Advice Needed C Band Right and Left

[Spiff]

Good evening from Mullion Cove Cornwall.

Having constructed a motor drive to rotate the polarizing plate in my C band LNB, I am now not certain of its use apart from peaking the signal.

On a C band LNB there are two slots, if I insert the plate so that right hand polarisation signals are converted to vertical, will it then automatically convert left hand signals to horizontal ?

Or is it necessary to take the plate out and put it back in the other slots ?

I should have thought about this more before making the motor drive up : )

No amount of searching online appears to spell out the answer to this question for me.

Perhaps because I am the only one who does not realise the answer : )

The motor arrived from China quite quickly and works fine, it should perhaps be obvious having used it as to the answer to my question, but it is not.

I find that a station that had been saved as both V & H where I had previously been trying blind scans with the plate in both fixed positions, requires me to drive the motor driven plate to both positions.

This I think is because it has been scanned and saved that way.

It has been very interesting constructing the drive, even if not to much purpose : )

God Bless Spiff

 

[s-band]

On a C band LNB there are two slots, if I insert the plate so that right hand polarisation signals are converted to vertical, will it then automatically convert left hand signals to horizontal ?

Or is it necessary to take the plate out and put it back in the other slots ?

Yes, you have to turn the plate through 90 degrees or switch to the other linear polarisation. The probe or waveguide need to be at 45 degrees to the plate. I'm sure there were some pictures here but can't find them at the moment. There is a view into the feed a bout 2/3 down this page Parabolic Antenna Tutorial : Informasi Tentang Antena Parabola dan Penerima Satelit - Index

Edit: For linear polarisations the probe needs to be in line with or at 90 degrees to the plate

 

[Spiff]

Yes, you have to turn the plate through 90 degrees or switch to the other linear polarisation. The probe or waveguide need to be at 45 degrees to the plate. I'm sure there were some pictures here but can't find them at the moment. There is a view into the feed a bout 2/3 down this page Parabolic Antenna Tutorial : Informasi Tentang Antena Parabola dan Penerima Satelit - Index

Edit: For linear polarisations the probe needs to be in line with or at 90 degrees to the plate

Thank you S Band for your reply.

As my C band feed horn had vertical and horizontal antenna, rotating the dielectric slab with a motor was pointless then : )

We live and learn.

There is a bar inside both KU and C band LNBS that is thicker than the aerial, and extends right across the horn between the two aerial rods.

Can you tell me what its purpose is, some kind of director or reflector perhaps ?

I read that there are C band horns made just for circular polarization, do they convert from circular to vertical or horizontal ?

Or do they use some other type of aerial rod to directly receive right or left hand polarization signals ?

There is one called a corilatorChaparral Corotor II Plus WideBand C/KU International Feed horn, it is dual band.

This device uses servo motors which unless a separate means to drive them is constructed will require a special receiver I think ?

Chaparral Corotor II + c/ku-band Wideband International Feedhorn Big Dish Feed | eBay

On your edit are you refereeing to receiving a linier e.g. vertical or horizontal signal not a circular one ?

Edit: For linear polarisations the probe needs to be in line with or at 90 degrees to the plate

In which case my motor could be used to move the plate to such a position as to revert the device to receive vertical or horizontal signals which would make it useful : )

Lovely day here.

God Bless Spiff

 

[s-band]

As my C band feed horn had vertical and horizontal antenna, rotating the dielectric slab with a motor was pointless then : )

>>>>No, see below

There is a bar inside both KU and C band LNBS that is thicker than the aerial, and extends right across the horn between the two aerial rods.

Can you tell me what its purpose is, some kind of director or reflector perhaps ?

>>>>>> Yes, where one probe is in front of the other it needs a reflector 1/4 wave behind the front one.

I read that there are C band horns made just for circular polarization, do they convert from circular to vertical or horizontal ?

>>>>>>> No, normally they are linear with something to convert to circular

There is one called a corilatorChaparral Corotor II Plus WideBand C/KU International Feed horn, it is dual band.

This device uses servo motors which unless a separate means to drive them is constructed will require a special receiver I think ?

>>>>>There have been a few discussions on here about them. You need something to drive the servo (singular). Whilst they work ok, there is some extra loss due to the complexity and dual banding. Try searches on this forum.

On your edit are you refereeing to receiving a linier e.g. vertical or horizontal signal not a circular one ?

