UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 22nd Jan 2019, 11:48 am   #1
John10b
Nonode
 
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,869
Default Modulation Distortion

A question has been asked, on a different workshop forum, about a possible change to the depth of modulation on medium wave transmissions by the BBC and /or others which is causing distortion on some vintage Radios. Can someone comment on this please?
Cheers
John
John10b is offline  
Old 22nd Jan 2019, 12:28 pm   #2
Andrew2
Nonode
 
Andrew2's Avatar
 
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,033
Default Re: Modulation Distortion

I believe that up to the mid-60's, BBC transmitters were modulated up to something like 60% or less to minimise distortion in the simple diode detectors of the time. When the offshore pirates came along with their 'loud' modulation and compression, the BBC fought back and turned up their own mod.
I haven't checked this for veracity, it's just a story that does the rounds.
The other thing is the 'power saving' technique now in use. This lowers the carrier level on positive modulation peaks to save the amount of electricity used by the TX. I wonder if some types of detector or AGC may be upset by this?
No doubt someone with greater knowledge will be along soon!
__________________
Andy G1HBE.
Andrew2 is offline  
Old 24th Jan 2019, 11:15 pm   #3
John10b
Nonode
 
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,869
Default Re: Modulation Distortion

Thank you Andy. No comments so far.
Cheers
John
John10b is offline  
Old 24th Jan 2019, 11:37 pm   #4
mickm3for
Heptode
 
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
Default Re: Modulation Distortion

Hi modulation types do upset the agc i remember using controled carrier mod on an AM transmitter and geting severe distortion on a receiver close by because the agc could not keep track of varing carrier levels this resulted in the RX being overloaded. Mod was ok when signal wasn't so strong may be the same reason ?
mickm3for is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:53 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.