lnb modification

[Huevos]

Unless I have read your post incorrectly, a digital stb with a functioning Local oscillator setup will not work to receive a lower working frequency than the local oscillator it is set up to use

Why not? IF is just the difference between the l.o. and the tuned frequency. Why would it matter which frequency came from the transmitter and which came from the l.o.? How would the mixer know? Personally I've built mixers that work both ways, but not at these frequencies. What would stop it working though would be a high pass filter.

[Channel Hopper]

The receiver will have an idea which way it is scanning based on the original software design. On Ku band settings it will scan positively and upwards, on C band it is downwards.

The local oscillator within the LNB provides a starting point and the filtering circuitry within the LNB provides the range of the scan

[Huevos]

The receiver will have an idea which way it is scanning based on the original software design. On Ku band settings it will scan positively and upwards, on C band it is downwards.

The local oscillator within the LNB provides a starting point and the filtering circuitry within the LNB provides the range of the scan

I really don't understand what you mean? When the receiver does a scan it just scans 0.95GHz to 2.0GHz. Knowing the l.o. frequency just allows the receiver to work out what frequency the IF it is scanning corresponds to. E.g. I want BBC1 CI which is on 10847. L.o. is 9750 so the receiver needs to scan 1.097GHz.

[Channel Hopper]

A Ku band LNB uses (from memory) low side injection, and the frequency available to enter the demodulator will be a positive from the local oscillator frequency.

In C band the high side injector circuit means the incoming signal pulled in is lower than the local oscillator.

Filters in the LNB (usually the tracks on the PCB - which become inductive chokes at these frequencies) are used to reject signals that are on the 'wrong' side of the scanning range, however since the LNB is unlikely to come across a similar strength set of signals whilst pointing at a specific satellite (or towards the horizon) this is less effective than the detection software within the tuner/demodulator circuit at the front end of the receiver.

There is a better chance that by falsifying the scan frequency (ie selecting a C band LO) , the receiver will lock into something that is actually below the local oscillator of a Ku band LNB.

Of course the modified LNBs that have been mentioned may have one fo the inductive tracks adapted to allow more signal from the lower frequencies, however if the dish pointing is accurate, this may not be necessary

[Satcom1]

the Coolsat/tecnomate type of receiver is capable of connecting to a C Band LNBF and blind scanning on the Ku Freq's and seeing and recovering the C band channels on Ku freq's.

They are consumer grade receivers.

[Tsiklon]

There's no great benefit to changing to LO on the receiver when doing a blindscan. The maximum the receiver can scan is from 950-2150MHz regardless of whether you specify a Ku or C band LO or any other custom LO.

In general, with most blindscan receivers, if you select the default C-band LNB settings, they blindscan from only 950MHz - 1750MHz (4.2GHz - 3.4GHz).

You are better off selecting the default Universal LNB settings as then the receiver will scan from 950-1950MHz (10.7GHz-11.7GHz) and 1100-2150MHz (11.7-12.75GHz).

Alternatively, select custom LO and by default most blindscan receivers will then do a full IF-band scan from 950-2150MHz.

[ralphmagno]

hello to all
the f-wave is a lnb that costs little 4 to 5 euro
there are t freq.adj screws onr for 9.750 ghz the other for 10.6 ghz.
the blue cap can be modifies some but to move it you would have to lower the frequency from 10 ghz l.o to 8.580ghz thats a long away fron the way it has been built.
the output of a standard lnb would have to pass through another mixer
a long time ago global made a frequeny extender.
there were only 10 ghz lnb's at that time.
so the extender would shift the frequency 250 mhz so the analog boxes would work on the old lnb's
you would have to have a extender after the lnb that would shift the spectrum another 1000 mhz or so to receive this.
so standard lnb and another mixer to shift this down to the receiver rasnge

ralph

[Tsiklon]

If the F-wave is just a standard Universal LNB, then it is practically very difficult or impossible to adjust the LO by 1200MHz in order to receive a signal on 9.54GHz as suggested by the OP.

What may be possible is to shift the LO by 150-200MHz max and then be able to receive channels transmitted on 10.54GHz.

[ralphmagno]

hello to all
ok doing the math here is whats true.
if you were able to lower the lnb lo by exactly 200 mhz the lowest frequency you could receive is 10.600 ghz thats still far away from 9.540 ghz.
you take the lo frequency and subtract from transmitted frequency and the result must be within the 950 to 2150 range.
this is the olly way.
after 11700 the cross over frequency the 22khz kicks in and 10.600 ocs
kicks in and we have the upper band.

ok a satellite frequency of 10.719 ghz using the math of minus 9.750 ghz and we have 969 mhz and the receiver will see this no problem and we have tv.
thats why i said the lo would have to drop from 9.750 ghz to 8.580 ghz not possible to make a 1160 drop.