>>>>>>Yes

In which case my motor could be used to move the plate to such a position as to revert the device to receive vertical or horizontal signals which would make it useful : )

>>>>>> Yes

 

[Spiff]

As my C band feed horn had vertical and horizontal antenna, rotating the dielectric slab with a motor was pointless then : )

>>>>No, see below

There is a bar inside both KU and C band LNBS that is thicker than the aerial, and extends right across the horn between the two aerial rods.

Can you tell me what its purpose is, some kind of director or reflector perhaps ?

>>>>>> Yes, where one probe is in front of the other it needs a reflector 1/4 wave behind the front one.

I read that there are C band horns made just for circular polarization, do they convert from circular to vertical or horizontal ?

>>>>>>> No, normally they are linear with something to convert to circular

There is one called a corilatorChaparral Corotor II Plus WideBand C/KU International Feed horn, it is dual band.

This device uses servo motors which unless a separate means to drive them is constructed will require a special receiver I think ?

>>>>>There have been a few discussions on here about them. You need something to drive the servo (singular). Whilst they work ok, there is some extra loss due to the complexity and dual banding. Try searches on this forum.

On your edit are you refereeing to receiving a linier e.g. vertical or horizontal signal not a circular one ?

>>>>>>Yes

In which case my motor could be used to move the plate to such a position as to revert the device to receive vertical or horizontal signals which would make it useful : )

>>>>>> Yes

Thank you for your reply, that is great : )

The reason I asked about the rod was that it would make a neater job to mount the motor on the rear of the LNB, but this would require drilling a hole through the mentioned rod for the motor shaft.

It would also be easer to water proof the motor than where I have it mounted at present on the rear of the scalar rings.

The speed of the motor which has a reduction gear box plus the small pulley to large pulley, is about right using three 1.2 volt cell in series, 3.6 volts.

The motor was designed for 6 or 12 volts, much lower than 3 volts and it stalls.

Fitting it at the rear of the LNB would require a direct drive from the motor shaft which could be too fast, though I am not sure about that.

God Bless Spiff

 

[s-band]

The Co-Rotor has the motor at the back and a cranked shaft/feed arrangement to turn the Ku feed. They us an RC servo derived motor which has a seal on the flange between its output and the back of the feed. You could do something like that to get past the bar. However, anything you do may degrade the performance and it is difficult to asses unless you do before and after measurements.

Another thing to note is that the fore/aft position of the plate in the feed can win or cost you a couple of dB. The best position is not necessarily at the back stop as suggested by Titanium.

 

[Channel Hopper]

Thank you S Band for your reply.

As my C band feed horn had vertical and horizontal antenna, rotating the dielectric slab with a motor was pointless then : )

We live and learn.

If it 's not absolutely clear, the inclusion of a permanent dielectric, revolving plate in front of the feed/LNB gives you all four polarities and the ability to adjust for optimum skew on each satellite, BUT the permanent inclusion means you have a minimum 3dB drop in each of the linear planes.

 

[Spiff]

The Co-Rotor has the motor at the back and a cranked shaft/feed arrangement to turn the Ku feed. They us an RC servo derived motor which has a seal on the flange between its output and the back of the feed. You could do something like that to get past the bar. However, anything you do may degrade the performance and it is difficult to asses unless you do before and after measurements.

Another thing to note is that the fore/aft position of the plate in the feed can win or cost you a couple of dB. The best position is not necessarily at the back stop as suggested by Titanium.

Good morning S Band, thank you for your input.

The idea of a crank in the shaft had occurred to me, but not too easy to set up.

Drilling through the reflector will be tricky in situ, it may be easier to perhaps remove it drill the hole and replace it.

As you say the front to back position of the dielectric slab is critical, on my LNB it produced the best signal far back, we did a lot of tests.

For now I have used Denzel tape to waterproof the motor, great stuff but not very pretty : )

God Bless Spiff

 

[Spiff]

If it 's not absolutely clear, the inclusion of a permanent dielectric, revolving plate in front of the feed/LNB gives you all four polarities and the ability to adjust for optimum skew on each satellite, BUT the permanent inclusion means you have a minimum 3dB drop in each of the linear planes.

Good afternoon Channel Hopper,

Yes it has all sunk in now, on the sats I have on C band at present there are no vertical or horizontal signals to test the effect of moving the slab on them, just circular.

The C band dish is in a temporary position at present, I have to take it and the KU band dish down and move the pole up.

God Bless Spiff

 

[blademedia]

A couple of pictures of mine Spiff, option to make C/KU

 

[Spiff]

A couple of pictures of mine Spiff, option to make C/KU
View attachment 106404 View attachment 106405 View attachment 106406 View attachment 106407 View attachment 106408

Good afternoon Blademedia,

Now that looks good, did you write a thread up on its construction.

