Dishes for Ka-band: what works - what doesn't?

[archive10]

Now that there's a increase interest in Ka-band on this forum, I am wondering:
From the enthusiast's perspective - what make and models of larger dishes (1.0m -> 5m) work well with Ka-band?

There are of course discussions on this forum with empirical evidence.
A few recent threads are:

KA Band Dish Sizes
New Inverto KaKu lnb

Most internet-over-sat operators seems to use specific Ka-band (Skyware/CM) steel dishes around 70-90cms.
Practical, easy-to-ship, not-too-expensive. Good for consumer installations.
And antennae for the professional market are usually marketed either as Ku/C models, or in models specifically for Ka-band.

There are the known criteria for Ka-band, where surface accuracy become very important the higher the frequency, and that the mesh embedded in SMC-dishes needs to have a fine mask to work properly for Ka.

But then the application questions come out:

1) Is a 20-year old CM120 up for the job of Ka-band D?
Considering it retains the shape very well, but may have been designed for Ku-band, and thus have a mesh-size that starts letting the higher portions Ka band through...

2) Or are the reflectors of the special Ka-band SMC dishes (eg from Skyware/Channel Master) made with a different reflective layers (i.e metal dust rather than mesh) that makes them better suited for Ka, even though the mechanically appear identical to the Ku-band versions?
In contrast, the GD Satcom (Prodelin) Ka-band range is clearly different from the Ku/C - much higher rigidity (more ribbing in the back).

3) Are there other generic models of SMC (eg Cahors) that by default have finer mesh etc, working better in Ka?
(The Ka-specific antennaes seem to priced markedly higher than the Ku ones!)

4) I know that the SMW ABS-reflector of the past had a layer of reflective paint instead of embedded mesh. Does this work for Ka as good as a steel dish?

5) Is a good steel pressed steel (or Alu) dish (eg Gibertini 125) as good as it gets, even though they're designed and marketed for Ku?


Of course, we should always try it out and see what works, but it would be great to hear your views on this, as getting the best out of Ka may require getting the right kit from the start...

 

[Archive-8]

Both my 1.25 & 1.5 gibertini dishes are fairly good from a ka point of view.

Not had a lot of luck with my ISS 1.0m dish.

 

[John]

I'm a believer in quality metal dishes for Ka use. I just feel happier that there is no 18 or 21 GHz wavelength signals passing through the mesh on a fibre dish . I am really happy with the performance of my 1.2 Gibby but only after it had extensive attention to assembly of the reflector / focal point / aiming accuracy / illumination /stringing etc. Ideally i would like to use a 1.5 Gibby or Precision 1.5 PF on Ka.
I think when the weather gets a bit more kinder / warmer i'm going to set up a bit of a test with my SSA sig generator on a 5th harmonic on one side of a spare CM 1.2 fibre dish and a Ka lnb on the other side of the dish into my Promax and see if there is actually any RF leak through.

 

[Llew]

I did some tests with my dishes here -

Considerations when choosing a dish for Ka band

Purely subjective, and limited in testing with the three dishes I had then at my location . Since that test, I still go back to the TD88 for most of my Ka reception, as it gives me a consistency not found on the Gibby 1.2 or especially the SMW 1.05, the latter performing especially poorly - maybe something to do with the reflector coating material used on SMW dishes, or perhaps the unusual design of the dish?

 

[blademedia]

Elite make a KA band dish,
Ka Band Satcom Antennas | Elite Antennas

 

[moonbase]

Elite make a KA band dish,
Ka Band Satcom Antennas | Elite Antennas

blademedia,

Elite charge a premium price for their Ka Band rated antenna, they are quite a bit more expensive than the same size non Ka Band rated antenna. I think that their Ka Band version is manufactured to a more precise tolerance than the non Ka equivalent.

Rgds

 

[John]

.... here's the beginning of what might tell us a bit more about 18 / 21 GHz RF leakthrough of a fibre dish. When the test rig is set up outside it will be looking through a 1.2CM offset fibre dish between the two devices instead of fresh air.
The test rig is working in pricipal, needs to go outside and test with the dish later.
RF sig is from the 5th harmonic of the frequency shown from the SSA device using Vitors (VMA) software and just using a simple dipole antenna cut approx for 18GHz.
Ka lnb is an XMW band D 21.2 to 22.2GHz DRO.

 

[blademedia]

blademedia,

Elite charge a premium price for their Ka Band rated antenna, they are quite a bit more expensive than the same size non Ka Band rated antenna. I think that their Ka Band version is manufactured to a more precise tolerance than the non Ka equivalent.

