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Anyone know what this is (from a 5150 model A)

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Springbok

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So I am in the process of restoring an early 5150 Model A. It has BIOS version 2, the 2nd version of the PS (the one with the sunken screws on the top), but appears to be the early version of the case (based on this link)

http://www.minuszerodegrees.net/5150/early/5150_early.htm

It has a 192 KB memory expansion card with the old black wider bracket, and an early CGA card (as seen in the link above). One thing puzzling me is the thing below. It was literally stuck to the inside of the case using some tape. It wasn't connected to anything. It looks like it has an analog input and an analog output, with a circular magnet looped through the wires. It has "BP3212 Astec 1980" written on the back. Google revealed nothing.

There was also a vintage modem card installed. Its a full length card with another card piggy-backed on it. I am assuming it was added later because the back-plate is silver. I don't know if the Astec card is related to the modem or not.

Thanks.

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That's an RF Modulator. Back when color monitors were expensive you could output the composite video signal from the PC graphics card through the RF Modulator and connect the RF output to a TV antenna input and tune it to usually channel 2 or 3.

Looks pretty much the same as the Sup'R'Mod RF Modulator that was very common in the Apple II days. I had one of those for my Apple II.
 
I think the BP3212 is an RF modulator of some kind. The connector that looks like a 3.5" floppy power connector throws me for a loop. Guess those appeared earlier than I remember. The traces on the bottom look like there a bunch of components that take power. A peek inside the metal shell will tell all.

Astec made RF modulators and power supplies in 1980.
 
krebizfan said:
The connector that looks like a 3.5" floppy power connector throws me for a loop
Click to expand...
Goes to P1 on the CGA, who's pinouts are:

1) +12V
2) Not wired
3) Composite Video
4) Ground

Connect that to P1 on the CGA, and you should get VHF output typically on channel 3 or 4.

P1 (composite) and P2 (light pen) were often handy places to grab power if not using them for their design purpose.

So yeah, RF modulator, turns the internal composite on P1 into a VHF channel. "Gslick" has it right in that it looks like one of the old ones sold for the Apple II in the back of BYTE. They were handy on a bunch of systems that had composite out but no RF modulator in the age before TV's having composite in or VCR's.

The "magnet" as the OP called it is a RF choke to try and cut down on interference since that's not exactly RF grade wire.
 
Thanks for the great responses guys and apologies for my lack I electronics knowledge.

The CGA card has a analog output, so why would this modulator be needed?
 
Because many tv's at the time didn't have composite inputs so they would have had to use the tuner. That would connect to the antenna input on the tv.
 
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A bit of history: The reason these exist is that the FCC regulations at the time made it all but impossible for themanufacturer to include TV frequency RF circuitry in the computer. And of course, like offensive_Jerk said, TVs at that time did not have composite inputs. That is, they did exist, but they were rarer than hen's teeth.
 
Springbok said:
The CGA card has a analog output, so why would this modulator be needed?
Click to expand...
Offensive_Jerk pretty much hit it on the head -- it's not "just" analog output, it's composite video. Composite video is a single NTSC data stream that most older TV's cannot display directly without turning it into a TV channel first. Older TV's had NO composite video in, half the time you were lucky if they had a 75 ohm F-type coax instead of JUST screw terminals for twin-lead 300 ohm antenna.

To display composite video on a old TV you HAD to have an RF modulator to turn it into an analogue TV station signal, typically somewhere ranging from channels 2 through 4. A number of older computers had the RF modulator built in if it was REALLY meant to be connected to a TV. Commodore VIC-20 and 64, TRS-80 Colour computer, Atari 400/800, etc, etc... Really wasn't until better quality VCR's came along that you started to see TV's with composite inputs, and you could use a VCR as a RF modulator since it too had to turn it's own composite video stream into RF VHF frequency data.

