A narrow tone has
been present at 1340 MHz for a long time. Dana mentioned that it was
probably leakage from the 1340 lo that the radar blanker (on the
platform) uses to mix 1330,1350 down to a 10 MHz IF before sending it
down to the control room.
- On 28sep10 we turn the radar blanker on, off while looking at the
birdie
- on 01oct10 after replacing the huffman box gasket, more data was
taken.
28sep10: Turning the radar blanker on,off
On 28sep10 we turned the radar blanker on,off while
taking data
The plots show
the
results of the 1340 birdie test (.ps) (
.pdf)
- az=267.5729, dome=8.4677
- Top: 500 second average with radar blanker on:
- 190 hz resolution, center frequency of band: 1340.02 MHz
- Birdie at 1339.983 MHz and is not resolved in a 190 hz channel.
- Bottom: total power in birdie channel vs time.
- 3 channels about 1339.9832 were averaged.
- a baseline was then removed and the results plotted.
- The green lines show were dana turned the radar blanker off and
then back on.
Summary:
- The 1339.983 MHz tone is coming from the lo of the radar blanker
on the platform.
- We went up and sniffed around the radar blanker equipment
on the platform with a spectrum analyzer and loop.
- The strongest birdie was coming from close to the top of the
huffman box.
- The conducting gasket has probably gone bad.
- The 1340 birdie in alfalfa data that turns on/off every 12
seconds with the radar is not the same problem.
- with alfa band centered at 1385 and using 100 MHz with the
wapps, the edge of the band is at 1335.
- the 1330 MHz radar raps 5 MHz around the edge coming out at
1340 MHz.
processing: x101/091028/birdie1340
01oct10: checking 1340 birdie after radar
blanker gasket changed.
On 01oct10 the gasket in the huffman box used the
radar blanker was replaced (it was corroded).
The setup was:
- interim correlator, 390 KHz bandwidth using 2048 channels giving
190 hz resolution.
- 480 secs on 1 second spectra
- cfr 1340 MHz (unlike 28sep10 when used 1340.02 to get the center
way from 1340.)
- az,za: 267.5729, dome=8.4677 (same as 28sep10).
The plots show
the birdie
after changing the conducting gasket (.ps) (
.pdf):
- there is now a birdie at 1339.985 and 1340.0 MHz.
- the polA birdie has gone from 2.3 Tsys to .48Tsys
- the polB birdie has gone from 1.4 Tsys to .4
Summary:
- Changing the gasket improved the shielding but the birdie is
still visible
- the 1340 birdie may or may not be coming from the radar blanker.
processing: x101/101001/chk1340.pro