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AO-40 Receive System Evaluator



I found the program I was looking for. It is MAGNIFICENT! The file name is:

ao40_s2.xls

It is an excel spreadsheet file and is extremely well done.

The URL is:

http://home.hiwaay.net/~mmarcus/download/ao40_s2.xls

Anyone trying to hear AO-40, or who contemplates same, NEEDS this file.

A couple brief comments on using it:

1. Enter values on sheet 1, where the nice diagram and graph are.
1.a. Enter the values in the bottom rectangular area taht has green number
values. Just type over them.
2. If just running a downconverter and no preamp, you can enter the values
for NF and Gain in either of the two Preamp/Converter blocks...but not both.
3. For which ever block you choose to enter values, put the coax loss in the
box to the right of that block. This is the coax running from your
downconverter to the radio in the shack.
4. To begin with I suggest Range at 65000 and Squint to 0 (you can play
"what if" later.

Once all the values are entered, you can look in the upper left corner of
the spreadsheet for how well your receive station works, as well as
observing the graph just to it's right.

Example: Going left to right

Coax Loss 0  (no feedline loss ahead of the first block)
Antenna Gain 21 dBi
NF 0 (first block)
Gain 0 (first block)    (these values show I don't have a "preamp", but a
downconverter follows)
Coax Loss 0 (no feedline loss after the first block and before the 2nd
block)

NF 3 dB (Noise Figure of your downconverter). If you have a preamp, put it
in block one above
Gain 20 dB (Gain of your downconverter) If you have a preamp, put it in
block one above
Coax Loss 2 dB (loss between downconverter and the radio)
Sat Range 65,000

Receiver:

NF 10 dB (Your Radio, like FT-847). If you don't know, put something between
10 and 15 dB in.
Bandwidth 2500 Hz (the width of your receiver IF on SSB...put in 300 Hz for
cw if you have a filter)
Sat Off Pointing Angle "squint"  0  (pointing right at you, play with squint
angles later)

Results:

System Noise figure 3.3 dB
MDS (Minimum Discernable Signal) -139.4 dBm
Beacon S/N  16.2 dB

This looks good....BUT the beacon is WAY STRONGER than ANY signal should be.
Look at the graph. You will see that 95% of the station signals are BELOW
your ability to even hear them. (the blue line). No wonder the alligator
syndrome is so present on the bird. No wonder Leila is going off like crazy.
(There may be other reasons for leila...like fine tuning from the command
stations)

Example 2:  UEK-3000 downconverter and HyperLink BBQ type parabolic section
dish 39" wide.

Antenna Gain = 26 dBi

Amp/Conv NF = 0.7 dB
Amp Gain = 30 dB
Coax Loss = 2 dB
Sat Range = 65,000

Receiver:

NF = 10 dB
Bandwidth = 2500
Squint/Offpointing = 0

Results:

System NF = 0.8 dB
MDS = -147.2 dBm
Beacon S/N = 29 dB

Again...the beacon is a poor reference, so let's look at the graph:

Nearly 100% of all signals are ABOVE your receiver noise floor (blue line)
(the signals are in green)

So, system 1 with a 3 dB NF and 20 dB gain converter connected to a 21 dBi
antenna = -139.4 dBm
      system 2 with a .7 dB NF and 30 dB gain converer connected to a 26 dBi
antenna = -147.2 dBm

Now...you can experiment by keeping all values the same except the NF and
Gain of the converter and watch what happens. The earlier posted comments
about downconverters with 5 dB NF and 20 dB gain were right on the money.

Look at the graphs and you will see what is happening...and what will happen
to you, if you don't pay strict attention to the system noise figure of your
receiving setup.

We are very fortunate that w3pm and gm4yr put this up for us to use...it is
absolutely invaluable. Have fun playing.

I could have fatfingered any given entry here...I'm just trying to get you
to look at and play with the spreadsheet.

73

hasan schiers, NØAN
schiers@netins.net



hasan schiers, NØAN
schiers@netins.net


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