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Current Radio Rules Mean Sinclair ZX Spectrum Wouldn't Fly Today

timothy posted about 2 years ago | from the figuratively-even dept.

Hardware 64

First time accepted submitter wisewellies writes "Ben clearly has way too much spare time on his hands, but he decided to see just how well an antiquated ZX Spectrum would hold up to modern EMC requirements. His blog is a good read if you're looking for something to do while pretending to work! From the blog: 'This year is the 30th anniversary of one of my favourite inventions of all time, the Sinclair ZX Spectrum. A few weeks ago, I finally bought one: a non-working one on eBay that I nursed back to health. Fortunately there was very little wrong with it. Unfortunately it's a 16K model, and a fairly early one at that, which won't run much software in its native state. This probably accounts for its unusually pristine condition. We took half an hour in the chamber to perform an approximate series of EN55022 measurements, to check its radiated emissions against today's standard. The question is, what have we learned as an industry since 1982?'"

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Hey Hey 16K (2, Funny)

Anonymous Coward | about 2 years ago | (#42274017)

Sorry, I couldn't help myself .....

Hey Hey 16k []

Obvious Solution (2)

lobiusmoop (305328) | about 2 years ago | (#42274045)

upgrade the motherboard. []

Re:Obvious Solution (1)

Anonymous Coward | about 2 years ago | (#42276931)

What a retarded article. So, some one wastes their time removing the innards off a dead ZX spectrum, cram it with modern day hardware running an emulator, and now somehow that's supposed to be a ZX spectrum.

Retards. This isn't even theseus' ship.

Re:Obvious Solution (0)

Anonymous Coward | about 2 years ago | (#42279043)

What If I replace components one at a time. At what point does it cease to be a ZX Spectrum?

Re:Obvious Solution (1)

Dot.Com.CEO (624226) | about 2 years ago | (#42279211)

I guess at the point when you remove the whole god damn motherboard like the guy in the article did.

Re:Obvious Solution (1)

Spacejock (727523) | about 2 years ago | (#42284277)

Later gen 16k models could have the memory upgraded by using the ram chips off a PC XT motherboard. I did this to one of the 16k speccys in my collection, while leaving another in original condition. Of course, these days it's probably harder to find an XT motherboard than a 48k speccy ...

Watching famicom on TV (0)

Anonymous Coward | about 2 years ago | (#42274131)

I remember if neighbor within ~100m distance played with famicom we could watch on TV on certain channels and how my grandpa got pissed when he couldnt watch TV...

EMC Rules? (0)

Anonymous Coward | about 2 years ago | (#42274163)

EMI, Electro-Magnetic Interference

Re:EMC Rules? (2)

bws111 (1216812) | about 2 years ago | (#42274491)

EMC - Electro-Magnetic Compatibility

Abject Failure? (5, Insightful)

mschiller (764721) | about 2 years ago | (#42274203)

"It’s not just a failure; it’s an abject one" Really? Now I admit the situation could be a ALOT worse with the accessories and cables, and until you've ran the test you don't know. But it's only about 6dB above the line, I've seen a lot worse problems [try 20dB!]. There is a good chance this would be a relatively easy fix when you start looking at the problem.

A ferrite bead on the power supply cable would probably fix the "bad power" supply if indeed that's what it is. And some judicious copper taping would likely fix the other problems. Worse case you do a board spin and add ferrite beads to the I/O and possibly move suspect traces into internal layers. Worse WORSE case you change the clocking to use spread spectrum which would likely not require any changes except in the clocking circuits. None of those would prevent a "modern" version of the product from going to market.. And a good engineer could probably implement them in less than 6 weeks in a production environment...

Plus it doesn't even manner, if you were going to bring a sinclair back to market it would draw about 20mA, run on USB power and be completely implemented on a single chip.... Because it has roughly the same processing power as a PIC uC.

Re:Abject Failure? (1)

NixieBunny (859050) | about 2 years ago | (#42275087)

Internal layers? What, do you think they used a 4-layer board on a $59 computer in 1980?

