- We needed to test the hf for the upcoming hf campaign (in
What we did:
- We measured the rf rise time through the TX as well as the
relative delay between the broadband "CW" and "CYCLE" modes.
- The hf was run at 5.125 MHz
- The broad band amplifiers have a keyline switch that
enables/disables the amplifier.
- To try and stop the broadband amplifiers from
overheating, for each broad bandamp, Alfredo replaced
the normal termination (broad band enabled) with a line
running back to the hf control.
- Each of the 6 lines is controlled by a switch in the hf
- Switch up: cw mode
- The broad band amplifier is always enabled
- Switch down: "cycle mode"
- the broad band amplifier is enabled when rf is on , and
disabled when rf is off.
- We did some tests to see the response times of the amps in
- The hf mesh was set to the 5 MHz position.
- 430 tx, dual beam
- gr -> usrp
- ch -> echotek [-5.5,5.5]
- tx 4 is off, tx 6 won't come up .. so using tx 1,2,3,5
- 09:36 start to bring up tx
- 09:54 move dome to za 1.06, mov ch to 11 (ch was
overloading at za=0)
- 10:00 switched echotek [-5.5,5.5] to [5.5,9.5]
- 10:15 hf back on with tx 1,2,3,5
- 10:24 60 KW on 4 tx
- 10:43 cable car moved to 1/2 way up the cable. has test
equipment for drone.
- 11:06 bringing up tx6
- 11:0x set ntp on raspberry pi hfmon to ntp0
- 11:12 power to 305KW with 5 tx: 1,2,3,5,6
- 11:16 turn off broad bands to see which is arcing.. looks like
- 11:22 turn off tx2 , broad band was overheating again.
- switch to another broad band that carlo had refurbished.
- 11:57 (11:27?) disconnect tx1,3 rf coupler
readback from spectrum analyzer.
- Attach to scope so we can measure the relative delays
between "cycle mode" and "cw mode" on the new switches.
- 11:38 tx2 new broad band installed
- 11:48 send tx1,3 rf coupler readback -> scope.
- rf coupler -> cable To hf control -> 10db pad ->
scope (50 ohm termination)
- auto toggle 2 sec on , 4 sec off
- Auto toggle was set to run 2 sec on 4 sec off.
- using autotoggle 2sec, 4 sec
- This would occur if the 5.125 MHz was getting into the ch
400 MHz Local oscillator.
Measuring the tx rise time and "cycle,cw mode"
- tx1 and tx3 rf coupler readback were disconnected from the rf
switch (that feeds the spectrum analyzer).
- the plumbing was
- rf fwd coupler output -> cable to hf room -> 10db pad
-> scope input with 50 ohm termination
- Put the broadband switches to "cw" mode
- we measured a negligible delay between the 2 signals. So tx1
and tx3 have similar delays.
- Leave Tx3 broadband as "CW" and set tx1 broad band to "cycle"
The plots show the rise times
and relative delays (.ps) (.pdf)
- Page 1: The rise time for the signal coming out of TX3 ("cw"
- The broad band amplifier was always enabled.
- the frequency was 5.125 MHz
- It took about .4 milliseconds for the signal to rise up to
- This does not show the delay through the tx, only the rise
- Page 2: compare "cw" and "cycle" mode delays
- Top: Start "CW" mode to start "Cycle" mode
- there is a delay of 3.9 milliseconds from the start of tx
3 (cw) to the start of tx1 (cycle)
- Bottom: extended time scale showing cycle mode rise time
- Time tx3 "CW" start to tx1 "CYCLE" full scale is 17.4
- So there is a delay of 3.9 milliseconds and then about 13
milliseconds of rise time.
- Tx 2 broad band was overheating.. it was replaced with a
- the timing for the "cw/cycle" mode switches for the
broad band amplifiers were tested
- Normal CW (always on).
- the rise time is for the signal is about .4 milliseconds
- Cycle mode (broadband on,off with rf enable)
- there is a 3.9 millisecond delay
- the rise time is about 13 milliseconds.
- So if you are doing fast rf enable,disable you need to
be careful about using the "cycle mode".
- If the broad bands are overheating, and you have a long rf
- start in cw mode
- wait for the rf disable
- switch to cycle mode (this turns off the broad band)
- before the rf enable, flip the switch back to cw mode
- If you don't care about a fast turn on, then you could just
leave it in cycle mode.
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