Just Sharing This 1.2 Precision / Octagon lnbf mod

[s-band]

G, mate, i'm only a little humble sparkie,

C'mon you've got more practical experience of this stuff than me.

 

[scopus]

I'm wondering if I can concoct something for 18Ghz for my spare Precision.....

 

[John]

I'm wondering if I can concoct something for 18Ghz for my spare Precision.....

... What you got in mind pray tell ?

 

[scopus]

... What you got in mind pray tell ?

Not sure yet. The big hurdle is getting it to fit the WR75 flange on the Hughes

 

[John]

Not sure yet. The big hurdle is getting it to fit the WR75 flange on the Hughes

Has it got to be 18GHz ?, one of the reasons i went with the Inverto / Precision mating is because the Inverto uses a throat of around 17.3mm which aint far off the Precision internal dia so a pretty good match to try and improve on.
Could you not graft a bit of copper tube onto one of those horns we got from Israel ?.

 

[scopus]

Has it got to be 18GHz ?, one of the reasons i went with the Inverto / Precision mating is because the Inverto uses a throat of around 17.3mm which aint far off the Precision internal dia so a pretty good match to try and improve on.
Could you not graft a bit of copper tube onto one of those horns we got from Israel ?.

I was also thinking along those lines...wanted to try this while you tried out the Inverto.

 

[John]

Nice work John. Let us know the outcome, particularly the Ka test figures.

Right then Llew, this is what we have so far. Just using simple display readouts from TM 5402 M3. (sorry G).

Last nights readings with slight cloud cover sampled at around 7.30pm:
16East--21577H.
1.2 Gibby ------------- Promax 9.3dB. TM5402 10.5dB absolute max.
1.8 CM -------------- Promax 10.4dB. TM5402 12.2 dB absolute max.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This mornings readings, slight cloud cover as well, sampled at around 11.05 am.
1.2 Gibby ------------- Promax 8.6dB. TM5402 9.5dB max.
1.8 CM ---------------- Promax 10.4dB. TM5402 11.5dB max.
1.2 Precision --------- Promax 9.1dB. TM5402 9.6 db max.
** Not a bad performance for a lashed up Precision, might be improved apon with slight lengthening or shortening of 1/2" Ka inner tube. More testing on that one.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Will do all three readings again around 7.30pm

 

[moonbase]

They are a thing of beauty those Precision dishes and already ahead of the 1.2m Gibby on your Ka test without fine tuning and it has the feed and arms blocking some of the dish face.

Re the channel master 1.8 Ka test results, is there any possibility of marginal dish distortion due to the heavy LNB configuration on it? I know you have it well braced but there seems to be something impacting the Ka signal level on the 1.8 CM. Perhaps on a slightly more fringe signal that all three dishes can receive it will come into its own?

Going back to Precision, or Elite Antennas as they have now morphed into, they sell a "Ka Specific" version of their antenna range that has been machined to finer tolerances for Ka reception. I do not know how much this improves the signal over a normal antenna from their range but one thing is for sure, the "Ka Specific" version from Elite is sold at a hefty premium over the equivalent normal model. They know how to squeeze the juice from the ripe fruit.

 

[moonbase]

That stepladder mount for the Precision is awesome, no planning required for that type of mount, briliant stuff.

 

[John]

That stepladder mount for the Precision is awesome, no planning required for that type of mount, briliant stuff.

Yep, you just fold 'em up and carry it all away

 

[John]

They are a thing of beauty those Precision dishes and already ahead of the 1.2m Gibby on your Ka test without fine tuning and it has the feed and arms blocking some of the dish face.

Re the channel master 1.8 Ka test results, is there any possibility of marginal dish distortion due to the heavy LNB configuration on it? I know you have it well braced but there seems to be something impacting the Ka signal level on the 1.8 CM. Perhaps on a slightly more fringe signal that all three dishes can receive it will come into its own?

Going back to Precision, or Elite Antennas as they have now morphed into, they sell a "Ka Specific" version of their antenna range that has been machined to finer tolerances for Ka reception. I do not know how much this improves the signal over a normal antenna from their range but one thing is for sure, the "Ka Specific" version from Elite is sold at a hefty premium over the equivalent normal model. They know how to squeeze the juice from the ripe fruit.