Re:Abject Failure? (1)

mschiller (764721) | about 2 years ago | (#42275259)

4Layer? It was probably 2. But a worse case scenario would've been to make it more. Remember we're talking today.. Today an 8-layer board is nearly as cheap as a 2-layer board and if it meant having a legal product it would've been done.

let's be honest here... (3, Funny)

Thud457 (234763) | about 2 years ago | (#42274205)

The ZX didn't fly back in the day either. /rimshot

Re:let's be honest here... (4, Funny)

The Grim Reefer (1162755) | about 2 years ago | (#42274543)

The ZX didn't fly back in the day either. /rimshot

That depends on how hard you threw it.

Re:let's be honest here... (1)

pjt33 (739471) | about 2 years ago | (#42277957)

They went to the Moon with less!

zx81? (1)

ckblackm (1137057) | about 2 years ago | (#42274539)

Yes.. but what about the zx81/TS1000?

Re:zx81? (0)

Anonymous Coward | about 2 years ago | (#42276061)

I never investigated the ZX81's flight properties (however, wedge shapes can have decent aerodynamics). I conducted unpublished research in the mid 1990s proving a ZX81 could work acceptably as a doorstop. If I can locate the box with my collection of ZX81/TS1000/TS1500 (I quit the insanity when the successors came out), I could re-test the effectiveness of a ZX81 as a doorstop with 21st century door technology. Hmmm - I smell a grant application.

Re:zx81? (0)

Anonymous Coward | about 2 years ago | (#42306411)

Hmmm - I smell a grant application.

And I smell a lawsuit.

You see, I got a patent on "Using a piece of equipment for a purpose other than the one it was designed for".

And if you're planning on simulating the experiment first, you should know I also got a patent on "Using a piece of equipment for a purpose other than the one it was designed for... On a computer".

RE: ZX Spectrum radiation (5, Interesting)

Siddly (675342) | about 2 years ago | (#42274565)

I have a ZX Spectrum in the loft I often see when I go up there. As far as RFI is concerned our regulations back then were non-existent. I once saw a BBC Micro for the German market, it was encased in metal and built like a tank. The ones on the UK market were plastic and caused havoc with my Amateur Radio gear until I quietened it a fair bit by coating the inside of the case with graphite spray and grounding it. TV's were another problem as they were susceptible to interference from Amateur radio transmissions operating within the legal limits and specifications and we had inspectors who audited our stations for compliance. It was all down to the manufacturers saving may be a penny or 2 by using a cheaper front-end transistor for TV's sold into the UK.

Re: ZX Spectrum radiation (1)

chthon (580889) | about 2 years ago | (#42275067)

Yeah, where are the days if a motorcycle passed ones house, that the TV reception was jammed?

Re: ZX Spectrum radiation (1)

Hatta (162192) | about 2 years ago | (#42276813)

That's today. I live within walking distance of downtown in the largest city of my state. It's very frequent that a vehicle will pass by and cause my DTV to drop out for a couple seconds. That's with a UHF antenna and amplifier. Not every vehicle, not every day, but it's often enough that I watch low def analog cable in preference to OTA free HD TV when a program is available on both.

Re: ZX Spectrum radiation (1)

Gr8Apes (679165) | about 2 years ago | (#42285941)

You need a better antenna, probably a much better antenna, and locate it higher. If you cannot do that, suboptimal antenna placement alone can cause all sorts of issues. I have an almost 2m rig in the attic, at a height of over 10m, and I'm on a hill. I get signal strengths no lower than 90% from about 25 channels, even 3 from a city 75 km away at a 40 degree angle from my primaries. Oh, and there's an entire suite of skyscrapers in between me and my primaries, which are roughly 40 km away. I tried the amplified rabbit ears, and other indoor antennas, and had extremely poor reception on the handful of channels I could receive.

