Suppose a signal comes from the satellite at a microwave frequency of 12 GHz but your typical receiver tunes up only to 1.75 GHz? (Also bear in mind that most cable will NOT happily pass frequencies much above 2GHz).
The function of the LNB is to reduce the frequency of the satellite signal. It does so by subtracting a frequency figure from the satellite signal frequency.
This figure is called the "Local Oscillator" frequency ("LO") of the LNB.
So an LNB with a LO of 10.25GHz will send a 12GHz satellite signal down the cable at 1.75GHz (just within range of your old receiver).
12GHz - 10.25GHz = 1.75GHz
Working in reverse, if your highest satellite frequency is 12.6 GHz then you will need an LNB with a LO of at least
12.6 - 1.75 = 10.85GHz
in order to reduce the satellite signal to a frequency that your receiver can "see" (1.75 GHz).
Now let's reverse the process again:
A "standard" LNB has a LO of 10.0GHz. So the highest satellite program frequency that your standard receiver can *see* is
1.75 + 10.0 = 11.75GHz
An "enhanced" LNB has a LO of 9.75 GHz
1.75 + 9.75 = 11.50GHz
A "universal LNB has TWO LOs. One is 9,75 (same as "enhanced") The other is 10.6 which is selected if it "hears" a 22kHz (just above audio) signal.
1.75 + 10.6 = 12.35GHz
Of course, if your receiver can accept signals up to 2.0 GHz then the highest acceptable signal frequency becomes
2.00 + 10.6 = 12.60GHz
And a receiver with a tuner that extends to 2.15GHz achieves
2.15 + 10.6 = 12.75GHz (which happens to be the top of the "Telecom" band!)
Now, you are still puzzled about the DBS LNB
This has a LO of (typically) 10.75GHz
So an old 1.75GHz receiver will get up to
1.75 + 10.75 = 12.50GHz
A final consideration has to be the LOWER limit on tuning:
Most old receivers can tune no lower than 0950 MHz (= 0.95GHz) whereas later ones might go down to 0.70GHz.
Check out the above calculations with these lower tuning range limits to see the overall tuning bandwidth for any receiver.
This is all very basic "sums" - nothing complex - so once you have a "picture" of what is happening, you can sketch little band plans for any combination of receiver annd LNB.
Once you know the value(s) of the LO(s) in the LNB and of the upper and lower tuning limits of the receiver in question, you can quickly figure out what can be received.
NOTE:
Older receivers *expect" an LNB with a 10.0 LO and the frequency display is arranged just for this. However, you can use an LNB with a different value LO. It just means that the *displayed* frequency will be incorrect.
Transponder - LNB Local = tuner frequency Frequency Oscillator 12750 MHz Telecom/Astra 1F DBS/Astra 1E 11700 MHz - 10000 MHz = 1700 Astra 1B Astra 1A Receiver tuning range without ADX Astra 1C 950 + 500 = 1450 Astra 1D Tuning range with ADX 10700 MHz - 10000 MHz = 700 + 500 = 1200
An old standard receiver usually tunes from 950 to 1700 MHz.
The map above shows the limited tuning range of an old standard receiver with an old standard 10.0 GHz LNB. The addition of an ADX Channel Expander moves the Astra 1D frequencies up by 500 MHz into the tuning range of the receiver.
To receive all Astra channels from satellites D to B without using an ADX, a receiver would need a tuning range of 700 to 1700 MHz.
Transponder LNB Local Frequency Oscillator 12750 MHz - 10600 MHz = 2150 Telecom/Astra 1F Receiver tuning range for Hi band (22kHz on) DBS/Astra 1E - 10600 MHz = 1100 11700 MHz - 9750 MHz = 1950 Astra 1B Astra 1A Receiver tuning range for Lo band (22kHz off) Astra 1C Astra 1D 10700 MHz - 9750 MHz = 950
An Enhanced LNB has a local oscillator frequency of 9750 MHz.
The receiver now needs a tuning range of 950 to 1950 MHz as shown in the map above.
If a Universal LNB is used, its local oscillator can be switched from 9750 to 10600 MHz by sending a 22kHz signal up the cable. Some receivers have this facility built inside. Some will need an external signal-inserter box connected into the cable.
If the receiver has a range of 950 to 2150, it will be able to receive programmes on both Hi and Lo band.
Another possibility is to use an ADX-Plus. This has an internal switch which, when moved across, makes the ADX-Plus move the frequencies DOWN by 500 MHz instead of up.
So a channel at 12750 MHz is moved down like this:
12750 - 10600 - 500 = 1650 MHz (with an ADX-Plus)
which is well within the tuning range of an old standard receiver.
