Just Sharing This 1.2 Precision / Octagon lnbf mod

[John]

... barrel joint silicone sealed up and plastic cover re-fitted..... bit of a untidy attempt but i was getting fed up. My top cover has a joint half way down but this is not required to be done.
As can be seen, no blocking by the lnbf at all and it does seem to be performing well with initial tests.
Ignore the queer looking angles between the bottom dish arm and the lnb position..... it's just a skew thing due to the temporary set-up. Once the installation is installed correctly the lnb cables will be dropping down parallel to the bottom arm.

 

[John]

John,

My next question was to be about the join between the Octagon LNB and the C120 flange harvested from the Black Pro. How did you join them, was it simply a matter of offering up one to the other and clamping them at the intersection with the O clip? Or was there a variance in the inner/outer diameters that allowed some degree of overlap? Lastly did you use any sealant/resin at the join point, ot looks like there might be some yellow sealant/resin underneath the O clip?

Re the variance in the output, could this be related to your observation that one of the LNB probes seemed slightly out of alignment? Did you notice the output level difference across the board or was it for a specific polarity or Hi/Lo band?

Thx

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... I'll get back to you, got brain ache .... need my afternoon nap lol.

 

[scopus]

Just butting in on this thread. I have 2 spare Precision dishes, and noticed Elite Antennas do a Ka feed and OMT for the reflector. I have asked for a price, sure it won't br cheap, but we'll see.

 

[John]

Just butting in on this thread. I have 2 spare Precision dishes, and noticed Elite Antennas do a Ka feed and OMT for the reflector. I have asked for a price, sure it won't br cheap, but we'll see.

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.... You kept that quiet m'boy

 

[scopus]

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.... You kept that quiet m'boy

I have 2 x 1.2's from my old mate Jason at Rugeley Aerials...

 

[moonbase]

Just butting in on this thread. I have 2 spare Precision dishes, and noticed Elite Antennas do a Ka feed and OMT for the reflector. I have asked for a price, sure it won't br cheap, but we'll see.

The price is astronomic from Elite for their Ka Feeds and OMT, £1750 excluding VAT for a dual port Ka feed with OMT and £1150 excluding VAT for a single port Ka feed was the price last year. I dont know if they have had a reality check since then?

 

[scopus]

The price is astronomic from Elite for their Ka Feeds and OMT, £1750 excluding VAT for a dual port Ka feed with OMT and £1150 excluding VAT for a single port Ka feed was the price last year. I dont know if they have had a reality check since then?

Jeez, your'e not kidding! Give that a miss then.

 

[John]

Jeez, your'e not kidding! Give that a miss then.

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Yep, i'll stick with modding £30 Hughes OMT's etc and will just have to accept the performance difference

 

[John]

John,

My next question was to be about the join between the Octagon LNB and the C120 flange harvested from the Black Pro. How did you join them, was it simply a matter of offering up one to the other and clamping them at the intersection with the O clip? Or was there a variance in the inner/outer diameters that allowed some degree of overlap? Lastly did you use any sealant/resin at the join point, ot looks like there might be some yellow sealant/resin underneath the O clip?

Re the variance in the output, could this be related to your observation that one of the LNB probes seemed slightly out of alignment? Did you notice the output level difference across the board or was it for a specific polarity or Hi/Lo band?

Thx

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... Now where was we

If a good job is made of cutting off the Octagon / C120 flange square it makes a good butt joint and the inner dimensions of both barrels , in my case at least were virtually identical. If using a different donor than the Black Pro the O/D might be a tad different.
And yes, the butt joint is covered by the 15mm or so long collar which i made from 25mm conduit. I had to take (file) off about 1/4 mil off the O/D of my Octagon barrel to try and match the two halves as near as equal to each other. I then cut a slot in the barrel so as to give it movement to clamp down on the two barrel surfaces. Before finally fitting the collar i applied "plastic metal" to the two barrel O/D surfaces, then fitted the collar, and finally a stainless steel jubilee clip tightened up onto the collar.
After doing a quick lnb test to make sure it wasn't a total flop i took the front off the Octagon white outer cover, the bit that would have gone over the feed scalar ring, fitted it over the unit and filled it up with silicone front and back and left it over night to cure.
Tested it again at 65West on the weak beacons and was pleased with the result to say it was very low elevation and the dish had a tad of blocking from the school house opposite. I think once it's up on the roof mount at 25ft up it will be laughing.
See the pics re: barrel collar, if you can use them, drop me a pm.

Re: Port gain differences ..... when my other Octagon comes in the week i'll put the analyser on that one as it will be totally as standard and not abused by me and see what results i get.

Edit: -- It might be beneficial possibly to use a bit of sticky back ali tape around the internal barrel butt joint to try and get a smoother transition ??.

 

[moonbase]

John,

Many thanks for taking the time to explain the barrel/butt joint. I think i will try to source an Inverto Black Pro C120 single or twin LNB as the donor for the C120 flange as it keeps the waveguide inner diameter equal for both donor and host. My Octagon LNB's should hopefully arrive in a week or so from Germany so once they are here I will get to grips with the mod. I have a spare 1.5m Precision dish as well as the Unicorn 1.25m dish so hopefully I can have a go with both of them so see how they compare.

Am I right in thinking the 25mm conduit that you used for the collar was tubular steel conduit as illustrated in the picture above?

Many Thx

 

[John]

John,

Many thanks for taking the time to explain the barrel/butt joint. I think i will try to source an Inverto Black Pro C120 single or twin LNB as the donor for the C120 flange as it keeps the waveguide inner diameter equal for both donor and host. My Octagon LNB's should hopefully arrive in a week or so from Germany so once they are here I will get to grips with the mod. I have a spare 1.5m Precision dish as well as the Unicorn 1.25m dish so hopefully I can have a go with both of them so see how they compare.