the band pass of the first stage of the lnb comes at about 10.700 and 10.600 ghz is no problem.
one would have to modify the band bass down to 9.5 ghz and the lo to run at 8.580 as well.
i have a friend who has a lab and the equipment to do this and has built transmitters up to 50 ghz as well and he builds tv transmitters as well and we talked about this on the phone the other day.
i have a satellite meter with a sprectum analizer.
i set up the dish on hot bird,find duna tv at 10.813 horz in analog and turn the lo screw untill i get duna at 10.903 and bingo i moved lo down 90 mhz.
and the lnb lo is running at 9.690 ghz.
when i receive a signal at 10660 i tune the receiver at 10750 and bingo it works with a 30 cm dish.
this in affect is at 1000 mhz and the sat tuner that runs at 950 to 2150 is in the tuner range.
you need a lot of equipment to modify the band pass and the lo to work 1200 mhz below its normal operating range.
1200 mhz is not 90 or 100 or 200 mhz but 1200 mhz.

if they sell the lnb modifies in a store in spain and you use a 30 cm dish the dish must point horz and the lnb will be towards the ground.



well hope this helps you subtracted the lo frequency from the frequency you are receiving and the diff must be within 950 to 2150.

ralph

[Huevos]

if you were able to lower the lnb lo by exactly 200 mhz the lowest frequency you could receive is 10.600 ghz thats still far away from 9.540 ghz.

Right now this is just a hypothetical game of guess the frequency. Anyway, before I read this thread I would have sworn that LNB was just a standard piece of kit and am still biased towards that view.

if [...] you use a 30 cm dish the dish must point horz and the lnb will be towards the ground.

No. The dish is normally mounted up-side-down with the LNB above the dish. Other systems use a cassegrain style dish.

[Tsiklon]

if you were able to lower the lnb lo by exactly 200 mhz the lowest frequency you could receive is 10.600 ghz

If you lower the first LO on a Universal LNB from 9750 to 9550, then you would be able to receive 10.5GHz i.e. 10700 - 200 = 10500.

[jimbofz]

thanks everybody for the posts
i now know how to do the math ,i understand if the freq is 9.54 ghz then adjustment of the local osc would not lower the freq enough to receive the signals
one thing i must stress is that with a standard uni lnb and a correctly aligned dish my signal strength meter shows a reading of about 3db lower than the modified lnb
finally the reason i thaught it may be transmiting on circular polarisation is that, as read on an american forum, that if you try to use the wrong type of lnbf you get approx 50%less signal, [i believe circular polarisation is not in common use in europe but is still used in America]

[purplemarina]

This is my experience with one rebroadcast company on the costa blanca. I connected my Technomate to my neighbours 30cm dish and did a blind scan , once i had the frequencies i was able to align my own dish and standard universal lnb . The channels are sometimes scrambled and other times free . The 30cm dish is mounted upside down i think this is because the signal comes from a transmitter on top of a building so comes in at a low angle rather than from a satellite .

[Huevos]

one thing i must stress is that with a standard uni lnb and a correctly aligned dish my signal strength meter shows a reading of about 3db lower than the modified lnb
finally the reason i thaught it may be transmiting on circular polarisation is that, as read on an american forum, that if you try to use the wrong type of lnbf you get approx 50%less signal, [i believe circular polarisation is not in common use in europe but is still used in America]

What signal strength meter? If you are talking about gross signal level that is meaningless. For example a Black Ultra is about 10 dB up on an Invacom quad but only around 0.5dB up in signal to noise.

Also, today I went to a job in Algorfa where they had updated to a big dish from a rebroadcast system. The rebroadcast dish had been taken down and was lying on the ground. The dish was Cassegrain and the LNB was just a normal universal LNB. I tested it by holding it up in front of a 1.8 metre dish aligned on 28.2ºE. Tried 10817V and got TVV International - tried 12246V and got Dr Dish. So there was no mod to the l.o. on that LNB for sure.

Lastly, circular polarisation is not used for omni-directional broadcast aerials, it is used where a signal is being beamed in one direction. (Try to imagine what a circular polarised omni-directional aerial would look like if such a thing existed.) As for circular polarised LNBs they are standard LNBs not universals. Universals are a European invention where there have never been ku band circular polarised transmissions.

[jimbofz]

in answer to HUEVOS AS YOU KNOW THERE ARE MANY OF THESE REBROADCASTERS ,IN AND AROUND COSTA BLANCA SOME BETTER THAN OTHERS SOME USE ENCRYPTION SOME DONT ,I SUSPECT THE ONES THAT DONT RELY ON NO ONE FIGURING OUT ABOUT THE MODIFIED LNB , THE ONES THAT DO USE STANDARD UNI LNBS
MY NEIGHBOURS LNB IS DEFO MODIFIED HIS FTA RECEIVER IS JUST A STANDARD BOSHMANN WITH NOT EVEN A CARD SLOT .I STARTED THIS THREAD OUT OF CURIOSITY AND HAVE BEEN AMAZED AT THE WEALTH OF KNOWLEDGE AND FOR THIS I AM VERY GRATEFUL

[Huevos]

SOME USE ENCRYPTION SOME DONT ,I SUSPECT THE ONES THAT DONT RELY ON NO ONE FIGURING OUT ABOUT THE MODIFIED LNB , THE ONES THAT DO USE STANDARD UNI LNBS

FYI this set up was using a SD Darkbox Rev 2007 without card... but as you say there are many different systems out there, and probably no standards.