|
Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
|
Thread Tools |
17th Jun 2020, 11:29 am | #1 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
|
"Forward Scatter" (Thorn 850 Service Manual)
I have just been looking through some manuals. The Thorn 850 description
of the 13-Channel VHF Tuner Unit says ; "The Aerial Filter incorporated provides high rejection (approximately 50dB overall) at the TV sound and vision intermediate frequencies to prevent interference from 'Forward Scatter' transmitters operating on 30-40 Mc/s." What would cause this interference. I am aware that scatter was used for communications e.g. to oil rigs, but that was at a much higher frequency. Did anyone experience this problem back in the day ? |
17th Jun 2020, 5:08 pm | #2 |
Heptode
Join Date: Jun 2007
Location: Durham, County Durham, UK.
Posts: 640
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
I have a vague recollection of the term scatter interference on the North East coast which the source was allegedly RAF Boulmer. An in-line filter in the aerial lead fitted by the field techs apparently solved the problem, l’m not aware of what the on screen effect was.
John. |
17th Jun 2020, 5:42 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,998
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
The original "Chain Home" RADAR operated between 20 and 40MHz; I wonder if there was still a legacy CH transmitter (not yet replaced under the ROTOR plan) operating at the time that service-bulletin was issued?
|
17th Jun 2020, 7:20 pm | #4 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
The 850 manual is 1963-64, and there is no mention of this in the manual for the next
Thorn 900 chassis, which is 1964-5. It was only 20 years after the war. |
17th Jun 2020, 9:28 pm | #5 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,715
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
I remember the reference to "Forward Scatter" in the 850 manual. I had, perhaps erroneously, assumed it was experimental ionospheric sounding activity, perhaps inspired by the IGY, a few years earlier.
I wonder what the last manual to reference "Shortwave Diathermy" as a potential problem?
__________________
-- Graham. G3ZVT |
18th Jun 2020, 6:02 am | #6 |
Hexode
Join Date: Jan 2007
Location: Faro, Portugal
Posts: 269
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
There were a lot of E. European and Soviet Union
signals in the 30 to 40 MHz band in the late 1950s and early 60's. Due to the sunspot maximum in late 1957 they could put a very high signal strength into the UK in the afternoon period. As the sunspot number declined Going into the 60's it was less of a problem. I remember next time round(peak is roughly every 11 years) in the late 60's hearing Russian voices counting numbers interfering with a fringy Crystal Palace Ch1 signal. Anything in that band ended up being referred to as Forward Scatter. There was even mention of a "radar" in Iceland giving trouble. Tried a quick Google search, couldn't find very much mentioned about the specific problem. |
18th Jun 2020, 8:41 am | #7 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
You have triggered a memory. Around that time I also heard Russian voices on our
Thorn 900 TV, it had a push button tuner so could tune all of Band I. I had thought this emanated from one of the boats known ostensibly as "Russian Trawlers" which were often around the Cornish coast then. |
18th Jun 2020, 8:52 am | #8 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
I was just reading the notes relating to the Pye PTV 14" portable of 1957.
'If R.F. interference is experienced from aircraft or marker beacons it can be attenuated by adjusting the core of L5. This filter circuit covers 33-40Mc/s.' It must have been a problem in certain areas. John. |
18th Jun 2020, 9:55 am | #9 |
Hexode
Join Date: Jan 2007
Location: Faro, Portugal
Posts: 269
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
The BBC were concerned enough in
1947 to do tests with an aircraft putting out "GH" pulses around 40 MHz. See the link below. https://www.bbc.co.uk/rd/publications/rdreport_1947_07 There's also another report, 1947_03 |
18th Jun 2020, 10:02 am | #10 | |
Hexode
Join Date: Jan 2007
Location: Faro, Portugal
Posts: 269
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
Quote:
refreshment must have been required to read out all those numbers for long periods. There were also multitone teletype signals at times making chirping noises. |
|
18th Jun 2020, 5:13 pm | #11 |
Pentode
Join Date: Sep 2018
Location: Devon, UK.
Posts: 152
|
Re: "Forward Scatter" (Thorn 850 Service Manual)
I read an old DX-TV reference; would have been in 'Practical Television' or its successor, to forward scatter propagation of signals from the Soviet space launch site.
I've also seen a reference to UK usage of forward scatter to enable communications with Malta.(!) Presumably a 'happy medium' between HF propagation vagaries and the cost of nascent satellite comms. |