Switching 1 satellite LNB between 2 receivers - Page 1
Forum section: electronics / rf-microwave

author: Delta
author_rank: Super Contributor
timestamp: November 12, 2016, 05:51:41 pm
content: I need to be able to manually switch 1 incoming satellite feed from the LNB between two set-top-boxes. Changing to a dual LNB and running an extra cable is not an option.I have seen A-B switcheslike this, but they are sold as being designed to switch 2 LNBs between 1 receiver. Would one of these work in reverse and do the job?It would need to isolate the LNB power supplies from each other, whilst still allow the power and tone from the selected receiver up to the LNB.I would guess that it is likely to work OK, but I know there are a huge amount of gotchas when it comes to RF black magic!

author: SeanB
author_rank: Super Contributor
timestamp: November 12, 2016, 06:37:28 pm
content: Well, if it is a manual switch, with no electronics inside, it will work in reverse, just like a wire.

author: Delta
author_rank: Super Contributor
timestamp: November 12, 2016, 06:53:34 pm
content: Quote from: SeanB on November 12, 2016, 06:37:28 pmYeah, that was my thinking. But I was hoping someone could confirm what's actually in these things...

author: SeanB
author_rank: Super Contributor
timestamp: November 12, 2016, 06:59:09 pm
content: Order one, open it and you will see a small PCB ( If you are lucky) with a slide switch on it, and traces leading to each socket. As the common is between the 2 outputs this is the most likely configuration.Will be a single sided cheap SRBP board with the switch, the sockets and nothing else on it, with some added random holes punched in it from reusing the punch die from the other mass made items that use the same size box and switch, like the setback amplifier that has the same size and switch, but has one input and 2 outputs to connect a remote set to the antenna, using a single transistor amplifier and an attenuator for the local set.

author: tautech
author_rank: Super Contributor
timestamp: November 12, 2016, 07:03:09 pm
content: On a setup we've got, the set top boxes have feedthrough connections so you just daisy-chain them to 1 LNB. With some set top boxes you can turn the LNB power off and use another in the chain to power them....a hunt through their menus will find which ones are capable of this.So rather than do any switching per se just let the boxes sort it out for you.Or get a splitter with 1 DC pass for the LNB power.

author: kripton2035
author_rank: Super Contributor
timestamp: November 12, 2016, 08:17:25 pm
content: you can use some box like this one, it's not too expensive (less than 50€) . some of them are even amplified so that you have 0dB power loss.also this simple 2 ways splitter is less than 10€ but is not amplified (so you lose some 3-4dB), and have NO switch it is automatic.

author: Delta
author_rank: Super Contributor
timestamp: November 12, 2016, 08:24:35 pm
content: Quote from: tautech on November 12, 2016, 07:03:09 pmI can't see how either of those options could work. The STB controls the LNB - a 13v supply sets the LNB to vertical polarisation, an 18v supply to horizontal; and if a 22kHz signal is modulated on the DC, the LNB uses the High Band local oscillator, if no tone then Low Band. Because of this, the LNBmustbe powered from the STB that is using it Shurely...?

author: tautech
author_rank: Super Contributor
timestamp: November 12, 2016, 08:33:18 pm
content: Quote from: Delta on November 12, 2016, 08:24:35 pmYes, if you need both polarizations, I don't and have used a single LNB with 1 connection to 2 STB's daisy chained for years now, worked fine for us.But some STB's have limited features and kripton2035's solution might be a better one for you.

author: Delta
author_rank: Super Contributor
timestamp: November 12, 2016, 09:36:04 pm
content: Quote from: kripton2035 on November 12, 2016, 08:17:25 pmThanks for the suggestion, but that's no use at all. That requires four feeds from aquattroLNB (which is different from a quad LNB - had a fall-out with an old purchasing manager of that issue...). The whole reason for requiring a (cheap and simple) way to select between two STBs is that there is only one feed from a single universal LNB available...PS. I have used units exactly like that for large TV distribution systems, and they are great for that, but completely unsuitable for this usage.The splitter cannot be used as only one receiver can power / control the LNB at a time. (please see my above post)