18" Dish Indoors

wbrown · 2019-05-06T23:40:30.411Z

TL;DR: I bought an 18" DirecTV dish, mounted the Maverick LNB on it, setup the dish inside my house pointing out through the wall, and got better than +0dB SNR.

I bought an 18" DirecTV dish to experiment with (from ebay, new-old-stock I assume). I watched the YouTube video that Konrad linked a while back (link) and decided to give it a whirl.

The dish is advertised as 18", and what I received was vertically oblong… about 18" wide, and 21" tall. The LNB bracket I ordered had the same “sweep back” angle as the LNB that came with the dish (the DirecTV LNB is circular polarized, which can work with slightly reduced signal output: See this thread Circularly polarized LNB for reception?). To start with, I chose to use the linear Maverick LNB supplied with the DC kit.

The height that the new bracket would hold the Maverick LNB was within an inch or so or the DirecTV LNB placement, so I decided to just go for it without doing the more exact LNB replacement/alignment shown in the YouTube link above.

For reference, with a bare LNB mounted outside on a 2nd story window, I average between -10 and -13dB over a 24 hr period, with an RSSI of about -79dB. I am located in Central VA.

At first I tried the dish setup outside, ground level, aimed between two big trees. Since the dish is small, the narrowing of focus isn’t bad at all. I had it aimed in short order. I was getting +6dB SNR without trying too hard.

Then I moved to my unfinished attic (3rd story). Shooting partially through a double-glazed window, and partially through exterior sheathing (and vinyl siding) I was getting in the -6dB range.

Then I moved the setup to an upstairs room (2nd story). I remembered I had achieved lock and data transfer with a bare LNB while inside, pointing straight at the outside wall of the room (so, drywall, insulation, sheathing, vinyl siding) but it was really hit or miss. I decided to try with the dish setup. After tweaking the dish elevation a little bit, as the foot for the dish sunk into the carpet some, I was shocked. Better than +0dB SNR, and -74dB RSSI.

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I will log data and monitor performance during periods of bad weather. As this is an “extra” room in my house, and is rarely used, having an 18" dish in the far corner, barely visible above the couch… just seems like a win-win. Someone in a similar situation with a closet on the correct outside wall (facing SES-2 or whichever covers your region) could have an invisible installation. Perfect for persons living in a neighborhood with an over-reaching HOA, etc.

I know using a dish is not the use-case for Othernet. I don’t know if an 18" dish inside the walls of your own home is considered stealthy or not. But for some use-cases, this seems great.

Side note on the LNB bracket positioning. I did try moving the bracket in closer to the dish by about 1", where I projected it should be based on visual cues from the DirecTV LNB. I encountered worse performance by a few dB, so I just left the bracket mounted in the pre-existing hole and seemed to have about optimal performance. I was going solely on the outer plastic radome of each LNB… could be the depth of the actual feed-points between the two LNBs matched up closer than their radomes. Just a guess.

Also, I was able to rotate the LNB in its bracket (as you do when using the bare LNB) to about 15 degrees for my location, and I got the few dB of extra SNR I expected. I had read some places you have to rotate the entire dish… maybe true for LNBs that cannot be rotated. This simplifies dish installation even further, not having to rotate the dish.

If interested in the parts I used:
dish: google 264155964386
bracket: google 361912323862

hobergenix · 2019-05-07T01:53:28.817Z

Hi
I have the same size Direct TV dish and LNB bracket that you have. Presently its setup for
Free to air Satellite reception and pointed at Galaxy 19. Its mounted on the balcony three floors
up. When I point the LNB directly at the satellite I was seeing about a -10dB signal. While
standing off to the side of the dish and pointing the LNB at the dish I was able to see a signal
of about +2dB. I started holding the LNB a little off to the side of the existing LNB and adjusting
for best skew and hot spot on the 18" dish. I believe you will have to mount the LNB further away
from the dish than the bracket will let you with existing mounting hole. I did all of this at night and
it was just a quick experiment. I was holding the LNB with my hand and at times I saw a better
than +2dB signal. And the dish is not pointed at the correct satellite SES-2. I used a portable
power pack and took the board outside with me and was juggling holding the setup and LNB.
You might get a better idea of LNB mounting by removing the LNB bracket and trying the same
experiment.

Mike

ac8dg · 2019-05-07T10:24:23.101Z

check this thread: I was able to use the ‘stock’ circular lnb-18 that
ships with the 18" oblong dish. you save the trouble of changing mounting
brackets and focal point adjustment. BUT… remember to set the custom frequency
to account the different local oscillator of the ‘stock’ lnb.

Circularly polarized LNB for reception?

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

wbrown · 2019-05-07T12:24:17.322Z

Thanks for the link to that thread @ac8dg. After reading it just now, I recall reading it before… evidently before I decided to buy a dish, so I forgot it existed. I will update my post above to remove the incorrect information about using circular LNB. I will also probably do a confirmation check later this week on my setup, and report the delta-SNR (linear to circular) with the dish inside (would expect the same values as everyone else).

And some general comments not directed towards anyone:

I generated a concise list of reception improvements into a PDF and uploaded it to a “15 degree horn” thread elsewhere in the forums. It shows the various designs people have made for the added horns, and their performance gains. I can update it with the dish stuff I’ve found, and the circular LNB data.

The issue becomes where to put something like this for people to find. I understand “search the forums” but even with good intent, it’s hard to find stuff here, and one can easily end up reinventing the wheel.

