White Noise Or Hum on 7406 Cordless Phones

[hspranza]

Has anyone experienced White Noise (cable induction hum) on Norstar 7406 cordless sets? Here's the situation:
Compact ICS with RLS 6.1 4-CO's and 16 Digital ports equipped - 10 T7308 Digital sets - 6 7406 Cordless sets with 2 radio controllers working the cordless sets. All equipment is brand new.
THE PROBLEM:
When using any one of the 7406 cordless sets when talking on a CO trunk call there is a hum or background noise. It's on all four co trunks.
Both inbound and outbound calls.
If you call another cordless on the intercom it's CLEAR.
It's NOT on any CO's when calling on the regular Digital sets.
All 4 lines are clear on the Telco demark. Unless someone is using a 7406 on a co trunk call.

Our testing shows the noise on the lines is only present when any one of the cordless phones is off hook on a co trunk. The noise is longitudinal imbalance (measured at 7 volts ac) that is being placed on the line some how by using the cordless sets.

So the 64 dollar question is:
Does anyone know to get rid of it.

 

[senk1s]

does it happen on all 6 sets - tested independant of each other?
does it happen on any particular transmitter?

set the CO trunk gain to medium or near CO and check the results ...

we have a BUNCH of them working fine ..., but each radio environment is unique at every point in time

 

[telemarv]

All 4 lines are clear on the Telco demark. Unless someone is using a 7406 on a co trunk call."

Do you mean if a cordless is in use all CO lines now have the hum?

 

[paul144]

Well, I am a bit stumped. At first I was assuming that you were getting interference from an external source, but that would also show up on cordless to cordless calls.
Does the problem show up if you are intercomming cordless to cordless on different tramsmitter/reciever bases? All I can think of is that one of the bases is getting interference but not the other and you somehow missed this in your trouble-shooting, but as it seems that you have a good grasp on the situation, I doubt it.
Good luck with this!

 

[skippy440]

Are the dip witch settings on the two cordless bases set to different ( one high, one low frequency) settings?
If the are set for the same setting, it might be causing the
problem.

 

[rhowlett]

I have heard that one of the vintages of T7406 was replaced with whatever the latest is due to signal problems. I don't know where you can find that ITAS notice, but I know I read it a few months ago.

 

[Arr]

I've had this problem. Relocating the base station fixed it on both occasions.

PhM