Turning DBS lnbs into linear lnbs

[shadyone]

I have a almost unlimited supply of old dtv and dn lnbs. I also need a lot of linear lnbs to construct the multiple dish and lnb setup I have planed. I see from a couple of old threads that it is possible to convert a DSS lnb into a linear by removed the wedge in the feedhorn and by adding ceramic material to the disc inside the lnb to lower the LO to the 10750 needed for FTA. The links for pictures in the old threads no longer work so it is hard to tell exactly how the ceramic was added and about what thickness was needed. If anybody has some photos of this mod I would appreciate it if you posted them. Some of you probably think I'm nuts but when you need 20+ lnbs the cost saving would be substantial. I'm actually planing to put mutiple dishs at two seperate houses and I am tired of messing with motors. My dream is to have enough fixed dishes to never have to wait for a motor to move

 

[Lak7]

Some of you probably think I'm nuts but when you need 20+ lnbs the cost saving would be substantial.

What is the budget?

 

[shadyone]

I don't really have a budget (If I ever sat down and figured up what I spent it would take all the fun out of this hobby). I already have the receivers and I have been collecting all the primestar and superdishs I can find. I enjoy the searching for and collecting of free equipment as much as anything. This is another reason why I want to be able to recycle these lnbs.

 

[Cadsulfide]

The fss lnb on a DN superdish is linear and bandstacked. Your idea of an array is a good one, it works for me. As for modifying a dbs lnb, good luck. The signal is so small to begin with, just a little detuning of the lnb may very well kill your signal.

 

[Lak7]

I think $200 would be hard to beat doing it yourself.....
LINEAR KU BAND SATELLITE FTA DISH LNB/LNBF FINDER TV T5 - eBay (item 390005258361 end time Jan-30-09 21:02:01 PST)

 

[Anole]

Taking into consideration the frequency stability and accuracy of your conversions, I'd look to buy stock LNBs, too.
Can't imagine DBS LNBs having all that good a noise figure rating.! -

The above deal of $10 shipped for each, is incredible.
AND if you were to order 5, 10, or 20 from that vendor, I'm sure you could get a much better price.

Couple of years ago, I tried some $6.95 LNBs.
Turned out, they were quite good.

I suspect if you contacted our Gold Sponsors, and asked for a quote for 20 pieces, you'd be surprised.

Had a recent conversation with a couple of members about multi-LNB dishes.
One guy had taken that path, and the other was following in his footsteps.
Seems the price he paid was in the very reasonable $15..16 range ?
Those were for dual-output LNBs.

How many receivers were you planning to have at each house?
Have you considered the wiring and design of the required switches?

I have been collecting all the primestar and superdishs I can find.

As mentioned above, these already come with decent FSS LNBs!

 

[Smith P.]

I would try to use existing trim at the LNBF to shift down a LOF. Just screw it down while watching signal on spectrum analyzer after removing that depolarize tab.

 

[sidha]

The tuning screw only allows a relatively narrow shift in oscillation frequency. Not all LNBF's can be detuned sufficiently to lower the DRO within reach of a KU band upper transponder. From my experience, turning the screw to an extreme position creates a problem by lowering the Q-factor of the oscillator as it becomes overdamped. Efficiency will suffer, and that means quality levels begin to resemble what you would expect from an LNBF of a much higher noise figure. An optimum window of adjustment maintains proper Q-factor. To remain within that sweet spot, plan to take note of the original factory calibrated gap between screw and puck. I use that measurement as a centering reference for KU operation. I then cement additional chips of ceramic material to the puck, without affecting the gap, along the perimeter or edge. A small amount, <10% additional mass usually does it. If the donor ceramic material isn't a close match, the results will vary. Working with what's available might mean using DRO ceramic material salvaged from old C-band LNA's. I prefer using blindscan to check results as I increase the puck mass. Once KU transponders appear near to proper frequency, I adjust the screw slightly to fine-tune the DRO. This completes the DRO conversion with a standardized set frequency of 10,750mHz, without aid of a spectrum monitor.

The KU performance is amazing, if the Q-factor is maintained. My converts have remained frequency stable for years. Some LNBF's require more work on the waveguide conversion to linear. I think I began this project because I wanted a KU LNBF that fit and matched a DTV dish, to receive some of the really hot KU transponders, like where 3ABN is on AMC-4. At the time, that transponder was pushing 99% quality readings using a smaller Primestar dish. I wanted to verify if an 18" reflector could do a decent job, but I lacked a compatible mount KU feed with matching feedhorn for that particular dish. So I converted the stock DTV LNBF to fit my needs. I now use the KU converts as feeds on regular KU dishes. From the appearance, who would ever suspect I'm watching AMC-4 programming and not DTV?


-sidha