Other systems like the PC and Apple II didn't really consider it an option as they were meant for 40 column or wider text, and colour artifacting made them unsuitable for going through an RF modulator. Converting to TV signal causes a lot of signal degradation at higher resolutions, and true composite always looks better than RF. In fact people dug into the circuitry of a lot of systems to bypass the RF modulator and extract the Composite signal for direct use on displays that supported it. Few manufacturers provided "out of box" options for both -- Commodore being the exception. Commodore even included an option for separate luma and chroma signals -- separating the color from a monochrome composite signal in a manner that is largely (with a resistor to tweak the voltage level) with the SVHS standard.

Basically, if you connected that RCA jack on the CGA to the antenna inputs on a TV, you aren't gonna see jack on any channel. Unless that TV has composite video in (something that you REALLY didn't see on TV's prior to ~1990ish) you need an RF modulator to turn that raw video feed into a VHF TV station.
 
Well, that is interesting!
I knew about the RF modulator headers on CGA, but I wondered if they were ever used for anything. Apparently they were!
 
KC9UDX said:
A bit of history: The reason these exist is that the FCC regulations at the time made it all but impossible for themanufacturer to include TV frequency RF circuitry in the computer.
Click to expand...

Is that so? Because various home computers from that era (VIC-20, C64, ZX80/81/Spectrum, Atari VCS etc) do have an RF modulator built in, and I assume they also had to meet FCC regulations.
I must say though, IBM shielding is the worst I've ever seen. Practically non-existent.
Compare that to an early C64, and it has a metal cage around the video chip and RF modulator, and a cardboard sheet covered with some kind of aluminium foil covering the mainboard: http://www.nightfallcrew.com/wp-con...64-uk-datassette-c16-suncom-tac2/IMG_6439.jpg
(RF Modulator is the box at the top). Making the PSU external probably also helped.
An Amiga 500 is even nicer. Instead of cardboard, it's some kind of metal 'box': http://oldschoolgameblog.files.wordpress.com/2011/09/amiga500beforelidopen.jpg
And apparently some C64s were also constructed more or less like that: http://www.computermuseum.li/Testpage/Commodore64-Inside.jpg

But IBM, they don't appear to have put in any effort whatosever to shield their machines.
 
Is that so? Because various home computers from that era (VIC-20, C64, ZX80/81/Spectrum, Atari VCS etc) do have an RF modulator built in, and I assume they also had to meet FCC regulations.
Click to expand...
Can't speak for the US, since I'm from Germany, but such regulations were different based on whether the computer was for business or home use, had a built-in or separated keyboard etc.
 
Timo W. said:
Can't speak for the US, since I'm from Germany, but such regulations were different based on whether the computer was for business or home use, had a built-in or separated keyboard etc.
Click to expand...

You might be right. Perhaps there were even regulations for having PSUs built-in for more industrial devices?
But then my explanation for the lack of shielding in the IBM PC would go something like this:
1) Shielding requirements for business/industrial devices are higher than for home devices.
2) Making the RF-modulator meet the FCC requirements would be prohibitively expensive, so it was dropped from the design.
3) Without an RF-modulator, the emissions are much lower, so IBM didn't find it necessary to use any shielding whatsoever, effectively making them much less shielded than most home computing devices of that era.

The uber-low quality of PCs has always bothered me... When I got my first soundcard (a Sound Blaster Pro 2.0), it made horrible hissing sounds, and you could hear lots of bus noise from the HDD and video card through the speakers.
Even my C64 was nowhere near that noisy. And my Amiga was pretty much completely silent.
Pretty horrible, considering that this sound card was as expensive as an entire Amiga. And the computer I put it in, was more than 3 times the price of an Amiga. The result was nowhere near as good as an Amiga however :)
 
Keep in mind that home computers such as the C64 required internal shielding due to their plastic housing. The IBM PC however uses a grounded metal housing. There's no lack of shielding in the IBM PC. At least not against the environment, which is all that is regulated anyway.

