Dish Network LNB pictures - Page 1
Forum section: electronics / general

author: reagle
author_rank: Unknown
timestamp: October 20, 2012, 02:03:03 am
content: Not being an RF guy, all I can do is take it apart and post pictures, in hopes somebody else may explain things

author: free_electron
author_rank: Super Contributor
timestamp: October 20, 2012, 05:36:27 pm
content: that round puck in the middle is the oscillator. they tune these oscillators by adjusting the position of the puck ( a disc of ferrite material )on the left is a ringmixer the prob on the right is the pickup. goes through a couple of amplifiers , bottom left slanted lines are a bandfiltertop sits a voltage regulator as the lnb gets a voltage between 12 and 18 volts. the so chip on the right is the disecq controller.using the supply voltage they modulate a bitstream to the lnb to control polarisation

author: reagle
author_rank: Unknown
timestamp: October 23, 2012, 07:34:37 pm
content: So the trace tab sticking in the middle of the opening is the pickup? There is also a gold coated pin soldered through the board and sticking from the back- does that serve as some type of a signal injection source into the waveguide?

author: SeanB
author_rank: Super Contributor
timestamp: October 23, 2012, 07:56:14 pm
content: That is the probe for the other polarisation. They each have a HEMFET connected to them, then the signals are selected for further amplification in the secong RF stage by switching the power to the unused section off and removing the bias supply. This is controlled by the IC above, which does the supply generation and switching, getting an input from the power applied up the cable, 12V selecting H and 18V selecting V polarisation.most common is to use voltage level to select, otherwise if you have a LNB with 2 bands you get a 22kHz signal injected up the cable as well to select the LO to use to do the mixing. There you will see 2 dielectric pucks and associated transistors each in it's own sealed shield with a tuning screw. The same IC regulator is used, as it is not fully used in this unit, it will handle the tone decode and drive as well.Lovely 1/4 wave transformer there used to both do impedance matching and inject the LO signal into the diode mixer. Note the output has a low pass filter to allow the IF signal under 1GHz to be passed out, while attenuating the 10GHz input and the LO, with the multistage filters used to separate the IF and the DC ( and low frequency signals) control and power.

author: Smokey
author_rank: Super Contributor
timestamp: October 23, 2012, 09:06:29 pm
content: I love real RF PCB porn.I can look at a normal embedded system type PCB and understand most of it these days, but that RF stuff is still magic and you guys that understand it are still wizards.

author: reagle
author_rank: Unknown
timestamp: October 24, 2012, 05:31:43 am
content: Quote from: Smokey on October 23, 2012, 09:06:29 pmI second that. Looking at the bottom of the board I may as well be looking at aerial pictures of area 51

author: Fox
author_rank: Regular Contributor
timestamp: October 24, 2012, 09:59:25 am
content: Quote from: reagle on October 24, 2012, 05:31:43 amOne of the most importand things in RF work is proper grounding and keeping in mind that ground "here" is not necessarily the same potential as ground "over there".And a wire is not just a wire in RF it has inductance an capacitance even if is just a few mm long.So not outright wizardry most of the time but there is some stuff that earns the Black magic lable

author: reagle
author_rank: Unknown
timestamp: October 24, 2012, 01:09:17 pm
content: I ma just wondering how they came up with some of the shapes- the filter in the lower left and the matching transformer "circle" above that. Is it purely the result of simulations?

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 24, 2012, 01:37:36 pm
content: Quote from: reagle on October 24, 2012, 01:09:17 pmLooks like the filter is just the right combination of inductance (the length/width of the strips) and the capacitance (the distance between the strips). Slanted because that takes up less space.The circle is 'just' the input transformer for the mixer, the oscillator signal coupled in at the center tap and the signal 90 degrees shifted.I guess it is calculated, and maybe simulated or just prototyped and tested after that.

author: reagle
author_rank: Unknown
timestamp: October 24, 2012, 07:39:02 pm
content: It is odd though that the result is so beautiful!

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 24, 2012, 07:43:32 pm
content: What I like about this is when you look at the PCB what you see is almost the schematics of the device :-)