Ferjo (05-09-19)
have a bopeep at this filter
ok you got my interest so ive dug out an old c band lnb and had a look when you look down the throat you will see two antennas and a impedance short the impedance short is to hide the vert from the hoz when either are applied to the local oscillator . therefore if you were to introduce another "short" at the frequency you want to get rid off it will be attenuated as much as the original lo is the only problem is the positioning of this , so then it could be made out of a metal insert in front of the existing antennas and if cut accurately to the frequency will remove a certain portion of the incoming signal from the other antennas . So you will need a strip of say ally plate say 0.25mm and a cutout of a 1/4 wavelength at right angles towards the center of the throat , ie a strip the same length as the internal diameter of the throat so when placed inside its ends touch each other so holds its self in there on one side you leave a 1/4 wave length long bit bent up and then position it for max effect . ps 300 over the freq in mhz gives a wave length so divided by four is the 1/4 wave or try this
this may help clear the mindset
Last edited by hinekadon; 04-09-19 at 11:27 PM. Reason: more
Mr 672A (05-09-19)
Cannot understand how in the hell 5G and other were allowed to share the CBand Frequency range consider its causing issue everywhere. Reading the last link in the above from member hinekadon it says "Since the interference can occur at any frequency point within the range 3.4-4.2 GHz, the problem cannot be resolved by simply using an off-the-shelf filter. A custom design filter is recommended as it can be designed to fit the specific requirements of that system".
Friggin Hell, could imaging how much MONEY it would cost.
Last edited by Mr 672A; 05-09-19 at 10:47 AM.
I think that weather radar uses S-band (a frequency of 2-4 GHz), which is below C-band.
products.norsat.com/UserFiles/NorsatDocs/BPF-C%20Spec%20Sheet.pdf
Last edited by hinekadon; 09-09-19 at 01:35 PM. Reason: more
yes they are expensive but you can make your own with a little preseverance .I have done it in the past and you have everything to make it work ( a dish with a signal , eyes to see if its better or worse) any improvement is a step in the right direction the materials are quite cheap too, a vernier caliper or a good steel rule , brass shimstock , drill soldering iron , time and patience and a calculator, HAVE A GO
you have a lnb with a flange on it , get a bit of ally and make this shape ,drill holes file out etc then purchase some brass shimstock from hobbie shop or engineering supply 1- 2 mm is thick enough . measure the inside of the lnb hole draw picture of it , fold it up to three sides into a "u"shape then make a cover with tabs to solder them together , solder 6 nuts for 4mm brass screws equally spaced on the middle of the "box cover " these have to be about min of quarter wave apart ,put the flange plates on the wave guide and bend .>6/8 mm outwards 90@ so that when bolted together they match with no holes to let out the rf . to get it into cutoff freq screw screws in and out to align then whilst watching signal you will soon get the method and then duplicate for the next one come on now that cant be too hard now can it
Mr 672A (12-09-19)
One of my dishes that will require the Filter
yes thats what I expected just build it and put it between the feedhorn and the lnb I see yourve got the right feedhorn setup for both lnbs . I can see one problem with it tho the dishes are too close to the ground so will pick up more terrestial noise . AT c band my memory say its 100 wave lengths to the bottom of the dish to be 70db down from earth noise ????
Hi folks,
I'm thinking about implementing a similar system to one of my solid dishes that is used for terrestrial microwave links, where a skirt if fitted around the dish, the inside of which is fitted with an RF absorbent mat.
The idea of this is to minimise side lobes and prevent stray RF from entering the "open" end, and what does come in (from unwanted sources away from the main lobe) is attenuated and not reflected by the inside surface of the skirt towards the dish and LNB.
Unfortunately I don't think this would be entirely practical to do this on a mesh dish..
Those mats are very effective , they can take a signal in the mud to clear and readable they were also used on the hoz bar type dishes , so I cant see why it wont work on a mesh dish as well . They do wear out tho as they are impregnated with carbon powder which falls off after a time cheers don .Having re read your post and the skirt etc yes these are good dishes the skirt makes them "pointy" and the pads make them ideal for terrestial noise suppression , from memory the skirt is several wave lengths long and has the effect of being a cutoff freq in some cases . You are very lucky to be able to get one as the scrappies are all over them , Is it a andrews dish ? cheers don
Last edited by hinekadon; 16-09-19 at 12:27 PM. Reason: more
Hi Don,
I've got a 1.8m solid Andrews, and I'm looking at getting a 3.2m solid Andrew as well. As for the skirt, if you have access to the tools to bend, curve and accurately drill sheet aluminium, you can make them, careful measurement and away you go. Skirt "length" is usually around 5 wavelengths give or take, so at 3.950 GHz (centre frequency), your wavelength is approximately 75mm, or a 375mm skirt.
Some of the dishes I have sourced (for others) are basically taken out of service, and come and get them from the site, as they say it's not what you know but more often who you know.
I have a 2.5m solid spun dish at one of the sites I look after, I just have nowhere to put it and no (legal) way of transporting it. It requires a little bit of panel beating as it has a small ding on one side, otherwise OK.
No skirt on that one.
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