Am I right in thinking the 25mm conduit that you used for the collar was tubular steel conduit as illustrated in the picture above?

Many Thx

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Ok good stuff.
Yep, the tube is 25mm galv steel electrical conduit.

 

[John]

... this turned up today for use as a dedicated dish for 18GHz and also to evaluate what a standard Octagon pll lnbf performs like on it, and also to take some weight off the 1.8mtr / changer.
Never had a Gibertini dish before and have to say i'm quite impressed with the build quality. I'm wondering whether to give it a quick coat of Waxol clear or similar around the hidden nuts & bolts on the back plate etc ??. Will string it later out of curiousity lol.

 

[scopus]

... this turned up today for use as a dedicated dish for 18GHz and also to evaluate what a standard Octagon pll lnbf performs like on it, and also to take some weight off the 1.8mtr / changer.
Never had a Gibertini dish before and have to say i'm quite impressed with the build quality. I'm wondering whether to give it a quick coat of Waxol clear or similar around the hidden nuts & bolts on the back plate etc ??. Will string it later out of curiousity lol.

Got one of those in the garage too...

 

[John]

Got one of those in the garage too...

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Check your garage when you get back

 

[John]

... this turned up today for use as a dedicated dish for 18GHz and also to evaluate what a standard Octagon pll lnbf performs like on it, and also to take some weight off the 1.8mtr / changer.
Never had a Gibertini dish before and have to say i'm quite impressed with the build quality. I'm wondering whether to give it a quick coat of Waxol clear or similar around the hidden nuts & bolts on the back plate etc ??. Will string it later out of curiousity lol.

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I'll just share this bit of info that raised it's ugly head that "stringing" revealed with the constuction of the 1.25 Gibby ....
Although happy with the build quality and the accuracy of all the bolt holes mating up precisely with each other whilst assembling..... BUT, when it come to stringing .
Bare in mind this is going to be used at Ka.

Stringing the reflector on it's own just stood up agains't a wall had a centre string gap of about 3mm or so which surprised me a bit.
Thinking , ahh .... when it's bolted to the pre-formed back plate it will pull out the 3-4mm and be absolutely perfect ... WRONG.
The string gap increased to about 8mm !... surprised me even more and absolutely a non starter for Ka use, or any other band for that matter. The culprit was the two middle fixing bolts and the miss-shape of the two items, ... the top and bottom ones when carefully tightened up and not over-tightened were ok and did not have any impact on distorting the dish shape but the two middle ones distorted the dish shape as soon as the slightest pressure was on the dish .
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I strung the 1.25 Precision and it was absolutely spot on and rightly deserves the name "Precision Antennas".
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SO .... constructive surgery was needed on the 1.25 Gibby to get the shape back.
The two middle dish fixings were left loose whilst the remaining gap between back of dish surface and back plate metal was filled with a good quality silicone and then will be tightened up just to just the point of tension without causing distortion to dish shape.
The two outer side edges of the dish needed very very slight forward pressure to get me perfect stringing so the shown bracing was constructed.
**Does leave you pondering though as to what is the right construction method to adopt .... Go with the book constuction guide with care and end up with an 8mm string gap ?, or "string" it for perfection and alter what-ever to suit ??.
Final note: The addition of the back bracing gave the whole dish structure a more solid feeling, well worth the exercise.

A few pics to go with the words ...
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[John]

.... Thinking ahead a bit, there's a good chance that i will be fitting the @ Trust1 design changer onto the end of the Gibby twin arms, so made a final vertical brace with the piece of ali tube i had left.
It's really robust now ..... but for a bit of good old over-kill i might look into two small mini-braces at the bottom of the twin lnb booms as they just flex a wee tad and the added weight of a changer + a couple of motorised lnb's might make it warranted..... we'll see.

 

[John]

... It had to be done.
More boom arm bracing and the start of fitting lnb changer to 1.25 Gibby.
Not keen on the motor bracket usage ..... looks a bit Heath Robinson, will need to improve on that bit.

 

[John]

... done a bit more on the 1.25Gib / changer work today, ready now for a bit of touch up paintwork etc.

 

[John]

... This particular installation when placed in it's intended position will be seen more easily from the road and will be mounted onto house brickwork, so as to reduce the impact it's had a bit of terracotta paint to try and blend it in a bit. Done a bit more with the Trust1 changer disc and will soon be ready for doing a bit of comparison testing on Ka between the Gibby 1.25 and the CM 1.8 .

 

[John]

... did a quick simple evaluation on Ka between the XMW DRO Ka D lnb and the Inverto Ka/Ku D lnbf using the Gib 1.25. You can't see it on the pic, but the Inverto has had it's nose cut off to try different feeds.
Tried an oval Hughes feed, worked slightly better when the oval was horizontal than vertical. Tried a Soarsat feed, and eventually back to the original Inverto feed. Result: The standard XMW + cone feed was a good 1/2 dB down compared to the Inverto. The original Inverto feed was a good 1/2dB up on the others. So on my 1.25Gib on Ka, the original untouched Inverto was the better choice it would seem but these small C/N db differences would mean diddly squat if a more comprehensive / rigorous test were to be done on the lnb's to reveal the ability to resolve a difficult signal..... some thing for another day ?.
Did a quick skew / Xpol test on the Octagon pll Ku on the 1.25 Gibby and found it to be very critical on the skew setting position .... very easy to get an opposite polarity signal show up on the analyser.... some thing to be aware of ?.