DIY Tripod assembly for Alcoa 1.8 dishes

[Vipersan]

Hi Friends ..
First let me wish everyone a happy new year ..
I'm having a tough time atm with my 'condition' but am trying to remain active ..
..to that end I've started work on a new DIY tripod assembly to fit my old Alcoa 1.8 pf dish ..
Which never had a Cband feed ..so This is the MKII lnb holder and MKI tripod ..
I'm sure Nelson will find it interesting as he has the same dish ..
Intstructions are for the most part pasted into the photo's ...and as yet I have not soldered the pipework up ....but _have_ had it all on the dish and it works ...just slotted together..
If you attempt this assembly ...only solder up the pipework with a blowtorch once you have it in place on the dish ...and fully checked for for plate height postion ...
In other words once you have checked it is set for the correct FD of your dish ..
mine is correct within 1/2 cm ..and allows for moving the lnb and attaching a 'proper' 3 ring choke.
I started by sacrificing the very basic one ring plate which came with the cheapo Pauxis lnb ....it useless as a choke ...but perfect for this project..

I'm happy to answer any questions ...
But rember ..although tested in situe the project is as yet not complete ...
Im awaiting a polythene 65mm collar from china ...to acurately clamp and position the lnb ..
..and as yet I have not soldered the pipework to make it rigid ...though it holds together well for testing..

 

[Vipersan]

The more detailed pix with assembly instructions ..

More pix to be added as the project progresses..
rgds
VS

 

[Channel Hopper]

Are they Yorkshire fittings ?

Great progress, but from experience I believe you will need aditional bracing near the feed as the weight of the LNB will force the scalar ring to move off from perpendicular.

Additionally, see if you can stick a second locking screw on each of the 15mm closed ends on the ring, just to stop the whole assembly from twisting inwards to the reflector.

 

[PaulR]

Looking good VS. I hope that copper tubing is going to be rigid enough.

 

[Vipersan]

The Tripod in place and a temporary LNB placed at the focus ...
Working at acceptable levels ...and as yet not even optimised..
rgds
VS

 

[Vipersan]

Thanks for the comments Paul and CH ..
You are quite correct CH ...I will be fitting extra screws as you suggest ...but waiting till I have the polythene collar in my possesion before I do ...Not sure just how much room I will have until I see it ..

Paul... the copper tube is plenty rigid unless someone deliberately attempts to bend it ..


btw The Cband LNBs are very lightweight so hopefully no counterweight will not be neccessary..


rgds 2 all
VS

ps ...yes they are yorkshires CH

 

[Vipersan]

Just a Quick addition ..
This is the Collar I've ordered which hopefully will complete the assembly and support the lnb...
rgds
VS

 

[Vipersan]

After reading CH's concerns about rigidity and movement where the plate meets the 3 inch supports I decided to add a brass tubular ring ..
Luckilly I had some in my scrap pile ..but I suspect a fine copper tube formed into a ring would work just as well though perhaps not as rigid it would be easier to solder..
rgds
VS

 

[Topper]

It's all looking good VS...
Happy New Year to you and I hope your condition improves in 2011

 

[nelson_b]

hi vipersan -
only just spotted this thread -- sorry to hear you health has been down again

you have been busy --
that,s a very tidy permanent conversion that you have made --
the adding of the outer ring for extra stability is a good idea --
and with the collar fitted as well, the assembly will work well i think -
also plenty of room for adjustment of the l.n.b and feed --
it looks " good " fitted up on the dish ----

As you know for the time being my Alcoa dish has a fixed mount and is in use for k/u at 42 east -- although i did make a workable mount for c band - ( strong but not as neat fitting as yours l.o.l.) i do hope to have another go with c band on this dish - at some point - for now the new BSC 421 C band l.n.b that you recommended as a replacement for the pauxis is properly fitted as a second l.n.b on the 1.8 offset channel master -
with good all round results

cheers nelson.b

 

[Vipersan]

Thanks for the replies m8s
Cheers Topper

..good to hear you are impressed with the new LNBF Nelson..
I have tried my dual feed lnbf as you know ..
I'm not sure its quite as good for DXing as the single feed version ..
Thats why I need to absolutely optimise the feed assembly ...and in doing so accomodate easy swapping of the lnbs plus the ability to adjust focus both with the lnb ...and the choke position to mm acuracy ..
I'm convinced this new assembly will allow that ...plus it masks even less of the centre area ...thus presenting less of a 'shadow' on the dish...
Cant wait to get it fully fitted and functional ...but preliminary testing will pull 80% of the channels I know I can get ...without any tweaking..so..
so far so good...
rgds
VS

