Bill sisk's radar blanker
rf pulse length: duration of transmitted pulse from radar
ipp: Inter Pulse period. The time from the 1st rf pulse
of a sequence
to the 1st rf pulse of the next sequence. During this time the
goes out and all of the echoes are returned.
Radars are pulsed signals with low duty cycles.
pulse is transmitted and then the radar waits for the return echo.
start of the next ipp another rf pulse is transmitted. The rf pulse
the echo's cause rfi in our receiver system.
A radar blanker synchronizes with the ipp of
radar and generates a blanking pulse that is high while the radar
present in our system. This duration depends on how much multi path
and echoes there are.
The observatory has a radar blanker for the
"FAA" radar and for the iridium satellites (they can be considered
since they have an 50% uplink, downlink duty cycle). The
signals are sent to the interim correlator and to the wapps where it
stops the lag accumulators.
iridium signal has a 50% uplink/downlink duty
ms downlink, 45 ms uplink). Since there are no iridium phones near
observatory, only the downlink cycle causes rfi. Iridium has
with a radar blanker that is synchronized with this 90 ms period. It
a square output pulse.
The "blank" signal is currently the uplink
You must send the /blank signal to the blanker mux.
This takes the iridium and faa blanking signals
multiplexes one of them to the interim correlator and wapp.
Radar blanker multiplexor:
It is currently under test. It also contains the circuitry to extend
the iridium blanking signal.
07feb06: radar multiplexor . calixto's box.
The iridium blank output from the iridium supplied box is synced
uplink cycle. You must pass the /blank to the multiplexor
want to blank the downlink (and positive is blank).
The front panel test point for the multiplexor can not drive 50
you plug a 50 ohm load into it, the blanking signals to the wapp
interim correlator will fail. This needs to be buffered and a 50
added. Someone should also check the drivers to the wapp and the
The "modified iridium" mode is supposed to change the duty cycle
more than 50% of the time is blanked. Currently the device is
"positive" pulse narrower. This makes the blanking period