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Re: UO-11 Beacon



>From: ken durham <kendurham@home.com>
>Well, using the UO-11 beacon for a signal source doesn't work for me
either. It just went
>nearly overhead and I couldn't hear anything
>near 2401.500. Guess the system isn't near good enough for AO-40
>yet. Got a .7dB NF primp ordered from Down East Microwave. Maybe
>this will help enough. Maybe a helical feed on the BBQ dish might
>give some improvement too. At this point, I don't know how far 
>the LO is off in the Drake downconverter. The IF is at 145 MHZ for
>2401 MHZ input and the NF is supposed to be tested at 3 dB. Don't
>have a way to calibrate either one. Wonder if there is a local HAM 
>who could xmt on 2400?
>Ken K5MBV Garland, TX

Hi Ken,

First I should relate that I had considerable difficulty hearing anything
for weeks with just my minimally modified Drake using first an 18 inch DSS
dish and later the current 33 inch dish.  You need to establish a couple
things before you are likely to have success:   AND DON'T GIVE UP!
1.  Is your Drake working?
If you hear a rise in noise when you turn it on that's a pretty good sign.
If you can see a slightly higher noise level {probably 1/2 s-unit} when
looking at the horizon or a big tree or building than when pointing
straight up, that's a very good sign...likewise seeing sun noise is good.
2.  What frequency is your Drake converting to?
I am currently using a totally unmodified Drake.  I checked its frequency
by using my home-built diode harmonic generator {see below} and it was 5
KHz low...2400-->121.995, 2401--> 122.995
I have a second Drake modified by changing the xtal to provide a 433.9 MHz
IF output
...when tested it was 2400-->433.832.  Don't assume you are on freq.,
measure it.
3.  The specs on the Drake are for operation from 2500-2686 MHz using an IF
of 222-408 MHz.
The unit will not have a NF=3 dB when used at 2400 MHz.  Most of the
writers of modifications and tests have reported a NF of about 8 dB for no
mods and 5-6 dB with a xtal change for 144 Mhz IF and removal of the IF
coils/caps.
My experience is that without a preamp or a very large dish, the modified
Drake doesn't cut it.
If you go all the way to modifying the first stage preamp in the Drake You
may get NF~2 or 3  dB.
4.  Antennas:  Here opinions may vary, but I believe you need at least a 30
inch dish, and that will require a preamp.  With no preamp you need a 3 to
4 foot dish [good for hearing the beacon, only].  I only heard AO-40 only
once without my preamp by using a  4-foot dish when squint was only 10
degrees.  A dipole or a helix feed will both work.
5.  Pointing:  you need a test signal to find out this.  My 33 inch dish
has a beamwidth of 10 degrees...you can miss the satellite very easy by not
pointing well.  If you can see a rise in s-meter looking at the sun then
compare your rotator readout with tracking software az, el numbers for the
sun.  Currently I am off 10 deg. in az and 5 deg. in el., but knowing this
I can compensate...better is to adjust the dish for proper alignment.
6.  Squint Angle:  If it is above 15 degrees and you have no preamp your
chances of hearing are slim.  With a good preamp you can hear the beacon
out to squints of 35-45 degrees.  I have detected it at >90 degrees.  "your
experience will vary with what you are using".
7.  Doppler:  The signal is never on the MB freq.  It is either below or
above it depending on whether the satellite is going away from or toward
you [approaching apogee or approaching perigee].  Freq. changes faster at
perigee than at apogee.  I have found that doppler can be as much as 25 KHz
at a range of 10,000 km.  I guess the beacon rest freq. is 2401.323 MHz
{any correction on this?}.
8.  If you have a soundcard, ao40rcv telemetry software is very usefull for
finding the signal when it is weak.
9.  Range: closer is stronger.  With a decent sized dish and a 1 dB NF
preamp you will hear at apogee.
10.  Don't give up.  Proceed through these steps and you will succeed!

Only test equipment needed is a signal source:  a 1N1004 and five 47K
resistors and a coax connector will produce a fine harmonic generator for
testing your convertor {all available from Radio Shack}.  You can drive it
with up to 2.5w with a 50 MHz radio [x48=2400], or 144 MHz [x17=2448], or
430 MHz [x6=2580].  I have a signal generator so I use 800 MHz [x3=2400]
using only .001 mw [-30 dBm] and it produces a signal that the unmodified
Drake hears over a foot away.

I later mounted the diode generator in a 1-pound coffee can and that allows
me to hear the signal 20 feet from the dish with ease.  With >1/2w you
should hear it 50 to 100 feet away (or more).  I plan to permanently mount
my coffee can with diode on a pole running coax from it to the shack, so
that I may check my 2.4G system at anytime.

Ed  
What am I using?  33 inch offset-feed dish, 5-turn helix, 0.6 dBNF preamp
with 35 dB gain, unmod Drake, FT-847.
  



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