Intro
The current 12meter receiver is a dual
mode : s and x band . There are two paths for the two
bands before being combined in the diplexor and sent
down to the control room via the fiber.
schematic of the system (.pdf).
When taking some data we would see
glitches in the xband output. On 19apr21 we found that the
sband portion of the system was overloading the system causing
lots of glitches in the system xband system (probably from the
fiber optic xmter saturating).
Looking at the post amp chassis input
On 20apr21 we went to the 12meter to look
at the power levels in the system. What we did:
- We hooked up the field fox spectrum analyzer to the polB
cables that came down from the hub.
- These cables were the input to the postamp chassis
(before any filtering)
- For sband there is just the lna before this.
- For xband there was the lna and a second amp up in the
hub.
- Looking at the schematic our connection point was at
dana's xb/sb reference plane.
- In our attempt to cover large spans, we ended up with
sum optimal sampling of the spectra. eg:
- page 2:
- 2 GHz span, 100Khz rbw, and only 601 points
- 10GHz span, 5Mhz rbw , 601 points.
- page 3: 10 GHz span, 1Mhz rbw, 601 points.
- When computing the power by adding the power in each
channel i corrected the total power by
span/(rbw*npnts):w
Plots of the spectrum input to the post amp
chassis (.ps) (.pdf)
- Black is the average of 10 sweeps, red is peakHold
- Page 1: sband input to post amp chassis.
- Top : 1.4 to 3.4 GHz
- Bottom: blowup 1.75 to 2.75 (this is the same measured
signal as the top plot)
- Page 2: xband input to post amp chassis.
- Top: 7.6 to 9.6 GHz . rbw (100KHz)
- bottom: 100 to 14.1 GHz rbw 5MHz
- I don't understand the large signal 3 to 7 GHz.
I doubt it is coming in through the horn since there is
waveguide to act as a cutoff between the horn and
the xband probes.
- Page3: 1 to 10 GHz antenna placed next to the
12meter and pointing south.
- Took this to get an idea of the power levels and if we
could add a preamp when doing the full scan.