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Re: AO-40 Update 2001-07-20

So how well will a 16 turn helix on S-band work? will I be happy?


At 06:00 PM 7/20/01 -0400, you wrote:

>A couple of updates and comments on amsat-bb postings.
>1. We are currently using Leila2, not Leila1 which was used 
>previously.  It appears that the thresholds for Leila2 are slightly 
>different than for Leila1, so some adjustments are needed to bring Leila2 
>to the proper threshold.  It does work, but the threshold currently 
>appears to be a little too high.  That is, it is not triggering as often 
>as it should.
>2. The U and L-band receive antennas are right-hand circularly 
>polarized.  This should be most obvious at very low squint angles.  As the 
>squint increases, the difference between RHCP and LHCP will be less 
>obvious and at some higher squints, LHCP may be slightly favored.  This 
>was also observed on AO-13 and is as predicted in modeling of circularly 
>polarized antennas at various offpointing angles.
>3. AO-40 is not deaf :-).  In fact its receivers and antennas are 
>incredibly sensitive.  It is, however, a limited resource.  It can only 
>output so much power and if the passband contains numerous strong signals, 
>the power available per signal will be reduced.  This may be reflected in 
>the S2 Tx ALC setting.  More importantly, if multiple strong signals 
>bombard a receiver, the receiver AGC will reduce its sensitivity by 16 dB 
>or more.  This can very easily be seen in the P3T telemetry for the U/L1 
>Rx AGC's when the passband is on.  So if one strong station causes the 
>U-band Rx to reset its AGC level, everyone's signal on the downlink will 
>be reduced accordingly.  This causes everyone to raise their power, which 
>causes the AGC to set even higher, and a vicious cycle ensues which the 
>user can never win.  Hence the reason for Leila, which, as noted above, is 
>not currently set optimally, but will be adjusted shortly.   ...so please 
>bear with us, we are still in a "check out" mode.
>4. There is no V->S2  passband currently in the schedule.  The V-Rx 
>alternates with the U-Rx when the passband is not active.  This can be 
>seen in the "N" schedule block.
>5. RUDAK tests are currently scheduled for Orbit 339, which begins early 
>on 2001-7-26.  The passbands will be off for this orbit and the S2 beacon 
>may be intermittently off as well.  Until then, the passbands will be 
>active from MA = 10 to 100.
>6. In the near future, we also will be testing the S1 transmitter 
>passbands during times of optimal squint angle.  The higher gain of the S1 
>antenna should give better signals farther out in the orbit, as long as 
>the squint is good.  This will probably be done as we move closer to 0/0.
>Enjoy AO-40 this weekend!!!
>  ________________________________________________________________________
>  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
>    Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
>  ________________________________________________________________________
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