HF dummy load tests
- transmitter 3b (#4) was connected to the dummy load.
- A monitor cable was run from the forward power directional
coupler to the hf control room to monitor the power
- (Note: the power monitor
cables were hooked up in correctly. We repeated this
test on 150506)
- The signal generator was used to inject the RF signal at 5.125
- into dana's box with no attenuators..
- The anritsu spectrum analyzer was used to record the power.
- To look at the higher harmonics, a 75 MHz hipass filter was
used (to block the fundamental).
- We ran 75 to 78 KW into the dummy load
- Reading from the transmitter front panel meter
- It would trip at 80KW.
The plots show the dummy load results (.ps)
- Page 1: the fundamental and 1st two
- the spectrum analyzer was set to :0 to 100 MHz,
rbw:1MHz, average 10 sweeps, preamp off,atten=40db
- If we had made the rbw narrower, we might have seen the
- The dotted red lines are multiples of the 5.125 transmitter
- The measured levels are:
- Page 2: 0 to 200 MHz with the
75 MHz hipass filter installed.
- The spectrum analyzer was set 0 to 200 MHz, preamp on, 1MHz
- The green dotted lines are spaced every 5.125 MHz.
- When comparing these plots with the transmitted power.
- Page one had fundamental at 17 dbm
- On these plots, the same scale would be a few db less
(from the filter loss).
- Top: first attempt shows intermittent spikes
- Red trace is peak hold, black trace is single sweep
- There were intermittent burst that filled in the red
- the spacing between the nulls was about 13.6 MHz
- bottom: 2nd attempt: no intermittent spikes.
- The black trace is now an average of 10 sweeps
- The intermittent bursts were not seen
- There is power starting around 100 MHz spaced by the tx
- The largest peak was at 128.125 MHz (25 times the
- Page 3: 0 to 500 MHz, 75 MHz HiPass
filter. Rf on the off.
- Top: 0 to 500 MHz, RF is on
- You can see the harmonics around 120 MHz
- Bottom: turn off the RF power
- The harmonics around 120 MHz went away, so they are coming
from the transmitter.
- The first two harmonics were seen on dummy load. down 37 db
and 54 db from the fundamental.
- We saw intermittent bursts with an envelope that was spaced by
13.5 MHz at the nulls.
- This did not repeat on the second measurement.
- Stronger harmonics were seen at 128.125 (25*F0) about 85 db
below the the fundamental.
- these extended from 100 MHz to around 160 MHz.
- When banging on the 300 watt solid state amplifier for 3B, we
would see power jumps in its output.
- We need to verify that we were correctly connected to the
forward power coupler correctly.
- I need to get the coupler and the hipass filter frequency
150506: tx4 dummy load, harmonics, no
- tx4 (3b) was hooked to dummy
- a single monitor cable was run from the control room to the
power monitor connector above the tx door.
- The anritsu spectrum was used (peak detection).
- Looked at harmonics and wideband glitches.
dummy load results:
The plots show tx4 dummy load results
- The RF drive was set to 3.05 dbm and the signal generator.
- page 1: look at fundamental and 1st 5 harmonics
- Top plot: 10 khz rbw
- bottom plot: 1 khz rbw
- page 2: 75 MHz hipass filter installed
- 0 to 500 Mhz.
- green lines are multiples of the fundamental
- black line: RF drive on
- red line RF drive off.. the harmonics went away.
- page 3: blowup hipass filter in
- top: 0 to 200 Mhz.
- The strongest harmonic: 128.125 . 5.125*25.
- bottom: 20 Mhz around 430.
- the strongest harmonic is at 425.x
- tx4. 3.05 dbm siggen drive
FN - F(N+1)
- After the 1st harmonic, they fall off at about 11db.
- The harmonics at higher frequency:
- I need to get the directional coupler frequency response.
- the insertion loss of the 75 Mhz filter is probably a db or
- the 128.125 (25*F0) harmonic is at -66dbm .. It is higher
than the 6th harmonic (without the filter)
- the 425.375 (83*F0) is at -110 dbm.
- We didn't see any broad band glitches... but we were not
running with peak hold on..
Calorimeter measurements using dummy load. (top)
The dummy load was used to do a calorimetric
calibration of the output power.
- connect tx to dummy load
- set waterflow to about 26.5 gpm
- use anritsu spectrum analyzer to monitor the forward power
- set the siggen RF drive, record the water flow, input, output
temps, compute power
- pwr=.264 * gpm* deltaT where deltaT is
(averageOuputTemp - inputTemp) degC.
- record the anritsu fundamental and 1st harmonic.
- increase the RF drive. and repeat.
07,08may15: tx4 calorimeter
The plots show the
calibration curves for 07,08may16 tx4 (.ps) (.pdf)
- page 1: Calorimeter power vs
60db RF coupler output.
*: 07may15 input water temp, red *, input
water temp 08may15
- Bottom: there are 2 output temp meters. compute the power
using meter1,meter 2, and the avg
- also over plot the avg pwr for 07may15
- Page 2: Dummy load
- Black is the input water temperature, red,green are the
output water temps for meter 1,2
- The x axis is the order we did the measurements.
- top : 07may15
- bottom: 08may15
- At the beginning of the test, the two output temp meters
varied by 2deg C.
