Intro

The receiver temperature (flange temperature) was initially measured for the cooled qrfh system at the antenna test building on:

25jan23 2 to 14 GHz with the fieldfox preamp off. polX and polY were measured
31jan23 4 to 14 GHz with the fieldfox preamp on. PolY was measured. We looked vertical and 30 deg to the north.

Some modifications were then made to the dewar (cal sma cables replaced with stainless steel cable).
The dewar was then remeasured on 31mar31 at the antenna test range.

This page shows the 31mar31 measurements as well as a comparison with the earlier measurements.

2-14 GHz field fox preamp off
10-14 ghz field fox preamp on

We tried 2-14 GHz preamp on, but the rfi around 2.5GHz caused overloads in the field fox.

Setup

cooled qrfh receiver placed on lift in the antenna test building and then lifted to the roof.

T16k was around 18K during the measurements

The sky was used for the cold load.

We started at 7:42am and finished around 8:27 (on the sky)
There were no clouds i the sky
the sun elevation went from 19 (at 7:47) to 28deg at 8:27

Absorber was used for the hot load.

It was suspended about a cm above the dewar
The temperature was measured at the center of the absorber before the first measurements and after the last measurement (8:27 start, 8:46 end)
The temp went from 76F to 77.6F

A warm postamp was used at the output of the dewar (26db?).

The sma cable was about 3 feet. The jan23 measurements had an 8" sma cable.

The field fox spectrum analyses was used to measure the signal:

2 to 14 GHz,bw 1MHz, 10001 points, attn 0, preamp off, rms detector.
avg 10 sweeps trace 1, pkhold trace 2
loop 10 times giving 10 avg spectra/measurement
This took about 70 secs / spectra or 12 minutes measurement

Since the field fox has only one input, we had to do 1 pol at a time
the sequence was:

Pol Y(file labeled a)
Pol X(file labeled b)
Preamp off sky,abs was done for both pols
preamp on sky,abs was done for just pola (ypol) since that was what we did in jan23.
Pre amp off 2-14 ghz sky

On sky. files: trcv_skyb_nnnnn.dat (nnnnn 0 to 9)

On sky files: trcv_skya_nnnnn.dat

Pre amp on 2-10 ghz sky

On sky. files: trcv_pa_skya_nnnnn.dat (nnnnn 0 to 9)
On sky files: trcv_pa_skyb_nnnnn.dat

On abs

2-14 ghz preamp off: trcv_absa_nnnnn.dat
4-14 ghz preamp on: trcv_absa_pa_nnnnn.dat
2-14 ghz preamp off:trcv_absb_nnnnn.dat

the file format is:

10001 points/register (2 registers: avg, pkhold)
32bit floats
data

freq[i],r1[i],r2[i], freq[i+1],r1[i+1],r2[i+].. ind 0 to 10001-1

files are located at /share/phildat/wbrcv/230125/

The datataking program, config file:

/share/megs/phil/x101/230331/ffdo.. program
config files:

cmd_230331_nopreamp.dat
cmd_230331_preamp.dat

I edited the cmd_..dat before each measurement to update the file prefix.

Processing:

There were 2 sets of measurements.. 2-14 then 4 to 14 GHz

cold spectra on sky, hot spectra on absorber.
Note:

we did not try tilting the rcvr north to get away from the 12-13GHz rfi
in jan23 the green lines had the rcvr tilted north.

For each set:

input the 10 hot and 10 cold spectra

convert each spectra to linear
compute rms/mean for the 10 hot, 10 cold spectra (to check for rfi)
avg to 10 hot, 10 cold spectra

compute the Yfactor : avgHotSpc/avgColdSpc (use the reg with avg sweeps).
compute Tflange (Trcv)

Tflange=(Tabs - Tsky*Yfactor)/(Yfactor-1)
For Tabs we used a single value for entire freq range(see above)
for Tsky we used interpolated values from Paul goldsmiths paper on Tsky vs freq

pfg Atmospheric contribution to sky temp(.ps). Sky temp 1 to 15 GHz (.ps).
at 2GHz - 5K, at 14 GHz - 14K

No scattered radiation was included in the computation..

Plotting the results:

2-14 GHz fieldfox preamp off

The plots show the results of the postamp off measurements (.ps) (.pdf)

Page 1: signal levels polY (polX gain was higher)

top:

Black on absorber
red: on sky
blue: noise floor of field fox spectrum analyzer

bottom: Signal level above the Noise floor of spectrum analzyer.

Black: absorber. worst case 5db at 14GHz
red: sky. worst case 1db at 14 GHz
The sky measurement will be impacted by the field fox noise floor.

Page 2: Power on hot load, cold load, and yfactor

each color is a different measurement:

black:polY, red:polX

Top: power vs freq on Absorber

vertical scale is linear in Power

Middle: power vs freq on sky

lots more rfi here. vertical scale blownup x10 compared to top frame.
there is a bump between 11 and 13 GHz . about 60% increase in power onsky.

This is not seen on abs (power level too high or not present?).

