On 22/04/2021 18:16, Scott wrote:
On Thu, 22 Apr 2021 16:34:02 +0100, Peter Able wrote:

On 21/04/2021 20:50, Scott wrote:
On Wed, 21 Apr 2021 19:06:42 +0100, Peter Able wrote:
[snip]

Just a couple of observations.

How many phones of the last 25 years need bell wires?

Probably very few but I think this one does. It stopped ringing then
I found the bell wire had come loose. Now it rings again. It is a
Cable & Wireless CWB 200H.

You don't get any significant radiation at "hum" frequencies from TVs -
unless they are similarly ancient Cathode-Ray-Tube ones?

It's in the kitchen so not a problem. I thought proximity to a ring
main was a problem due to inductive effects like a transformer.

I take it you hear this hum when you've made the call as well as when
you've answered them on the humming ext? Try the ext1 - ext2 handset
swap. Then swap back and try disconnecting the bell wire - everywhere
you can - and then make a call using the hummer - or call yourself from
a mobile and pick-up on the hummer handset, see if the hum is gone.

Yes, incoming and outgoing. I swapped the handsets and the C&W worked
okay at point ext 1. The other phone (BT Relate 250) worked okay at
point ext 2. Given these circumstances, the bell wire does not seem
to be the problem.

By the way, what actually is ext2? is it a mains (or anything else)
-connected thing e.g. a fax machine?

Not mains. The only distinctive feature is the headset. I have tried
again and if I grip the cable to the headset the buzzing gets much
worse. Even at point ext 1, gripping the headset cable creates
humming.

I could buy a replacement headset phone but they seem to be few and
far between and none of them seem to get good reviews.

Are we not getting VOIP by 2025 anyway?

So the problem appears to be the phone not the extension cabling. Now
you say the effect is related to your closeness to the headset cable.
That reinforces that conclusion. I can find nothing on Google about the
C&W phone - except a site for the 100H - which AVG reckons is infected.

I tried that too, and another site. One was infected and one took me
to a gambling site.

If the C&W can be operated without the headset - try it.

Done that. It's fine using the handset. To my mind the cable to the
headset is acting as an aerial. It gets much worse if you grip the
cable. Maybe I am acting as an aerial too.

Looking increasingly like a bin job; just what to bin - the headset or
the lot.

I had to replace the headset about a year ago. I think the previous
one did the same. Could this be a characteristic of all headsets? I
could replace the phone but none of the present generation seems to
review well. According to R4 this morning, landlines are a thing of
the past anyway!


Good. As you revealed more and more detail, I was ever more convinced
that this was nothing to do with the cabling running parallel and close
proximity to mains cabling. And I was pretty convinced from the start !

Once upon a time, a hum on a line was usually put down to earth leakage
on one of the pair. I.e. loss of balance. People could live with that
hum; but the internet is no so flexible. BT's response to this was the
"Iplate", a device sandwiched between the Master Socket and your house's
telecom winding. This was advertised as a line re-balancer - which it
was - but it also filtered the bell wire. If you have one it may be
worth trying it - either at the master or the Ext2 socket.

As for why, I assume that there is some electronics between what should
be a balanced system and your ears - maybe in that little bulge on the
headset wiring. I'd guess that some of that circuitry involves some
pretty high impedances - making it more susceptible to fields around it.
As you say, making it work like an aerial.

Just to give an example of this, this PC is connected by twin, screened
cable to my hifi. It works fine - until I pull the jack out of the PC,
when I get a loud hum. Why - when it is, after all, just a couple of
metres of shielded wires?

The amplifier has a relatively high input impedance, so only a little
induced hum current manifests as quite a high voltage (Ohms Law).
Generally PC LINE OUT sockets expect to see about a 32 ohm load. I could
totally fix this by connecting a 33 ohm resistor between each of the
pairs' screen and inner. Just too damn lazy, I guess !

As for landlines, we once had three, now just one. The number we give
third parties is my mobile number, so I guess that we are part of the
transition. It took a long time for me (professional engineer) to
convince my wife that the broadband didn't need its own landline - and
then to convince her that we should integrate landline and internet with
one ISP to radically reduce costs.

We've saved several thousands, since - plus there's the benefit having
the phone available (almost) wherever we are.

Gotta go, three texts already this morning warning me that I'm overdrawn !!!


PA