Waveguide extension as LTE filter for Ku band?

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irkfi

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My problem is interference which is apparently coming from the LTE in 700, 800, 900 and 1800 MHz bands. Shows up as low signal quality on many Hot Bird transponders despite indication of 100% signal power. On satellites 3 deg apart there is no interference at all from which I guess a base station is shooting in the antenna directly (I am in low antenna elevation area and found candidate base station for this). Trying to solve this I ended up with Inverto 100cm dish and Inverto flange PLL LNB with Gibertini feedhorn. There is thus nothing to improve on the receiving side (except bigger antenna but this is not convenient in my case) and the signal quality improved a bit but is still low.

Here is question to experts: If some additional matched circular waveguide extension would be put between the feedhorn flange and the LNB flange, would this possibly help attenuating the LTE signals? The thinking is that longer Ku band waveguide would act as a stronger attentuation filter for the LTE due to the huge difference with the LTE frequency, but on the other hand the waveguide loss is low so it does not impact the satellite signal much. The thinking then goes the longer the waveguide the better the LTE rejection would be (within reasonable limits)?

Is this thinking right or I am missing some deadly flaw here?
Will appreciate your thoughts on this.
 
You could try using better quality cabling to the LNB, ensuring it is installed behind the metal parts of the reflector and pole. This is if the interference is at L band and not at the satellite downlink frequencies.


About the only way you can remove Ku band interference (without getting expensive with inline tubes running perpendicular to the reflector)is to dig a hole and fit the dish inside, with a ramp that allows signal to the satellite only.
 
What you would need is a bandpass filter in the range of 900 MHz to 2.5 GHz attached at the output of the LNB, this would cut down on the signals below 900 MHz and above 2.5 GHz, but these filters are very expensive.

Do you know what direction the LTE signals are coming in from?

If off to one side and not directly in front of the dish then a side panel could be crafted to help reject these signals.
 
Do you think any of these could help you?
Filter
LNB
 
That filter is the wrong band, the LNB would work out better as it has an LTE filter built in, it has -70 dB of attenuation at those frequency's.

That may be enough.
 
I would like to thank for all comments and suggestions regarding the LTE interference:

- installing antenna in the ground and make a ramp in front of it: do not forget there is still (heavy) snow falling in some areas of the planet:).
Besides, there are trees nearby in my location.

- better coaxial cable: I will install cable with best screening available which I already have.

- install bandpass filter in the range of 900 MHz to 2.5 GHz at the output of the LNB: I tend to think this would not help as the interfering
signal is already mixed into this band inside the LNB.

- check Fraccaro LNB: I tested earlier several "LTE protected" LNB's like the ones from Dur-line and Fuba. In particular, Fuba shows in the pdf specs of its x17-series LNB's a display with 30 dB LTE signal attentuation. But there was no effect in tests with both of them. Fraccaro has in specs 70dB LTE attenuation which is entirely different level and worth testing! I ordered Fraccaro for test.
 
Fracarro , good.

Somewhat better than the others tested here (check other threads)
 
Channel Hopper said:
Fracarro , good.

Somewhat better than the others tested here (check other threads)
Click to expand...

My target is not so to say nit-picking of fringe reception, but LTE interference rejection which apparently was not tested by anybody earlier(?). Fracarro stated -70dB level is very impressive and I think unique in all the LNB area including high-end professional devices. It remains to be seen how that will work in practice.
 
irkfi said:
My target is not so to say nit-picking of fringe reception, but LTE interference rejection which apparently was not tested by anybody earlier(?). Fracarro stated -70dB level is very impressive and I think unique in all the LNB area including high-end professional devices. It remains to be seen how that will work in practice.
Click to expand...
Would it be impolite to ask your approximate location ?
 
irkfi said:
- better coaxial cable: I will install cable with best screening available which I already have.
Click to expand...

This action point is executed. Installed "masterpiece" coaxial cable with 6 layers of screening which was more like a hobby activity than technical necessity. As expected this had no impact on interference which remains as it was with a cheap coaxial.

Channel Hopper said:
Would it be impolite to ask your approximate location ?
Click to expand...

You are overpolite which is not necessary:). My location is not a secret in any way but as my problem is not related to geography like in the case of fringe reception, I will postpone revealing it until solution is found. Otherwise there might be recurring thoughts like "maybe this location is somehow special" while I strongly believe this is absolutely not the case. Thinking is thus to be focused onto "how to reject strong LTE interference", without any reference to location. In principle this should not be too hard as there is such a huge difference between the LTE and Ku bands. The best point for would be input to the LNB to avoid overloading the critical input amplifier. The feedhorn and waveguide to the Ku antennas in the LNB can be seen as are already acting as an LTE filter. Extending the waveguide or even introducing a gentle bent in it should thus be improving this filtering but how significantly I don't know. In the commercial LNBs the size of the LNB is limiting factor but for me it is not.

