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11 posts

Geek


#73607 17-Dec-2010 11:10
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Hi Everyone,

I thought id post this question here as ive posted on the GBPVR site and have yet to get a reply... maybe its in the too hard basket at the moment.

I currently use a EMP Centauri 154AP satellite Multiswitch (8 sat input , 8 output) with GBPVR... this is working perfectly.  While this multiswitch (as all others i guess) is strictly 4 sets of H and V.  I have used some for V only Sats (e.g. AsiaSat4) etc.  so i was actually getting around 6 satellites using the 8 inputs.  each of these inputs could be a different LO for the LNB (i have a mixture of 10700 duals/ 10750 and 11300 to avoid any blind scan issues).

To get to each input it uses first either A or B dieseq, then from there it sends a 22Khz gone to get to the right "pair" of H an V.. then obviously the frequency , polarity and SR of the channel does the rest.

Ive noticed that NPVR (and also winTV - and probably others) - have now moved to software that detects the sat cards, and give you the option of the following when configuring them:

- no diseq switche  (gives you 1 lnb dropdown box)
- A/B (which gives you 2 lnb dropdown boxes to configure LO / SW etc)
- diseq 1.x (which gives you 4 dropdowns -- you get the idea).

Under GBPVR - while i had 6 satellites running off the 8 inputs - i could set a different set of LO / SW for each "capture source" - and point them all at the same satellite card.  No problems at all.

Under NPVR (and WINTV) - they only list 4 satellites for the diseq 1.x option (diseq A-D).   I suspect this is because the multiswitch has been designed for 4 dual polarity satellites,  its just that here in NZ we have butchered it a bit to use one or two of the "dual" ports for single polarity satellites, which in turn could have different LO.

IT now appears that i can no longer use the multiswitch in this manner with NVPR / WinTV (or probably one of any of the newer generation PVR's).

Under my current setup - i would need a way to have multiple occurences of diseq A and B  (as below).

Diseq A - 22 Khz On
Diseq A - 22 Khz Off
Diseq B - 22 Khz On
Diseq B - 22 Khz Off

I just dont seem to have found a way to do this with the software anymore - which is a shame.

Then again - im not sure how many people out there use these multiswitches , so maybe im a lone voice :(

It would just be great if there was a way to have a 'custom' option instead of the 3 fixed options.  As im really keen to get into testing the newer generation NPVR.

Even if i only had 4 sets of dual polarity satellites connected - i still wouldnt be able to access them all - due to the simple fact the multiswitch only uses Diseq A and B (2 variants of each as you see above), and the A/B diseq option only gives you 2 dropdowns (i.e. 2 satellites).

Thoughts / Comments / Flames?

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1148 posts

Uber Geek

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  #418553 17-Dec-2010 16:43
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You're not completely alone - I have an EMP Centauri Profi Line 9x8 multiswitch. Probably almost exactly the same as yours except it has a terrestrial antenna input too Smile

Okay, so I'm happy to help but I'm also thoroughly confused! I think you're saying that you've only got 2 or 4 satellite inputs in the software (based on what kind of switch you select), but you want to hook up 6 satellites with the additional complication that you have different local oscillator frequencies for some of the satellites that are on the same group of 4 inputs (I call this a "port").

Have I got that right?
I'd call that a tricky problem, but if you know what you're doing it can usually be solved with a bit of hackery Tongue outInnocent.

First things first: the only way that I can think of to solve this problem requires you to edit the programs' transponder lists. I have no experience whatsoever with either of the programs you're talking about (or GBPVR for that matter) so you'll have to figure out where the lists are for yourself. They're very often stored in files but they could be stored in a database too. If they're hardcoded into the source code of the program and you don't have the code, or binary files for which you don't have a format specification, or they can't be edited for whatever reason then I think you've got no chance...

Do you understand why the local oscillator frequency is important?
Satellite signals are broadcast at ~12GHz, however cables can't carry those kinds of signals very well. The LNB's job is to translate the signal into a frequency that is better suited for antenna cable. The frequency that the satellite signals get converted to is called the intermediate frequency (IF). This intermediate frequency is what satellite tuners actually tune to. You can work out what the intermediate frequency for a given transponder is using the following formula:

Intermediate frequency (IF) = Transponder frequency (TF) - LNB local oscillator frequency (LOF)

Some examples?
LNB LO = 10750 MHz
Transponder = 12456 MHz
==> Intermediate frequency = 12456 - 10750 = 1706 MHz

LNB LO = 11300 MHz
Transponder = 12456 MHz
==> Intermediate frequency = 12456 - 11300 = 1156 MHz

So as you can see, the IF is different for the same transponder with different LNB LO frequencies. The IF is generally between 950 and 2150 MHz, but can be up to 2500 MHz. If you go higher than that, you can't use long cables. If you go lower than that you start entering DVB-T or analog frequency ranges. We don't want that because we want analog, DVB-T and DVB-S signals to be able to be multiplexed (combined) into one cable, and that requires that the frequency ranges don't overlap.

