Darth's New Idea: No-cost Modification on SuperDish121 to get 118.8 Anik F3
Darth Vader:
A no-cost modification on SuperDish 121-119 LNB assembly to get 118-119
This mod has many advantages: no-cost (what could be better?); no dish adjustment; no switch change (thus, no headache for multi-sat and multi-receiver system); no local frequency change; etc...
Background: a linear (standard or universal) LNB can be easily modified to receive circular signal from Anik F3. I've done this successfully a few times, by just inserting a piece of dielectric plate into the central hole. Teflon is the best, but PMMA (plexiglass) also works fine. Basically it works by shifting wave of one polarity by phase of 90 degrees - thus change the circular polarity to linear polarity. No change on frequency. No need of change on switch or LO settings. See:
ht*p://forums.f2atv.c*m/showthread.php?t=171702 and ht*p://lea.hamradio.si/~s57uuu/emeconf/eme06.htm
Proposal: Simple modification on SuperDish-121 LNB assembly to receive 110-119-118 with no extra hardware cost. What I propose is: unscrew the 119-121 combo and rotate it around view line axis by 180 degree; stick a plexiglass plate into 121 tube (now at the location of 119). Now there is no problem for LNB121 to get 118 signal. The question is will the LNB-119 (now at location of 121) still be able to pick up signal from 119? It very likely could, although not optimal, since 119 has much stronger signal. But I need yet to put the idea into test before making such statement. I may try it when I have some free time and weather permits. Hopefully a few brave souls here will try it and report back much sooner. --------------------------------------------------------------------------- Olliec:
Excellent post, let me ask you this, it should work in theory in my head but what do you think?
i have a super dish 105 pointed at 97 right now. it connects to the LNB IN port on my dish 500 with a DPP Twin Lnb. so now i have 119, 110 and 97. my dad wants Detuche Welle (might be spelled wrong) and its on 118. so if i made this modification and aimed to 118 i should be able to pick up everything just fine right? --------------------------------------------------------------------------- Nalin Nyda:
On its own a linear LNB will give a 3 DB signal drop - this could be annoying enough.
"a linear (standard or universal) LNB can be easily modified" Darth Vader 's suggestions are for the technically minded.
With a spurt of activity in this area (118.7), there are 2-3 LNBs Universal LNBs out in the market for $20-25.
lroy tipit gave the right direction. The other alternative is to buy the DN repointing kit (sold by DN) if you already have a dish pointing to 121W. It is a bit expensive though.
Yes, you can always buy things but that is not fun for a real hobbyist.
The point is, beside of cost, there are other considerations: A. Physical limits (different size of LNB bracket, limited space); B. Reuse of the LNB and dish; C. No need for dish install or re-alignment; D. No change on existing switch and STB settings (some walked through many troubles to get their switch/configuration work) -- no system debug; E. Saving the earth (where do you put your old LNB/Dish?)
On the 3dB signal drop: You wasted 50% signal strength (3dB) by using linear LNB to catch Circular signal. Insertion of the dielectric plate, if perfect, by delaying the phase of one of the two components of the polarity 90 degrees, gets the perfect phase match for both components of the polarity, thus, enables full use of signal strength.
tyson01 Location: Out west in Canada Join Date: Jul 2005 Posts: 9,932 Re: New Idea: No-cost Modification on SuperDish121 to get 118.8 Anik F3
Tyson01:
Yes that can be done to the 121 LNB but you would rotate the 119/121 LNB 90deg so feeds are stacked, one on top of the other so they are aligned at the same orbital slot (118.7/119). You would adjust the height of the LNB for best signals on 118 TPs, i.e. align the 121 feed for max gain. The orientation of the 119/121 LNB has no effect on signal because both signals are circular polarity.
This is a very innovative idea! Definitely worth of trying if the 180-deg rotation cannot catch 119. The 180-deg way is preferred because it feels physically more sound and don't need to drill any holes. My guts feeling is stacked feeds (90-deg way) has better chance to catch both birds. Anyway, we need to put the idea on roof for an ultimate answer.
Just out of curiosity, why is it true that, if you have to be off, off vertically is better than off horizontally? My experience indicates this is true, received signal strength is more sensitive horizontally than vertically. I wonder if this is due to the design of the antenna at the satellite.
Yes that would depend on the curve of the dish and your focal point.
There no need to rotate the 119/121 LNB at all unless you do it 90deg. Install your dielectric plate in the 121 feed, repoint dish east 2 deg to get 118w, reposition 110w LNB(closer to 119/121 LNB) for best reception, 119 will be low but there.
118w and 119w are not 1 deg apart they are 0 degs apart, its 118.7 and 119 so fliping the 119/121 LNB around is of no benefit.
I must say this is another great thinking out of the box. It saves trouble of rotate 119-121 assembly, and better final looking for keeping the shroud. So now we have three configurations of DIY "repointing".
Rotating 119-121 assembly still has benefits though--you don't need to readjust LNB110 and you don't need readjust the dish (only in theory, you may need minor adjustment in reality).
MadFlea, If your SuperDish is a standard SuperDish, standing behind the dish from left to right, it will be lnb 121-119-110. Or, you can think in logic: 121-119 are only 2-deg apart, the two closer LNB assembly must be 121-119, and 119 must be at the middle of 121 and 110.
All you need is a 33" or larger Dish Replace your existing 119 LNB with this new CB2008A LNB sold at eBay for $25.00. Don't waist your time on jerry rigs they don't last long
CIRCULAR Dual Twin LNB-118/119 Dish NET ... $25.00 - eBay
That bracket yo have to be careful with rotation Yo need to rotate bracket in multiple directions for the circular and linear LNBs Unless yo use a 90CM with skew capabilities
To install all 4 sats on one 90 CM dish it can take yo all week long
Well Yukon maybe right if you start from ground zero and only interested in 119/118.7. But there are many existing SuperDish121 on the roof and you shouldn't threw them away lightly, and there are people who also want 110 but can not accommodate two dishes. Plus, I bet the price for superdish121 is falling. I made a few mods for 118 and for more than half year there is no durability issue.
To install a new 33" dish (assuming you have the enough space), or to play a little with your screw driver, which is easier? you make the call.
One additional benefit with SuperDish is, with the help of LNB 110 and 119, it is much easier to hit the weaker 118. In fact it is a common practice to use a DSS LNB as a pilot first to catch a nearby "strong" satellite and then fine tune the dish to weaker FSS satellite. Aiming cluelessly without knowing which direction to try is a major source of frustration, especially to newbies.
Darth In the first place I was not putting down your way of doing things.I was just basing my opinion. Like they say different strokes for different folks.
