Circularly polarized LNB for reception?


#1

I believe that older LNBs from DirecTV and Dish Network were circularly polarized. Is anyone using one right now? @kenbarbi @maxboysdad @ac8dg


18" Dish Indoors
18" Dish Indoors
#2

I have the 18" directV common offset dish. It originally had a circular lnbf … I have it, but found a linear one that fit in the retangular support arm and kept everything at the focal point…

I could swap back in the circular one… it uses the same offset:

Here is the tuner report on the linear non-pll lnbf


#3

Instead of using the dish, could you show the linear and circular LNB while directly receiving?


#4

ran into a little problem… the circular lnb has an offset of 11.250
the difference between 10.750 and 11.250 = 500 mHz

so I am trying to do the math… if 11.9024 is what

so I set the custom freq to 11.9024 - .500 = 11.4024
or… 11.9024 + .500 = 12.4024


#5

11.4024


#6

got several packets… this is using the 18" dish directv LNB-18 lnbf
the diagnostic say normal lnb current flow 0x23 and voltage 14.2

but … not happy… after 7 packets it has stopped flashing on the DC board

update: after 21 packets it stopped receiving


#7

I could try some of other linear lnbf:
I have
Averger Universal by DMS
Geosat-pro SL1PLL
Geosat-pro SL2PLL
XtremeII
ROC 785A


#8

This is just the circular LNB pointed at the satellite?

Do you have a Maverick MK1? If not the Geosat is a good one.


#9

ok with a dc un-plug - restart… it is now receiving well … yes with the 18 dish just for consistancy with
early post in the thread showing my 'linear lnb.

A 4db decrease in SNR but it is decoding well…

using the circular lnb 18

tuner report:


#10

I have the one from the MotoSat, but all the markings are gone, so can’t exactly identify it. I think it still works, but didn’t not have the right default settings to work othernet. If I knew the offset, as Jim did, we could power it up and try it… I believe you are right about circular, as there was no skew adjustment available on these…


#11

Circular probably doesnt work well because you are literally trying to catch a line ( ~ ) with a circle/spiral ( O ) and most of it goes right through (in theory).

The dish with a linear PLL LNB such as the Maverick will work (I get about 4dB), but it is still not the most optimal solution because the DirecTV dishes are designed to pull in 3 satellites so rather than focusing on one, you are kinda wideband with the dish. In my experience I had to tune the dish elevation, dish rotation, LNB skew, and even the angle that the LNB points at the dish (though this could be because of the static nature of the DirecTV mounting kit)


#12

You shouldn’t need a dish at all. The larger the reflector the more narrow the field of focus. Reception is fine at very low SNR.


#13

For me personally with the equipment I had available, using the dish was just easier. :slight_smile:


#14

A circular LNB won’t work. Needs to be linear. Ken


#15

That’s wrong in theory…

If you mismatch Liniear, so Horizontal with vertical you loose 30db, so the Signal is gone.
On the other Hand, when you mismatch circular with a linear, you only loose 3db, so it is fine.

But, i see no sense in using a so uncommon LNB type, when you just adjust the skew to fine tune the linear polirazation.

regards - Manuel - DO5TY


#16

It’s just to test the SNR hit. Not only will there be a 3 dB loss from the linear to circulation mismatch, there are also the additional signals coming in on vertical polarization causing more interference.


#17

Looking through the manual for the Sony SAN-18D1/SAN-18S1 (intended for use with the Sony SAT-A1 and SAT-B1 DSS receivers), this antenna/LNB has the following specifications:

Input Frequency: 12.2-12.7 GHz
Output Frequency: 950-1450 MHz
Output Connector: F-type
Power Consumption: 3 W Max
Supply Voltage: DC +11.5-14.0 V for RHCP, DC +16.0-19.0 V for LHCP

If you want to see a copy of the manual, search for L0409644.pdf and see page 50 (PDF page and original document page numbers are identical). A lot of these are probably gathering dust in various places.


#18

I just ran a test with my Invacom Quad Polar LNB (QPH-031) comparing Dreamcatcher performance with a linear polarized LNB and a circular LNB. The Invacom has 2 linear and 2 circular LNBs. It is connected to an offset feed 80 cm dish 500 feet away from the Dreamcatcher board.

Connected to the linear LNB I had fine reception

linear

Connected to the circular LNB I had no indication of signal. I checked to make sure my bias T was OK, and it was.

circular

I can’t say for certain if the problem was interference causing low SNRs or lack of signal. In my experience, if I get any signal with bad SNRs, my status display will display something.

Any thoughts out there? Ken


#19

Odd, you should still be seeing something. I wonder if it’s a completely difference LNB IC, which means the there might be a bit of drift in the frequency.


#20

Here’s a set of specs on the Invacom QPH-031. Interestingly I have never paid much attention to circular sources. Ken