And the lowest channel receivable will be:
950 + 500 + 10600 = 12050 MHz (with 22kHz signal ON and ADX-Plus)
By fiddling with the ADX-Plus switch and the 22kHz signal inserter you can probably receive the full range of channels if you have a Universal LNB and a standard receiver!
Note: MHz (MegaHertz) = GHz (GigaHertz) x 1000
So 9750 MHz = 9.75 GHz
Please let me know if you have any other thoughts on this and maybe we can add it to the FAQs.
Astra broadcast frequencies range from 10700 Mhz (Astra 1D) through to
11700 Mhz (Astra 1B). So I need to calculate which of these frequencies
each of the two L.O.s on the LNB in conjunction with the tuning range
of the receiver, I can receive, thus:
L.O. 1 of 9750 Mhz
950 Mhz (lower tuning capabilities of receiver ) + 9750 Mhz (L.O. 1)
= 10700 Mhz
1700 Mhz (upper tuning cap. of receiver) + 9750 Mhz (L.O. 1) = 11450
Mhz.
Hence able to receive frequencies of 10700 Mhz to 11450 Mhz.
L.O. 2 of 10600 Mhz
950 Mhz (lower tuning capabilities of receiver ) + 10600 Mhz (L.O. 2)
= 11550 Mhz
1700 Mhz (upper tuning cap. of receiver) + 10600 Mhz (L.O. 2) = 12300
Mhz.
Hence able to receive frequencies of 11550 Mhz to 12300 Mhz.
Being an old crappy Amstrad SRD400, I presume my receiver isn't able to
signal the LNB to switch to the upper of the two L.O. frequencies, so I
can't access anything above 11450 Mhz. With a 22kHz signal inserter I should
therefore be able to access 11550Mhz - 12300Mhz?
You are doing OK so far.
However, this leaves a gap in the middle between 11450 and 11550 of
frequencies which I can't access! Presumably with an ADX (and 22kHz signal
inserter) I can shift those frequencies into tunable ranges?
Presumably, all I need now is an ADX and a 22kHz signal inserter in order to
receive all Astra frequencies (and then some ... )? Oh yes, and a Sky
subscription :-)
You don't really need a 22kHz signal inserter.
Would I be better off buying an ADX plus, so that I shift the
frequencies down rather than up? So as to ensure my receiver is happier
about it?
Yes, I would think so. There's nothing on the higher frequencies for your Amstrad to receive from Astra at 19.2 degrees East.
Sky Sports 3 would be the highest useful channel, with a couple of foreign stations just above that.
How much would I expect to pay for an ADX and 22kHz signal inserter?
If you have a Sky subscription they will post you an ADX-Plus for just £9.99.
Otherwise you can buy one for £12.95 upwards.
Many thanks for all your help. It all seems so much simpler now. Or have
I missed something?
Nope. I told you it was simple. People become frightened because they think it's too technical. The truth is that you simply need to be able to add and subtract - roughly to primary school level or lower! You don't need *any* technical knowledge. Just realise that there are various ways to add or subtract the frequencies. Specifically: there are various fixed values that you can use - Typically 10.00 GHz, 9.75 Ghz, 10.6 Ghz etc. for an LNB. Also +0.5GHz and -0.5GHz for an ADX-Plus Channel Expander, dependent on its internal switch position.
______________________________________________________
LNB Universal จะมี LO อยู่หลายค่า เช่น 2 ค่าสำหรับ KU Low Band กับ KU High Band คือ 9750 กับ 10600
ส่วน LNB 11300 เป็น LNB สำหรับ UBC จะมี LO อยู่ค่าเดียวคือ 11300
สังเกตว่าความถี่ช่องต่างกๆของ UBC จะมากกว่า 11300 เสมอ เมื่อนำมาหักล้างกันจะได้ออกมาเป็นความถี่ที่ Receiver จะสามารถรับได้ ถ้าใช้ LNB 10600 เมื่อเอามาหักล้างกันแล้วอาจจะเกินช่วงที่ Receiver สามารถรับได้
การเปลี่ยนค่า LO ของ LNB Universal ใช้สัญญาณ 22 KHz แต่มันจะทำโดยอัตโนมัติไม่จำเป็นต้องสั่งเอง
สาเหตุที่ต้องมีการหมุนองศาของหัว LNB เพราะว่าภายในจะมีแผ่นรับสัญญาณซึ่งจะวางตั้งฉากกันเพื่อรับสัญญาณจากทั้ง V และ H จึงต้องหมุน LNB เพื่อให้ขั้วรับสัญญาณได้ดีที่สุด
สรุป
- ค่า LNB C Band คือ 5150
- ค่า LNB KU Band คือ 9750,10600
- ค่า LNB UBC คือ 11300
จานที่ LNB อยู่กลางจานเรียกว่า Prime Focus