LNB arm lengths unknown ..?

[Vipersan]

As some of you guys will know ..I inherited due to a mistake by the vendor ....a substandard 1.1m dish ..
The most important problem here is the lack of an LNB arm ...so I figured I might try to make one ..
This dish will never perform well in Ku or Ka ...
but C and L are much more forgiving of dish surface inaccuracies ...so worth giving it a go ..
The dish is a maxx brand ...
So obviously I'm going to need some measurements ..
I figured an angled L shaped ..manufactured in 30mm x 15mm alluminium box section would suffice ..
If anyone has the same dish ...I'd appreciate measurements of the down section from the rear spider to the angled section ...and then the length of the section sticking out which carries the lnb ..
Finally the angle of this L if possible ...?
If not then the measurements of the arm of a TD110 ...would probably be close enough ..since it is a similar sized dish ..
Yes I have one of these myself ..but it is up at House Apex Height so dont wat to go there unless I have to ..
Someone who has one at a more accessible height might be able to help ?

here is a basic drawing of what I need..

This dish is never going to perform as it should ..but even with the missing parts and imperfections should prove useful for my experiments ..
rgds
VS

 

[Analoguesat]

On my Triax td110 the lnb arm is 62cm from the front of the dish to the end of the metal. The lnb holder clips into the end of the arm so its a bit longer to the lnb holder. The arm is very slightly curved upwards at the dish end too which probably increases the length by 25mm or so.

 

[Vipersan]

On my Triax td110 the lnb arm is 62cm from the front of the dish to the end of the metal. The lnb holder clips into the end of the arm so its a bit longer to the lnb holder. The arm is very slightly curved upwards at the dish end too which probably increases the length by 25mm or so.

Cheers AS ..
A good starting point ..
If I work to those lengths and articulate it at the joint I should be able to get close to focus ..
much appreciated..

 

[RimaNTSS]

In reality, it does not matter at all what is feedarm length. Most important is fact that LNB's phase center is co-located with antenna's focal point. So, I would suggest firstly to calculate position of antenna's Focal point and only then start to design feedarm and LNB-holder.

 

[Analoguesat]

Cheers AS ..
A good starting point ..
If I work to those lengths and articulate it at the joint I should be able to get close to focus ..
much appreciated..

If you need any more just shout, my dish is easy access.

 

[Vipersan]

In reality, it does not matter at all what is feedarm length. Most important is fact that LNB's phase center is co-located with antenna's focal point. So, I would suggest firstly to calculate position of antenna's Focal point and only then start to design feedarm and LNB-holder.

I dont doubt you would approach this correctly Rima ...but I only want to use the defective surfaced dish for L band experiments ...so I really dont think it needs such critical arrention to detail ..
My Helical antenna seems to work within a large range roughly at the focus ..

As discussed in another thread ..
where exactly is the focus of a helical antenna about 200mm long ..?
rgds

 

[RimaNTSS]

What do you mean by "defective surfaced dish" , is it bended? Could you show picture of it?

 

[Vipersan]

What do you mean by "defective surfaced dish" , is it bended? Could you show picture of it?

Tricky to get a photo of the defective area ...
Doesn't look like its impact damage or folded etc ..
More sort of ...blistered is the only way I can describe it ..
The fault isn't visible from the rear ..only the front when looking at a shallow angle ..
It's actually more evident to touch ...
ie simply not smooth ..
A manufacturing defect I think ..probably in the pressing ..or the powder coating..?
and only over a small area in the centre ...roughly about the sweet spot ..
Imagine it as blistered or bubbled paint ...
it's the only way I can describe it..

I was actually prepared to put up with it providing they sent me the missing parts ..
but as it worked out ...they refunded my money ...and told me to keep it ..
win win I spose

 

[Vipersan]

The box section ally arrived today ...so made a start ..
This is the story so far ..
the upright is a stand in ...as the correct piece is already on the dish..
rgds


scuse the mess in my workshop errr kitchen..
It is afterall just a workshop annex...
;)

 

[Ghostleader]

Vipersan that's my mum's old cooker!!, a quality product so it was

Sent from my thl 2015A using Tapatalk

 

[Vipersan]

Vipersan that's my mum's old cooker!!, a quality product so it was

Sent from my thl 2015A using Tapatalk

Yep ..quality it was/is ...
still works just fine for the limited cooking I do ..

..and the oven ...is excellent for shaping alluminium ...
I made my homebrew C band scalar in there ..
lol

 

[Ghostleader]

Does the PP3 ("Square battery" in auld speak up here) still work in the ignition switch box?

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[Vipersan]

Does the PP3 ("Square battery" in auld speak up here) still work in the ignition switch box?

Sent from my thl 2015A using Tapatalk

Yep ...still working...

 

[Ghostleader]

Another "Don't make em like that anymore.." example, the whole thing is enamel paint, modern stuff be garbage in comparison. Have you had any measurements passed to you in regards to the original dish arm length??

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[Vipersan]

If you check back in the thread I've had an estimate ...but not exact..
So will have to experiment to find the sweet spot...
Close enough will be good enough I suspect.

 

[Vipersan]

Spent about 2 hours so far outside with a lump of wood substituted for the arm as a temporary measure ..
Can't cut the actual arm till I know the required length to withingn a cm ...
I have the dish receiving 1W atm ....and anm closing in I think ..
I positively identified this transponder ...and is able to lock at around 7db ...
Much tweaking to do ..
rgds
VS

 

[Vipersan]

Pardon the pun ..but ...thank god ...
Now receiving the gospel channel locked at 6.7db ..
Anyone any idea what I _should_ expect from this channel on a 1.1m dish ?
roughly max signal ?
This will be my reference channel as I get closer ....

 

[Vipersan]

Started rainig here ...but the gospel channel holding steady in light rain (atm) ..at 8db ..
I guess I'm close ...but would like to see if I can squeeze a bit more ...
Could someone with a 1.1m dish in the NorthWest UK ...give me a figure to aim for ?
the only 1.1 I have is at height and currently fitted with a C band LNB ....so cant reference that one ..
rgds
VS
...Time for a cuppa whilst the rain hopefully stops..

 

[Vipersan]

Some help today as Nelson has been here a few hours ...
Significant progress made ...
Damned close I think ..
Solid around 8 db ..and have seen Gospel up around 10db today ...
Run short of nuts n bolts ...but here is the photo of the job so far ..

 

[Archive4]

Are you sure that blue clothesline is not causing a 2dB loss?