Sinclair RF signal

[bwinkel67]

So this is a somewhat curious question. Part of my retro hobby is exploring different facets of 80's gear and I focus much of it on Sinclair stuff since that is what I grew up with (oddly in the US so I was only ever part of a tiny community, though that made it fun). I also explore these things for my YouTube channel to share with others.

So I recently bought this (only $23):

eBay link here:

https://www.ebay.com/itm/254051981718

Which is an odd TV USB stick. I say odd because it doesn't do digital TV, only analog. Additionally odd, it seems to have been produced in the last few years, as it has Windows 11 drivers. I have no idea what market there is for these...I'm thinking maybe for cable boxes? But the cool thing is, this stick can grab an analog RF signal from both UK computers and US computers (it can actually grab any RF analog signal used around the world).

It's actually quite handy for anyone not technical that, say, wants to explore a Spectrum but lives in the US. They buy this stick, and plug their Spectrum into the antenna connector (either Belling-Lee or SubMinture A) and quickly can get a pretty nice picture.

In any case, I tried it on all my gadgets and got a beautiful RF signal on channel 36 for my Amiga 600. I realize, not needed since the Amiga has both composite and RGB, but still cool to be able to get that. Next time I get a Spectrum and need to debug it to see if it works, I can just use that stick before opening it up to do the composite mod...so a handy tool.

I also tried it for my US-based ones (1 QL and 2 TS1000). The odd thing was that the US version had a crappy signal. They have a very good signal on US TV's, but when using the stick, each one had a repeating flicker that pulsed. I tried to add shielding to the USB stick and it didn't help. I thought maybe it was my WiFi, but that wasn't it either. Initially I thought the USB stick just could not handle an NTSC signal well, but then I plugged in an old cable box that gave out an NTSC RF signal, and that was perfect.

So what would be causing the pulsing flicker? Focusing on the QL, has it to do with the power supply somehow? Or the internal crystal? Note that both the QL and the TS1000's are better shielded for the US models due to FCC regulations. They each have a metal coating of paint on the inner parts of their plastic. Curious what's causing the pulsing flicker. I have one more gadget from the late 80s/early 90's to try, a SEGA CDX, but I've misplaced its power supply so looking to make one or search for the original.

Any insight would be appreciated.

[Martin_Head]

Doe's the Amiga 600 use the same kind of modulator as the Sinclair's. I was wondering if it's some kind of beat between the oscillators in the modulator and the tuner in the USB stick.

I don't think the modulators used by Sinclair were particularly good quality. So maybe you need a filter of some kind in the aerial lead.

Or maybe the RF signal level out of the modulators is too high, and is overloading the USB stick, So you need an attenuator in the line.

[bwinkel67]

Doe's the Amiga 600 use the same kind of modulator as the Sinclair's. I was wondering if it's some kind of beat between the oscillators in the modulator and the tuner in the USB stick.

I don't believe it's made by Aztec, like the Sinclair one's are. The Amiga's seem bigger (almost twice the size).

I don't think the modulators used by Sinclair were particularly good quality. So maybe you need a filter of some kind in the aerial lead.

I can try that. I was also thinking of just broadcasting the signal (I've played with antenna boosters as transmitters) to see if that gets rid of it. The other option it to try a really long cable.

Or maybe the RF signal level out of the modulators is too high, and is overloading the USB stick, So you need an attenuator in the line.

That's probably true. The Amiga 600's signal seems to be weaker, needing a really good cable to avoid interference on a normal TV. I will see if I can fine an attenuator to see if it fixes it. Not that I need to, but just curious what's causing it.

Thanks for the feedback. I figured this question wouldn't get much interest since most people would scratch their heads to "why use RF?" but I've been on an old-school TV kick lately.

Here's my review of the stick. I'm still curious what the market for it is since it seems to be a new production, but it's nice to have something that can grab any RF signal standard for those cases when I get a computer from around the world so that I can test before opening it up.

https://www.youtube.com/watch?v=NXmaj0Y7nc8

[bwinkel67]

So I tried an attenuator (7db) with no effect. Wondering if it needs to be more like 30db, though those aren't normal. I then added 10 ferrite toroid cores on the cable to the TV stick with no effect. Finally, I tried a 25 foot coaxial cable with the computer two rooms down on a different power circuit, again with no effect.

I played with transmitting the signal by using an antenna booster on the TS1000 side with it hooked an antenna, and then added an antenna to the TV stick, with still no effect. I still need to try and change the power adapter to the TS1000 (using the original one that came with it). I also may try 9 volts via battery to see if that would make a difference.

I'll probably eventually try and use my Spectrum's RF signal to see if it is all Sinclair computers, since then it may just be the Aztec modulators somehow putting out noise that a very sensitive receiver picks up but most TV's are able to filter out.

[Martin_Head]

I had a quick look at your video, and I was wondering if it's something to do with the timings of the video signals.

The QL overscans the picture, and the ZX81 has the white border, Which may be confusing the USB stick if it's looking for a black level on the front or back porch area. But the ZX81 is white at that point. Although the idea dos'nt quite fit for the QL's start up page.

[jobdone]

https://www.elektormagazine.com/magazin ... 8499/45517

[Derek_Stewart]

Hi,

The Amiga A600 modulator is: Mitsumi UD3626 423T

The QL modulator is: Astec UM1233, seems to be the same as the Spectrum.

Here is a link to the description of the UM1233 in Hungarian, use Google Chrome to translate

http://www.ep128.hu/Sp_Hardware/SP_Modulator.htm