Express-AM1 - The loudest Cband source over the UK ?

[Vipersan]

OK...
Too cold to stay outside for too long atm ..
but managed to try a quick experiment with the temporary rig pointed at 5.0°W Atlantic Bird 3

here are a few pics of
Télé Africa DVB-S 2143-5/6
4114 L

pics show the signal strength using both the standard dielectric plate ..
..and with my adapted polythene T plate installed ..
The difference is such that the picture locks up ..ie insufficient signal @3.8db (standard plate)
but over 6db with the T plate ..and the picture is rock solid ..
there is also a picture of the 2 plates to compare ...
perhaps I should patent it ...lol

but it just goes to show ..
even with a 70x80cm dish _some_ Cband reception is possible.
rgds
VS..
off for a cuppa now to warm up a bit.

 

[Llew]

Well following on from VS's experiments with AM1, thought I'd bite the bullet and give it a try. Got myself a DMX242 LNB and conical feed for my TD88 and more or less copied what VS has done. Complete novice when it comes to C-Band, so thanks to VS and everyone for the info gleaned from here.

One thing I notice is that there doesn't seem to be any peak position for the LNB compared with a ku-band LNB; an inch or two in or out makes little difference re the focal point. Different with a larger dish no doubt.

So... will now consider trying it on the SMW motorised dish. It's only a little larger than the TD88 (1.05m, actual dimensions 1.2m x 1.0m) so won't expect miracles as far as other C-Band sats are concerned.

 

[Vipersan]

Nice one Llew ...I'm so pleased you decided to give it a go ..
You should have no probs getting at least 1 channel from 5W ...27W 40W using a dish equal or larger than1Mtre
Yes indeed ..as to accuracy ..the smaller the dish the less accurate you have to be ...but of course the less the signal received ..
We all know this when setting up a dish in ku ..but you rarely see this effect so dramatically displayed as you do with Cband ..
you can be 2 or even 3 degrees off target and still see the satellite spectrum ...with a small dish ..
As I said already great results Llew ..but if you want an extra 2db for free ...please do try making one of my 'T' plates ...the increased 2db gain is obvious and dramatic.
rgds
VS

 

[sonnetpete]

Llew : does that fit in a standard 40mm LNB collar? I'd have a go with my 1m Gibi and even the 1.2M Laminas but it was fitting the LNB that was putting me off.

 

[Vipersan]

Hi Pete ..
No the Cband lnb doesnt fit in a standard 40mm collar ..
But the blue conical feed as used by Llew and myself ..comes with the correct size collar to fit the wider C band lnb
rgds
VS

 

[Llew]

Llew : does that fit in a standard 40mm LNB collar? I'd have a go with my 1m Gibi and even the 1.2M Laminas but it was fitting the LNB that was putting me off.

No Pete - it's a 60mm collar that comes with the conical feed, and will easily fit onto a square section LNB arm. I will have problems fitting it onto my SMW offset arm, as that is tubular designed for 23mm LNB collar. I did a fix for a 40mm LNB on the dish, so I may be able do something similar with the C-Band one.

(Edit - VS has answered that one)

@VS -

Yes, I've got a pice of clear perspex that may do for the modified dielectric insert, bot it's only 5mm thick, so it may not be suitable.

 

[Vipersan]

No Pete - it's a 60mm collar that comes with the conical feed, and will easily fit onto a square section LNB arm. I will have problems fitting it onto my SMW offset arm, as that is tubular designed for 23mm LNB collar. I did a fix for a 40mm LNB on the dish, so I may be able do something similar with the C-Band one.

(Edit - VS has answered that one)

@VS -

Yes, I've got a pice of clear perspex that may do for the modified dielectric insert, bot it's only 5mm thick, so it may not be suitable.

Up to you m8 ..
by all means try it ...but I can totally recommend the polyethylene type chopping boards ...

A typical example here ebay item 270677168614

If you get the right one ..the thickness of the board is almost perfect requiring a minimum of rasping down at the edges to fit..
rgds
VS

...in addition ..
Ask the vendor for details of thickness before buying..
Also ..the rough dual sided non slip ones are the best..
;)

 

[Vipersan]

Ok ..
here are a couple of pics of an offcut from the polyethylene cutting board I used..
Sorry I cant make 'em clearer ..but the edge on shot gives an idea of thickness ..(slighly thicker than the supplied with lnb) ...plate ..
The other pic shows the non slip micro diamond shaped lattice on the board surface ..
dual sided so both surfaces the same ..
hope it helps..
rgds
VS

 

[Llew]

OK, I'll have a scout around. Incidentally, why does the LNB cap have small holes (slits) around the circumference? At least mine has. To equalise air pressure in the LNB throat? Surely it'll let rain/moisture in?

 

[Vipersan]

OK, I'll have a scout around. Incidentally, why does the LNB cap have small holes (slits) around the circumference? At least mine has. To equalise air pressure in the LNB throat? Surely it'll let rain/moisture in?

