Intro

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

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.
Hot and cold loads were used (absorber,sky).

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 7am and finished around 9:00 (on the sky)
There were no clouds i the sky
the sun elevation went from 5 (at 7:30) to 24deg at 9:00

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 and after each absorber measurement.

We started with an infrared thermometer but go inconsistent readings (turns out the emissivity value was set wrong.
After the 1st absorber measurement, we switched to a temperature probe plugged into a fluke meter
We waited a few minutes after inserting the probe to get a stable temperature.
We used the 2nd absorber reading for the first.
first Set: polY used 2nd sets readings
2nd set: polX 68.5 start,66.66 end. avg: 67.3F - 289.8K
3rd set: polY (redo) : 67.3F start, 71.4F ed, avg:69.4 - 290.8K

A warm postamp was used at the output of the dewar (26db?). The sma cable was about 8 inches.
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)

On sky. files: trcv_skya_nnnnn.dat (nnnnn 0 to 9)
on Abs. files: trcv_absa_nnnnn.dat

PolX (file labeld b)

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

PolY (file labeled a2)

On sky. files: trcv_skya2_nnnnn.dat (nnnnn 0 to 9)
on Abs. files: trcv_absa2_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/x101/230125/ffdo.. program
... /cmd_ffwbrcv.dat
I edited the cmd_..dat before each measurement to update the file prefix.

Processing:

There were 3 sets of measurements:

cold spectra on sky, hot spectra on absorber.

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:

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

Page 1: signal levels:

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 10db at 1GHz
red: sky. worst case 3db at 14 GHz
For most of the band we had at least 6db above the noise floor

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

each color is a different measurement:

black:polY, red:polX, green: polY 2nd try

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

On abs is about 10 times on sky until 10GHz were 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)
there is a 500 MHz ripple in the absorber measuremenit. seen in both pols (so probably not a cable in dewar)

this about 8 inches in a cable with a velocity of .7c .. might be the short cable from dewar to postamp.
It's probably also in the sky measurement but harder to see because of the lower power levels.

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 11 GHz.

The vertical purple lines show where the bump was i the on 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, green is polY on sky
red , polA 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:x101/230125/wbtrcv_25jan23.pro

31jan23 : measure polY with 20db field fox preamp on

The 25jan23 measurements from 2 to 14GHz had the fieldfox preamp off (leaving it on gave a/d overange errors from the strong birdies around 2.5 GHz.
On 31jan23 the observations were repeated (using only PolY) with:

the25jan23 sky measurement was only 5 to 8db above the fieldfox noise floor from 12 to 13.5 GHz.

If the Tsys was 40K (around 12GHz) and we were 7db (a factor of 5) above the noise floor, then 1/5 or 20% of Tsys could be coming from the field fox (about 8K)

We had the preamp off because we were getting a/d over range errors (probably from the 2.5 GHz Rfi.)

For 31jan23 we turned the field fox preamp on and only measured 4 to 14 GHz (to stay away from the 2.5 GHz RFI.. at least at the a/d). Running this way, we never saw any a/d errors.

There was also a broad bump in Tsys around 12 GHz.

Hamdi thought the Tsys increase around 12 GHz was coming from satellite transmissions in the 11.7 to 12.2 and 12.2 to 12.7 GHz.
these satellites are in geostationary orbits and he thought that tipping the horn about 30deg north should decrease this signal (if it was the geo satellites).

We redid the polY measurements with:

polY looking vertical on sky
polY tilted 30 deg North on sky
polY on absorber (absorber temp=73.2 F)
the Field fox on a 50 ohm termination.
The field fox setup was;

4 to 14 GHz, 10001 points, average detector, 0 db attn, 1 MHz Rbw, vbw auto, preamp on.
the 26 db amp after the dewar was still installed.

The acquisition was similar to 25jan (avg 10 sweeps, repeat 10 times at each setup).

The plots show the results of the 31jan23 measurements (.ps) (.pdf)

Page 1: spectra, noise floor ratio in dbm

top : Average spectra in dbm

black: on absorber
red: on sky looking vertical
green: on sky looking 30 deg north
blue: field fox noise floor with 50 ohm load (preamp on)

At 14 GHz this went from -68dbm(preamp off) to -86dbm (preamp on)

Bottom: Ratio Spectra to field fox noise floor

black: absorber
red: sky vertical
green: sky 30deg North
all values are at least 19db above the noise floor.

Page 2: average powers with linear plots

top: on absorber
middle: on sky

red: looking vertical
green : looking 30deg north.

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

red: on sky vertical
green: looking 30deg north.
The tilted y factor is a little worse

It sees more atmosphere and there may have been a few more clouds.

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
green: PolY looking 30deg north
the same absorber hot load was used for both.
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
green: looking 30deg north

Page 6: compare the 25jan23 (nopreamp) Tflange with the 31jan23(preampon) Tflange.

Top: plot 4 to 14 GHz

smooth to 31 MHz
black: polY 25jan23 (looking vertical, no preamp)
red: polY 31jan23 (looking vertical, preamp on)
green: polY 31jan23 (looking 30deg north, preamp on.
The vertical preamp on is a few Kelvins better than the preamp off across the band.

Bottom: blowup 11 to 13 GHz

11.7 to 12.2 GHz (fss band) looking north 30deg is better than looking vertical
Outside 11.7 to 12.2 looking 30deg north is worse than looking vertical

So this is probably not related to the geostationary satellites.

Processing: x101/230125/wbtrcv_31jan23.pro

Summary:

The receiver temperature for the cooled 12meter wide band receiver was done

25jan23 at the antenna test building starting at 7am

2 to 14 GHz with the preamp off
looking vertical polY,polX sky and absorber
No clouds

31jan23 at the antenna test building starting around 7:45

4 to 14 GHz with preamp on.
looking vertical PolY, looking 30degNorth PolY , and absorber.
a few clouds.
the measured signals were at least 19db above the field fox noise floor.

A lot of the structure in the band is extremely repeatable 25jan to 31jan.
Trcv was around 20 to 25k till 10 GHz (this is below the receiver spec of 30K)
with the preamp on, Trcv was above 30K 11.3 to 12.5 and 12.6 to 12.9 GHz.
Looking north 30 deg Trcv decreased 11.7 to 12.2 GHz (the fss band).

This is probably mostly rfi.

In the rest of 11.3 to 13 GHz, looking north had a worse Trcv than looking vertical

This is probably not caused by the geostationary band.
most of this was above the 30K Trcv spec.

Looking at hamdi's yfactor measurements (.pdf) (page 30)

PolY Trcv using sky,absorber (red line) and absorber,ln2 (yellow line) both showed bumps at 11.3,11.9,12.2,12.7GHz that were all above 30K

the abs, ln2 measurements would point against this being any kind of rfi.

Some other Notes from the measurements.

we saw some condensation on the outside of the mylar cover.

after wiping it dry, it reformed in a few minutes.
The dome with dry air was not used during the experiment.

Monitoring the16K stage in the dewar:

on abs T16k was about 18K
on sky T16K was about 22K

putting a shade between the sun and the dewar started to lower in back to 18k

Treceiver for wideband cooled rcvr