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 > Television Standards Converters, Modulators etc

Notices

Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

Closed Thread
 
Thread Tools
Old 16th Jan 2017, 6:15 pm   #1
pastyboy
Hexode
 
pastyboy's Avatar
 
Join Date: Nov 2015
Location: Cornwall, UK.
Posts: 270
Default Playing back 405 material on VHS

Hi all, I have recorded the testcard C on a sharp portable VHS m/c and it plays back well through the aurora's video input. I am wondering if the video inverts the video info to neg going mod when it records it. I have tried playing it back via a VHF modulator and can't resolve the display. I will look at a simple transistor inverter CCT and taking the output off the collector.

Seeming to suggest the video is recorded as neg going, playing the same 405 testcard into the modulator set for UHF on a thorn 1400 running in 625 the test card is present and not a neg image, although the aspect ratio is off but oddly I only needed to twiddle the line hold a bit to lock it..most odd

I am sure plenty have used VHS for this purpose, I need to run sets at work where I sort them out without having to buy another aurora or take the one from home.
__________________
I'm a callins, get me outta here ! (I am also an erie but it's my day off)
pastyboy is offline  
Old 16th Jan 2017, 6:48 pm   #2
cmjones01
Nonode
 
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
Default Re: playing back 405 material on VHS

The VCR doesn't invert the video signal, but you will need a System A compatible VHF modulator that supports positive video modulation in order for your 405-line TV to receive it properly. Almost all VHF modulators available off-the-shelf use negative modulation, because that's what most of the world's analogue TV systems use.

Inverting the signal at baseband before feeding it to the modulator might work, depending on how fussy the modulator is.

Chris
__________________
What's going on in the workshop? http://martin-jones.com/
cmjones01 is offline  
Old 16th Jan 2017, 9:27 pm   #3
colourking
Pentode
 
Join Date: Nov 2007
Location: Cork, Ireland
Posts: 134
Default Re: playing back 405 material on VHS

A VHF modulator for use in France (If you could easily get one) would work OK as they used positive modulation for their 625 system.

Sound would not work though, but if its an older modulator I'd expect it would not be too difficult to get sound working by changing the sound carrier frequency (it being AM also) to match the 405 system
colourking is offline  
Old 17th Jan 2017, 4:54 pm   #4
pastyboy
Hexode
 
pastyboy's Avatar
 
Join Date: Nov 2015
Location: Cornwall, UK.
Posts: 270
Default Re: Playing back 405 material on VHS

hmm, I didn't think the VCR would invert the video, I used to have a nordmende multiband set that I used for TV DX and made a video inverter for that which worked well.

I have a VHF / UHF modulator that has no model no on it, it has buttons like the dragonsat to change channel and runs in the sequence of C1 and then goes to S followed by the channel number - I must be missing the obvious, the channel allocations on VHF don't seem to tally with bands 1 and 3 though.

Thanks guys for the input !
__________________
I'm a callins, get me outta here ! (I am also an erie but it's my day off)
pastyboy is offline  
Old 17th Jan 2017, 9:58 pm   #5
kan_turk
Hexode
 
kan_turk's Avatar
 
Join Date: Mar 2014
Location: Dublin, Ireland
Posts: 396
Default Re: Playing back 405 material on VHS

Hi
If the modulator was intended for the western european market it will conform to the normal signal parameters appropriate to that region ie VHF System 'B' - Ch 2 - 4 (Band 1), Ch 5 - 12 (Band 3) and UHF System 'G' Ch 21 - 69 all with negative vision modulation

Hope this helps
Rgds to all
John
kan_turk is offline  
Old 18th Jan 2017, 12:23 am   #6
dragonser
Heptode
 
dragonser's Avatar
 
Join Date: Aug 2009
Location: Carshalton, Surrey, UK.
Posts: 734
Default Re: Playing back 405 material on VHS

Hi,
sorry if this is off topic. on some of the modulators available ( dragonsat ? ) you can change the sound vision spacing. But not to the am sound needed for 405 lines or positive modulation for the video.
but what I don't know is if you select the different sound vision spacing does it also change the VHF and UHF channels to be correct as well ?
regards Peter B
dragonser is offline  
Old 18th Jan 2017, 4:27 am   #7
kan_turk
Hexode
 
kan_turk's Avatar
 
Join Date: Mar 2014
Location: Dublin, Ireland
Posts: 396
Default Re: Playing back 405 material on VHS

The channel vision frequencies will remain constant irrespective of vision - sound spacing selected - this is correct
kan_turk is offline  
Old 19th Jan 2017, 11:38 am   #8
Focus Diode
Octode
 
Focus Diode's Avatar
 
Join Date: Jan 2006
Location: Borough of Gateshead, UK.
Posts: 1,420
Default Re: Playing back 405 material on VHS

The old dodge was to run the timebase on 405 and keep the IFs on 625, an easy matter on sets with separate IF and timebase panels and switching. It'll have to run 405 at UHF of course!
Focus Diode is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 6:53 pm.


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.