 

[nelson_b]

Thanks for the replies m8s
Cheers Topper



...plus it masks even less of the centre area ...thus presenting less of a 'shadow' on the dish...

yes every little bit counts --with the fringe levels that you,v been operating at --
i lowered the positioning yesterday of the side arms on my offset dish as i felt one of them was too close to - and may be affecting the feed to the BSC 421 --

cheers nelson.b.

 

[Vipersan]

Hi friends ..
The black nylon capacitor collar arrived today ...
The hole diameter could have been a few more mm accross ...but still very usable ..once the bottom capacitor support flange was cut away ..
The flange formed a 5mm shelf which partially blocked the lnbs passage through the collar ...but a sharp knife fixed that ..
The end results are shown in the 3 pics below ..
A small plastic packing was needed towards the lnb end of the waveguide ...under the collar to accomodate the fact that the lnbf waveguide is not a cylinder ..but in fact tapers a few a few mm along the legth of the waveguide..
You can see the clear polythene packing protruding slightly above the collar ..in 2 of the pictures..
rgds
VS

 

[Vipersan]

....couldn't resist mounting the plate assembly and fitting my green laser pen centrally in the waveguide throat ....
..just to see how accurate the thing was ..without any adjustment..
You can see how far out it is by looking at the green dot on the black centre of the dish close-up pic..
rgds
VS

 

[nelson_b]

coming along well --
looking very smart for an elderly dish --
cheers nelson.b

 

[Vipersan]

Just a quick picture of the 'old girl' showing off her new 'legs'...
The tripod has been fitted and centred..hopefully for the last time ...
all tubing has been sprayed with undercoat and matt black topcoat ..ready for the plate and lnb..
The mount ring assembly is approximately 1cm off centre ...but I'm going to invest in 3 compression springs to mount between the lnb blate and the 3inch support arms ...
this will allow for some final 'fine' adjustment of the way the lnb mount plate faces the centre of the dish..
rgds
VS

 

[PaulR]

Really nice job you're doing there VS. Hats off to you.

 

[Channel Hopper]

Nicely done, hope the rain holds off for the final fettling.

 

[Vipersan]

Thanks Paul ..
Thanks CH ..
Been raining all weekend so had no chance to geta receiver and monitor outside ..
Because I'm after squeezing the pips to the max ...on this setup ..I'd rather use this method to optimise the new setup.
..in the meantime...I was trying to locate some suitable compression springs for fine plate adjustment ..
So far without success ..
If anyone can help me out ..
I need 3x comression helical springs ...which have sufficient thrust that they cannot be compressed by hand or rather between fingers ..
Each spring needs to be about 3 > 4 loops ..
uncompressed around 10 > 12mm ....fully compressed approx 6 >8 mm
and an internal hole diameter capable of passing a 6mm bolt through its length ...ideally with a small amout of play so 6.5 > 7mm hole diameter..
If anyone has something simillar to this lying around ...or know where I can pick some up ..I'd be very grateful.
No rush ..as the cold has affected my hands atm ..and the weather isn't on side..
..But then ..patience isn't one of my virtues ..so itching to finish the project.
At the moment I have simply placed my lnbf at the centre of the tripod ..unoptimsed...and I'm pulling around 70 - 80% of the channels I have previously captured at 55 West..so all looking good so far..
rgds
VS
..forgot to add ..the springs should resist rust ideally..

 

[Channel Hopper]

..
I need 3x comression helical springs ...which have sufficient thrust that they cannot be compressed by hand or rather between fingers ..
Each spring needs to be about 3 > 4 loops ..
uncompressed around 10 > 12mm ....fully compressed approx 6 >8 mm
and an internal hole diameter capable of passing a 6mm bolt through its length ...ideally with a small amout of play so 6.5 > 7mm hole diameter..
..forgot to add ..the springs should resist rust ideally..

Damn, I was going to suggest those nifty hold-down springs that keep drum brake shoes in place on millions of cars.