It is currently Sun Aug 20, 2017 7:01 am

Curious microphony on incoming DEL

Phones- Digital, Analogue, PABX, Receivers, transmitters & military equipment.
 
Posts: 3028
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Curious microphony on incoming DEL

Post by Katie Bush » Sun Jun 08, 2014 12:32 am

Hi all,

I just wondered if anyone had any thoughts on this curious little fault.

For several weeks now, I have been plagued by a lot of crackle, pop and hiss on my telephone line.. Lastnight, I lost the line completely.. So, annoyed at this interference with my nightly "web-fix", I took to tapping around the sockets and junction boxes, only to find that the outside junction box on my incoming line was the cultprit.. It was too late and too dark to star messing with it, but a couple of sharp taps restored my line for the night.

Earlier this evening (Saturday) I climbed up to have a look inside the box, expecting to find a broken wire - but it was not so.. Instead, what I found was two loose terminal screws on the terminal strip.. Just poking them was enough to cause the line to be lost and regained, so without further ado, I tightened the screws which seemed to solve the problem, however, as I tapped and probed about looking for any more problems, I was aware of a definite microphony from the junction box.

What I was wondering is this.. If those screws have been loose for many years, then there is likely to be a layer of oxide inside the junction block, and on the screws.. Is it even remotely possible that that such an oxide might have a seniconducting, or resistive property about it that might cause the microphony?

In all other respects, the line is fine now, and noise free, as long as I don't go whacking the junction box with the handle of a screwdriver.. Obviously though, the connection is not perfect, and as such cannot be good for my broadband, even if it isn't real issue for voice traffic.


Marion

 
Posts: 4203
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Curious microphony on incoming DEL

Post by Refugee » Sun Jun 08, 2014 3:37 am

You have to scrub the wires or cut them back and strip again.
They had to come out and replace the master socket on ours in the end.

 
Posts: 55
Joined: Wed Oct 12, 2011 9:24 pm
Location: Nr Penrith, Cumbria

Re: Curious microphony on incoming DEL

Post by Russell W. Barnes » Mon Jun 09, 2014 12:26 pm

Your oxide layer may have given your line a rectifying property. One of the BT tests is for 'rectified line loop' caused by the corrosive effects of moisture on a d.c. line. It happens when wet wallpaper paste (for example :ccg ) gets into the LJU.

 
Posts: 4203
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Curious microphony on incoming DEL

Post by Refugee » Mon Jun 09, 2014 12:35 pm

The corrosion sometimes tries to AM demodulate ADSL signals causing bad data rates and drop outs.
We had it in a master socket.

 
Posts: 2516
Joined: Sun Jun 10, 2012 7:23 pm
Location: Basildon

Re: Curious microphony on incoming DEL

Post by crackle » Tue Jun 10, 2014 4:19 pm

Could it simply be microphony in the cable as you get in microphone cables.
Mike


Return to Telephones, Telegraphy, Amateur comms & Military equipment



Who is online

Users browsing this forum: No registered users and 1 guest