Never did fathom that one Llew ..
I just assumed it was to allow air to circulate ...so as not to build up moisture vapour inside.
The holes aren't really big enough to allow rain directly in ..and do remember these lnbs are sort of designed for BUD's ..prime focus dishes so would normally be pointing downwards ..so rain couldn't enter in quantity ..thus the holes would allow the interior of the lnbf to 'breath'..
In fact I leave mine open to the elements completely ...on the Alcoa PF ..
Only when using one on an offset dish have I improvised a cover ..out of a tupperwear bowl ..on account of the T plate extending out of the open throat of the lnbf..
rgds
VS

 

[Huevos]

the T plate.

Can you post some more detailed photos of this, maybe with some measurements.

 

[Vipersan]

No probs Huevos ..
I'll borrow the one out of the Big dish tomorrow ...but strictly speaking it doesn't appear measurement critical ..
Basically the part which fits ito the lnb throat is tapered a little to fit snuggly inside (narrower at the bottom of the T ..furthest inside ...
The insert part of the T is cut to extend as fully inside as possible ...
The external outer crossbar of the T is roughly as tall as the insert is wide ....and is as wide as the scalar plate ...
..but no probs Ill photograph it tomorrow ..and put some measurements on it ..
The one used on the conical feed was futher modified to follow the steps of the feed ...plus a couple of slots cut to anchor it firmly into the feed horn.
I'll post pics of both ..

Not sure how or why it works so effectively ..but I do know an inserted plate of the same material without the crossbar of the T ...works ok ..but doesn't give the extra gain that theT plate achieves..
I suspect what is happening ..is that the signal is being pre polarised outside the lnb throat before being funneled inside with minimal losses ..

Like extending an aerial outside the throat into the signal 'cloud' which forms at the focus outside the lnb throat.
..thats my guess anyhoo..

rgds

 

[Vipersan]

I also should mention that similar results have been achieved with the 'Doktor of Sat' plate ...
But there is a difference in that his design although fitting completely inside the lnb throat ..is effectively tuned ..and resonant at specific frquencies ..requiring adjustment to get best results ..
Nelson B will confirm this ..
The T plate isn't tuned and gives a flat increase in gain accross all frequencies ...
Not frequency specific ..
I guess this is why measurements aren't critical.
rgds
VS

 

[Llew]

Yes, a few dimensions for forming the cutout to follow the outer contour of the feed would be perfect VS. Otherwise I'll probably end up wasting a good cutting board

 

[Vipersan]

Yes, a few dimensions for forming the cutout to follow the outer contour of the feed would be perfect VS. Otherwise I'll probably end up wasting a good cutting board

No probs Llew ;)

btw ..You should easily get 2 plates out of 1 cutting board if you're canny with the placing of your outlines..
rgds
VS

 

[Channel Hopper]

OK, I'll have a scout around. Incidentally, why does the LNB cap have small holes (slits) around the circumference? At least mine has. To equalise air pressure in the LNB throat? Surely it'll let rain/moisture in?

Somewhere in the past I used the plastic from a generic paint tub lid, the sort you get from any large DIY store.

The holes are there to let out heat from the feed, not so much from the electronics in the LNB, but from the build up occurring on warmer days (which we get once a year or so round here). If this was allowed to cool in the enclosure without air gaps, then condensation would form on the front end of the LNB.

 

[Vipersan]

Ok ..as promised ..
Diagram showing the dimensions of a Basic plate ...and a modified plate for conical feeds..
As mentioned previously ..
Dimensions are not critical ..but the material is to some degree..

To confirm this I made an identical Stadard T plate (same dimensions ) from a sheet of 6mm thick smooth faced Teflon about 6 months back..
It didn't perform as well as the polyethylene plate

maybe its the rough micro diamond surface ..but I doubt it..

rgds
VS

If you make one please report any increase in gain ...just to confirm mine isn't a fluke.
;)

 

[timo_w2s]

I've mentally marked this on my "to do" list but I won't be able to order those LNB bits n pieces until later on after summer.

 

[Vipersan]

The holes are there to let out heat from the feed, not so much from the electronics in the LNB, but from the build up occurring on warmer days (which we get once a year or so round here). If this was allowed to cool in the enclosure without air gaps, then condensation would form on the front end of the LNB.

Yeah ...we had ours day before yesterday ...
gone cold again here ...looks like I'll have to wait another year till the next one

Thanks for clarifying the reason for the 'pepper pot lid' on these lnbs CH
;)
rgds
VS

 

[Llew]

The holes are there to let out heat from the feed, not so much from the electronics in the LNB, but from the build up occurring on warmer days (which we get once a year or so round here). If this was allowed to cool in the enclosure without air gaps, then condensation would form on the front end of the LNB.

Thanks for that. Covered mine with tape now, could be a cosy nook in there for Arachnids.