Background:

• Previous test 18jan17:
• covering the center of the dish cut down on arcing
• tx 5 shut itself down. Heard arcing in the tx cabinet
• tx 2 tripped once at 5 MHz and  twice at 8 MHz with reflected power.
• Arcing was found on the fingers on the plunger for the 5 MHz output filter (tx output stage). it was cleaned up.
  

What we did:

• 16:00  start
  
• mesh to 5 MHz position.
• tx 5 tripping. arc detect.
  
• later found to be in the  in 5 MHz output filter.
• 18:00 - stopped interim cor monitoring (for arcs)
  
• 18:44 - bring up 430 for monitoring
• tx2 and tx 4 tripping with reverse power.
• 19:05  started datataking monitoring
• az=285.7  , zagr=11, zach=0.
  
• gr -> echotek[1-10 MHz)  plasma line monitoring. tpsd and clp..
• ch -> usrp.
• 19:51  tx2 and tx4 are tripping together (3 times) on reverse power.
  
• 20:23 restart 430 ch interim cor monitoring for arcs.
• 20:48 switch to 8 MHz
• 21:03 start bring up  8.175 MHz.
• 21:09 tx2 trips on reverse power when output power level 20KW.
• continued to trip at output power 20 to 35 KW.
• switched card 2 (trip levels)  between tx1 and tx2.. problem continued with tx2.
• 
  
• 21:40 tx4 tripped on driver a/c
• 21:42 tx2 brought back up.
• 22:00 tx4 trips, back up.
• broadband for tx6 had 400 watts to get  78KW output (others 150 to 250 watts).
• 22:22 6 tx up .. 471 KW output power (about 80KW each).
• 22:22  lower tx drive .5 db and then start auto toggle (about 70 KW avg per tx).
  
• 3 sec on , 3 sec off
• 22:40 switch pulsing to 5 sec on, 60 sec off.
• 22:45 shutdown hf.
  

Plots of output and drive power:

The plots show the data we took while the hf was on (.ps) (.pdf)

• Each page has 3 frames:
• each color is a different transmitter (1 through 6).
  
• top  frame: rf power (in dbm) measured at the output of the rf coupler.
• middle frame: the same output power, but displayed in KWatts
• bottom frame:
• The synthesizer drive amplitude used
• The dashed green line shows when the rf was on
• the red line at the bottom is the total power from the carriage house 430 receiver (polA 425-435 MHz). When we have arcing, there are jumps in this power (rfi can also make jumps).
• Page 1: 16:00 to 18:00 5MHz testing
• tx5 (purple) tripping with arc detect
• When tx5 is up we had lots of arcing (bottom frame red trace) shows.
• When tx5 was off, there was minimal arcing.
• Page 2: 18:48 to 20:58 5MHz testing
• tx 5 remains down.
  
• there was no arc monitoring data taken during this time.
• the blue and red dropouts  are tx2 and tx 4 tripping on reverse power.
• 20:24 to 20:45  about 75 KW on the 5 transmitters... then tx2 tripped.
• Page 3: 21:00 to 22;45 8 MHz testing.
• interim cor arc monitoring  restarted..
• tx 5 can be brought up with 8MHz (since it uses a different  filter).
  
• the red trace frame 1,2 shows tx2 tripping on reverse power.
• tx4 (blue  trace) tripped at 21.67 and 22.00  on driver a/c
• 22.0 to 22.4 6 tx up at 75 KW each
• 22.4 start  auto toggle 3 sec on , 3 sec off
• 22.6 switched to 5 sec on , 60 sec off.

Looking at spectra of the arcing.

    The 5 MHzMhz tx5 arcinas coming from the tx output filter. The spectral density function of the arcs looked different from arcs coming from the main reflector.

The plots show arc spectra from 29oct15 and 26jan17 (.ps) (.pdf)

• spectra were taken with the interim correlator.
• 1 second integration, 25 MHz bw, crr1 polA
• Page 1 spectra:
•  10 1 second spectra overplotted around some arcing.
  
• top: 29oct15. with arcing on the dish.
  
• The 1 MHz  spectral ripple is the distance from the dish to the platform.
• bottom: 26jan17. arcing in tx 5
  
• the spectral ripples are closer together.. about .3 MHz.. which means a longer distance,
• Page 2: spectra and ACF's
• top: single spectra during dish arc.
• the green lines are harmonics of the hf transmitter. they are not part of the reflected standing wave.
  
• middle: spectra during  tx5 arc
  
• bottom: ACF of the spectra.
• black: dish arc
• green line at 1.09 usecs is the delay dish to platform
• red: tx arc
• peak at 2.68 usecs.
• dana's shorted cable measurements for tx 5 (heliax 5b) was 3.098 usecs.
  
• the other cables were 2.5 and 2.7 usecs..

plasma line movies while hf on

• 19:05 to 20:48  transmitting 5MHz
• 21:03 to 22:45  transmittting 8 MHz
• 22:22 auto toggle.
  

Summary:

• we had lots of arcing from tx 5.
• The arcing was in the  5MHz output filter.
• The spectral shapes of transmitter arcs look different than arcs out on the dish.
• By looking at the arc spectra, you should be able to tell if it is a transmitter or out on the dish.
• If we had arcs on different transmitters, we might be able to use the arc spectra to tell which transmitter it is coming from (or at least differentiate between different dipoles with different heliax lengths.
  
• tx 2 and tx4 were tripping on reverse power on 5 and 8 MHz.
• tx 4 trip may have been a  glitch from the tx2 trips (since sometimes tx2 tripped by itself).
  
• tx 4 at 8MHz had a driver a/c power trip.
• At 5 MHz we ran 5 tx at 78KW for about 1/2 hour
• at 8 MHz we ran 6 tx around 75 KW for about 10 minutes.
  
• we ran cycling for a total of 20 minutes with the 8MHz system. we tried:
  
• 3sec on, 3 sec off
• 5 sec on, 60 sec off .
  
• power levels were around around 75 KW for each tx.. We had  no problems..
  

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