LNBF holder for PFA

[RimaNTSS]

As I know from high school geometry lessons, any 3 points can make up a plane. Extrapolating this clause to satellite hardware language, I could say that star-holder is more than enough to hold LNBF or LNB in perfect position when LNB's Phase center is perfectly co-located with antenna's Focal point. Star-holder allows to do so. And there is no need to overmedicate things .... Points are A, B and C, and their positions are dependent on length of the 3 feedarms (in some cases there are 4 feedarms). I've got several out-of-shelve star-holders, and I've made several myself. Of course, nothing can be better than proper pipe-clamp (made of INOX and wide enough). That is my IMHO. Holder for C-band LNB/LNBF looks more or less same but has another clamp as a central part. Actually, C-band LNB holder is more universal, as it can hold not only C, but also Ku and Ka LNBs, only proper spacers should be used.

 

[RimaNTSS]

Have cut couple of 30mm pieces from 168mm (diameter) pipe. To make holders for PFA out of them. When? I do not know...... when have some spare time.

 

[RimaNTSS]

Some time ago I made feedarms and Ku-band LNB-holder for 2.4m PFA of friend of mine. And now, after he is satisfied with Ku-band reception he asked a question whether C-band LNBs with 40mm neck. Of course no, I've said, and you need another holder. So, I've one today. Used 4mm thick 110mm in diameter "O" ring as a base, 63.5mm clamp. Also made spacer to be able to install Ku-band LNB in the same holder. He already has length-adjustable feedarms, so it is possible to place LNB exactly in the focus of antenna.

 

[moonbase]

Some time ago I made feedarms and Ku-band LNB-holder for 2.4m PFA of friend of mine. And now, after he is satisfied with Ku-band reception he asked a question whether C-band LNBs with 40mm neck. Of course no, I've said, and you need another holder. So, I've one today. Used 4mm thick 110mm in diameter "O" ring as a base, 63.5mm clamp. Also made spacer to be able to install Ku-band LNB in the same holder. He already has length-adjustable feedarms, so it is possible to place LNB exactly in the focus of antenna.

Inox ?

Nice job.

 

[John]

Inox ?

Nice job.

Seconded

 

[RimaNTSS]

Yes, sorry, did not tell.... all INOX except 2 brass nuts and plastic spacer.

 

[RimaNTSS]

People! I have a question: What is most common size of the neck of C-band LNB? I have stored some scrap (some even brand new) C-band LNBs. And size of the necks are 55-57-62-65-66-72mm. There maybe other sizes of necks I do not have. Perhaps there is some kind of standard for all new C-band LNBs? Will I be wrong by saying this standard is 65mm? However, American Chaparrals are 66mm.
I am still trying to build some kind of universal LNB-holder for PFA which could hold any C-band, any Ku-band, and any whatever-band LNB (depending on ring spacer used.
Basically, I would narrow down my question: What size of clamp I should use for this holder. Would 66mm be proper size?
i have added some holes in the O-ring in case somebody would like to make multifeed in his/her PFA, so there will be possibility to attach another LNB holder close to central one.

 

[Channel Hopper]

I always thought the feeds here were 65mm regardless of the manufacturer but will check tomorrow with the calipers.

 

[moonbase]

 

[RimaNTSS]

thanks @moonbase , then I see that ideal (does not mean perfect) LNB-holder for PFA should be made for 66.4mm and then it can also fit any smaller feed. Who cares about very seldom 71.5 and 76.1mm feeds!

 

[moonbase]

thanks @moonbase , then I see that ideal (does not mean perfect) LNB-holder for PFA should be made for 66.4mm and then it can also fit any smaller feed. Who cares about very seldom 71.5 and 76.1mm feeds!

The 71.50mm and 76.10mm items are polariser barrels and not LNBF. They offer an alternative to using a dielectric plate for LHCP and RHCP signals. Most people would probably use the LNBF with dielectric plate inserted?

 

[Channel Hopper]

My own measurements of the stuff that is in the shed, outside diameters only.

The Eric LNB wall is substantially thicker than the other two, which are not far off 1mm.

 

[Channel Hopper]

Almost forgot. I also found a Chaparral C Band polarotor, pictures soon, but I assume it has the same measurements as the CoRotors.

 

[Channel Hopper]

i have added some holes in the O-ring in case somebody would like to make multifeed in his/her PFA, so there will be possibility to attach another LNB holder close to central one.

Further to your post and the additional holes. These could be used for the even number petalised (four feed arm) systems such as Channel Master / Wineguard centrefed antennas and the Prodelin 1252 model, though you will need to remove/ adapt the existing brackets from 120 degree spacing to 90.
Many designs of this type, in particular Chaparral, use a second bolt hole on the scalar to lock the feed into the pattern, preventing twisting and a different focal point as a result.

Just a thought - It might be worth have the feed clamping attachments displaced by 90 degrees in the manufacture, running in line with boresight which offers two advantages, no twisting and on smaller dishes, a minimal shadow of the electronics if the scalar ring is discarded.

 

[RimaNTSS]

Thanks for that. I have thought about 90* spacing between ears... I think it can be made something universal 90/120* universal , even it will look awkward
I have original Chaparral LNB shipped right from USA. I measured it's diameter bu old-school sliding calipers (electronic ones got their batteries flat ), so I see diameter something about 65.75mm (for sure it is not 66.4mm)

 

[Channel Hopper]

Thanks for that. I have thought about 90* spacing between ears... I think it can be made something universal 90/120* universal , even it will look awkward
I have original Chaparral LNB shipped right from USA. I measured it's diameter bu old-school sliding calipers (electronic ones got their batteries flat ), so I see diameter something about 65.75mm (for sure it is not 66.4mm)

The difference is about a coat of paint (plus the corrosion underneath). I really wouldn't worry as you have the sleeve and tolerance of the two clamping bolts. Whilst I might be concerned at a Ka band system, a mm either way, even on a 1.8m reflector is going to be less than insignificant for C band reception.

 

[RimaNTSS]

I really wouldn't worry as you have the sleeve and tolerance of the two clamping bolts.

That what I am worrying less about. Cuz all smaller diameters of the feeds (like 40mm or 23mm) will be settled down by inner diameter of the spacer rings, as heir OD will always be same, something like 66mm.

 

[Channel Hopper]

Chaparral always had a double stop on their scalar feed clamping system, with a single clamp screw, so their design team was never worried about a boresight arrangement that might be off by 1/8 of an inch.

 

[RimaNTSS]

Did some brainstorming on the topic today. I know that some people like to use some kind of multifeed on their PFAs. I mean, to be able to use C-band and Ku-band LNBs in case the dish is motorized. I think most common way is to use Ku-band LNB in focus of the dish and C-band LNB goes to multifeed. Although it is possible to do opposite.

 

[Channel Hopper]

With a four feedarm system, bolting a C band feed to one side that covers the arc has rarely been an issue until the satellite goes rogue.

The (generous) feed support system of the US dish manufactures of old (Orbitron and clones with the bucket) ensures one bolt hole is always clear to fit a C band scalar next door once the plastic is removed.