Band 1 405 line modulator using 1ZH37B

[Kalee20]

Good work Trevor!

It's DSB rather than vestigial sideband of course, but who cares?

Feeding audio in rather than video, you should be able to get really good quality sound - the 405-line AM sound channel on many TV's is capable of better results than the SW radio you showed on another YouTube video.

As you say in one of the videos, if you can get a pair of crystals with the right frequency separation, you can make twin modulators for sound AND vision.

I'm disappointed I'm not a TV fan - else I'd be having a go myself!

[Murphyv310]

Thanks Peter.
In fact Channel 1 from Ally Pally was DSB so as you say not a problem.
I think the simple circuit really proves the versatility of these valves. A simple introduction to valves for novices with the added advantage of much lower voltages for safety.

[Kalee20]

So you know what the challenge is now, Trevor... Add an inverter to the video signal between your Aurora and your transmitter, change the chokes and crystal, and get the test card on UHF

[Murphyv310]

Well that is a challenge Peter.
I think inter electrode capacitance would be the limiting factor TBH.

[Kalee20]

I know, and yes it probably would...

But as you've got it oscillating at 45MHz, between g1 and g2, if you put a tank circuit in the anode tuned to the 4th harmonic, you might find you get transmission on Band III VHF. And if so, extending the technique might just get you to Band IV, UHF!

It's purely thoughts - my own experience with crystal oscillators is limited, and I've not ventured beyond 11MHz.

[Murphyv310]

Hi.
The final assembly needs more screening. The matrix board isn't the best form of construction for this project. Either a dedicated PCB or copper clad laminate board and manhattan construction. The valve needs to be screened and grounded, at present moving the board around causes some bending and roll of the frame. This is due to some instability.
In fact the project was to finish the MW pantry tx on matrix board but now I'm a bit unsure. I'll transfer this over in a day or two onto manhattan type of construction unless someone could make me a one off PCB?