Band 3, System A modulator circuit info.

[murphyv310]

Hi.
I need to construct a band 3 Modulator for 405 lines system A, preferably for the old Channel 9. I have no info for a suitable circuit using readily available parts (with the exception of crystals if needed).
Would anyone have such information please.

PS its for both sound and vision

[terrykc]

There are a number of modulator circuits around but most use the MC1496 which will do BI but won't reach BIII frequencies.

However, here's a suggestion you might like to try: build one of these modulators but for IF. The frequency isn't critical, within reason, so you can use any available pair of crystals with the correct spacing but remember to make the sound 3.5 MHz above vision.

Then add an oscillator (crystal of VFO) and mixer to frequency-shift your modulator's output to the channel you want.

[ppppenguin]

If you have a spare Aurora to hand it can be used as a modulator by setting it to bypass mode. A rather expensive but convenient solution.

The Freescale modulator chips used in the Aurora will do the job but aren't the most convenient things to use. They are SM devices and need to be programmed via a digital interface. You could use a PIC for this.

[FERNSEH]

Hello Trevor,
The band three modulator designed by Mr. Jardine might be suitable for your needs. Originally designed for 819 line TV, I'm sure that it could be adapted for channel B9.

Here's the link to the Retro Forum:
www.retro-forum.com/viewtopic.php?f=15&t=8181

DFWB.

[murphyv310]

Yes the 819 modulator would most likely do, I don't see a circuit though. I would also need to build a sound section.

[terrykc]

There is a link there but it no longer works.

I found another reference to this modulator elsewhere on the web which says that Monsieur Jardine, the designer, has deleted the page containing the details!

However, this anonymous contributor has recreated the details and made them available on the web

An translation into English can be found here.

[murphyv310]

Terrykc.
Thanks very much for the link. It looks like what I am looking for with of course a change in the audio for the correct 3.5mhz spacing.

[murphyv310]

I have studied the modulator very carefully today and I will build one possibly two, one for 405 and another for 819, and possibly do another 819 restoration. I could of course switch the audio/video spacing for 405/819.
One thing though I have nothing to make a PCB and have never tried it, perhaps some kind soul could help out, with costs paid
I also think it would be possible to use 3rd overtone crystals in the circuit for greater stability.

[ppppenguin]

Don't worry about a PCB. Use some copper clad board as a ground plane. Drill and clear round holes for component mounting. Use pins if you like. Hardwire on the back of the board.

[murphyv310]

Good Idea Jeffrey, I have plenty of board, so will go down that road.