Is the part at the front a director for KU ?

Is it motor driven for skew ?

It makes mine look like something out of a scrap yard challenge : )

God Bless Spiff

 

[blademedia]

Good afternoon Blademedia,


Is the part at the front a director for KU ?

Is it motor driven for skew ?

It makes mine look like something out of a scrap yard challenge : )

God Bless Spiff

They are manufactured not hand made Spiff , yes for KU motor for skew, two different types ones C/KU, other is C with a make up KU,

Your work is very good

 

[moonbase]

...on the sats I have on C band at present there are no vertical or horizontal signals to test the effect of moving the slab on them, just circular.

Spiff,

If you can receive 46E it has some linear H/V signals in C band that you might be able to check with?

Rgds

 

[hvdh]

If it 's not absolutely clear, the inclusion of a permanent dielectric, revolving plate in front of the feed/LNB gives you all four polarities and the ability to adjust for optimum skew on each satellite, BUT the permanent inclusion means you have a minimum 3dB drop in each of the linear planes.

I've been wondering about this. I understand when the plate is oriented at 45° w.r.t. the probes, both H and V signals suffer equally (3 dB as you say). But when oriented horizontally, I would think V signals will hardly suffer?

 

[s-band]

I've been wondering about this. I understand when the plate is oriented at 45° w.r.t. the probes, both H and V signals suffer equally (3 dB as you say). But when oriented horizontally, I would think V signals will hardly suffer?

That's the way I see it. When the plate is in line with the linear wave, it delays it by 90 degrees so the loss should not be much different to the linear to circular conversion loss (i.e. the dielectric loss of a dB or so) In the case of the AVComm, lambda guide is different for the major and minor axes. If the incoming wave is at 45 degrees to the axes, it splits it into +/-45 delays to give circular. If the wave is in line with either axis totally, it is only the delay that changes when switching between V & H. The barrel type polariser should have minimal loss for circular & linear as there is no dielectric loss.
A simple circular polarizer for 10GHz has drawings of the plate case.
I think I got that more or less correct but it's been a long day, so e&oe.

 

[Spiff]

That's the way I see it. When the plate is in line with the linear wave, it delays it by 90 degrees so the loss should not be much different to the linear to circular conversion loss (i.e. the dielectric loss of a dB or so) In the case of the AVComm, lambda guide is different for the major and minor axes. If the incoming wave is at 45 degrees to the axes, it splits it into +/-45 delays to give circular. If the wave is in line with either axis totally, it is only the delay that changes when switching between V & H. The barrel type polariser should have minimal loss for circular & linear as there is no dielectric loss.
A simple circular polarizer for 10GHz has drawings of the plate case.
I think I got that more or less correct but it's been a long day, so e&oe.

That looks an interesting read : )

I have just moved the dish round on the pole as it would not reach 46E, problem is a temporary 12 inch Jack on it at the moment.

Doing a blind scan for some V / H C band signals, but nothing so far, it could be that the dish is not elevated correctly because of moving it on the pole.

No nothing, I shall have to wait until we shift KU and C up the pole and set the C band properly tracking a full ark..

God Bless Spiff

 

[moonbase]

Spiff,

I have just uploaded a table showing satellite frquency bands and polarisation types to the forum. The table might be useful to you for your C band tests?

Just Sharing This - Satellite Frequency Band & Polarisation Type List


Rgds

 

[Spiff]

Spiff,

I have just uploaded a table showing satellite frquency bands and polarisation types to the forum. The table might be useful to you for your C band tests?

Just Sharing This - Satellite Frequency Band & Polarisation Type List


Rgds

Thank you Moon base that is going to be very useful : )

Alanna and I went to out local boot sale today so no work done on moving the dishes as of yet.

Hopefully tomorrow we will make a start.

We had intended leaving the bottom of the two SSS 550mm stand off wall brackets in place and fitting anther further up making three in all, but SSS wanted £110 just for one extra bracket, seems a lot.

I think I will leave it with just two wall brackets, the new top one which was the original bottom one will be close to the top of the wall, this is why I had considered three.

It has a 3 meter 76 mm pole, with a 1.3 and a 1.4 mm dish plus the mounts and jacks mounted on it : )

Both the dishes are aluminium.

Picture of items found at the boot sale.

In the centre a nice waterproof junction box, some large bolts and spacers, two external lights, two personal head lights which are better that holding a torch in your teeth and some nice cloth for vintage radio speaker frets.


God Bless Spiff