Re: ZX Spectrum radiation (0)

Anonymous Coward | about 2 years ago | (#42276323)

Don't store it in the loft. The large fluctuations in temperature aren't good for it and summer weather has probably already dried out its electrolytic capacitors.
The good news is that it can probably be brought back to life fairly easily. However, don't just plug it in without making some basic checks first or there's a good chance the lower RAM ICs will die.
Seek advice on the forums at if you want more information.

Re: ZX Spectrum radiation (1)

NixieBunny (859050) | about 2 years ago | (#42277419)

The TVs were made that way on purpose, to allow the TV police to easily sniff the sets' internal oscillators to track them down for taxes, right? (I'm American.)

Relaxed rules (0)

Anonymous Coward | about 2 years ago | (#42274599)

The original Atari 800s were built to the old emissions rules, and had some horribly slow serial I/O as a result.

FCC class C was specifically relaxed to allow PCs to get to market in the early 1980s.

Happy Birthday Sinclair (5, Interesting)

mt1955 (698912) | about 2 years ago | (#42274883)

I wrote my first real program on a Sinclair. It was for TV troubleshooting and it took you down to the section. Storage was a cassette tape and the output was composite video for black & white TV.

Then I bought the memory expansion, took it to work and made a program for it to do cost estimate calculations. It was the 2nd computer anywhere in the company. I got promoted from cost estimating to Systems Administrator all in one go. I stayed with that company almost 30 years, then I left to start my own software company.

A few years ago I was telling that story to a client. He pulled a mint condition Sinclair -- still in the original box -- out of his desk and gave it to me. He said it bought it to learn computers and never used it. It was like giving me the keys to my first car.

Re:Happy Birthday Sinclair (1)

Anonymous Coward | about 2 years ago | (#42275281)

Likewise. I was in business school 30 years ago, and a professor gave us an exercise to optimize return on a marketing budget, subject to a set of equations and constraints. "Go to the computer center on campus - it's in the DECsystem 10 there. Log in and see what values of the variables - print versus radio versus TV versus billboard - gets you the best sales revenue." Trial and error to see where to spend my marketing budget? When I have a Timex Sinclair 1000 at home, including the memory expansion option? No way! Print out the code from the DEC machine, type it into the Sinclair, put a few DO loops around it, and let it run overnight, brute force trying every combination of all the variables, and keeping track of which combination gave the best results. Woke up the next morning to discover that all my marketing budget should be put into one thing (I have long forgotten what).

I still have that computer, in its box, in the basement. It was very much the starting point of my career in technology. Great product.

Re:Happy Birthday Sinclair (0)

Anonymous Coward | about 2 years ago | (#42283207)

A simple optimization problem like that? The maximum revenue is going to be at one of the vertices of the convex hull of the expense space. With only three variables to optimize, you've only got seven vertices to check (you can assume the "spend nothing" vertex isn't optimum), which you should be able to do by hand in 15 minutes or so.

16k was good enough (2)

safetyinnumbers (1770570) | about 2 years ago | (#42274885)

Unfortunately it's a 16K model, and a fairly early one at that, which won't run much software

Hey! I was still supporting the 16k version with a game released in NINETY-two.

We know this already (0)

Anonymous Coward | about 2 years ago | (#42274935)

Anyone who held a radio near a Spectrum was well aware of this.

I seem to remember some people even used it as a way to play better music than the internal speaker could produce by finding the notes that different code loops would produce?

You could hear it (1)

hackertourist (2202674) | about 2 years ago | (#42274973)

The Spectrum made audible noises when running. Not via the speaker AFAICT, actual noise made by the chips themselves. I've never head that with other devices.

Re:You could hear it (1)

Colourspace (563895) | about 2 years ago | (#42275369)

Until I read this I'd completely forgotten about that little squeal that was always in the background when the Speccy was on - I suspect it was the quartz oscillator.

Re:You could hear it (0)

Anonymous Coward | about 2 years ago | (#42276681)

It's due to the windings of the DC-DC converter's inductor vibrating.

