On the 18th June Dave ZL3FJ wrote--

Subject: LF: Re: Broad band QRM-500khz

Is the Panasonic system capable of being operated from an external
battery supply? A lot of the modern ones can use a backup battery but
are not designed to operate from an external DC source. But if it CAN
operate from an external DC supply then you could try that-your DC
supply may be a lot cleaner than the mains operated one in the system
itself.
But it may not  be the power supply. Switching garbage (internal
processors etc) could be getting out via the copper extension and
trunk cabling.

This is more of a challenge.  Does the Panasonic system have external
trunks or is it purely an internal system? If you can easily
disconnect all the internal extensions and reconnect one by one,
(listening for noise increase) you may get a better idea of the
coupling mechanism. You need to try disconnecting the trunks as well
if it has any.

The printer supply should probably be replaced with a quiet one-wont
be difficult unless it is providing multiple output voltages.
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Many thanks for your comments Dave.
We have not yet had an opportunity to open up the equipment.
It does not appear to operate with an internal battery because it becomes
inoperative when the mains are removed.
It does have an external trunk. It provides up to 6 incoming lines and up to
20 internal extensions ie.PABX
Will do what you suggest and report back.
Thanks again

Best regards

Mike  GW4HXO.