Triax 2140 prime focus aluminium antenna w. polar mount

My latest project:



I acquired this dish in spring 2016, specifically to use it for C-band as a "micro-bud".
1.2 meter offset dishes are nice, but while being only marginally larger visually, a 1.4 PF dish is 36% larger area-wise than a 120cm - could make a real difference with C-band.

Seller said it was mounted on a house he had just bought, and he just wanted to get rid of it.
Feed-arms are visibly bent, looks like handling damage. Should be ok with a little twisting.



There is evidence of some slight bending and scuffs on the edge of the dish here and there.
But the surface seems generally ok too.
I strung the dish to check for any warping, and it seems to be in very good shape.








The dish came with a nice sturdy wall mount, which I wanted for other projects to begin with.



The polar mount, unusually, included it's own, welded-on bit of 60mm pipe.
This fits right into the wall mount, but is not directly compatible with anyhting else I have.

Two apparent challenges with the dish:

1) Feed-holder was originally for small bore feedhorn, now somewhat crudely butchered to accept 40mm LNB.
2) Polar mount with the 60mm tube is not easily mountable on normal mounts.

Unfortunately, the original feed-horn was not supplied with the dish.
Instead it came with old universal Ku-band LNB strapped on with a cable tie.
I am curious to see how much signal is lost from the f/D mistmatch if I compare a universal with a PF LNB...

The polar mount is steel-plate rivetted job, and has nylon/plastic bushings.
Metalwork is galvanised then powder coated.
Channel Hopper thinks it's a Lenson Heath mount - perhaps the dish is a Lenson Heath thing too?
There was no actuator - only a metal rod for manual installation.



The plan now is to set-up and align dish with Ku in a test configuration, to get my bearings.
Then I will swap the feed for a C-band one and see what I can find.
Later options include permanent mounting on wall, and multi-feed options.

Nice looking dish :-)

st1,

That's a very nice looking dish and has cleaned up well. I hope you get some good catches on C band with it.


Rgds

Sten! Nice dish and interesting project! If you wish, this holder is yours
I think, I also could help you with new feedarms.

Could you show couple of close pictures from both sides of the dish how the feedarm is connected to it?

RimaNTSS said:

Sten! Nice dish and interesting project! If you wish, this holder is yours View attachment 107343 View attachment 107344
I think, I also could help you with new feedarms.

Could you show couple of close pictures from both sides of the dish how the feedarm is connected to it? View attachment 107345

Click to expand...

That's very kind of you - I will be happy to try the LNB holder.
I'll go and take some more photos later today.

First I need to put all this stuff back in the outhouse, as the cold front is approaching and will be here in about an hour...

@st1 I think you will be happy about performance of the holder, as it can grab anything (which is round and proper diameter) and hold it tight but gently.

RimaNTSS said:

Could you show couple of close pictures from both sides of the dish how the feedarm is connected to it?

Click to expand...

Here's a few close-ups of the feed-arm ends, both dish-end and feed-holder-end.
The arms are 685 mm long. But I think the original feed-horn is quite long, so that the focal point of the dish is quite a distance in front of the original feed holder (see picture).
I was considering just using a triple of threaded rods as feed-arms. This will allow quite a good range of adjustment.
But on the other hand - I am wondering if the threads on the rods actually make them induce more noise in the reflected signals than smooth arms...
Incidentally, I found this installation diagram of the Triax 2140 - nicely hand-drawn, and showing the analogue heritage...

Nice pictures @st1 , thanks. What is the diameter of the pipes? And I suppose the bolts fixing pipes to the dish are M8. So, if you have a ne feedarms they could be 685mm and extendable another 100-150mm..... would that be enough?

RimaNTSS said:

Nice pictures @st1 , thanks. What is the diameter of the pipes? And I suppose the bolts fixing pipes to the dish are M8. So, if you have a ne feedarms they could be 685mm and extendable another 100-150mm..... would that be enough?

Click to expand...

Just went and measured - they're 12mm arms. They feel like aluminium.
I think new arms should be shorter; perhaps 570 mm or so, to allow for some adjustment room for both C-band a long-neck Ku-band LNBs.
And who knows - maybe it will do Ka-band as well; it does seems very well made...

@st1 Feedarms for your antenna are ready. In case if you wish to use Ku-band LNB, there is also 63mm/40mm adapter in the set. And several 40mm wooden (oak) cylinders to hold laser-pointer. Unfortunately I just broke couple laser-pointers, but, I think you can find one locally, not a big deal. ;) But, mind you, laser-pointers are far from perfect, their body not always parallel to the beam they make. So, it is advisable to calibrate pointer in the cylinder. INOX thread like to be greased ..... I use copper grease for all nuts&bolts, so they never stuck together.

do you fantastic !

RimaNTSS said:

@st1 Feedarms for your antenna are ready. In case if you wish to use Ku-band LNB, there is also 63mm/40mm adapter in the set. And several 40mm wooden (oak) cylinders to hold laser-pointer. Unfortunately I just broke couple laser-pointers, but, I think you can find one locally, not a big deal. ;) But, mind you, laser-pointers are far from perfect, their body not always parallel to the beam they make. So, it is advisable to calibrate pointer in the cylinder. INOX thread like to be greased ..... I use copper grease for all nuts&bolts, so they never stuck together.