Re:You could hear it (1)

Colourspace (563895) | about 2 years ago | (#42289275)

Interesting - I've never heard of that before but sounds plausible. Still doesn't answer why me and OP have never heard the sound elsewhere, and DC-DC converters are used all over the place. Maybe it was just that specific part number.

Emulation (1)

SternisheFan (2529412) | about 2 years ago | (#42274977)

Nowadays, there are emulators and roms for just about every piece of older hardware, including the "Speccy". Here's a quickie google search link: []

Re:Emulation (1)

itsdapead (734413) | about 2 years ago | (#42275557)

Nowadays, there are emulators and roms for just about every piece of older hardware, including the "Speccy".

There must be plenty of dead Speccys around, and a Raspberry Pi would fit inside the box nicely. Hooking up the Speccy keyboard to the Pi's I/O pins and knocking up a driver can't be rocket science, then you could...

...install a BBC Micro emulator on it and have a decent computer (ducks and runs for cover...!)

Aaah, we had proper platform loyalty wars back in the good old days - so much better than all this cissy modern Fanbois vs. Fandroids rubbish. Tim Cook and Eric Schmitt might talk up a storm but you wouldn't see them in a pub sorting it out like men [] (See about half way down the page...) Anyway Tim Cook would probably have ended up in the wrong pub.

Re:Emulation (0)

Anonymous Coward | about 2 years ago | (#42276485)

If you have a dead Spectrum and want a working one, why not repair it or use one of several repair services available? There isn't much that can go wrong with a Spectrum that can't be repaired, so long as it hasn't been smashed to pieces.

16KB is way too large! (0)

Anonymous Coward | about 2 years ago | (#42275229)

you guys really waste memory. 16KB? way too much ... real programmers used the ZX80 with its whopping 1KB of ram. If you didn't mind really short messages you fit versions of games from the People's Computer Company into it. For a measely $199 in the later 1970's

Re:16KB is way too large! (1)

GumphMaster (772693) | about 2 years ago | (#42279057)

1k less the memory used to hold the characters currently on the display. But you try and tell the people of today [] ...

The TRS-80 had this problem too (5, Interesting)

idontgno (624372) | about 2 years ago | (#42275277)

The original TRS-80 was a wideband RF jammer. Cheap PCB design, plastic (unshielded) case, lots of ribbon cable external interconnects operating at megahertz frequencies.

One of the better ways to see whether the machine was frozen or just processing a long-running (but productive) internal loop was turn on an AM radio in the same room. Within about 3 feet, the RF noise would override all but the strongest stations and allow you to monitor the CPU's execution by the hums and burbles of the RF noise.

It's why the original TRS-80 became the Model I, rapidly superseded by the all-in-one Model III (with lots of internal shielding). []

Re:The TRS-80 had this problem too (1)

CohibaVancouver (864662) | about 2 years ago | (#42275543)

The original TRS-80 was a wideband RF jammer

It sure was - I remember our Model I used to sit in a room upstairs in our house, directly under our TV antenna. You could tell whether my brother was playing Sea Dragon or Scarfman based on the interference on the TV.

Re:The TRS-80 had this problem too (1)

Animats (122034) | about 2 years ago | (#42277485)

The original TRS-80 was a wideband RF jammer. Cheap PCB design, plastic (unshielded) case, lots of ribbon cable external interconnects operating at megahertz frequencies.

Not only was the TRS-80 an RF noise generator, it was sensitive to other RF sources in the vicinity. It was noted at the time that a TRS-80 and a Milton Bradley Big Trak [] would both crash if operated near each other.

Re:The TRS-80 had this problem too (2)

Megane (129182) | about 2 years ago | (#42278911)

I remember I had to turn mine off if the family wanted to watch TV channel 12. We lived far enough out in a rural area that we had to use a nice big antenna. which only made things worse.

The cassette port was often used for sound output from games, but the very act of doing the timing for sound made it not much worse to just put an AM radio next to it. You kids and your Bluetooth headsets, we had REAL wireless audio back in the day!