- later in the day they came closer together
- Page 3: Gain variation of
- Top: RF coupler power/ rfDrivePwr (linear)
- red line is input water temperature
- Bottom: value of RF output output in dbm.d
- the curves do not remain linear over the entire measurement
- The input water temperature dropped by 25 C during the tests.
- The transmitter gain (or the RF coupler output) varies ..
probably with the temperature
- Things to do to improve the measurements:
- Try to stabilize the water temperature
- Check the water meters before anything is turned on.
- measure any offsets between the input and output meters
- Measure the RF coupler output before and after measuring the
dummy load temps
- wait a little longer between raising the RF drive and doing
the measurements to give things a chance to stabilize.
- when using low rf drive, we should use a narrow rbw so we
don't add in too much of the noise baseline.
12may15: tx 4 calorimeter
measurement and fit
We replace one of the output temperature
sensors on dummy load 4. It differed from the other 2 temperature
sensors with no power input.
The input water temperature remained stable for the entire
measurement (29 to 31 degC)
The plots show
the data and a linear fit to the data (.ps) (.pdf)
- Top: output power vs rf coupler for 12may15 data
- black: measured points
- green line: linear fit
- red points: excluded from fit.
- the linear fit was
- pwrKw=-.121221 +
- Bottom: over plot data
from all tx4 dummy load measurements
- the different days do not overlap
- changing the temperature sensor, and stabilizing the input
water temperature probably helped.
12may15: tx 3 calorimeter measurement
tx3 dummy load calibration. we got
measurements till 50 KW then the tx would faults with ac drv Amp
fault. The water temp was stable for the entire run. (input 29 to
The plots show Calorimeter power vs coupler power and
the linear fit (.ps) (.pdf)
- Top: data (black) and fit (green). The red * were
excluded from fit.
- The linear fit was:
- Pwr=-7.04039 + 1.27153* 10^(clprDbm*.1)
- the y intercept should be 0. Non zero causes the bending
of the line on the log,log plot
- Bottom: same points, force fit yintercept to be
We need more high power points to get a better fit.
22may15: tx6 calorimeter measurement
Transmitter 6 was put on dummy load. We used the
calorimeter to calibrate the 60db rf coupler output.
23jun15: tx 4 on dummy load, calorimeter
Note: At end of run we found that connectors
in the back of the broad band amp were loose. This was probably
causing the changes in the drive input vs coupler output. This
data wasn't used for the calorimetric fits (although it might be
Dana first measured S11 on coax from tx4 to dipole 3b (with
dipole end shorted). This is the dipole that had the arc. Saw
about a 40 ns wide reflection at the far end.
Then ran tx 4 on dummy load the rest of the afternoon.
What we did:
The table below records the power levels, water temps as we
varied the drive level.
- recorded drive, power levels and water temp as we increased
- it eventually tripped with PA Amp dc fault at 93KW
(from coupler value).
- as we were raising the power, the drive level was 3 or 4db
higher than what was needed normally for tx4.
- The PA cathode current was also high.
- After the trip, the drive level needed to get to a
particular power was 3 to 4db less than before the trip.
- We looked at the lowlevel broadband amp to see if it was
varying. banging on the front caused the power to drop out.
- We found that the output of the broadbad (that goes into a
coupler and then on to the next stage was loose.
- Looking at the other tx's some of them also had loose
connections on the output of the broadband amp.
- We had 26.5 gallons/minuter for the entire time).
- the reflected power always read less than 1 kw.
|tripped: PA amp DC
- The last two columns show the delta db in drive level and
coupler reading. At the higher levels we were compressing
- after the trip, the drive power need to get to a particular
output power dropped by about 3.5 db.
150629: tx4 on dummy load
We started with tx2, but kept getting trips
with drv AC A .. with less than 10Kw of output power.
So we switched to tx4.
#drv cpl1 cpl2 tIN tout1 tout2 gpm
- we adjusted the bias's first. the data
- took data till 5.8 drive. The spectrum analyzer readout
wondered a bit
- This data was then added to the previous tx4 calibration
data and fit for coupler value vs calorimetric power (see
0 9.7 9.7
30.5 32 33 26
3 13.6 13.7 30.5
36 37 26
5 15.94 15.94 31 40.5
5.5 16.7 16.7 31
43 43.5 26
5.8 17.0 17.0 31.5 44
44.5 26 16:22 17.5
6.0 16.96 16.55 31.5 42.5 43.5
26 16:22 17.5
Tx2 dummy load calibration was done on 150811.
Prior to starting the calibration:
- pa screen was 400 ma with 0 drive
- at 100KW tripped with drv A amp after about 5 minutes of
- At 80KW the PA bias was about 180 instead of 380 (at 80 kw)
- this data was fit coupler value vs calorimetric power (see the
#drv cpl1 cpl2
tIN tout1 tout2 gpm hh:mm cathI
-5 9.01 9.16
31. 32 32.5 26.5
-2 11.94 11.97
31. 34 34.0 26.5
0 13.87 13.83
31. 36.5 36.0 26.5
1 15.10 15.10
31.5 38.5 38 26.5
2 16.40 16.33
32.0 42.0 40 26.5
2.5 16.70 16.84 32.0
43.0 41.5 26.5 15:00 18.0
3.0 17.38 17.38 33.0
45.5 43. 26.5 15:00 19.0
We then moved to tx5.
After taking a few measurements, a water hose
broke inside the transmitter.
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