SatSig topic:

Spectrum Center Frequency

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Jul 28^th, 2009 at 9:59am

Hello ,
Please I have a Question regarding the Measurement

I have an installtion in Afganistan and I am pointing my 2.4 Prodelin antenna on EutelSat W5 70.5 E(My Network is Ku Band)

As I know from this site that the beacon frequency is 11451.09 MHz & I have LNC( L.O Frequency ) = 11.30 MHz

So to adjust the frequency on the Spectrum I know this Equation

RX(L-Band) = BEACON Frequency - LNC ( LO Frequency )
= 11451.09 MHZ - 11.30 MHz
= 151.09 MHz

Is this result is okay to be put on the spectrum Center Frequency? Please give me advice

Note: there is 2 other Beacon frequencies for this Satellite

Thanks
Ahmed Maher

Jul 28^th, 2009 at 10:47am

An LNB with a LO=11300 MHz is not suitable for receiving a signal at 11451.091 GHz as there is a filter at the front end of the LNB that blocks input frequencies below 12.25 GHz, but passes intended wanted frequencies in the range 12.25 - 12.75 GHz. The output range of the LNB starts at 950 MHz and extends upwards to, typically, 1450 MHz or 2150 MHz according to type.

If you set your analyser centre freq to 1500 MHz and span to 3 GHz you will see the full noise floor range of frequencies in the cable from the LNB ( 0 to 3 GHz). There will be almost nothing in the range 0 - 900 MHz. There will be a broad band of high level noise from say 950 - 1450 MHz or 950 - 2000 MHz. Beyond the upper end the spctrum may drop off slowly. My LNB has 9.75 GHz LO and I can see signals in the cable all the way from 950 - 2900 MHz (corresponding to 10.7 - 12.65 GHz from the satellite) The upper end signals are well above the design range of the LNB, and are rather attenuated but are quite detectable.

Try looking for one of the other W5 beacons at 12501 MHz; this should appear on your analyser at 1201 MHz.

Alternatively, peak up using the wanted carrier or any steady high spectral density carrier in the range 12.25 - 12.75 GHz.

More details about how LNBs work

Best regards, Eric.

Jul 28^th, 2009 at 10:54am

you are tottally right Eric, that's why i was wondering the satellite operator gave me a beacon out side the range of my LNB

so if i use 12501 beacon

then the calculation should be 12501 - 11300 = 1201 or 1.201 GHZ

and this should be the center frequency,

Please Eric Correct me if i am wrong..!!

Thanks
Ahmed

Jul 28^th, 2009 at 11:10am

Quite right.

Your LNB must be suitable for the downlink frequency of your wanted carrier.

Different LNBs suit different ranges of the Ku band.

W5 has beacons at 11200, 11451.091 (or 11452.57) and 12501 MHz. All linear and on X pol.

If reception of a beacon is important then check with the satellite operator as to exactly which beacons are switched on and visible at your location.

Best regards, Eric.