Antenna's focal point - "le point G"

[bim]

Ah with you. It's a calibration lazer not a lazer sight.

 

[skomedal]

May we presume its work still in progress?

Regards

 

[RimaNTSS]

O, I see, one week is over ;)
No big changes yet, boresighter is shipped from PRC. Not many new dishes in stock to do precise measurements.
Will only show picture of couple of very useful devices to do antenna's measurements and installations.

 

[RimaNTSS]

I was wrong yesterday by saying that boresighter is still somewhere being shipped.... it was already in the post office from last Friday. So, delivery took only 5 days!
My FIR is: nice toy, very small one. Laser turns on when all 4 tiny batteries are inserted, and there is no button to turn it off. To stop laser working cap should be unscrewed and batteries should be removed. I do not like this, will probably need to make external power supply.
Another thing which can make life more difficult is fact that body is conical (11,4mm at front and 11,8mm at the other end.) and to make it inserted in the adapter perfectly I will need to make hole also conical.
Can not check right now whether beam is parallel to the conical body, will do it when adapter is made. Adapter is going to be cylindrical 40mm in diameter (like LNB ) and about 30mm long.

 

[skomedal]

Wish you good luck when machining the adapter/holder, not an easy job making/turning something to hold ammo shaped object.
When the adapter is made and the laser ammo inserted with snug fit, put marks ( fiber tip marker ) at 90 degree angles on the holder, then rotate noting the hit point at each mark to check if laser diode is true or off center.

Regards

Reason edit :: changed laser led to laser diode

 

[Channel Hopper]

It looks very much like the laser that used to power the children's (well adolescent sprog's ) wall animation pens of a decade ago. The end cap could be removed to put in various diffraction gratings, usually in mood styles - hearts/thumbs up/two fingers etc.

I paid about a fiver for one a few years back, and used it on the air rifle as a quick sighting aid. The batteries cost more than the pointer did.

 

[bim]

I was wrong yesterday by saying that boresighter is still somewhere being shipped.... it was already in the post office from last Friday. So, delivery took only 5 days!
My FIR is: nice toy, very small one. Laser turns on when all 4 tiny batteries are inserted, and there is no button to turn it off. To stop laser working cap should be unscrewed and batteries should be removed. I do not like this, will probably need to make external power supply.
Another thing which can make life more difficult is fact that body is conical (11,4mm at front and 11,8mm at the other end.) and to make it inserted in the adapter perfectly I will need to make hole also conical.
Can not check right now whether beam is parallel to the conical body, will do it when adapter is made. Adapter is going to be cylindrical 40mm in diameter (like LNB ) and about 30mm long.
View attachment 68306

Just a thought any gun smith near you as they may have barrels that are out of proof which you could cut about to fit. This may work out cheaper.

 

[RimaNTSS]

That will be not so easy to find gun with barrel's outside diameter 40mm
I will probably try to give boresighter to lathe-man and ask to make it cylindrical! It has quiet thick walls and taking off 0,3 mm will not make big difference to the strength of the body.

 

[sonnetpete]

That will be not so easy to find gun with barrel's outside diameter 40mm

One of these?

 

[RimaNTSS]

One of these?

Yes, but seems this one has inner diameter little bit too big

 

[skomedal]

""" Another thing which can make life more difficult is fact that body is conical (11,4mm at front and 11,8mm at the other end.) """

That`s normal brass ammo cartridge design, hinders jamming the mechanism and to aid the ejection of the cartridge when desired, especially with rapid fire devices ( machine guns ).
Do not know if the same design with shot gun cartridges.

Regards

 

[RimaNTSS]

You are right about ease of ejection.
I made some measurements, and my plan will probably be to order adapter 40mm x 18mm with inside hole 11,5 mm. Then make 20mm part of boresighter (marked it green) to exactly fit in the adapter's hole. Expirienced lathe-man would do all this manipulations in 15 minutes.
There is small (about 2mm) hole in the boresighter about 25mm from edge. I asked seller about this hole, he did not know why it is there. I think it is technological and not for use.

 

[RimaNTSS]

At the end of the day I will get something like I already have, but much better manufactured. Adapter I have in stock has little bit too big inner hole.

 

[skomedal]

How will you copy/estimate the lnb focus point in the lnb holder, when project is ready to test, some have long necks for fine tweaking?

Sorry for all these questions.

Regards

 

[RimaNTSS]

LNB has only one Focal point. I think it is where I marked red dot on the picture. And even IBU or other LNBs have long neck it does not make any sense to tweak LNB closer/further from to/from antenna. If you move it closer to antenna, than it goes out of focus and antenna's elevation should subsequently be adjusted. Basically, Red dot of LNB must be placed instead of laser diode, which is exact location of antenna's focal point. Only one, proper position, other ones will be wrong ones.


Questions are OK. There is only one stupid question - Not asked one!

 

[skomedal]

Thanks for your reply.

Mine is that the focal point is the middle pin between where the horizontal and vertical pins collect the signals.

Might be wrong.

Regards

 

[RimaNTSS]

Mine is that the focal point is the middle pin between where the horizontal and vertical pins collect the signals

Could you elaborate on this little bit more? I am not sure I fully understood that.

 

[skomedal]

Meant the two pins H & V in the circular space.

As stated might be wrong.

Regards

 

[Trust]

Thanks for your reply.

Mine is that the focal point is the middle pin between where the horizontal and vertical pins collect the signals.

Might be wrong.

Regards

Indead wrong , put a 25 mm ball in the feedhorn , the centre off that ball is the focal point .

 

[battenfan]

I have a scrap dish that was given to me (this one) that I thought would be fun to play with as it has an adjustable feedarm. Measuring it reveals it is actually wider than taller. AB=787 mm CD=795 mm EH=63 mm. Parabola4 wont let me enter those numbers, it adjusts both to 795 and thinks I have pf dish. Now I'm confused.