How to build RF-converters

[German Dalek]

Hello again,

For my personal world converter I wanna build some HQ converters, as far as
possible with crystals.

This is what I need:
Ch. 08, belgian standard/Brussels, AM sound, 5,5 MHz, pos. picture modulation
Ch. 08A, french standard/Lille, AM sound, pos. picture modulation
Ch. 07 & 08 CCIR/PAL
Ch. ~ 07 or 08 CCIR/Pal-Italy (different frequency to european CCIR channels)

Here is a schematic of a Paris 819 line converter with transistor-assy, no
crystals, but should fit for the both AM sound channels

http://819lignes.free.fr/Regarder_le...819lignes.html

Info comes from this web-site:
http://819lignes.free.fr/

Anybody with experience to lead me to a good result?

Best regards,

The German Dalek

[dragonser]

Hi,
an interesting question and link.
I have been wondering if anyone else here had thought about how to make a VHF modulator that doesn't use a hard to find integrated circuit.
my only concern [ I should point out that I'm not a RF engineer ] is that if you modulate the supply rail to the oscillator you may get a bit of Fm modulation as well as the required Am modulation.
I had been wondering about using a lower frequency crystal and a couple of multiplier stages, with only the last stage [ before the output ] having the amplitude modulation, might be one method of producing a video signal.
But would it be worth all the electronics, skill and time to build it ?
I wonder if any of the frequencies of easily obtainable crystals would multiply to the frequencies you require ?
if you required a modulator that was tunable then I did find the following ic mentioned.
http://electronicdesign.com/article/...applicati.aspx
But I appreciate they may not be appropriate for this application.
regards Peter
P.S. I hope I don't get exterminated by anyone here !

[German Dalek]

Hi Dragonser,

No, I want them in seperate boxes, have to deal with 9 volts DC.
I have crystals from a French sweep generator which was sold for Germany for CCIR/Pal use.
So a part of the crystals are ready to build a clean construction.
But how?
I have the schematic of my National VCR which works with VHF PAL channels 3 and 4.
But there is a part inside I don't know, could place the schematic tomorrow.
Anyway it could be a beginning.

Best regards,

German Dalek

[dragonser]

Hi,
Thanks for the additional info. There was an article in Elektor magazine many years ago for a vhf/uhf modulator here but of course this uses a lower frequency (27 mhz) crystal and then you tune to one of the harmonics produced 54? 81? I'm assuming they used a 27mhz crystal because this was one of the frequencies used for model control, (or at least I think it was).

Again this is only a start, but I hope that someone here with more RF experience will provide some input.

regards Peter

[German Dalek]

Hi Peter,

I tried it in an other forums, got the same link, but nothing more.

Overtones are a lousy solution, this set has no sound, no information about bandwidth according the official standard. My personal experience is that most people have only a "half-knowledge"
about electronics, are specialized, I include myself, learned everything, or better most from
reading books and old mags.

A friend of mine who made his "master" in television repair in the 80s said that he never learned how to use a sweep generator in practice.

This shows that a lot of knowledge of the past is going down the river, if the army of recappers don't start now to collect knowledge and to spread it for the future generations. It is the same with cabinet restoration.

Best regards,

The German Dalek.

[Sean Williams]

I think your best bet will be to look at the modulator designed by Darius, this will give you a good grounding in the design of the modulating (video and Audio) stages - the RF sections will be fairly simple Ham Radio type stuff - xtal osc, buffer, amp, and output stage.

Changing between AM and FM mod wont be that difficult - AM is simple, FM will need a varicap in series with the crystal - the main difference will be that for FM you will need a low frequency crystal to multiply up, in order to get decent deviation.

Just a few thoughts.....

Sean

[German Dalek]

Hi Sean,

Thanks for your thoughts.

I can build a audio-tube-amp from parts laying around, when studying amp schematics I can see how to make something better or worse. But my knowledge and the knowledge of most over forum members here and in other forums is not good enough to construct a good buffer,
output stage regarding the standard rules.

So that might be the reason why no radio/TV forums and electronic forums ever
discuss a good construction.

O.K., there were people which said to me that it is simple, but I by myself can talk a lot,
if the day is long enough.

I need a schematic with description.

Best regards,

The German Dalek

[Sean Williams]

Part of the issue I see with the design of this system is that of bandwidth - Ham, or Amateur stuff is inherently narrowband - I have so little experience of broadband techniques that any design input from me will be worthless.

I think perhaps a question of the British Amateur Television Club might be handy - some 70cm (430Mhz) Amateur Television stuff will have covered this sort of area, the techniques will be scalable for the lower frequencies.

