Positioner set up success. Signal Feed question.

Discussions about controllers used to position your dish and track the satellite arc.
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belter-one
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Positioner set up success. Signal Feed question.

Post by belter-one » Thu Aug 23, 2018 11:57 am

Hello,

We recently had great success in setting up our V-Box II positioner in tandem with the most excellent ZGemma-H7 receiver. Works great and now we can schedule recordings automatically on multiple satellites. I am also looking forward to scanning multiple satellites in one automatic scan session, to see if that is possible as well. The tutorial on positioner setup was very helpful. Many thanks to "The Professor" for providing the tutorial.

The V-Box II has one LNB feed for one LNB. I do not want to use a 22K switch to switch from C and Ku, as the .5 or greater SNR loss might jeopardize some awesome channels we are currently enjoying. Could I crack open the V-Box II and replace the single LNB terminal with a dual terminal, or would this also induce a SNR loss? Has anyone tried anything like this before? Any suggestions would be greatly appreciated.

In C band veritas, :smile:

belter-one

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Re: Positioner set up success. Signal Feed question.

Post by Titanium » Thu Aug 23, 2018 6:52 pm

It is necessary to use a switch to select between feeds. The insertion loss of a 22KHz or DiSEqC switch is negligible with typical high gain LNBs, average coax run lengths and factored into line and fitting losses. It would be quite easy to increase the signal amplitude by simply shortening the feedline or using a higher grade of coax. You might also find that using a quality tap or splitter used instead of passing through the controller IO may pick-up a few points. Not all switches are created equal and you will find some switches with higher insertion loss and worse isolation between ports.

Why is is not possible to use a splitter or add a second parallel f-fitting? Both C and KU signals are down converted in the LNB to a IF (Intermediate Frequency) range block between 950 and 2150MHz. The two LNBs occupy the same IF range and would conflict if they were merged.
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Re: Positioner set up success. Signal Feed question.

Post by belter-one » Fri Aug 24, 2018 10:47 am

Thank you Titanium,

For the useful information. I will lose the idea of merging the signals through two terminals and experiment with 22k switches and look for one that has no signal loss. I am very impressed with the ZGemma-H7 and its ability to use the positioner so seamlessly. I need to study up on how to eliminate the noise in the SNR. I am pretty sure there is little to no noise from my surrounding area as the nearest above ground power lines are ~380 feet away (google earth) and behind some trees.

Sunny here in the beautiful Northwest,

belter-one

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Re: Positioner set up success. Signal Feed question.

Post by tek2000 » Sat Aug 25, 2018 11:18 pm

belter-one,

You can find a good analysis of noise for TVRO systems in Coop's Satellite Digest (Sep. 1983 edition, page 35 and 65).

http://theoldcatvequipmentmuseum.org/22 ... ressed.pdf

The formulas everyone uses are those by Friis:

https://en.wikipedia.org/wiki/Friis_formulas_for_noise

The effective noise of a system is usually modeled by a single noise source placed at the front-end of the system. In other words, you have to bring all noise sources to the front to derive the SNR. To do this, you have to divide the noise figure of each stage by the gain of the previous stage(s). This is why the noise or losses introduced by the coax or the switch are mostly negligible. If you placed your switch or cable before the front-end amplifier, then yes, your SNR would be a disaster!! By placing the switch after the gain and mixing stages, the signal degradation will be minimal.

The sometimes poor performance of switches is due to poor isolation between ports. If you are switching between c-band and ku-band signals, it won't be a problem unless they fight each other in the L-band (e.g. 4000 MHz and 11750 MHz will both get downcoverted to 1150 MHz). The chances of this happening are almost nil, unless you are aimed at a directv or dish satellite which tend to use all of the available ku spectrum.
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Re: Positioner set up success. Signal Feed question.

Post by belter-one » Mon Aug 27, 2018 8:28 pm

Thank you Tek2000,

I will study the documents, and also try the 22k switch and see if it works as hoped.

Really enjoying this hobby,

belter-one

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