3.7m Prime Focus Prodelin project: any ideas?

[pitussat]

Hi everybody,
at last I INSTALLED PRODELIN 3m PF dish, very similar to NELSON's old prodelin dish ....just a question , first of all
does it really perform 49dBi if correctly assembled and aligned?
Mine was without original feed, and I found one very similar or equal to 3,7m dish...........but f/d of mine is 0,3 , very dep dish( 63,8cm) and 3,7 m is 0,38 f/d:
is it possible using the same feed with aperture angle so different ?

 

[s-band]

I don't know the dish so can't comment on it. By saying 49dBi, I presume you are talking about Ku. I used to have a deep Winegard 3m (I think @Feedsat_DXer still uses one). For that I used a Chaparral "Golden Ring", on C band, which is an add on for dishes < f/d of 0.32. It extends the feed by about 5mm and has a small ridge on the inner front edge. See attached.

If there is no other ready-made solution, you could make something similar for Ku. It would be a case of try it and see it it improves anything.

 

[Channel Hopper]

The feed in all of the designs will cope with the 0.3, 0.36 and 0.37 of the prime focus antennas. Matching is improved with careful attention to the feed distance from the reflector and alignment to the centre (boresight), hence the relatively large adjutment on the four feed arms where they meet the reflector panels.

I don't have the gain figures to hand but if they are stated on paper, then careful assembly means they will be met. A specific gain will be matched to a frequency of the incoming signal, if the antenna is assembled correctly the overall gain figure changes in proportion to the lower and upper frequencies , hence why a C band system has a lower number to that of the same dish working at Ku band.

Please post some images of your installation in the appropriate section.

 

[moonbase]

pitussat,

If you know the focal length and the beamwidth angle of your dish then you can calculate the distance from the dish for the C band feed throat aperture. There are a couple of topic links below that cover feed alignment for a prime focus dish installation. In the 2nd topic linked to below there are some useful tips for fabrication of an adjustable C band feed holder.

Good luck with your dish, I hope you get the C band feed location resolved.


2.2m Precision Resurection (part 2)
Just Sharing This - 2.2mtr Elite / Precision resurection... Part 2.

2.4m DH Installation
2.4 DH Antenna installation


Rgds

 

[Channel Hopper]

Pitussat mentioned a gain of 49dB on the 3metre Prodelin, which suggests he is attempting Ku band at his location, now he has upgraded from the Channel Master.

 

[moonbase]

Pitussat mentioned a gain of 49dB on the 3metre Prodelin, which suggests he is attempting Ku band at his location, now he has upgraded from the Channel Master.

Ah yes, my mistake.

The 2.4m DH install topic has a feed holder design that can be used for Ku band with adjustments to the feed for focal optimisation. If the fabrication of the feed ring in the 2.4m DH topic using a ring roller is an issue it can ge got round by cutting a section from an aluminium pipe of appropriate diameter to create a ring. It should then be straightforward to attach 4 lugs with correct bend in them to anchor the ring to the feed support arms.


Rgds

 

[RimaNTSS]

cutting a section from an aluminium pipe of appropriate diameter to create a ring.

To be honest, I am skeptical about usefulness of using of such a ring. But that is IMHO, OK ?! Some time ago I got couple of rings (not aluminum, but should be fine as well ;) ) 168mm in diameter. And then, if there are going to be 4 bolts installed in the middle to orient the feed, then it would be possible to move the feed along the red arrows or along the yellow arrows. There is no way the feed could be moved along the green lines. So, IMHO again, why this ring is needed? It is easier to connect 4 or 3 feedarms (depending on the dish design) directly to the feedring.

 

[RimaNTSS]

I see value of using a ring on bigger dishes with subreflector. Then the ring is firmly tightened to the feedarms but position the subreflector can be fine-adjusted (cuz this is very important).

 

[Channel Hopper]

To be honest, I am skeptical about usefulness of using of such a ring. But that is IMHO, OK ?! Some time ago I got couple of rings (not aluminum, but should be fine as well ;) ) 168mm in diameter. And then, if there are going to be 4 bolts installed in the middle to orient the feed, then it would be possible to move the feed along the red arrows or along the yellow arrows. There is no way the feed could be moved along the green lines. So, IMHO again, why this ring is needed? It is easier to connect 4 or 3 feedarms (depending on the dish design) directly to the feedring.

If you substitute the vertical locking bolts for a small actuator, you could have inclined orbit tracking without the need to raise/lower the whole reflector assembly.