Sean

[jhalphen]

Hello German Dalek,

you wrote:
This is what I need:
Ch. 08, belgian standard/Brussels, AM sound, 5,5 MHz, pos. picture modulation
Ch. 08A, french standard/Lille, AM sound, pos. picture modulation
Ch. 07 & 08 CCIR/PAL
Ch. ~ 07 or 08 CCIR/Pal-Italy (different frequency to european CCIR channels)

a nice mix of scan rates, RF transmission standards and RF channels here!

Here is reliable data, Scans from a Rohde & Schwarz training book.

one lists the scan rates, channel width, type of modulation per system.

the other gives the frquency plan for all countries.

I have left out UHF. Sorry! for the low-res forum documents, but my originals 3500x2500 won't pass on the forum.

For 625 video signals, there are easy to find 30 Eu generic RF modulators such as the one in the photo which are sold under a variety of brands.They are PLL (quartz lock) controlled with a 7 segment LED display during set up. The manual lists that this one can be set up for CCIR (PAL) B/G, D/K, I, H, SECAM L, K, H, & NTSC M.

Be careful! all look alike, but there is a VHF/UHF version and a UHF only model.

The OEM is Prime Creation International (China) model MS2169EUP multistandard modulator.

Search the Net to find a seller.

For your 819 line TV(s) use Darryl H.'s Aurora SCRF series either the "real" French version with 625 to 819 line change and full 819 frequency plan.

Or you can convert your TV(s) first to 625 scan, not particularly easy and use a 625 modulator.

To be noted, Darryl's SCRF Series can all be run as straight to RF modulators for vintage TV standards without using the line scan conversion feature.

About the 819 site, i built the original Jardine 819 modulator. It works but needs very serious shielding as it puts out a powerhouse RF signal which adiates a lot.

I also captured from Jardine's site all the original data including PCBs so if you want all this drop me a line by PM.

To be complete, the French vintage magazine published a revised version of the Jardine design 2-3 years ago which has less spurious radiation and better stability. Here is the link to the Forum's TV subsection.

http://retro-forum.com/viewforum.php?f=15

Sign up (it's free) and ask a member for a Scan of the relevant article.

Best Regards

jhalphen
Paris/France

[ppppenguin]

The Motorola (now Freescale?) chips used by Darryl in the Aurora are very good little universal modulators. They are obsolete but supplies are still available. They are contolled via I2C and so will need a microcontroller to make them useful. A PIC would probably be suitable.

I can't remember the part number at present. This may be it: http://www.freescale.com/files/app_s.../MC44CC373.pdf

[German Dalek]

Thanks for Your inputs!

@ppppenguin
Sorry, but I don`t like these elements, I am not common to upload any kind of software to it and
I don`t like to solder this kind of material and however who likes to repair this in 20 years?
I have these kind of ICs in my Philips solder set, thats more than enough.
https://www.vintage-radio.net/forum/...ad.php?t=81171

@Jhalphen
I just bought 3 Auroras, 405 GB, 455 F/Paris and 819 F/Paris.
I have a lot of the other stuff, I shall introduce my "personal world converter" if the schematic
is ready to upload in this forum.
The chinese construction you offered is not handsome to me.
I have 29 french TV sets, 14 or 15 are 819 lines sets (one Grammont is a dual standard set for 819 F & 625 CCIR),
and 4 belgian one-channel 819 lines sets which can do nothing more then the french standard.
For most sets I have no schematics, alignment instructions anyway, so it will be a job for
a lifetime to make them running good on 625 lines.
I figured this out after dreaming about it over the years.

Best regards,

German Dalek

[John_BS]

if you modulate the supply rail to the oscillator you may get a bit of Fm modulation as well as the required Am modulation

Peter: You're absolutely right. Not too important for B&W, but a real issue for colour. It's normally termed "differential phase", and is traditionally measured by superimposing a colour sub-carrier on a luminance staircase.

John

[German Dalek]

Hello to everyone,

I have now somebody who likes to help me with the construction.
He wants to know from me if the modulator has to work with only one side-band or if it is
allowed with dual sideband.
He said that the use of dual sideband saves the use of an expensive SAW-filter (what is the price
of a SAW-filter?) and another step of frequency managing.
Please correct me if I`m wrong, but my oppinion is, that only 405 and 455 lines transmissions were
aired with dual sideband.

Best regards,

German Dalek

[ppppenguin]

Double sideband is OK. Later sets, designed for vestigial sideband, will simply ignore that remainder of the other sideband. The only time it will matter is if you are trying to feed 2 adjacent channels along the same cable. DSB signals will interfere with each other.