[VWestlife] ended up with an obscure piece of 80s satellite TV technology, shown above. The Micro-Scan is a fairly plan metal box with a single “Tune” knob on the front. At the back is a power switch and connectors for TV Antenna, TV Set, and “MW” (probably meaning microwave). There’s no other data. What was this, and what was it for?
Satellite TV worked by having a dish receive microwave signals, but televisions could not use those signals directly. A downconverter was needed to turn the signal into something an indoor receiver box (to which the television was attached) could use, allowing the user to select a channel to feed into the TV.
At first, [VWestlife] suspected the Micro-Scan was a form of simple downconverter, but that turned out to not be the case. Testing showed that the box didn’t modify signals at all. Opening it up revealed the Micro-Scan acts as a combination switchbox and variable power supply, sending a regulated 12-16 V (depending on knob position) out the “MW” connector.
So what is it for, and what does that “Tune” knob do? When powered off, the Micro-Scan connected the TV (plugged into the “TV Set” connector) to its normal external antenna (connected to “TV Antenna”) and the TV worked like a normal television. When powered on, the TV would instead be connected to the “MW” connector, probably to a remote downconverter. In addition, the Micro-Scan supplied a voltage (the 12-16 V) on that connector, which was probably a control voltage responsible for tuning the downconverter. The resulting signal was passed unmodified to the TV.
It can be a challenge to investigate vintage equipment modern TV no longer needs, especially hardware that doesn’t fit the usual way things were done, and lacks documentation. If you’d like to see a walkthrough and some hands-on with the Micro-Scan, check out the video (embedded bel0w).
As far as I know even modern-ish LNBs use the DC phantom power level to select the polarization mode
Polarisation is controlled by the power supply voltage. There’s also a 22kHz pilot tone to select the upper or lower band.
I went through all of that while building a kind of “camera” for 12GHz RF.
https://josepheoff.github.io/posts/rfcamera4
The solution of the ™mystery” lies in the first comments to that video. Another proof that editors here just generate articles from video transcripts without even reading or watching the source material.
You can’t feed a downconverted analog satellite signal directly into a TV’s antenna input, Analog satellite uses FM modulation while analog OTA uses AM.
This box is not for sat tv, its for early “cable TV” that was beamed over microwave.
I remember the kits in the back of electronics magazines that would let you decode a service called “Wometco Home Theater” WHT, the movie network. As cable became more popular and widespread, over the air scrambled TV services faded into history.
Looks to me like the control box for a pirate MMDS receiver, AKA “wireless cable”. It was a pay TV service that was sent unencrypted via microwave in the 80s. We had it in Houston back in the day. Pirate boxes were very popular for receiving it, since it included XXX movies after 10:00 PM.
My suspicion as well. We also had this kind of “Wireless cable” in the Tampa area. Service was called Videotron. I believe it transmitted in the 2.3ghz band and carried a few dozen channels. The antenna was a directional yagi and the antenna included a down converter to downconvert the 2.3ghz channels into UHF channels you turned on your TV. Sprint bought the chunk of spectrum they used for this to deploy their failed WiMax service on.
MW – Medium Wave, not microwave…
https://en.wikipedia.org/wiki/Medium_wave
“Medium wave (MW) is a part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band.”
ugh, I’m pretty sure there are some leaky caps, and it’s not supposed to be passing AC to the MW input. Also suspect the “tuning” is just a crude impedance matching circuit.
The biggest BS ‘magic box’ I ever bought was a Lectra Search long range metal detecting dowsing rod. Just a Turbo Rat board inside and the only wiring was to a test switch and pot that were only connected to the battery. I do have an old 80s “video effects box” which I am sure baffled the original buyers since it was just a source switcher lol. I guess the effects were whatever was on at the time. I still DO very much love these magic box investigations and teardowns :)
The circuit shown inside this box appears to be a bias-T that powers an LNB (“Low Noise Block” downconverter) for terrestrial MMDS broadcasts popular back in the day. The “Tune” knob is likely part of a varactor-tuned VCO, and turn the knob and vary the oscillators voltage and thus change the frequency. Likely this drives the mixer LO (local oscillator) as part of the downconveter inside the LNB and voila, you can tune in different MMDS bands. Geeking out here…fun stuff and takes me back to the early 80s and my teenage years.