Hair Brained Scheme for LNB....

[jollyrgr]

....or ERROR in LO frequency? Please let me know if I have an idea that won't work or if I've got something else wrong.

I'm trying to setup a FTA receiver at my parents. The setup there is a mesh 7.5ft dish with C-Band only feedhorn and LNB. There is a second coax there for Ku. So here is what I'm attempting....

I want to use an old DirecTV LNB from an 18" dish on the 7.5ft dish. What I'm attempting to do is mount the LNB slightly off center of the focal point. In other words strap it to the side of the C-Band feedhorn LNB assembly. I'm figuring if this LNB will work with an 18" dish off center feed it will work just fine slightly out of the focal point of the big dish.

So I hook up the LNB to the spare coax from the big dish and connect the other end to the DVB receiver. I positioned the dish on G10R and peak the settings using the sat finder on the C-Band LNB. I then move the DirecTV LNBf to the focal point. I have my sat finder at the dish now connected to the Ku LNBf and move the LNBf to find a place where the meter jumps up and the tone changes in pitch and level stating it has found a signal. Back at the receiver I get a signal but no quality indication. So I tried moving the LNBf to different positions, changing orientation, changing F connectors etc. to no avail.

Thinking this, in theory, should work just fine I figure something else is wrong. I swap coax cables (no help). My thinking is I am doing something wrong in the way the LNBf operates; namely it does not have the same L.O. frequency of 10750 MHz like a standard LNB for "big dish" setups. So I start searching the forums and come across this thread:http://www.satelliteguys.us/showthread.php?t=107462

Here I read some interesting items. Namely Pete's post of a DBS LNBf L.O. of 11250 MHz. Still later I see 9750/10750 MHz (but I don't think this applies). Another suggestion is L.O. of 10600 MHz with 22KHs ON. This last one has me as what does the 22KHs ON mean? Is this supposed to be 22KHz ON and is this a setting on all receivers? What did the original LNBf devices have as their L.O.?

(The DirecTV LNBf I'm using is part number BSNA5-2108 or 1022995-0002 if that matters. It is the single LNBf with two F connectors.)

I didn't try setting different L.O. as I did not know for sure if this could be an issue and I didn't find the above posting until after I'd put everything away. I did change the voltage to the LNB from 14 to 18 volts (this changes the polarity, right?). The voltage settings also allow for a resistor and the same two voltages. Tried those as well. I did try changing the physical polarity of the LNBf, its location next to and in front of the C-Band feedhorn etc.

Am I on the right track in attempting this? Or is the focal point too sharp? Is it more of a question of Local Oscillator frequency? Or quite possibly a bad LNB in the first place? I don't think it is a bad LNBf but more of how it is setup as both the sat finder and the receiver indicate that they are getting SOME signal.

If anyone has done what I'm attempting, please let me know if/how you accomplished this feat. If it is a LO issue, what do I use and is the 14 Volt 18 Volt the "polarity" switch for this type of LNBf? If so what voltage is the "horizontal" as a standard?


Neat discovery/interesting observation: While playing with the coax connections I connected the C-Band LNB to the DVB receiver (using the Ku coax) and the satellite signal meter (at the dish). The C-band LNB coax was hanging at the dish but still connected to the analog receiver. I did this just to see if I could peak the dish slightly better using the power from the DVB receiver.

While moving the dish back and forth I was viewing the C-band receiver and I was getting a picture on the C-Band receiver! Not super strong like when it was connected directly, but a signal that was mostly steady and in some cases a full color image with sparklies. Thinking I'd done something wrong I disconnected the coax from the DVB receiver to cut power to the LNB and sure enough the picture went away. Seems that there is a powerful signal at the C-Band LNB.

 

[anik]

I want to use an old DirecTV LNB from an 18" dish on the 7.5ft dish.

This would work for picking up, say, the audio feeds from one of the DBS satellites, but most likely you would need a different LNB for G10R. The reason is that a DirecTV LNB is meant for satellites that are circularly polarized, which G10R is NOT.

Now, if you had an LNB from an old PrimeStar dish or perhaps from a one-way DirecPC dish it might work. But really, the best thing would be to try and find something like a Chaparral Corotor II Plus feedhorn and then attach a standard Ku LNB to that, or alternately, use a separate dish and LNB (again, old PrimeStar dishes are great for this) pointed at G10R. Note that if you use an old PrimeStar dish, you will have to set the skew on the LNB (meaning you have to loosen the four small hex-head bolts so you can rotate the LNB until the quality is best).

Note that not all C-band dishes will work with KU - if it's a mesh type with holes large enough to shove a pencil through (or nearly that large) it probably won't work well for Ku. If it has smaller holes, it should work great if you can get a Corotor II or similar feedhorn, or perhaps if you can get a horizontal/vertical type LNB (not circularly polarized) and try your original plan again.

 

[jollyrgr]

Thanks for the repsonse. The mesh on this dish is the same size as mine and I receive Ku just fine. I have a Corotor II on my dish and am fully aware of changing the feedhorn out.

But you bring up an interesting point; that DirecTV is circularly polarized. I had thought this to be true with the newer "two satellites" setups like I have for my Dish Network (110 and 119 degrees). I thought the single LNBf dishes were H/V but checking Lyngsat shows the Echostar and DirecTV birds are all L/R circular. Quite possibly I was thinking Primstar.

This solves my problem. Maybe an LNBf from a Star Choice Canadian system?

 

[PSB]

With the correct LNBF in place .....

L = H

R = V

When setting up on a DVB receiver.

 

[jollyrgr]

Even More Questions

L = H
R = V

Okay, I'll give this a try. But does the device itself have to be modified physically? I recall there being an insert for the "big dish" feedhorns to convert Linear to Circular. How about the other way?

Are the old DirecTV LNBf controlled by voltage or by some sort of "tone"? I've been reading up and searching this out. (I was going to use the DirecTV LNB as it was something I had already.) I'll check the menus again but all I saw was different voltages for polarity on the one receiver and an H or V on the other.

I can't tell if it is the LNB that is at fault or my approach. I know RF of some sort is getting into the LNBf that I have. Are the DirecTV ones voltage controlled or "tone" controlled?

I also discovered why I thought the thing was linear instead of circular. The Dish Network bird at 105 degrees, AMC 15, is linear polarized.

Searching eBay for a Corotor II and LNBs is showing some expensive (about $150 to $225) items. Jokingly I said something about getting a Star Choice from Canada in my previous post. For grins I checked eBay and found that there are devices like this:

http://cgi.ebay.com/BeSat-0-3-dB-Universal-Linear-Ku-LNBF-LNB_W0QQitemZ5822088837QQcategoryZ11726QQrdZ1QQcmdZViewItem

Would one of these do what I want? Basically use a 7.5ft dish and kludge a Ku LNBf to the C-Band feed horn. I can find the above and similar all over for about $25 or less including shipping. This is a bit more reasonable than replacing the full feedhorn.

Either I've been extremely unlucky or they don't sell them at ham fests anymore. But the last ham fests I've been to have not had any C/Ku feed horns as I've been looking since last spring. One seller had a bunch of FTA DVB boxes but sold out in the first hour. Maybe an ECM will bring a glut of these receivers and accessories to the market.