netgear prosafe gsm7238fs network switch emissions
The netgear prosafe
gsm7328fs is a network switch with:
- 24 SFP gigabit ports
- 4 i/o bays for 10Gigabit uplinks
- 4 copper 10/100/1000 links (shared with the last 4 SFP
- cpu running at 666 MHz.
One of these switches is in the new
engineering building. Another will be placed in the electronics
Luis checked this
device in the screen room on 17oct12
17oct12:netgear gsm7238fs switch
emissions in the screen room:
Luis measured the emissions of the netgear
prosafe gsm72398fs switch in the screen room on 17oct12.
and results (.pdf)
The setup was:
- Agilent E4445A spectrum analyzer:
- average 20 sweeps
- 8192 points/spectra
- 6db attenuation , preamp on
- 100 MHz span, 12.5 Khz/rbw. covering 0 to 3000 MHz in 30
- 904 Efield probe with a 15 foot coax cable.
- copper port (lower left) was plugged into ao net
- linksys 1GbE SX Mini-GPIC SFP module installed, but no
fiber connected to the module.
- Luis measured the emissions with the 904 Efield probe
close to the connected copper Ethernet port.
- He also measured the emissions at the rear of the device
where the power cable left the device.
The plots show the emissions from the
- The first page shows plots of 0-1000 MHz, 1000-2000MHz and
- The 2nd page shows some blowups around some of our
- 300-500 MHz (327,430)
- 1350-1550 MHz (lbw)
- 2000-3000 MHz (lbw)
at copper Ethernet port (lower left) (.ps) (.pdf)
- The strongest birdie is around 800 MHz at -78dbm
- Two combs were found (probably more exist)
- 125 MHz (red dotted line)
- It goes from dc to near 3ghz.
- the strongest birdie is at 1875 MHz ( -74 dbm)
- 330 MHz (green dotted line)
- the documentation say the cpu clock is 666 MHz. My
guess is that it is 660 MHz.14.2854 MHz . 330 MHz is
have the frequency.
- There are also some spikes separated by 82.5 MHz.
This is 330/4.
from the power supply (.ps) (.pdf)
- These emissions are similar but much weaker than the
port8 output. Nothing is seen about 800 MHz.
- The emissions from the switch are much stronger than the
- there are at least 2 combs
- 125 MHz
- 330 MHz (1/2 the cpu frequency)
- There may also be an 82.5 MHz comb in lband.
- The table below summarizes the strongest birdies
|330 comb strongest
birdie. The cpu clock is 660 MHz.
|330 comb srongest
birdie in 327 rcvr.
birdie in 430 rcvr
|125. comb. strongest
element in lbw
|These 3 birdies look like a 82.5 MHz comb.
|125 MHz comb.
strongest element in 1-2 ghz
|125 MHz comb
- Most of the birdies are about 1 MHz wide. I wonder if they
are chirping the cpu clock?
- The baseline has lots of variation. reflections from
- the 1402 MHz birdie could be a real problem for HI
- We also need to test this switch with a fiber optic cable
installed to check on the fiber transceiver.
- These switches need to be checked on the telescope where
ever they are installed. The best thing would be to shield
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