water in the waveguide, network analyzer
The sband transmitter measures reflected power
using directional couplers at:
- the output of each klystron window. These are reported on the
individual klystron pages as reflected power.
- the waster load. This is between thecombiner and the waster
- just before the turnstile. This is called antenna reflected
- as the 4th port of the turnstile. this is called turnstile
power. When power reflects back from the horn, some of it will
go back towards the combiner, while some will go to this port of
the turnstile. The amount depends on the polarization of the
The waveguide path is:
- klystron window. start
- directional coupler to
- waveguide switch for dummy load
- to combiner input
- combines power from both klystrons.
- output to directional coupler, then waster load .,. or
- output to antenna direction
- combiner to top of vertical waveguide column down to rotary
- rotary coupler attaching fixed to rotating waveguide (at top
- waveguide column down to rotary floor
- waveguide along rotary floor out to turnstile, horn
- directional coupler (antenna reflected power)
- turnstile directional coupler, turnstile load.
During the aug15 runs, there were a large number
of reflected power faults. From the individual klystrons, and from
the antenna reflected power. When we went to waster load (by
switching the combiner), we never had a reflected power fault. This
showed that the waveguide from the combiner back to each klystron
It was then noticed that the antenna reflected
power would mainly occur at low za.
So the antenna reflected power at low za pointed
to water in this section of waveguide.
- the rotary floor is level at 10 deg za.
- When the sb tx horn is at the focus:
- at high za, the waveguide along the rotary floor is tilted
so the horn side is higher than the other side. Any water in
this piece of waveguide would flow away from the antenna
reflected power coupler that is next to the horn
- at low za, the waveguide along the rotary floor is tilted so
that the horn side is lower than the center of the floor edge.
Any water in this piece of waveguide would flow toward the
horn directional coupler side.
On 17aug15 the waveguide along the rotary floor was opened and water
was found inside it. This was cleaned out.
Later that evening the transmitter came up again and ran for about
20 minutes. It then started to have klystron reflected power faults
again (but no antenna refllecte power faults).
measuring the waveguide with the network analyzer.
The Rhode and schwartz network analyzer was used
to measure S11 on the sband waveguide
The plots show the time domain
reflectometer results (.ps) (.pdf)
- A termination was put at the top of the vertical column that
connects the tx room to the rotary floor room. It was placed on
the transition above the rotary coupler (so the rotary coupler
was included in the measurement).
- A second transition was place where the 90 degree elbow
attached the waveguide to the turnstile
- 2000 to 2500 Mhz bw was used for the measurement.
- The measurement was done at:
- sband tx on turret focus
- za=11 degrees
- za=1.07 degrees
- za=19.69 degrees
- za=11 degrees
- za=11 degrees with the turret rotated 180 degrees.
- for the distance axis i used the group velocity at 2380 Mhz:
- Page 1: reflected power vs distance, time.. all measurements
- top: reflected power vs time (usec)
- bottom: reflected power vs distance (feet)
- At za=1.07 deg there is a peak close to the analyzer
- at za=19.69 this peak moves away from the injection point by
about 6 more feet.. this
- At 11 degrees the waveguide is almost level..
- the layer of water may or may not be evenly distributed
(depending on the viscosity).
- With the za= 11 deg and the floor is rotated:
- The peak moves closer to the horn (just like za=1.1).
- This may just be centripetal forces pushing the water out
during the rotation.
- Page 2: show 11,1.1 and 19.7 degree traces.
- I averaged the 2 11 degree traces and then displayed
the 1.1,11,19.7 deg trace to make comparison easier.
- water in the horizontal portion of waveguide (on the turret
floor) caused reflected power faults
- With lots of water
- low za gives antenna and klystron reflected power
- high za only gives klystron reflected power
- With less water (after the cleanup) we only got klystron
- We can see a changed in the reflected power as we go from high
to low za (if water in the waveguide) using the network
- the null at 25 feet is probably the distance from the
turnstile to just beyond the rotary coupler
- Later that day we found water seeping from the elbow at the
bottom of the waveguide column. There must be a leak into the
Dana's notes on measuring S11
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