SATELLITE DISH RECEIVER TEARDOWN

Welcome to part 3 of the satellite dish teardown.  Today we will be looking at the receiver of the satellite dish that has spent the last 10 or so years being an ornament on my house.  This will include looking at how the unit was sealed, the key components of the circuit board and the layout of the circuit board.  If you want to read part 1 where we look at the dish installation as a whole or part 2 where we look at the feed horn please have a look at: https://swamphen.co.uk/new-blog/2019/6/24/satellite-dish-teardown and https://swamphen.co.uk/new-blog/2019/7/1/satellite-dish-feed-horn-teardown

 

The receiver, a low-noise block downconverter (LNB), sits on the end of the receiver arm which is at the focus of the parabolid of the reflector.  In this picture the receiver is more clearly seen as the top of the plastic housing has been removed.  You can see the cast metal housing of the receiver electronics, where this flares to make the feed horn, and the plastic radome on the top of the feed horn. 

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Once the receiver has been removed from the receiver arm, disconnected from the coax cable and the radome removed I could start to cut into the receiver electronics.  The top cover on the receiver is thin metal, although still difficult to remove as I was concerned the electronics were directly underneath it and I didn’t want to damage them. 

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However, once I had taken a can opener approach and got the edge up I soon realised that there was another layer of rigid protective metal underneath there which made the job much easier.  Although, this layer did not escape unscathed, as you can see the dents I made in it when removing the soft metal outer layer. 

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I thought this would be easy to remove when the screws were undone, as on closer inspection this was the back of the circuit board. 

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But, no, there was a further round of prising this rigid layer of circuit board off.  Partly caused by the metal prongs of the coax to waveguide going from the circuit board through to the waveguide, partly the dowels and partly the metal edges holding it in place which all caused obstructions.  Here is the first look at the circuit board after a lot of hard work to get some movement on it.

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Unfortunately, in this process one of the coax to waveguide transitions and the coax cable inner pin came off.  Surprisingly, other than that and a couple of dents on the edge, the circuit board had remained unscathed. 

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The circuit board itself is a single layer low cost, mass produced board.  It has been nicely manufactured and was very well sealed, so has survived living outside for 15+ years unscathed.  You can see that the design uses surface mount and through-hole technology to mount the components.  I have noted a few of the main components in the image below, and I am going to look at the parts where the circuit board intercepts with the incoming and outgoing RF signal separately. 

It would be possible to remove this receiver totally from the design and have the signal that the dish collects straight to the set top box.  The dish receives signals in Ku band (12-18GHz), and you can move signal at this frequency through coaxial cables.  However, the cost of manufacturing everything to work at this frequency would be prohibitive.  For the coax cable alone to work at Ku band think of the order of £100 per meter and then work out how many meters are used to route the signal from the dish to your set top box (I had about 20m for this installation!).  So, instead you use a mass manufactured LNB and convert the signal to L band (1-2GHz) where you can use standard and cheaper components and cables. 

This LNB design is a dielectric resonance oscillator design, with the expected array of surface mounted amplifiers, regulators, resistors and ceramic dielectric resonance oscillators.  There are also transmission lines evident on the PCB showing low pass filters, hair pin filters etc. 

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Here are some specifications and more details on the parts of the Printed Circuit Board (PCB) that I have highlighted:

ZNBG3211 – FET bias controller with polarization switch and tone detection.  This provides the bias and polarisation switch, depending on input tone, to the Field-Effect Transistor (FET), a type of low noise amplifier. 

AA37AK/5AK – amplifier, to increase the power of the signal.

UTC78D08 – 3 terminal 0.5A positive voltage regulator, to maintain a constant voltage. 

Resistors – Surface mounted resistors of varying values, to adjust the signal levels. 

Distributed element filters – electronic band pass filters.  These perform different functions: allow a range of frequencies to pass, but block others; limit noise; multiplex signals. 

Dielectric Resonator – a ceramic dielectric resonance oscillator, used to control the frequency of the radio waves generated. 

 

The coax to waveguide pins are mounted directly through the circuit board.  The bend in them occurred at the point where the pin goes into the circular waveguide at the end of the feed horn, which will set the correct orientation for them in the waveguide.  The gold transmission lines can be clearly seen bringing the co and cross polar signals together from the two coax to waveguide pins with some amplification.  The set top box will send a tone to the FET to select which polarisation it wants to receive on.   

coax to waveguide.png

The centre part of the SMA connector comes out of the other side of the circuit board after the signal processing has been completed.  It goes straight from the circuit board into the SMA connector. 

sma connector.png

I hope you have enjoyed this teardown of an old home satellite dish as much as I have enjoyed doing it.  If you have any comments or questions, please ask!  I’m now wondering if I can get the old low gain analogue TV Yagi off the chimney and do the same.  That might be a bit too dangerous to get to without specialist ladders?!?