Can I adapt an LNB ?

**koansrc** · 15-11-2007

Hello all,

I have a cheapo lnb 0.6 f/d and I would like to convert it to 0.4 f/d and try it on a prime focus dish. Can it be done ?

I assume I must shorten the length of the feed but it would be nice if someone could confirm this before I actually start hacking away at the lnb

Of course the next question is "by how much"

**Analoguesat** · 15-11-2007

LNB's might not look it but are precision engineered bit of kit - if you start hacking bits off its not going to work properly at all......

**koansrc** · 15-11-2007

Originally Posted by Analoguesat

LNB's might not look it but are precision engineered bit of kit - if you start hacking bits off its not going to work properly at all......

yup I realize that much !
But this is something I've got to try. I just can't ignore the voices inside my head .!.

but maybe I won't use the axe or the chainsaw after all. More like a precission cut with a fine blade. Sooooo, do I shorten in order to reduce the f/d ?

**jimbo** · 15-11-2007

I think a 0.2 would be cheaper than a fine blade. So have one waiting in the wings when your experiment fails. Oooppps I meant if it does.

**koansrc** · 15-11-2007

Originally Posted by jimbo

I think a 0.2 would be cheaper than a fine blade. So have one waiting in the wings when your experiment fails. Oooppps I meant if it does.

Hey jimbo, I guess you share Analoguesat's pessimism ( to put it mildly ) and since I believe in "waste not want not" I'll reconsider !

But I like your use of the word "experiment" !! Great choice. Brings Braniac and exploding caravans to mind somehow. But ... what's a 0.2 ?

**Analoguesat** · 15-11-2007

0.2 is the dB noise level on the lnb

By all means hack some bits off --> sorry do some careful re-engineering on the lnb --> but make sure you have a replacement lnb to hand "just in case"

Please report back one way or another.

And if you re-engineer it by dropping a caravan onto it I want to see the video on Youtube!

**Robbo71** · 15-11-2007

Originally Posted by koansrc

Hey jimbo, I guess you share Analoguesat's pessimism ( to put it mildly ) and since I believe in "waste not want not" I'll reconsider !

But I like your use of the word "experiment" !! Great choice. Brings Braniac and exploding caravans to mind somehow. But ... what's a 0.2 ?

Perhaps Jimbo is talking about a F/D of 0.2 not its noise figure?

Confused though because you wanted a 0.4 F/D anyway.

**Low Profile** · 15-11-2007

Simply rip the cover off the front of the lnb, measure the internal diameter of the feed horn, wedge a bit of (the same size) very thin pipe in the end, and cover the protruding pipe with tin foil. This will change the illumination to that equivalent to one with a lower F/D.
Mess around with the length of protrusion to give max signal to noise.
You will lose a bit due to the thickness of the pipe, for best results the bore should be constant and the same size as the original LNB.
Good Luck.
Yeee Haaaaa!

Steamgauge · 15-11-2007

Shortening the LNB will not make it more suitable for a smaller F/D ratio, for that you need to change the angle of the "flare" bit. What you could try is -make a skirt (I'd guess at 10mm depth) to fit around the existing flared end of the LNB and either have the skirt parallel with the aperature or perhaps incline it forward a bit.
Cutting the LNB will not work, the skirt might not either! but it is a move in the right direction.- Good luck

**jimbo** · 15-11-2007

Originally Posted by Steamgauge

Cutting the LNB will not work, the skirt might not either! but it is a move in the right direction.

Sounds interesting. I might pop a skirt on tomorrow.

**PaulR** · 16-11-2007

Originally Posted by jimbo

Sounds interesting. I might pop a skirt on tomorrow.

Nah. Won't go with the halter top you normally wear.

**4dbennett** · 16-11-2007

ok 0.6db to 0.4db easy,

measure length of flare

divide length by 3

then lengthen flare by that much

ie

length of flare = 30mm

divided by 3 = 10mm

make flare 10mm longer

= 30% gain

DEEP JOY

dave

**koansrc** · 17-11-2007

ehm ... I've changed my mind. Sorry guys. It all sounds very tricky and ify. I do believe the techniques would produce functional lnbfs, but can't imagine them increasing my extreme fringe reception of 2D which I had in mind.

It is a bit of suprise that the feed must be lenghtened in order to lower the f/d even though the maths prove it. My logic would have been to shorten in order to "move away" from the dish and widen the angle ( I assume signals enter through the opening of the feed and not "through" the feed sides ). Thanks!

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)