component to
enter into it.

Regarding your transmit situation, the 9-element beam may be a bit minimal,
especially if you have a long run of coax to it.  At 435 MHz the coax needs
to be low-loss and kept short, or most of the power is absorbed in the coax
and never gets to the antenna.  Half your power will be dissippated by
50-foot of RG-8.  One should use either Belden-9913 or Times LMR-400!

I started out with about 35-feet of RG-8 to my 436CP42 (16.5 dBdc), and
found at times I needed more than 50w out of my FT-847.  So I mounted a 50w
amp near the antenna and it did make a difference when conditions were
tough getting in.  But many times I only needed 10w.  Your 9-element beam
is probably only 10 dBd gain and suffers another 3 dB of loss due to it
being linear not circular (that is nearly 10 dB weaker than me!).

Hope all this advice is useful.

Ed - AL7EB

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org