Syed · 2019-05-07T19:01:22.449Z

@wbrown Where do you think is the best place to put the document you created? I agree that searching for it is not the most helpful.

How long did it take you to point the dish when you were outside? Just eyeball or did you use a compass and level?

What is the gain of the dish?

wbrown · 2019-05-07T19:40:22.488Z

@Syed ~~Regarding the PDF document… there is that FAQ category that is linked at the top of the forums… I guess I could create my own post there.~~

Ken’s instructions currently don’t really seem to have a home, either. I don’t know if creating an “instructions” forum area that perhaps only you or some other sysadmin could create posts and make available PDFs such as these. (I’m not suggesting my document is at the same quality or usefulness as Ken’s) Limit the availability to post to just a few people, to keep the content SNR high. It would be a little more consolidated, without having to create special webpages (eg the forum is already in place).
Edit: Below, Ken pointed me to the Wiki. I have made updates there. An embarrassing miss on my part.

As far as pointing the dish, the focus is narrower than a bare LNB, but it’s not ridiculously so. I had the dish pre-set to 45 degrees elevation, but the patio let the mounting foot for the dish wobble maybe 5 degrees or more, but that didn’t kill the signal. I had a comfortable amount of wiggle room wherein I would get enough signal to make the DC radio LED start flashing, and then I could use the SNR on the readout to fine tune. It was a lot easier than I thought. I did it all by eye. You can rotate the dish in azimuth back and forth “an inch or so” and see the SNR change and dial it in that way. I’ve gotten pretty used to where to point in the sky from experimenting with the bare LNB all over my house and property, so I just guessed by eye to get it to roughly the correct region of the sky. From reading in the past about aiming satellite dishes in general, I was sort of expecting “don’t breathe on it” levels of aiming sensitivity, but it was just the opposite. A little more touchy than a bare LNB, but after maybe a minute of initial fiddling, I found I could re-aim a jostled dish as quickly as a bare LNB.

The dish came with no information, and I did a quick search online and found nothing. I used an online dish antenna calculator, and came up with about +30dB of gain (0.457m, 50% efficiency, 11.5GHz). I don’t know if this is accurate for an offset-feed like this model or not.

wbrown · 2019-05-07T21:40:31.930Z

A strong, short rain-storm passed through this afternoon. I actually have two v3.03 DC running at this time. One with the bare LNB, and one with the 18" Dish (indoors).

Interesting to see the daily rise-and-fall of SNR tracks equally on both setups. During the rain-storm, the bare LNB lost signal entirely. The 18" dish lost quite a bit, but remained just above -13dB SNR the entire time.

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kenbarbi · 2019-05-07T21:43:04.668Z

I would suggest editing the Wiki and putting your information there. You can include text and pictures just like in the Forum posts. Ken

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wbrown · 2019-05-07T23:20:43.405Z

@kenbarbi that’s a good idea. I have to admit, for some reason my eyes glaze over the wiki link all the time. I think I’ve viewed it once. A little embarrassing to miss that.

wbrown · 2019-05-16T22:33:22.147Z

I tried using the DirecTV LNB-18 (circular polarized) just now with the following results:

Maverick LNB / 11.9024
0db SNR
-74 dBm RSSI

LNB 18 / 11.4024
-2 to -3 dB SNR
-82 dBm RSSI

So SNR dropped by about 2-3 dB, and RSSI dropped about 8 dBm.

I will let it run like this, with continuous logging, and see how it handles a weather event.

wbrown · 2019-05-18T00:16:18.182Z

Had another comparable weather event while using the circular polarized LNB on the indoor 18" dish. About the same results as with the Linear LNB on the dish, just about -3dB lower across the board.

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ac8dg · 2019-05-20T00:05:03.947Z

There is one advantage to the circular polarized lnbf. You don’t have to figure out the ‘skew’ angle since there is no horizontal or vertical.

kb3cs · 2019-05-20T00:14:22.465Z

the skew varies as ionospheric conditions change. the Europeans settled on circular polarization for this reason, while in the States, linear polarization was “good enough”.

Syed · 2019-05-20T16:28:12.113Z

Yeah, I think skew adjustment is a pain point and might limit mass adoption. The problem is the SNR hit that we take.

kb3cs · 2019-05-20T17:21:46.851Z

i have not noted any particular sensitivity to skew. i did add the wire mesh horn, though. it matters most when the skew error is 90 deg. even with circular polarization finesse for maximum cross-polarization attenuation, ionospheric effects distort the perfect circle at the satellite into a varying ellipse at the LNB.

wbrown · 2019-05-20T17:35:34.655Z

With a bare linear LNB (or even on a dish for that matter) I experienced maybe 3dB of SNR improvement from 0 degree skew to 15 degrees for my location.

kb3cs · 2019-05-20T18:46:05.488Z

yes, a mild effect. weather events make for larger changes.

wbrown · 2019-05-20T19:00:23.636Z

weather events meaning ionospheric effects (skewing the polarization), or simply rain-fade? (Or both, to greater or lesser degrees)

kb3cs · 2019-05-20T20:16:54.557Z

terrestrial weather, not space weather. those events are more often and produce the famous Ku band deep fades. the space weather would have to be extreme (record setting?) to have as much effect.

wbrown · 2019-05-20T20:23:47.042Z

haha. need to brush up on my atmospheric layers

thanks