It's true, pressing the SHIFT key... (1)

iMadeGhostzilla (1851560) | about 2 years ago | (#42275323)

would interfere with sound from the radio station, I discovered as a kid. And just when I had thought the Spectrum couldn't be any cooler...!

Since 1982? (2)

falzer (224563) | about 2 years ago | (#42277011)

>The question is, what have we learned as an industry since 1982?

Quite a bit.
I have three books on electromagnetic compatibility. The most recent, Electromagnetic Compatibility Engineering (2009), is comprehensive and thick enough to stun an ox.

QBasic sleep (2)

Lord Lode (1290856) | about 2 years ago | (#42277197)

I once made a QBasic program named "NOISE.BAS" on a 386 computer.

When ran, it made the radio which was playing, produce noise for 7 seconds.

All the program contained was:


I'm not surprised (1)

DrXym (126579) | about 2 years ago | (#42277601)

My ZX Spectrum(s) (I had a few) used to buzz when they got hot and they had a fairly big large power brick which got hot too. Anyway, there is no reason a modern reproduction should suffer from the same issues - assuming Z80 processors were still in production they're likely conformant with modern standards, or produce an ASIC (like the C64 all-in-one a few years back), and if not I'm sure an ARM soc could emulate the ZX Spectrum with no trouble at all. Throw the board into a ZX Spectrum case complete with a rubbery keyboard, maybe enable flash some games in and it's more or less all people need.

I'm kind of surprised it hasn't been done yet. Same for the generation after like Amiga and Atari ST.

We're lucky the FCC clamped down (4, Interesting)

Animats (122034) | about 2 years ago | (#42277717)

We're really lucky that the FCC clamped down on RF emissions from electronics. Otherwise, we'd all be looking at big electromagnetic compatibility charts before buying anything, trying to find combinations known to work well together. Offices would need RF spectrum analyzers to figure out who brought in something that was messing up other gear. I mentioned in another post that you couldn't operate a Milton Bradley Big Trak and an TRS-80 near each other. The other side of stopping RF emissions is that the shielding makes electronics much less sensitive to RF interference.

The development of really good RF noise management technology made modern cell phones possible. The concept of a handheld device with four radios (GSM, WiFi, GPS, and Bluetooth), all operating simultaneously within a few inches of each other, was totally beyond the RF technology of a generation ago. Two generations ago, it was so bad that marine radio stations [] had miles of separation between the receivers and the transmitters.

Re:We're lucky the FCC clamped down (1)

Vegan Cyclist (1650427) | about 2 years ago | (#42279035)

...and perhaps something like this is the source of the ridiculous 'turn off ALL electronic devices' warnings on flight take-off and landings...?

Re:We're lucky the FCC clamped down (0)

Anonymous Coward | about 2 years ago | (#42284591)

It is.

Re:We're lucky the FCC clamped down (1)

yuhong (1378501) | about 2 years ago | (#42281455)

Not to mention the RF emissions would likely be able to used as a side channel to break crypto, which is much more common today than in the late 1970s. []

Yeah I remember that (1)

MichaelSmith (789609) | about 2 years ago | (#42278901)

I tried a spectrum in a shop. Every time I pressed a key on the keyboard the TV monitor lost its vertical sync.

Re:Yeah I remember that (0)

Anonymous Coward | about 2 years ago | (#42280715)

That's how it worked... The CPU drew the picture on the screen - when you pressed a key, it had to stop drawing the screen, and take care of your keypress. The Sinclair computers were STINGY in their engineering.

Re:Yeah I remember that (2)

carou (88501) | about 2 years ago | (#42281915)

You may both be thinking of the ZX80 or ZX81, which used this hack to drive the screen. The ZX Spectrum (released 1982) had proper display circuitry and did not suffer from this issue.

