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Cable Signal amplifier and splitter: a peek inside

Jan Cumps

In the basement of my house there's an obsolete device hanging from one of the walls:
A Cable TV dispatcher / splitter, amplifier. With a few separate signal paths for bidirectional data (internet).
I've been looking at it for 6 years now. Time to look inside of it.

As you can see, the power connector has been cut off. I can safely assume that it's not in use anymore. My TV and internet enter via a different line, twisted pair.

The front mentions 2002-03. There's a printed label on the backside with 2002-5.

The connector on the left is Cable in.
The two next ones, for internet, are covered by a dummy. These are stubs that can only ne removed using special pliers (and by me :) ).
The last two ones are amplified TV signal. The last one includes a DC, so that it can optionally power an amplifier upstairs.

The whole set is not pretty. But it's well made. You'll see that it's of decent build inside too, in the photos below.
There are only two transistors. All other components are passives - and one relay.

Wall mount and backside

   

Connectors and the two dummies / terminators

Inside

 

Penetrator for the power and details of the very simple supply

 

Shielded RF circuit with the connectors

Inside the can

PCB top side 

Active circuit

The SMDs seem to be place by hand. 

PCB Underside

I have more photos. But this should give an impression of how it's built.

Anonymous
  • in reply to jc2048

    Yes, it's a mistake. 

  • in reply to Jan Cumps

    I think you meant 9GHz for the fT.

  • in reply to shabaz

    It is ineed a 75 Ohm device. 

    These weren't installed by default. The cable signal was intended for 1 TV.

    If you wanted more TVs to work at the same time, the cable company would come and install this device.

    They'd stub all outputs you didn't pay for with those unremovable terminators.

  • So glad that in 50-ohm world at least (guessing cable TV is 75 ohm, I don't know much about it), things are simplified these days with (admittedly more expensive) ready-matched MMIC parts, it's a far longer procedure to have to impedance-match and then tweak each inductor since they might not fall onto popular values! (Sure simulation software can do it but perhaps only the larger orgs would use that, and besides these boxes were probably designed a decade or more ago - at one place I worked at, it was all manually done by their RF expert, sitting in front of VNA all day). Still, I guess once it's done then millions of these cable-TV amplifiers can be churned out cheaply.

  • Transistors seem to be:

    BFG540 N37 (120 mA, 20 V, 9 MHz)

    BFG520 N36 (70 mA, 20 V, 9 MHz)


    Both NPN NXP, UHF / Satellite-TV use.