Pineapple standards converter.

[Geordie McBoyne]

The first attachment shows a recently repaired Bush TV22 connected to the modulator unit and my Pineapple field store converter along with a 625 line Test Card C generator which bought some twenty years ago from HS Publications.
The converted 405 video output will be connected to a modulator which was built around the David Looser circuit which appeared in the August 1984 Television magazine.
The owner of the Bush TV22 also owns a Pineapple converter which was fitted into an instrument case along with a modulator which may be recognisable to some forum members.
See second attachment.
The integrated circuit which was a surface mounted device had failed and it wasn't possible identify it's type. What we do know about the circuit design is that the IC was intended for negative modulation systems with intercarrier sound. In fact the AM sound carrier was generated by a 3.5Mhz oscillator and mixed with the baseband 405 line video. Performance of this modulator was never satisfactory because intercarrier sound is not suitable for positive video modulation systems because of the interruptions to the carrier signal during the period when the synchronising pulses are in the video signal. Intercarrier sound is possible with negative modulation systems because the signal carrier does not go down to zero or near zero level.
Both Pineapple converters are working very well. As for my clients converter, this will be used along with the Bush TV22 and the modulator which accompanied the TV set.

Geordie McBoyne.

[ppppenguin]

I think intercarrier modulation is possible on +ve systems, so long as it's done right. Needs a good linear upconverter to take the baseband video plus 3.5MHz sound carrier up to RF. Intercarrier demodulation is not possible, for the reason you have stated.

I remember the Pineapple converter. It's a very potent RFI generator - there's no ground plane and lots of fast digits. Needs to be in a metal box with filtered connections.

[Geordie McBoyne]

ppppenguin wrote: "I remember the Pineapple converter. It's a very potent RFI generator - there's no ground plane and lots of fast digits. Needs to be in a metal box with filtered connections."
My Pineapple converter is installed in an Eddystone box. An aluminium plate is interposed between the SMPSU and the converter PCB.

Geordie McBoyne.

[ppppenguin]

All good except for the mains lead which will be radiating nicely. A filtered IEC inlet would be ideal.

[Refugee]

The SMPSU would be best in a screened box with filters on both input and output.

[bobhowe]

HI my 2P worth I would be more worried about RFI interference from cheap switch mode power supplies and LED & CFL light bulbs . Had a temperature controlled soldering iron from Maplin despite it been CE rated it would wipe out MW Radio reception kind regards Bob

[Murphyv310]

Hi.
I've had Bobs old Pineapple here and the RFI was horrendous, wiping out 80 and 40 meters. It's been housed in an alloy screened box and filtered IEC connector. The RFI also escapes from the video input lead and from the modulator. To be fair I didn't pursue any further attempts to reduce the RFI as it's now very rarely used, perhaps twice in the last three years.
So yes indeed they do need extensive filtering, let's hope you don't live next door to a radio amateur! You won't be popular.

[Geordie McBoyne]

Sync pulses generated from TTL can be a source of RFI. The frequency response during the sync period should be reduced to say, 10 X fH to soften the leading and trailing edges of the sync pulses.

Geordie McBoyne.

[ppppenguin]

Indeed they can and sync edges should always be correctly shaped. But that's not the main problem with the Pineapple. There's a lot of high speed logic on a PCB that lacks a ground plane. It's radiating from virtually every track on the board.

[Geordie McBoyne]

The first attachment shows the other Pineapple converter which will be used with the 1984 David Looser modulator.
As for the modulator previously fitted alongside the converter PCB. It might be possible the MC1374 IC could be employed as a replacement for the SMD device.

Geordie McBoyne.