 

[moonbase]

To be honest, I am skeptical about usefulness of using of such a ring. But that is IMHO, OK ?! Some time ago I got couple of rings (not aluminum, but should be fine as well ;) ) 168mm in diameter. And then, if there are going to be 4 bolts installed in the middle to orient the feed, then it would be possible to move the feed along the red arrows or along the yellow arrows. There is no way the feed could be moved along the green lines. So, IMHO again, why this ring is needed? It is easier to connect 4 or 3 feedarms (depending on the dish design) directly to the feedring.

If "pitussat" uses the 4 original feed support arms to hold the feed ring in position and the feed ring is a reasonably accurate circle then I dont see the need for such a wide range of movement that is shown by the green arrows.

The 4 feed support arms should hold the feed ring centrally over the dish and allow backwards and forwards movement to optimise the focus of an LNB supported inside the feed ring. There should only be a small amount of up/down or left/right movement required to get the LNB to aim at the centre of the dish.

 

[RimaNTSS]

But why there is a need for additional piece of metal near feed if all 3/4 feedarms can be connected directly to the feed?
I am not insisting, but just do not understand the logic behind that.

 

[Channel Hopper]

But why there is a need for additional piece of metal near feed if all 3/4 feedarms can be connected directly to the feed?
I am not insisting, but just do not understand the logic behind that.

The Ku band feed on the Prodelin - prime focus - dishes have no adjustment at the feed end, using single bolts only. Theoretically it would be impossible to get the boresight incorrect if all feed arms are exactly the same length but it can happen, for example if the reflector panel tolerances are out, or the dish has been de-installed and moved to another site.
The informal adjustment can help in the event of a change of feed from that supplied by the manufacturer, technology does advance in dish design, beyond the 20+ year old files used to construct a complete 1304/1374 antenna, but as you say, it is overkill.

 

[moonbase]

...The informal adjustment can help in the event of a change of feed from that supplied by the manufacturer...

Exactly, "pitussat" does not have the original feed supplied by the manufacturer, an after market feed will be used. In this instance the fine tuning of the feed location offered by the feed ring may possibly help with the installation, especially the backward/forward movement for focal optimisation.

It's not an issue if "pitussat" wishes to look for other options to help with the correct positioning of the feed. The feed ring fabrication in the 2.4m DH installation topic is simply an option for "pitussat" to consider. I am sure that there will be other options that are just as accurate.

 

[Channel Hopper]

Focal optimisation is catered for in the Prodelin design. If anything the feed arm threads have too much adjustment and this can annoy the average installer looking to fit and go.

 

[moonbase]

Focal optimisation is catered for in the Prodelin design. If anything the feed arm threads have too much adjustment and this can annoy the average installer looking to fit and go.

Let's see what solution "pitussat" comes up with if he reports back on how he fitted the after market feed. Until then we are simply speculating on options.

I have provided "pitussat" with one option, ie, the feed ring solution from the 2.4m DH install topic. Despite numerous posts on the subject, unless I missed it, I have not seen anyone else provide an alternative option for "pitussat"?

 

[Channel Hopper]

Despite numerous posts on the subject, unless I missed it, I have not seen anyone else provide an alternative option for "pitussat"?

Rima suggested installing a subreflector.....

 

[moonbase]

Rima suggested installing a subreflector.....

I read the post from "Rima..." as a general declaration that a feed ring was appropriate for instances where a sub reflector was being used. I did not read it as a recommendation to "pitussat" to use a sub reflector as part of his installation. As far as I am aware, "pitussat" has never mentioned a sub reflector?

Since "pitussat" created the post yesterday morning asking about using an after market feed they have not replied to the topic. We are none the wiser about any direction that "pitussat" may wish to take regoarding the feed or options under consideration.

 

[RimaNTSS]

I think it would be better to discuss the ways of installing the feed after seeing some pictures of the antenna, feedarms and feed itself. Installing of subreflector to big dish (and 3m is big enough) is good idea. The only question here would be where to get the SUB! Fabricate it is not an option, at leas not feasible one.

 

[moonbase]

I think it would be better to discuss the ways of installing the feed after seeing some pictures of the antenna, feedarms and feed itself. Installing of subreflector to big dish (and 3m is big enough) is good idea. The only question here would be where to get the SUB! Fabricate it is not an option, at leas not feasible one.

Yes, it would be nice to hear back from "pitussat" to see how they plan to move forward.

 

[Channel Hopper]

I think it would be better to discuss the ways of installing the feed after seeing some pictures of the antenna, feedarms and feed itself. Installing of subreflector to big dish (and 3m is big enough) is good idea. The only question here would be where to get the SUB! Fabricate it is not an option, at leas not feasible one.

They can be fabricated, I have the formulae in the old works notes, but as mentioned, photos speak a thousand words.

With the correct design sub reflector on the dish, the 0.37 aperture feed acquired could be matched exactly.