How to reverse polarityfor toroidial dish

[Irish]

How do you change the polarity in a circular lnb?

[Nostradamus]

those dishes require a special LNB unless of course you want to manually edit every transponder in your sat list to the opposite of the default

[Irish]

I have heard you can do a blind scan if you use regular lnb's and the receiver will assign transponders accordingly, I have also heard you can manualy change the polarity of a reg lnb which is what I am trying to find out how. I have been told the majority of reverse polarity lnb's on the market are made in China and do not last long. There is a way to convert a reg lnb, anyone have any ideas?

Cheers

[Irish]

Anyone heard of how to modify a reg lnb to reverse polarity? Apparently there is a way, turn the head or adjustment inside the cap? A supplier told me he used to have a guy do it for him so he had better quality lnb's than the cheap made in china reverse polarity lnb's on the market. He can no longer contact the tech so I am looking to see how I can modify a good lnb for my dish.
Any assistance is appreciated.

Cheers

[Terryl]

Well the problems with trying to modify an LNB for reverse polarity is the fact that the internal antennas are soldered in place and you have to do some internal circuit board mods to swap the internal antennas around.

A T55 or T90 dish has a second reflector on it, (called a gregorian reflector) this makes the satellite signal bounce a second time before it gets to the internal antennas inside the LNB, this second bounce puts all the signals 180 degrees out of phase compared with the normal signals on a standard dish.

Wave Frontier makes the LNB's that are used with their dishes, there are cheap clones out there and it's these cheap clone LNB's that are failing, buying cheap does not save you $$$ over time with this type of stuff, I would pay the price for the good stuff and wouldn't worry about it.

You could try mounting the standard LNB's upside down, but this will expose the connectors to the weather. (and may not work)


Besides the LNB's from Wave Frontier are not that expensive, look here.


http://www.sadoun.com/Sat/Order/LNBFS/Toroidal-Reverse-Polarity-LNBF.htm

The only problems with those LNB's is the fact that they are the old style legacy type, and you have to use a legacy switch to run them.

[Irish]

Thanks, I was looking at that site but single output are not what I am looking for, the sadoun dual ones I am unsure what they are

[jvvh5897]

With a linear LNB, all you have to do is rotate the LNB 90 degrees from the way one would normally twist the LNB for best signal.

With a circular LNB, they often have a small piece of plastic in the waveguide of the LNB and the dielectric properties of the plastic (teflon is a good one to use) converts the circular signals to linear, so the guts of the LNB are the same as a linear LNB save for the frequency of the LO--now I don't know why one would want to swap polarity of circular signals, but I would think that with this style of LNB you could twist it 90 degrees and swap them--maybe not though, as I recall I've mounted circular LNBs every way one can and the R and L stay just that.

I would think that it would be a lot easier to just swap the 14/18V selection for the TP in the LNB setup.

[Terryl]

Thanks, I was looking at that site but single output are not what I am looking for, the sadoun dual ones I am unsure what they are
If your trying to run more then one receiver then go with a 4x4 legacy switch, 4 legacy LNB's to a 4 output legacy switch would have 8 inputs from the LNB's to 4 outputs.

Don't get fooled by a SW44 legacy switch as that is only for 2 satellite locations.

Some of the newer legacy switches are listed as a 9x4, the extra input is for an OTA antenna input.

The Sadoun LNB is a standard type circular LNB, it has two outputs to run 2 receivers, it uses the legacy switching of +14 and +18 volts on a single "F" connector, this will let you use 2 receivers on the one LNB.

Diseqc switch settings for this type of LNB would be "Diseqc OFF", if you use a single LNB, and what ever you want if more then one, using a Diseqc 2.0 switch you can go with 16 of these LNB's, but you would need the T90 dish to handle that many.

Only problem with the reverse LNB's is that they do not have one for the 118/119 satellite combo, and you can space them close enough to use 2.

[Irish]

I have been running two elliptical, one for 110/119 and 82/91, I would like to get 129 so rather than adding another dish I picked up a t-55 toroidal, it does not come with lnb's, and it requires reverse polarity lnb's as the signal is reflected twice, reversing the polarity when it reaches the lnb. Most of the lnb's sold as reverse polarity are cheap...made in china...and do not last. My supplier had someone modifying lnb's for him to reverse polarity, but that tech is no longer available, so we know it can be done, he mentioned rotating the head as did jvvh5897 above. I am running an EMP-Centauri 13x8 switch which requires two inputs per port...a dual lead lnb.
I am looking to either find a quality reverse polarity lnb, or how to modify one to reverse the polarity. The sadouin reverse polarity have his name directly on the lnb, so are these the cheap ones ordered with his tag on them, or the sticker replaced? Are they the good wave frontier ones? Or did he have someone modify them as did my supplier previously? I am skeptical not knowing the quality, so it seems my best option going forward is to learn how to modify one myself. The toroidal dishes, to my knowledge, are no longer being produced as they are expensive to manufacture, and in turn, expensive to buy so sales have not been tremendous, add in the need for a reverse polarity lnb.....my concern is in the future if the lnb's become obsolete, I will have to modify one.

Thanks everyone

[Terryl]

Buy them from WaveFrontier as they are still around.


http://www.wavefrontier.us/Online%20Store.htm

And I would not buy a modified (by anyone) LNB, too much to go wrong, this may be why the guy does not do this anymore.

Contact Sadouin and ask them about their LNB's.

[Terryl]

As far as internal mods to an LNB here is a photo of a Dish 500 LNB's internal antennas for 110W, the other types of LNB's have about the same type of setup.

19886

As you can see, one antenna is a PCB trace,( the "R" antenna) the other is a wire with a dielectric insulator on it,(the "L" antenna) trying to mod one of these would be fun.

What is not being seen is the special cavity in the signal forcing cone that this antenna fits in (I will try to see if I can get a photo of it) this is what helps it detect the "L" polarity signals.