Bottom: Yfactor:PowerAbs/ PowerSky

The ratio is 7-8 db until around 9GHz where it starts to fall.
the dips,spikes are from rfi.

The two polY measurements were separated by about 2 hours.

the power levels remained nearly constant (not drift in gain).

Looks like the lna gain in polX is higher than polY (factor of 2 at 2ghz down to close to 1 at 14GHz)

Page 3: Same plots as page 1, but use the peak hold spectra

this shows a little more rfi in the onsky spectra.

Page 4: rms/mean by freq channel showing rfi

the rms/mean was computed for the spectra of each freq channel and then plotted.
top: on absorber
bottom: on sky
rfi tends to be variable so these plots will show rfi.
the area around the 11 to 13 GHz bump does not show any variation.

Page 5:Receiver (flange) temperature.

Top: Tsky vs freq (taken from paul goldsmith's plots .. see above).
Middle: receiver temperature

the blues line was the project spec of <30K from 2 to 14GHz.

it meets the spec up to 10 GHz for polX, polY is higher than this level

These temps are high because we didn't have enough gain in front of the fieldfox.

the dewar, amps were the same.
It must have been the change from 8" to 36" sma cable between the dewar output and the postamp.

The vertical purple lines show where the bump was seen on the sky power

Bottom: on sky power

replot the on sky power to show the bump 11 to 13 GHz.

Page 6: Blowup of Trcv 11 to 13 GHz.

Black is polY on sky
red ,polA on sky
these are much higher than the jan23 measurements because the input signal was close to the fieldfox noise floor on sky.
the light blue lines

12.7 - 12.2 GHz. FSS: fixed satellite service space to earch

dark blue

12.2 to 12.7 : DBS: direct broadcast satellite (space to earth)

processing:x101/230331/wbtrcv_31mar23_nopa.pro

Pol Y field fox preamp on.

We redid the measurements with polY with the field fox preamp on. This was to compare what we had measured in jan23.

The plots show the results of the 31jan23 measurements (.ps) (.pdf)
The field fox setup was similar to the preamp off, except the span was 4 to 14 GHz.

Page 1: spectra, noise floor ratio in dbm

top : Average spectra in dbm

black: on absorber
red: on sky
blue: field fox noise floor with 50 ohm load (preamp on)

Bottom: Ratio Spectra to field fox noise floor

black: absorber
red: sky vertical
all values are at least 13db above the noise floor.

Page 2: average powers with linear plots

top: on absorber
middle: on sky

red: looking vertical

Bottom: Ratio hot(abs)/cold(sky)

red: on sky vertical

Page 3: rms/channel for the 10 spectra of each measurement

Top: on absorber
bottom: on sky

Page 4: Flange temperature

Top: Tsky used (4 to 14 GHz)
middle: Tflange

Red: PolY looking vertical
the blue line is the 30K spec for the receiver.

bottom: replot the on sky measurements to compare the bump around 12 GHz.

Page 5: blowup 11 to 13 GHz Tflange

Red : looking vertical

Page 6: compare the 31mar23 (nopreamp) Tflange with the (preampon) Tflange.

Top: plot 4 to 14 GHz

smooth to 31 MHz
black: polY no preamp.
red: polY preamp on.
Trcv is below 30K for the band (excluding the rfi regions).

Bottom: blowup 11 to 13 GHz

11.7 to 12.2 GHz (fss band)

Processing: x101/230331/wbtrcv_31mar23_pa.pro

Compare Tflange before, after dewar changes.

The flange temperature before (jan23) and after (mar23) the dewar modifications to see if anything had changed.

the plots show the tflange comparison (.ps) (.pdf)

Page 1: power levels at input to the field fox

Black: sky,absorber jan23
red: sky,absorber mar23
blue: field fox noise floor.
top: 2-14 GHz no preamp
bottom: 4-14 GHz with preamp on.
The black (jan23) lines are 3 to 4 db higher than the 31mar23 lines

This is either a postamp difference (felix says no) or the change from 8" to 36" for the line from dewar to postamp.

Page 2: Flange temperature before and after dewar changes.

Black: jan23 flange temps (before changes)
Read: mar23 flange temps (after changes)
Top: 2-14 GHz field fox preamp off

the jan23 temp is much lower than the mar23.

This is mainly from the power level into the field fox was too low during mar23.

Bottom: 4-14 GHz field fox preamp on

above 7.5 GHz the values are identical
below 7.5 GHz, the differences are probably rfi changes..

processing: x101/230331/wbtrcv_cmp_jan_mar.pro

Summary:

The flange temperature for the 12meter wide band rcvr was measured at the antenna test shack on 31mar23 after the changes were made to the dewar.
hot,cold load measurements were done: 2-14 GHz with the field fox preamp off

the measured Tflange was higher than that measured in jan23.
The higher Tflange was caused by the lower power level going into the field fox.
switching the dewar to postamp cable from 8" to 36" was the major config change.

hot,cold load measurement were also done 4-14 GHz with the field fox preamp on (polY only)

The Tflange was identical to that measured prior to the changes.

Trcvr after dewar mods