Fixed mount for Channel Master

[RimaNTSS]

I think that key-word here could be "X-pol", which is by the way one of the parameters of the performance of the dish. And antenna on Az/El mount will have greater X-pol effects, especially on inclined satellites (far-West and far-East). Polar-mounted (skewed) antenna will have better X-pol characteristics, therefore it will perform better. Will not argue anyway.
Back to my idea to make CM dish skew-capable: made small frame from 20mm square tube to which welded 4 segments with holes in them. Of course, made a small mistake and with this frame will be able to skew antenna only 15* each side (was thinking about 30*) . Angle (step) between holes is 5*. Next time will do better. Now should think about elevation mechanism... I think 2 M10 threaded rods will do the job.

 

[a33]

@st1 and @RimaNTSS :

Mmm, you got me thinking again. Crosspolarisation is a relevant point in the difference between gregorian dishes and normal' dishes; but is skewness of the dish also relevant to crosspolarisation?

I'm afraid I don't know much about crosspolarisation, so that is beyond my knowledge I'm afraid.

Greetz,
A33

 

[Trust]

In 2010 I made a test with a Echostar 1.2m offset that could rotate (by hand) in the elevation angle direction (wheel hub) .
Also used a motor skewed lnb .
Checked the signal and Q and Ber with a Satlook meter from and with a another sat4all member .
We could not find a position with better result , test made at Nilesat .
I started that test because with the rotating little square BSB dish I find a better position . ( dish ± 45º tilted)
Probably caused by the square "ears"

That test was made at Astra 19.2
My conclusion is its useless to do that with a normal offset dish with one lnb in the centre .

 

[RimaNTSS]

Does somebody know how to practically check negative effect of the X-Pol? I am not exactly sure, but feel that 2 transponders (V and H) from one satellite should be picket. Frequencies on those transponders should be very close if not the same. And then start to skew the dish and observe changes of signal on both transponders.

 

[RimaNTSS]

More or less finished with fixed mount. Some parts are not INOX , so need to be painted. This mount is also giving possibility to skew the dish 15* each side. I think this will become my experimental mount not only for CM dishes but also for any other dish, only additional plate will be needed to hang other dish. Of course, I am speaking about maximum size of dish something about 1,5m.

 

[RimaNTSS]

Painted not INOX parts and hanged antenna on the mount. It holds it very firmly. It goes on top of 76mm pipe and still has the possibility to adjust plumbness. Elevation adjustment is slow but very precise.

 

[nelson_b]

Nice Job - RimaNTSS ....

 

[Channel Hopper]

Does somebody know how to practically check negative effect of the X-Pol? I am not exactly sure, but feel that 2 transponders (V and H) from one satellite should be picket. Frequencies on those transponders should be very close if not the same. And then start to skew the dish and observe changes of signal on both transponders.

Apologies, I missed this post.
The usual method of reducing cross polarity effect at source is to do exactly what you have achieved, by tilting the whole antenna reflector on the boresight. This only goes some way towards a cure since deficiencies within the system remain, owing to the reflector and feed design.
Changing to a highly elliptical shaped antenna

http://www.satellite-bandwidth.net/NewEra-2015/equipment-manuals/Prodelin/ds-ku-0.95-1950-1951.pdf

(and suitably matched feed as per the following) will remove more of the unwanted polarity signal,

however there is further improvement by use of a dedicated one polarity waveguide and WR75 (at Ku band) matching feed adapter, preferably tuned to around 250MHz of the frequency that is being received.

There are further design changes that can be made, though this does involve highly specialised waveguide tuning, and dual reflector technology, in the next post if you are still awake.