Dual band feed with LNB 21 type

Hi David,

I did not use this LNB model before, but perhaps have some hint how to use it without further modifications to make it work as a dual band feed.

I have done some measurements with an Octagon Twin PLL (27MHz) and a 5,25 turns LHCP helical combination (G3RUH/G6LVB design). The interaction is very small between them: SWR of the helical, mounted as depicted below, is abt 25dB and watching the strenght of a beacon the LNB signal degradation was <1dB when the Helical with reflector was slid over the LNB frontcover. All this was done at the focus-point of an offset dish. Yes, I know the helix is not exactly in focus, but the error seems acceptable.

I was not able to finish actual transmission tests as my Kuhne MKU2424A Up-converter currently is back to the company for the modifications...

Several people do have good results with similar constructions.

73 Ed PA1EW

Some more pictures here. When "boxed" this adds weather protection and makes it also less fragile. I figured out how to fix the box, but need some more time...

73 Ed PA1EW

The above solutions are good. The easiest, non-destructive and safest way, is to simply use 2 dishes ?

No, that is a POTY in one dish ; -)

G4NRT It is not absolutely necessary to chop the horn off. You can also drill a 22mm hole into the plastic cap and slide it over the tube until it makes contact with the inner parts of the horn/waveguide. Some (acid free!) silicone to make it weather proof, et voila : -)

This is the idea:

Remco...very nice solution...

I will try thais also ....

Hallo,

here is another example. It is an Octagon Twin. The feed horn of the LNB is removed. The coupling between the LNB and the 22mm copper tube is done with a brass disc. Meanwhile I am not sure if the thermal coupling with all the copper and the LNB is a good idea really? It is all soldered with hot air. The S-Band antenna seems to work, 2 Watts and a 80cm dish give a satisfied transponder response.

My home made return loss brigde has to be improved before showing a pattern.

73s
Andreas, DL5CN