Gilat AN8004 mod.

[John]

Ok I already have the components separated, now I just have a question...

View attachment 148661

Can I use the same F socket I removed from ODU, right?
Socket F is for soldering to one of the pins that are on the edge of the lnb?

View attachment 148662

Added graphics added to your picture Just for added info only ....
Ps: Don't forget to waterproof it really good if leaving it outside, the metal Rx module will let water in, slow but sure, as i have found to my horror
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[Zapping]

Yes, but i have only PFA antennas. I made everything myself.

c120 adapted or was it made from scratch?

I am not sure if the waveguide/cone feed that you have attached to the Gilat LNB is optimised for a PF dish?

Is not but it might work, I'll test in the next few days.

Ps: Don't forget to waterproof it really good if leaving it outside, the metal Rx module will let water in, slow but sure, as i have found to my horror
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View attachment 148700

Interesting point of view about the waveguide twist, I had also noticed that the opening position did not coincide with the pcb probe,
why was it built that way, is it better for circular polarizations?

 

[dreamsat]

It was completely rebuilt. No adapter to C 120

 

[John]

c120 adapted or was it made from scratch?


Is not but it might work, I'll test in the next few days.


Interesting point of view about the waveguide twist, I had also noticed that the opening position did not coincide with the pcb probe,
why was it built that way, is it better for circular polarizations?

>>why was it built that way, is it better for circular polarizations?<<
I can't say for sure and i don't really know as iv'e never used my Gilats using the OMT on the Rx board - forum members s-band, dreamsat, Trust are the ones that have a better idea of how the OMT section worked.
As far as i know the main circular polarity reception & Tx is determined by the aditional poloriser - - I made a motorised rotary joint between the Circ to WR42 adapter to the end of the Circ poloriser to give me a H/V/L/R polarity choice which also gave me a fine tuning of the skew option. This idea was used mainly on my AN8002 modded Rx board for Ka Band A reception etc from 42° East (LHC) but also for H/V signals from other satellites.

 

[dreamsat]

The pictures show more than words. This is the depolarizer for circular reception. This is precisely aligned with the antenna in the linear range. The LNB rotates above this depolarizer, enabling reception of all four polarization levels. Linear H/V and clircular H/V. The other motor moves the focus in order to always be able to optimally adjust the system.
If you leave out the depolarizer, you can only receive linear and you have to turn the LNB.

 

[Zapping]

Great job @dreamsat but what I questioned and I think @John was also referring to this, is the position of the pcb probe being in horizontal position and the OMT/aluminium case hole being in vertical position.

Will there be improvements if the hole is enlarged to match with the pcb probe and why did the manufacturer build it this way?

 

[Channel Hopper]

Since you are playing about with an ODU I would suspect it is to filter out the outgoing power on the opposite polarity to prevent swamping the LNB.

Can you enlarge the image in that area ?

 

[s-band]

Can you enlarge the image in that area ?

@Zapping It's probably done with the waveguide twist to keep the losses down my minimising the length of PCB tracks. I guess it worked out that way in the overall design with the OMT. I'd be very careful modifying it. I was never happy with the results taking the WG directly from the back of the PCB. If it ain't broke...

While I was looking for the pics above, I found this one of a PF feed on a band D.

 

[Channel Hopper]

View attachment 148737View attachment 148736
That looks like an E to H transfer. I've not worked on one that short before, the length of the probe and groundplane may be adjusted to optimise the throughput on what is a mass produced casting for a wide number of frequencies.

 

[Zapping]

First experiment done on the PF 180 antenna, initially with c120 feed but results were bad, back to the original scalar feed and surprisingly the result was much better, +2 dBs than 135cm offset antenna without changing anything on the Gilat.



It was not expected that a scalar feed would behave so well in a PF antenna, I will try to get a wr42 waveguide to make adjustments easier.

 

[Channel Hopper]

First experiment done on the PF 180 antenna, initially with c120 feed but results were bad, back to the original scalar feed and surprisingly the result was much better, +2 dBs than 135cm offset antenna without changing anything on the Gilat.

View attachment 148747 View attachment 148746

It was not expected that a scalar feed would behave so well in a PF antenna, I will try to get a wr42 waveguide to make adjustments easier.

They can, but it is most likely down to an imperfection within the dish surface.

Stringing is going to provide some answers, but if the reflector is not designed around Ka frequencies you may not get a workaround without a lot of modification.

 

[dreamsat]

Under no circumstances should you make any changes to the waveguide system. It always leads to losses.

 

[zorrin]

Great job @dreamsat but what I questioned and I think @John was also referring to this, is the position of the pcb probe being in horizontal position and the OMT/aluminium case hole being in vertical position.

Will there be improvements if the hole is enlarged to match with the pcb probe and why did the manufacturer build it this way?

View attachment 148721

I had found this article which shows a double circle very similar to that of AN8004 and AN8002

 

[Zapping]

Ps: Don't forget to waterproof it really good if leaving it outside, the metal Rx module will let water in, slow but sure, as i have found to my horror

To waterproof the lnb I isolated the entire surface with cling film but I don't like the result, as it is very stuffy and without air circulation it makes the temperature rise in the hottest hours and the signal drops about 2 dBs.

Is it necessary to insulate the whole surface or just the top part (pcb probe) and the bottom part (lnb connector)?

Does anyone have a picture of how to isolate the lnb correctly?

 

[John]

To waterproof the lnb I isolated the entire surface with cling film but I don't like the result, as it is very stuffy and without air circulation it makes the temperature rise in the hottest hours and the signal drops about 2 dBs.

Is it necessary to insulate the whole surface or just the top part (pcb probe) and the bottom part (lnb connector)?

Does anyone have a picture of how to isolate the lnb correctly?

Yes it can be a bit tricky to waterproof it. My forum freind s-band will be horrified when i say this but i cover over the hole on the lid and then i spray the whole unit with a spray sealer that get's into all the little nooks and crannies. I use the standard feed cap with a 1mm hole drilled into it for ventilation . I'll find the unit out tomorrow and take a pic.

 

[s-band]

I prefer proper environmental protection with good ventilation.

 

[Channel Hopper]

I prefer proper environmental protection with good ventilation.

View attachment 151012

Some foil glued on the outside of the bespoke container will help in the current tropical weather

 

[Zapping]

I prefer proper environmental protection with good ventilation.

View attachment 151012

I hadn't thought of that, a very rudimentary option but it seems extremely effective.

 

[scopus]

DIY umbrella on mine...

 

[Manikm909]

thats a beautiful setup!