SatSig topic:

LNB types DRO or PLL ?

(Read 17361 times)

May 21^st, 2011 at 12:50pm

Hi Sir ,

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

What are the advantages over another.

May 21^st, 2011 at 1:42pm

NJR make both DRO and PLL LNBs.
see: http://mc.njr.co.jp/eng/products/vsat/ku-lnb.html

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

Feb 4^th, 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)