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Re: Don't Hear Nothin'



Bill

I think that Ed's comments are a good list to work from except 
for one error which I made on the first few passes in getting my 
system working, (It's a "I can't believe I did that!" kind of 
error.)  The N3iyr dish uses an off-set feed arrangement.  So, 
you can not use the Sun centering process that Ed referred to. 
The beam is actually formed above the axis of the dish.(The 
perpendicular line from the surface of the center of the dish.) 
Think of the reflection off of a mirror when you shine a flash 
light(the feed) at an angle to the surface.  In the case of the 
N3IYR dish, the dish is "pointing" about 20 degrees above its 
"axis" .  The N3iyr website has a comment on pointing the dish by 
using the support arm for the feed as a guide. To measure the 
elevation, you can buy an inexpensive (Sears, about 6 bucks) 
"inclinometer" with a magnetic mount and just set it on the 
support arm.  (Setting the support arm elevation with the 
inclinometer, the dish will point about 5 degrees too high)

The only other suggestion I have, is to watch out for trees (even 
trees with no leaves - another of my errors)  This story is told 
by WA4SXM in the January issue of the AMSAT journal.

Bill W3FB

Edward R. Cole wrote:
> Bill,
> 
> I noted you said you were looking on 123.1 MHz, and assuming your convertor
> translates this to 2401.1 MHz, you will not hear the beacon.  The beacon
> with no doppler offset is at 2401.323 MHz.  If your convertor xtal is dead
> on frequency (most are not) then you want to tune 123.312-to-123.330 MHz to
> find the beacon.  Doppler can shift the beacon as much as 25 KHz above or
> below the published frequency.  Most everyone getting started on AO-40 has
> to first find out where their convertor frequency is.  It can easily by off
> 100 KHz high or low.  Best way to check is with a signal source on 2400 MHz
> (see where that tunes on 122.xxx).  If it is off then you have to mentally
> add or subtract that to know where to tune.  You say you you used a freq
> source so maybe you have done this already.
> 
> Of course high squint may make the signal too weak to detect as well.
> Knowing for sure you are pointed dead on the satellite is another thing to
> check.  Being off even a few degrees makes huge difference at this
> frequency as the dish is very narrow beamwidth.  Best way to check your
> pointing system is to point at the sun (so the shaddow of the feed is
> exactly centered in the dish) [DON'T LOOK AT THE SUN FOR THIS].  Now
> compare the readout of your rotator system with what NOVA has for the sun.
> If it is off more than 3 -degrees adjust the rotator until it reads out
> correctly.
> 
> Oh be  careful not to transmit into the Drake with the FT-847 it will still
> make "shhhhhhh" but no signal ;-)  If you have a signal source then it is
> easy to check.  The preamp should raise the signal level by 10 dB when it
> is used.  Without a signal you should hear a definite rise in background
> noise when you power on the preamp.  If not then the preamp is broke :-(
> 
> After checking all this I think you will find the beacon (with patience).  
> 
> GL,
> Ed - AL7EB
> 
> At 01:51 PM 4/23/03 -0400, Bowman, Greg wrote:
> 
>>I see squint calcs are around 43 degrees for the time period for Houston,
>>you probably won't hear anything.
>>
>>Greg
>>N4EN
>>-----Original Message-----
>>From: William P Gravett [mailto:wgravett@juno.com]
>>Sent: Wednesday, April 23, 2003 1:07 PM
>>To: amsat-bb@AMSAT.Org
>>Subject: [amsat-bb] Don't Hear Nothin'
>>
>>
>>Well, I am showing my ignorance probably but I am sitting here with my
>>N3IYR pointed at where NOVA with the latest Keps says AO40 ought to be,
>>my computer synced to wwv, a new DEMI ULN pre amp I just built (and
>>checked out with a 2.4 gig signal source) an unmodified DRAKE 2880 with
>>13.8 vdc going to it , and  all I hear is sssshhhhhhhhhhhhhhhhhhhhhhhh at
>>123.1 MHz with my FT847. GMT is about 1700, AZ at 123, el at 40.3
>>Is(are) there something(s) I don't know and should?????Please help>
>>Thanks 73
>>
>>Bill, W5PGZ, (AO40 neophyte)
>>
>>________________________________________________________________
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>>----
>>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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>>----
>>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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> 
> 
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 
> 


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