However, the RF modulator being separate from the CGA card may also had another reason: when exporting/importing, the IBM PC may have fallen under a different category with higher import taxes. Even today, many electronic products are gelded to save import taxes. That's why still cameras sold in the EU won't take more than 29:59 minutes of video. Starting with 30:00 minutes of record time, they would no longer be still cameras but video cameras with higher import taxes. I don't think this was much different 30 years ago.
 
Scali said:
Is that so? Because various home computers from that era (VIC-20, C64, ZX80/81/Spectrum, Atari VCS etc) do have an RF modulator built in, and I assume they also had to meet FCC regulations.
Click to expand...
The VIC-20 does not have a built-in RF modulator. It shipped with an external RF modulator box, just like the TI-99/4A.

I believe the FCC loosened the rules regarding TV RF modulators in 1981. Prior to that, most home computers either didn't have a built-in RF modulator, or had a large amount of metal shielding inside the case to meet the earlier, more stringent FCC requirements (such as the Atari 400 and 800 and the "Heavy Sixer" 2600). After the rules changed, almost every new home computer then came with a built-in RF modulator, and existing computers were redesigned to reduce the amount of shielding inside and cut production costs (the Atari XL series, beige TI-99/4A, CoCo 2, etc. -- as well as cost-cutting redesigns of the Atari 2600 and Intellivision).
 
That is correct. And, you bring up a good point: the change can be evidenced in the vastly different designs of those machines. If my memory serves, the change in regulations was protested by many people worried about computers interfering with radio reception. In retrospect, this turned out to be a very serious problem over time.But, the VCR importers had better lobbyists. Ah, politics..!

If I think about it, I'll see if I can find this documented online somewhere. It is a very important part of home computer history.
 
Also, the change from U-shaped holes in the back of the Apple ][ to that very inconvinient RF-tight metal plate-with cable clamps on the Apple //e happened at the same time. Apple history might be a good place to start research.
 
Timo W. said:
There's no lack of shielding in the IBM PC. At least not against the environment, which is all that is regulated anyway.
Click to expand...

Well, that was my point. I've seen other PCs that also had more shielding IN the case. For example, my PC20-III has a metal plate over the entire motherboard, except for the 3 ISA slots.
I've seen various other early clones that were constructed similarly. The nicest machine I've ever seen was some Olivetti. They had all the ribbon cables folded down into the case via special routes, rather than just flopping around freely in the case. Very neat design.
And my experience is also that the noise inside a PC (as you can hear through the sound card for example), varies wildly between different computers. Better motherboard design, better components, better shielding...
Most PCs are rubbish, but there's a few gems here and there.

Another funny thing I noticed... My Commodore MDA monitor is very susceptible to interference. I first noticed it when I had a fan on my desk during summer. The image would 'wobble'.
I found out that when I have my Philips P3105 open, it does that as well. But with my PC20-III open, at the same distance to the same monitor, there is no wobble.
 
Scali said:
Another funny thing I noticed... My Commodore MDA monitor is very susceptible to interference. I first noticed it when I had a fan on my desk during summer. The image would 'wobble'.
I found out that when I have my Philips P3105 open, it does that as well. But with my PC20-III open, at the same distance to the same monitor, there is no wobble.
Click to expand...

Magnetic fields can be a real bugger in some of the older systems that integrate the display in the same enclosure that has disk (particularly floppy) drives. The effect goes both ways--the display can seriously mess up the disk read signal--and the spindle motor can cause the "wobble". If the two have to be physically close together--i.e., the display is placed immediately above the (vertical) disk drives, it's pretty difficult to shield them--even 16 ga. steel isn't enough and Permalloy is very expensive. Add a dot-matrix printer to the works and things really get interesting. If you have an old Panasonic word processor with the built-in printer, you can see the slight wobble in the display when the printer is operating.

But we're not talking about RF shielding here, but magnetic. AFAIK, there are no consumer regulations for that.
 
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