Now why does any of that matter?
The reason is that you can "trick" the software into tuning the correct transponders frequency if you change the transponder or LO frequencies in such a way that the true intermediate frequency (the frequency that the tuner actually tunes to) is tuned.

That's tricky to understand, so let's try an example. Lets say you have 2 LNBs on the same DiSEqC port but the LNBs have different LO frequencies and you are only allowed to enter one LO frequency. A problem right? Not any more! Continuing our example, let's say you want to tune the following transponders:

LNB 1 (LO = 10750 MHz): 12456
LNB 2 (LO = 11300 MHz): 12706

What do we do?
1. Pick the highest LO frequency and use that (it gives you the biggest possible range of possible IF frequencies).
In our example, we'd enter 10750 MHz. This choice means that the satellite on LNB 1 should work straight away.

2. Translate the transponder frequencies of the other LNB to maintain the same IF frequency.
LNB 2 has an LO frequency of 11300 MHz. That isn't going to change. That means the IF isn't going to change either. The IF for 12706 MHz is:

IF = TF - LOF = 12706 - 11300 = 1406 MHz

Okay so far? Now comes the important step. What would the transponder frequency be if the LNB LO frequency was actually 10750 MHz (the LO frequency we chose in step 1)? We can rearrange the formula to calculate it (a little algebra for you Tongue out):

IF = TF - LOF
TF = IF + LOF
TF = 1406 + 10750 = 12156 MHz

So if you change the frequency for the 12706 transponder to 12156 it will work! Cool

Now I'm sure the satellites you're tuning to will have more than one transponder. You don't want to have to calculate the IF for each transponder! There is a better way: work out the translation from one LNB to another. The formula is:

LNB Adjustment = LNB 2 LO - LNB 1 LO

Carrying on with the example:

LNB Adjustment = 11300 - 10750 = 550 MHz

So if we had wanted to calculate the frequency for 12706 faster we could have simply done:

TF (adjusted) = TF (original) - LNB Adjustment
TFA = 12706 - 550 = 12156 MHz

Cool huh!
Alright, now that we've done all the maths we can move on to the software. What you have to do is pick the LNB LO frequency that you're going to use for each DiSEqC port, and then adjust the transponder frequencies for all the LNBs that don't have the same LOF. You do this in the software's transponder lists. Nothing else needs to be changed except the transponder frequencies. You will probably also have to combine the transponder files because the user interface will only allow you to select one satellite for each LNB. Hopefully you are able to figure out how to do that by yourself.

Good luck! Smile



11 posts

Geek


  #418570 17-Dec-2010 17:04
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thanks for the reply - ill print this out and digest it at home.

my multswitch does have the terrestrial input - so it is a 9/8 also   (8 sat - 1 Terr input / 8 outputs).

sorry if ive been a bit vague or anything - i just wasnt sure of the correct terminology.

anyways - ill read through your reply tonight and see how i get on.

thanks again.


 
 
 
 


sub

356 posts

Ultimate Geek


  #418740 18-Dec-2010 08:55
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kbrophy:
Ive noticed that NPVR (and also winTV - and probably others) - have now moved to software that detects the sat cards, and give you the option of the following when configuring them:

- no diseq switche (gives you 1 lnb dropdown box)
- A/B (which gives you 2 lnb dropdown boxes to configure LO / SW etc)
- diseq 1.x (which gives you 4 dropdowns -- you get the idea).


Under GBPVR - while i had 6 satellites running off the 8 inputs - i could set a different set of LO / SW for each "capture source" - and point them all at the same satellite card. No problems at all.

Under NPVR (and WINTV) - they only list 4 satellites for the diseq 1.x option (diseq A-D). I suspect this is because the multiswitch has been designed for 4 dual polarity satellites, its just that here in NZ we have butchered it a bit to use one or two of the "dual" ports for single polarity satellites, which in turn could have different LO.

IT now appears that i can no longer use the multiswitch in this manner with NVPR / WinTV (or probably one of any of the newer generation PVR's).
kyle, you should be able to recreate same setup in NPVR that you've been using in GBPVR.

NPVR now auto-detects the devices in the machine because this is much simpler for the majority of the users, rather than requiring you to manually create the device. This does lead to the appearance of not allowing for some of the more complex DVBS setup like you're trying, but that isnt the case.

The important thing to remember is that a snapshot of the LNB/switch settings are stored within each channel at the time you scanned, and are permanently associated with those channels. You can then change those settings to something else, and scan for more channels using different parameters. The already present channels arent changed (they still have the same diseqc port number and LOF1/Switch/LOF2 values as the original configuration).

...so, by changing the settings and scanning with each the configuration values you need, you should end up with a full set of channels, all usable without having to go and change the LNB settings.

That said, I have one LNB and no switches these days, so its not something I actively test.



11 posts

Geek


  #419353 20-Dec-2010 11:21
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thanks guys for both your answers.

ill have a crack at this tonight (time permitting) - and feed back my findings.

Sub - thanks for your info - you were right - i had just assumed that since it looked like i was unable to do that complex setup anymore - that it was no longer an option.   Im very happy to know this isnt the case, and will  give it a go as soon as i can :)

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