The ZX80's display hack was all a cheap way to get the data streamed out of RAM. To do this they placed the cpu's program counter(!) at the start of display memory, every time it tried to execute an instruction it would read a byte from memory - which was picked up to generate the display - but the data wasn't returned to the CPU and instead it was fed a byte of zero bits. 0x00 is the NOP instruction on Z80, so it would just increment the program counter and read the next byte. This means successive bytes appear in sequence on the data bus, without having to include a second agent that was capable of making accesses into the RAM - a considerable design simplification. Later, for the Spectrum, a separate circuit which generated and incremented its own address was able to access memory, and it had to be arranged that it would get priority over the CPU (which meant the CPU was considerably slower when running programs in the bottom 16k of memory).

Re:Yeah I remember that (1)

Hank the Lion (47086) | about 2 years ago | (#42312975)

Yeah, the display hardware of the ZX81 was brilliant in its simplicity.
Not only did it use the program counter as the character point er for the display, but the I/R (interrupt and DRAM refresh) register pair was used as a pointer into the character ROM. These were output automatically by the processor directly after the fetch of the instruction.
And each line of the display was ended by a HALT instruction, so short lines did not need the full 32 bytes.
And, and, and... I loved that machine for its (albeit just a _little_ bit convoluted) design!

Not just computers... (1)

DocMAME (933222) | about 2 years ago | (#42279495)

Last night we found out that my Mattel Electronics "Las Vegas" pinball from 1977 broadcasts its sounds across 96.1Mhz to 107.9Mhz! We started hearing the game on the boom box 30 feet across the room!

How are mobile phones legal then? (1)

necronom426 (755113) | about 2 years ago | (#42279927)

I've always wondered how mobile phones are allowed to exist when they interfere with anything that has speakers. I remember circa 1999 when I started noticing this strange d d d...d d d coming from computer speakers at work. We eventually realised it was that someone had a mobile phone in the room. Our VT terminals once completely freaked out when someone made a call and ever since I've wondered how this is allowed.

I remember hearing that the Vic 20 was delayed because it needed to have shielding added, and I've never noticed interference from any device apart from phones. Even new ones cause terrible interference on radios. My Dad has a Blackberry and he can't put it in the small holder near his radio as it constantly makes noises on it.

Can anyone explain any of this?

Re:How are mobile phones legal then? (0)

Anonymous Coward | about 2 years ago | (#42283335)

your mobile phone is a transmitter.

Re:How are mobile phones legal then? (1)

Jamie Lokier (104820) | about 2 years ago | (#42286681)

As the AC implies, that's not interference from bad or unshielded electronics in the mobile (or it shouldn't be).

An ideal mobile transmits only what it's supposed to, on the correct RF channels to communicate, and nothing else.
Like all devices there will be other emissions, but let's assume it's very well made and effectively perfect.

The sound on the speakers is because the speaker circuit is effectively an RF receiver, converting those high frequencies to audio. They actually demodulate the signal - unintentionally. See []

If the speaker circuit is made well enough, it won't do this.

PCs before 2006 are Much Noisier than the ZX (0)

Anonymous Coward | about 2 years ago | (#42280321)

New EMI rules are required to keep modern offenders in check. The old ZX is a weak example.

What have we learned? (1)

nurb432 (527695) | about 2 years ago | (#42280355)

That if marketed properly we can bilk the public out of their money every year with shiny new objects that really are not much different than last years shiny object.

Didn't fly originally either (0)

Anonymous Coward | about 2 years ago | (#42282155)

Flying PCs come after flying cars, dammit.

Can't have been all that bad... (1)

Chuffpole (765597) | about 2 years ago | (#42286567)

I used to SAVE programs over the CB airwaves for other people to LOAD, and never noticed any great problems with the Speccy interfering with my CB :)

(I put a socket on the back of my CB fist-mic - this was at the height of the CB craze after UK legalisation in Nov 1981 - so that I could plug in other mics, or line-level audio via a resistive dropper. I found that hooking it up to the Speccy I could SAVE over the air with a nice clear modulation (CB is FM in the UK - 27MHz) with enough quality that other people were able to hook up their CBs to the line-in socket of their Speccy and LOAD what I was sending to them. It worked just fine!)

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