LNBF won't change polarity

Status
Please reply by conversation.

SignalHill

Well-Known SatelliteGuys Member
Original poster
Pub Member / Supporter
Oct 30, 2013
30
17
Newfoundland, Canada
My C band LNBF will only work in V polarity. I've swapped out RX to no effect. How does the LNBF polarity
switch work? How do I test it?

Next steps are to remove the LNBF from its icy perch and bring it inside to warm and thaw.

Any help greatly appreciated.

73
fred
 
An LNBF is most normally voltage switched. The receiver will output 13V +/-1 to put the LNBF in Vertical Polarity.
The receiver will output 18V or thereabouts to put the LNBF in Horizontal mode.

Do you have switches or a controller in the coax line from receiver to LNBF?
If so bypass everything and run straight to the LNBF, select a Hoz. transponder and check voltage on coax at LNBF.
If near 18V then you may have a bad LNBF.
Which receiver and LNBF do you have?
 
For LNBFs, the polarity is typically controlled by the DC voltage supplied to the LNBF via the coax. If I remember correctly, 13V=Vertical, 18V=Horizontal.

It could be caused by a damaged cable or connection (water in a connector), which could cause the voltage to drop enough that the LNBF never gets enough voltage to switch to Horizontal

Or maybe a defective LNBF.
 
ah KE4EST you beat me by a few minutes :)
Yes, but you threw in a very important point, that I was thinking but not enough coffee I don't guess.
That was about water in coax or damaged coax. :)
 
  • Like
Reactions: Brct203
The RXs are Geosat Pro HD and Openbox S10 HD. The LNBF is a Titanium C1 PLL. No switches of any kind in the signal path.
Tomorrow I'll get out my voltmeter, stepladder and snow shovel and investigate further. Thank you for pointing me in the right direction.

Cheers
fred
 
I'm making good progress. After doing a string test and checking the alignment of the scalar ring with my homemade laser alignment tool I discovered the dish has some major alignment issues. Not surprising given the 140+ kph winds we had during the last blizzard. I have the C1 PLL
back in service and am picking up most horiz polarized signals I was looking for. Next is another bash at the dish with a rubber mallet after loosening all the bolts attaching the reflector to the polar mount and making another alignment tool that fits into the throat of the LNBF as there
is quite a bit of freedom of movement of the LNBF within the scalar ring.

It seems like I start to lose channels in Nov. and it keeps getting worse over the winter until I've had enough and get the wrenches out in early
spring. I'm glad the dish had a little bit of give to it, the alternative is a post winter pile of scrap metal.

Thanks for you help and moral support guys.

Cheers
fred
 
@SignalHill
You guys have been getting some rotten weather this winter/spring, hope you can get your dish squared away. Check the mount where it clamps onto the pole, that can slip in high winds too. Also check the pole to see if it's still vertical after that much wind.
Hopefully your snow shovelling is over for this season!
 
Thanks Cham,

those are things which I have not checked yet. I also noticed some saltwater corrosion in the throat of the LNBF. Living close to the
Atlantic makes everything corrode. Who would have thought that a hobby that is primarily electronics would involve so many wrenches :)

Winter is letting go slowly, Snowblower repair season gives way to lawnmower repair season.
My life with wrenches....

cheers
fred
 
Status
Please reply by conversation.
***

Users Who Are Viewing This Thread (Total: 1, Members: 0, Guests: 1)

Who Read This Thread (Total Members: 1)