Tanioka with help from Fujii-san and Hirata-san

As we mentioned (5404, 5407), some cable problems cause BS Geophone noise.
In short, we have not found noise sources yet.

We measured the spectra with shorter Dsub cables which connect between the flange and BS rack in order to investigate the effect of long cable.
As a result, the noise level did not improved enough.
(It seemes very slightly better than longer cable one.)

Next, we we tried to find out the adapter cable effect.
We used SR3 Geophones.
We attached adapter cable which is used for BS Geophone now to one of the Geophone for SR3 on the optical bench (Geophone H3).
However, the noise levels were same - did not get worse.
So the noise is not derived from the adapter cable.

After that, we connected Dsub cable from BS Geophone to SR3 Geophone distributor to know whethe the circuits were healty or not.
Since still noise level was high, BS rack circuits are O.K.

We need to open the BS chamber and investigate Geophone pods and cables.

By the way, Yokozawa-san pointed out cables around BS area are in undesirable situation.
We should modify them.