405 lines from Raspberry Pi 5

[Mike Watterson]

So does anyone sell this SOIC 16 version? It has the AUX in!
The PLL obtains its reference from a low cost 4 MHz crystal oscillator.
The devices are available in a 16-pin SOIC, Pb-free package. These parts are
functionally equivalent to the MC44BS373/4 series, but are not direct drop-in re-
placements.
All devices now include the AUXIN found previously only on the 20-pin pack-
age option of the MC44BS373. This is a direct input for a modulated subcarrier
and is useful in BTSC or NICAM stereo sound or other subcarrier applications.
The MC44CC373CASEF has a secondary I2C address for applications using
two modulators on one I2C Bus.


Table 10. Chip Address by Orderable Part Number (R, W)
Orderable Part Number
MC44CC373CA, MC44CC374CA , MC44CC374T1A xCA xCB

MC44CC373CAS xCE xCF

Bit 8
I2C mapping: System L enable-selects AM sound and positive video modulation. (MC44CC373xxxx only)
System L Enable - Selects AM sound and positive
video modulation. (Applies to MC44CC373xxx
devices only. For the MC44CC374xxx devices this
bit is set to 0 and may not be modified).

[Mike Watterson]

The MC44CC373/MC44CC374 seems to replace earlier MC44BS373/MC44BS374 with a different process and some slight differences (such as AUX in on the 16 lead part).

The MC44CM373/4 seems to be later still and a replacement for the BS

  MC44CM373.pdf (Size: 165.06 KB / Downloads: 2)
(Shortform, not a a datasheet, from Mouser who don't stock it)
Also has AUX IN on the 16 pin SOIC package

The MC44CM373CASEF has a secondary I2C
address for applications using two modulators
on one I2C Bus.

[`FRANK.C]

AliExpress has some MC44CC373 listed for sale. They are described as regulators.
https://www.aliexpress.com/item/1005005665945030.html

I tried some years ago looking for the newer versions of the MC44BS373 but there was none to be found back then. It would seam that only the MC44BS374 version was made in quantity.

Frank

[Mike Watterson]

AliExpress has some MC44CC373 listed for sale. They are described as regulators.
https://www.aliexpress.com/item/1005005665945030.html

I tried some years ago looking for the newer versions of the MC44BS373 but there was none to be found back then. It would seam that only the MC44BS374 version was made in quantity.

Frank

Thanks! From NXP/Freescale datasheet page 1:
MC44CC373CAEFR2 defaults 591.25 MHz, 89 dbμV, Address 0xCA
PAL & NTSC Yes
SECAM L Yes
Aux in Yes

Replaces
MC44BS373CAD
MC44BS373CAEF
MC44BS373CAFC

Document Number: MC44CC373
Rev 3.2, 04/2009
(Uploaded earlier).

I may get one to play with

The 374 parts don't do the positive modulation.


EDIT:
Oh, that price is for 5 parts!

10000 Pieces available

Edit2:
Might be useful for ATV on 60 to 69 MHz band which is now allowed here (EI9FEB)

[OldTVEnthusiast]

While I’d happily tackle bit banging on an 8 bit Atmel I’d be cautious about attempting it on a single board computer and grappling with issues that the operating system might throw up in terms of timing. The address shifter is the easy way out!
The idea of a varicap based filter is good, and output filtering is something I should pay more attention to generally, I live too close to Gatwick to start radiating harmonics in the low hundreds!

[Mike Watterson]

The Minicircuit VCOs have 3 or 4 varicaps. One is the VCO and the others are part of a pi or similar LPF. They use the osc varicap voltage as the series Ls are appropriately chosen and a LPF isn't so critical in component values for such an application.
I've made copies on Stripboard with copper foil on the plain side and all the SMD parts on the track side. A track cut slightly less than half width , using a part to side of the holes can work at GHz tuned by the varicap as the oscillator. Below 800 MHz coils are simpler.

Three early prototypes without the low pass filter and a commercial filtered one at 850 MHz
   

Bottom left is mad "veroboard" stripline at GHz (I forget frequency)
Top two are VHF
Bottom right is the Minicircuits filtered VCO on vero/strip as a DIL adaptor.

Each homebrew VCO using I think 4 GHz or 6 GHz transistors.
They were used with NS synth chips, early prototype controlled by bit banging on PC parallel port. Later PIC18F series using JAL to program. Much superior to assembler, BASIC or C for the PIC family.

Pity the internal VCO varicap voltage isn't on the MC44CC374, unless the external loop filter has a version of it that could buffered/scaled for the two varicaps in a three series coils LPF.

[OldTVEnthusiast]

Some results from a prototype modulator HAT showing a YouTube video in 405 Line Sysrem A Channel 1 Video 45 MHz, Sound 41.5 MHz.

Still plenty to do, audio level is too low from DAC so a stage of amplification is required before the modulator. And then it’s about getting a media application written and a program to select standards and frequencies via I2C bus.

The noise on the video is actually from the Pi5 fan running.

https://youtube.com/shorts/HnQP40D3f9s? ... W67PoJjMXh

[`FRANK.C]

Hi Mike
Great results so far keep up the good work

Frank

[ppppenguin]

I visited Mike yesterday and saw his Pi and HAT in action. He's done a very good job. Without a scope and, ideally a spectrum analyser, it's difficult to assess exactly how well the modulator is working.The sound level is indeed low. The attached is the entire modulator from the first iteration of he Aurora SCRF. There were several later mods, including a built-in tone generator using a PWM output from the FPGA and the reduced drive to the xtal inputs. Note that audio is fed to the video input of U9, the audio modulator. R49 seems to set the DC bias on that pin. R55 sets audio gain.

To check what's happening you really need to look at the modulated audio on a scope with the vision carrier switched off.

The very first example of a System A modulator using these chips was by David Robinson.  Again I've attached the schematic. There is no gain in the baseband audio path. Frank's Hedghog is similar.

I don't know if Darryl knew of David's work when he designed the SCRF.

One thing that's clear is that the DC bias on the audio modulator is important.

[`FRANK.C]

Hi Jeffrey
The DC bias on the audio modulator sets the audio carrier level so it can be adjusted to the correct level with respect to the video carrier.
From memory the way it works is it overrides the clamp circuit in the chip.

The audio level determines the modulation depth.

Frank