Rgds

All antennas have a wavelength KA band is different to C/KU etc, Elite specially make the KA band antenna, I presume the spinning process is slightly different/extra work to get the wavelength for KA frequency range, reason for the premium.

 

[John]

.... here's the beginning of what might tell us a bit more about 18 / 21 GHz RF leakthrough of a fibre dish. When the test rig is set up outside it will be looking through a 1.2CM offset fibre dish between the two devices instead of fresh air.
The test rig is working in pricipal, needs to go outside and test with the dish later.
RF sig is from the 5th harmonic of the frequency shown from the SSA device using Vitors (VMA) software and just using a simple dipole antenna cut approx for 18GHz.
Ka lnb is an XMW band D 21.2 to 22.2GHz DRO.

View attachment 103200 View attachment 103201

.... Right then Gentlemen, do you want the good news or the bad news ?.
Outdoor testing on the 1.2 CM fibre dish done.
Any guess's to the outcome ?.

 

[Llew]

Assuming you do get a reading, whereabouts on the dish do you place the dipole John? Dooes it have to be almost touching the surface or a particular distance away?

 

[Vipersan]

Logically because it is a mesh embeded dish ..ie has small holes..
It might be allowing Ka signals to pass through..
So slightly inefficient at Ka compared to a solid dish..
But ..
no doubt your results will say otherwise ?
;)

 

[John]

Assuming you do get a reading, whereabouts on the dish do you place the dipole John? Dooes it have to be almost touching the surface or a particular distance away?

Because of the low output of the SSA Llew i tried the dipole at approx 10mm away from the rear dish face and also further back at a distance of 200mm or so with similar results.
I'm just going to upload a few pics as well.

 

[John]

Logically because it is a mesh embeded dish ..ie has small holes..
It might be allowing Ka signals to pass through..
So slightly inefficient at Ka compared to a solid dish..
But ..
no doubt your results will say otherwise ?
;)

Please excuse the state of the laboratory in the test set-up.
Yep, they seem to leak but i would like input from more qualified persons than me.

Queries from looking at the pics:
How pure is the generated 5th harmonic output of the SSA ? .... is that reduced leakage spike really 21.200 or is it a higher harmonic of it ??.
I don't think the metal truss that's holding up the dish is aiding RF to sneak around to the lnb pickup.
I should have reversed the equipment setup, SSA source at the front etc just to establish if the same leakage is the same just to satisfy curiousity.
The dish is about 15yrs or so old.
A few pics to study, suggestions welcome.

Note: Is there a reason some of the posted pics get flipped ? ... the original posted image was horizontal.

 

[Llew]

How pure is the generated 5th harmonic output of the SSA ?

Vitor may be able to help there John.

Can you get the correct lower harmonics down to the base frequency showing in the Promax?

 

[archive10]

.... Right then Gentlemen, do you want the good news or the bad news ?.
Outdoor testing on the 1.2 CM fibre dish done.

Yep, they seem to leak but i would like input from more qualified persons than me.

And the good news (I presume it is?) ;)

 

[John]

And the good news (I presume it is?) ;)

The good news ST is that i got some kind of a result lol .
Gives the old grey matter something to think about

 

[John]

Vitor may be able to help there John.

Can you get the correct lower harmonics down to the base frequency showing in the Promax?

... youv'e lost me Llew, give me some guidance

 

[Llew]

... youv'e lost me Llew, give me some guidance

Ignore. Not helpful.
Might be worth replicating the experiment with Ku, to see if there's any stray signal picked up outside the dish boundary that's getting to the LNB.

 

[Channel Hopper]

blademedia,

Elite charge a premium price for their Ka Band rated antenna, they are quite a bit more expensive than the same size non Ka Band rated antenna. I think that their Ka Band version is manufactured to a more precise tolerance than the non Ka equivalent.

A softer broom perhaps

 

[John]

Ignore. Not helpful.
Might be worth replicating the experiment with Ku, to see if there's any stray signal picked up outside the dish boundary that's getting to the LNB.[/QUOTE
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Apologies ST1 for drifting off topic a bit ...
Did the internal setup for a Ku mesh leak test Llew using an Octagon Twin pll universal lnb. Used the stronger third harmonic and had to bung some absorber up the wave guide to attenuate.
Using lnb freq 12500 on the Octagon needed the third hamonic of 4166666 from the SSA and was pleasantly surprised that it hit the mark spot on and displayed good gain. Tried an old Inverto and an Invacom and they were well off.
Will take it outside on the CM 1.2 tomorrow for a quick leak test.