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VSAT technology and installation >> iDirect Forum: hubs and terminals >> LNB types DRO or PLL ?

Message started by techtest on May 21st, 2011 at 12:50pm

Title: LNB types DRO or PLL ?
Post by techtest on May 21st, 2011 at 12:50pm
Hi Sir ,

What are the differences in between NJR and PLL lnbs ..

What are the advantages over another.

Title: Re: LNB types DRO or PLL ?
Post by Eric Johnston on May 21st, 2011 at 1:42pm
NJR make both DRO and PLL LNBs.

DRO (dielectric resonator oscillator) LNB types have very poor frequency stability and are suitable only for the reception of wide bandwidth carriers, such as a 27 Msps satellite TV or VSAT outlink carrier, where the receiver tuning circuits can lock onto the carrier despite frequency errors of up to +/-500 kHz or +/- 2 MHz and second's delay (or more) locking up is of no consequence.

PLL (phase lock loop) LNBs use an internal 10 MHz crystal oscillator (which has high stability) and a phase locked oscillator at say 10 GHz. Frequency accuracy is very good (say +/-25 kHz) and phase noise is low. Use this type for the reception of low symbol rate carriers and higher order modulation carrier like 8PSK and 16QAM. External reference PLL LNBs are also available. These need a 10 MHz supply up the cable from the indoor equipment. External reference PLL LNB accuracy can be extermely good if you use an atomic derived oscillator such as one based on GPS receiver. All teleport hub earth stations should use external reference PLL LNBs. The 10 MHz supply should have excellent phase noise characteristic so make sure its power supply is well smoothed and it is not located next to a motor (e.g. a fan which give out both vibration and an oscillating magnetic field).

BUCs must have an external reference 10 MHz supply since the transmit uplink carrier must fit into the satellite transponder between adjacent carriers just a few kHz apart either side. In TDMA uplinks even higher accuracy is requred so the sequential bursts from different uplinks all have exactly the same frequency. This helps the TDMA burst reciver (line card in iDirect) lock up on each burst very fast to minimise wasted time.

Best regards, Eric

Title: Re: LNB types DRO or PLL ?
Post by Apek on Feb 4th, 2019 at 11:10am
Yes, absolutely correct.

Go for DRO LNB for wide bandwidth carrier and PLL LNB for TDMA carrier...use internal 10MHz reference for VSAT site and external clock for hub station (get from GPS receiver)

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