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PLL Lnbs

G

gcohen

Guest
#1
Are PLL Lnbs really better than ordinary Lnbs - ie Invacom.
The figures that Sweedish Microwave give for their range have noise figures of 0.6 or 0.7 dB
Geoffrey
 
O

Old Fred

Guest
#2
gcohen said:
Are PLL Lnbs really better than ordinary Lnbs - ie Invacom.
The figures that Sweedish Microwave give for their range have noise figures of 0.6 or 0.7 dB
Geoffrey
I wouldn't put too much faith in noise figures. I've read reports that say, for example, that the Manhattan MTI 0.6dB LNB works better (for Astra 2D) than the Invacom 0.3 or the Syntec 0.3. And consider these points:-

1. It's very difficult to measure such low noise figures.
2. They are measured under laboratory conditions with "perfect" 75 Ohm cable simulation. In practice, "75 Ohm" cable can be anywhere from 65 to 85 Ohm (worse if you kink it!)
3. It's not feasible to measure noise for every LNB across the entire two frequency bands (high and low). So the manufacturers make a couple of "spot" measurements at specific frequencies and "extrapolate" (= guess) that those measurements are "typical" for the whole spectrum. And they measure only a few LNBs in each batch of thousands.
4. Even Swedish Microwave *allegedly* have only a dozen little graphs which they print and put in LNB boxes at random! (I don't know if this is true but it makes sense). But at least their graphs really are "typical".

As for "PLL" (Phase Locked Loop), I don't know of any other way to establish an accurate and virtually drift-free Local Oscillator frequency, so I guess ALL LNBs must use a "PLL".

Kinda like boasting "bread made with REAL flour!"
As if there was some other kind of bread.
 
G

gcohen

Guest
#3
This is what SM say : -

"Dear Geoffrey
high stability LNBs (e.g. PLL) will not improve a standard Digital TV signal. To improve your signal you need an OMT and two seprate LNBs (WR75) to have high isolation (cross polarization). E.g. our Quattro.

Best regards
SMW - Swedish Microwave AB

e-mail [email protected]
Tel. +46 141 216135
Fax +46 141 215224
Web www.smw.se
 
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My Location
Madrid
#4
Hi.. In no way am I as technically inclined as some of the other people who have responded to your post. What I can tell you is only from practical experience.

I am located about 30 KMS to the west of Madrid am have a 1.2m offset dish with a twin output Invercom 0.3 db LNB. The results I have achieved are very good considering my location. I recieve all Astra 2A & 2B channels with the exception of Movies premier and Max for a couple of hours in the morning only. Most Astra 2D channels are available, eg sky sports news and regional BBC and ITV. The regular London ITV and BBC 1 & 2 are not with the exception of a 2 hour slot in the mornings when them come in albeit a little jerky sometimes.

I have a friend who is also a member of this forum and lives about 10 KMS from me. He is using a 1.8m dish, with a 0.6 lnb. Admittedly his reciever does not alegedly have a low threshold tuner but his results are far poorer than mine with a much bigger dish. NO beeb at all and many north beam transponders are not received for most of the day.

My personal experience says that the Invercom LNB was well worth the £25 extra as it's appears to be the difference between viewing and not viewing in my fringe reception area.

Hope that this is of some help.
 
G

gcohen

Guest
#5
Swedish Microwave told me about a local supplier and again assured me that their solution would improve on an Invacom. The local supplier allowed me to have a WR75 mount SMW LNB and an OMT on a sale or return basis.

A direct comparison in Israel on my 1.8M prime focus dish with a SMW XM140 feed showed the Invacom to be slightly superior - ie with the Invacom I was able to get Bravo and with the SMW I could not.

I use a Spectralook (made by Emitor A:cool: to set the skew - this setting is critical.

Geoffrey