Well, this is something that i noticed when i started to use offset dishes way back when my 2.2 PF got trashed ..... when i had a 1.8 PF Precision and also the 2.2 PF Precision i found that it was quite easy to see and obtain the point of focus. As soon as i had the 1.8CM offset even in its original state, unmodified in any way, the focus point was "soft" , a lot harder to define the exact precise spot compared to the PF dishes. My dish at the mo is braced to high heaven due to it's bits and bobs on it as you know, and is permanently strung, which shows perfect string kissing. The results i get with the 1.8 CM are not flagging up any worry messages with me at the mo. I do feel that solid metal dishes are better performers on Ka band than the plastic varieties though, there must be a tad of Ka signal just squeezing through the mesh lol.
Thanks for the transfer btw.

 

[moonbase]

Well, this is something that i noticed when i started to use offset dishes way back when my 2.2 PF got trashed ..... when i had a 1.8 PF Precision and also the 2.2 PF Precision i found that it was quite easy to see and obtain the point of focus. As soon as i had the 1.8CM offset even in its original state, unmodified in any way, the focus point was "soft" , a lot harder to define the exact precise spot compared to the PF dishes...

Yes, I agree, for Ku and Ka with the Precision dishes you are pretty much guaranteed to be on an accurate focus by virtue of the feed and dish location points for the three support arms. If you use the support arms and feed matched to the dish then its automatic unless something is distorted.

For C Band with Precision/Elite prime focus dishes there is some scope for varying the LNB aperture distance from the dish. However, this is dependent on the type of C Band feed/scalar arrangement being used. The Viking SatCom (ADL) C Band feed arrangement used by Elite Antennas allows movement of both the feed barrel and the scalar so some tweaking is required to get an accurate focal point.

 

[John]

Yes, I agree, for Ku and Ka with the Precision dishes you are pretty much guaranteed to be on an accurate focus by virtue of the feed and dish location points for the three support arms. If you use the support arms and feed matched to the dish then its automatic unless something is distorted.

For C Band with Precision/Elite prime focus dishes there is some scope for varying the LNB aperture distance from the dish. However, this is dependent on the type of C Band feed/scalar arrangement being used. The Viking SatCom (ADL) C Band feed arrangement used by Elite Antennas allows movement of both the feed barrel and the scalar so some tweaking is required to get an accurate focal point.

I'll have a quick look at the Viking site for that feed, they used to send me monthly or so email flyers but not seen any recently

 

[Llew]

Very good John. It's handy that the throat aperture of the Ka/Ku LNBF is of a standard Ku LNBF ( internal Ku to Ka matching chamber inside). Well worth experimenting with the pipe length.

Precision figures pretty good considering the ad hoc arrangement of the dish. I like the steps stand

I have tried the Ka/Ku on the 1.2 Gibby, but the expected Ka signal improvement wasn't significant compared to it on the TD88. I'm not convinced that dish size makes a huge difference until you go up to 1.8M as you have, with the dish in very good condition and the Ka feedhorn precisely positioned.

 

[John]

Right then Llew, this is what we have so far. Just using simple display readouts from TM 5402 M3. (sorry G).

Last nights readings with slight cloud cover sampled at around 7.30pm:
16East--21577H.
1.2 Gibby ------------- Promax 9.3dB. TM5402 10.5dB absolute max.
1.8 CM -------------- Promax 10.4dB. TM5402 12.2 dB absolute max.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This mornings readings, slight cloud cover as well, sampled at around 11.05 am.
1.2 Gibby ------------- Promax 8.6dB. TM5402 9.5dB max.
1.8 CM ---------------- Promax 10.4dB. TM5402 11.5dB max.
1.2 Precision --------- Promax 9.1dB. TM5402 9.6 db max.
** Not a bad performance for a lashed up Precision, might be improved apon with slight lengthening or shortening of 1/2" Ka inner tube. More testing on that one.View attachment 98139 View attachment 98140
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Will do all three readings again around 7.30pm[/




Right then,
All three dishes measured again at around 7.30pm.

1.2 Gibby ----------- Promax 9.1dB max. TM5402 9.9dB max.
1.8 CM ------------- Promax 11dB max. TM5402 12.4dB max.
1.2 Precision ------ Promax 9.4dB max. TM5402 10.1dB max.
Conclusion: The Precision 1.2 has the slight advantage over the 1.2 Gibby. Using the Ka adapter tube of 12.5mm I/D tube down the middle of the Inverto and potruding 3mm out of the original Precision feed certainly works. Tried lengthening & shortening the centre tube by 3mm and did not offer any better results.
Removing the Ka centre tube drops the Ka performance down quite a lot, around 3dB.
So: Not really worth butchering a new Inverto Ka/Ku lnbf just to give good results on Ka only, but enjoyed doing the research.