Click to expand...

Nice work and a very kind gesture.


Rgds

@RimaNTSS: Absolutely fantastic!
Thanks you so much for this gracious work - almost can't wait to put this on the dish!

Some Christmas presents arrived 7 months early...
Feels like excellent quality - and wrapped contemporarily as well.

Unfortunately, I will have to wait until the weekend (possibly later) for mounting, due to chores things like "work" and "family".



Thanks, @RimaNTSS!

Finally got some dish time this evening.
I wanted to fit new feed-arms on the 2140 to be able to mount the C-band LNB.

First, I needed to remove the original, but somewhat bent, feed-arms from the dish.
Based on bitter learnings of rusting machine bolts, I applied multiple serving of WD-40 to the bolts, but they were still very tight.
Was fearing that the bolts had rusted solid in the threads.
As it turned out, that was not actually necessary...

When I finally got the bolts to move, they turned out not to be machine bolts, but hex-cap screws!
Arms are just pieces of 12mm diameter alu-tubes.
The arms have no thread inside, instead Triax used rawl-plugs that fit snugly in the tube.
Carefully set aside the stand-offs that support the angle of the arms wrsp to the dish surface.









Removed the arms, and dug out the nice INOX-set of arms that @RimaNTSS so kindly manufactured to handle the C-band LNB holder.

Darned!
Much to my discontent, the holes in the dish turns out NOT to be for M8 bolts (as integrated in the RimaNTSS design), but for 5mm screws as in the Triax design.



Maybe not so big a problem, I have a 9mm metal drill.
But I cannot use the stand-offs any more.
GRRR.

SO - the question is: What do I do now?

Do I drill out the holes in the dish to take M8 bolts, and attempt to make new stand-offs (eg through 3D printing)?
Or should I try to find some sort of adapter from M6 to M8 (Meccano-pieces come to mind), and re-use the old stand-offs?
Or is there a simpler way?

Sten! Just drill bigger holes in the dish and also in the adapters shown on picture #4 in your post.

RimaNTSS said:

Sten! Just drill bigger holes in the dish and also in the adapters shown on picture #4 in your post.

Click to expand...

Yes, but the adapters are made of rubber, which by now has turned to brittle, hard stuff.
I'm afraid drilling will vapourise them.
I think I will try find some sort of plastic or rubber tube that can be made into new stand-offs...
Or even wood, perhaps? Suitably dipped in varnish or something??

Took some time out in the winter cold today and sorted out the 2140.
First put the mount on the test-bench, and levelled it.



Then drilled out the holes for the new feed-arms in the reflector.
(After visiting hardware store for a new metal-drill...)

Then semi-fitted the new feed-arms so kindly provided by @RimaNTSS.



They work well, but

a) the "ears" on the feed-holder needs adjustment, and
b) they are really shoddily attached to the dish.

So, in the near future, some more work needs to be done to the system.

Then, to get some picture, I slapped the dish back on the mount (after sunset, so some dodgy flash-photography is evident).



The mount has BTW been treated in the past couple of days.
Disassembly, the lubrication of plastic/nylon parts with Silicone Gel.
Then re-assembly - and everything seems to be working nicely.

The dish is now up again in the manual adjustment configuration.
Next up (when the weather improves): Proper feed adjustment.
(Right now it's pretty much slapped on!)

Day-time possibilities for tweaking.



First-up: Checking the placement of the LNB.
To eliminate any irregularities from a badly aligned polar mount, point dish at 13E (which is almost due south here).



New feed-arms adjusted to replicate old feed-arms (same ~60cm distance from dish face to holder).
Then check the in-out placement of the GI prime focus LNB.
As with the old feed-arms, best reception is when LNB is as close to dish face as possible.



(and also not a very impressive result in terms of strength and quality!)



This seems to indicate that the feed-horn opening might benefit from being even closer to the dish face.
That'll be next steps.

But just to experiment, I slapped on an Inverto BUQ with it's 0.6 f/D feed-horn.



Amanzingly, the performance is better than the GI!



And it too performs the best when pressed as far as possible into the feed-holder.

(But it does look weird - having a high-performance offset LNB looking at a PF dish for best performance!)



To get the LNB closer to the dish face, I will have to redrill the feed-arm holes in the dish, and bend the LNB holder somewhat. But it was inevitable.

What do you think - will the performance improve? Will a properly-positioned GI overtake the IBUQ??
Even though they have about the same distance-to-the-front?

Looking amazing, love that dish and your work, RimaNTSS's bits look fantastic!
What vintage is that dish, I haven't seen that logo for a while.

Talking on Inox, I was helping my friend earlier who's moved house, I unpacked a new set of cutlery for her that she bought and they looked incredible, a really nice colour. Turns out they are Inox, I have never seen this before