The next action point is testing Fracarro LNB with its stated -70 dB LTE attentuation and Fracarro is on its way to me.
 
You might be able to work out the direction from where possible interference is coming from by using a metal tray, a frying pan or similar. Then see if its possible to build a shield in that general direction.

its even worth wrapping the lnb in aluminium foil to see if it helps. - the worst that can happen is it does nothing! (keep the front on the lnb uncovered obviously!) :D
 
irkfi said:
This action point is executed. Installed "masterpiece" coaxial cable with 6 layers of screening which was more like a hobby activity than technical necessity. As expected this had no impact on interference which remains as it was with a cheap coaxial.



You are overpolite which is not necessary:). My location is not a secret in any way but as my problem is not related to geography like in the case of fringe reception, I will postpone revealing it until solution is found. Otherwise there might be recurring thoughts like "maybe this location is somehow special" while I strongly believe this is absolutely not the case. Thinking is thus to be focused onto "how to reject strong LTE interference", without any reference to location. In principle this should not be too hard as there is such a huge difference between the LTE and Ku bands. The best point for would be input to the LNB to avoid overloading the critical input amplifier. The feedhorn and waveguide to the Ku antennas in the LNB can be seen as are already acting as an LTE filter. Extending the waveguide or even introducing a gentle bent in it should thus be improving this filtering but how significantly I don't know. In the commercial LNBs the size of the LNB is limiting factor but for me it is not.

The next action point is testing Fracarro LNB with its stated -70 dB LTE attentuation and Fracarro is on its way to me.
Click to expand...
As mentioned previously the only way to reject ground based interference at the frequencies mentioned is to put a metal tube to the same dimensions as the dish diameter, up to the position of the satellite of interest.

Anything else (including digging down and fitting the dish below ground level) are compromises owing to non line of sight aberration.
 
irkfi said:
- check Fraccaro LNB: I tested earlier several "LTE protected" LNB's like the ones from Dur-line and Fuba. In particular, Fuba shows in the pdf specs of its x17-series LNB's a display with 30 dB LTE signal attentuation. But there was no effect in tests with both of them. Fraccaro has in specs 70dB LTE attenuation which is entirely different level and worth testing! I ordered Fraccaro for test.
Click to expand...

I received Fracarro LNB (Quad) and made first quick test. The result: this is absolutely the best LNB for the LTE rejection and its reception performance seems to be also top. Know this from the comparison with the best Inverto PLL flange with feedhorn which just pale to it!

BUT this does not mean that signal quality from Fracarro is good, on bad transponders it is just getting from very bad bare minimum to an acceptable one:oops:. Two reasons for this I can guess is that Fracarro LTE rejection filter works excellently but the interference is really strong, and/or (even more importantly?) this LNB (like all others) has no protection for 5G as its design is quite old. Old LTE was in the 1800 MHz
band but 5G/LTE is nowadays in 450, 700, 800 and 900MHz bands which may hugely contribute to the interference.

Channel Hopper said:
As mentioned previously the only way to reject ground based interference at the frequencies mentioned is to put a metal tube to the same dimensions as the dish diameter, up to the position of the satellite of interest.
Anything else (including digging down and fitting the dish below ground level) are compromises owing to non line of sight aberration.
Click to expand...

Huge metal tube on the roof? In the current climate that would be attracting AI surveillance from satellites thinking it is a rocket launcher:cool:
Seriously, that is beyond technical possibility for me.

Realistically, Fracarro is already a bright light in the tunnel and thus I can try big step to do conversion of Fracarro to flange as the feedhorn is improving antenna performance.

With the conversion to flange I can also prepare and test adding longer waveguide serving as additional rejection filter.

Unfortunately this will take time, most likely I will have to buy another Fraccaro and collect information how to convert it to flange.
Questions will follow.
 
I would like to test circular waveguide as a potential 5G/LTE interference rejection filter. The waveguide is to be installed between the feedhorn and LNB like the usual waveguide which is also used as the LNB mount to the holder, the only difference it would be would (much) longer. The idea is that the longer the waveguide the more attentuation of interference as it can not get deep inside the waveguide, while the satellite signal will be propagated with no or very little attentuation. One can also think about bending the waveguide which practically would block the interference by reflecting it. This is theory but for practical implementation a Ku band ciricular waveguide is needed and apparently there are no such waveguides readily available, only rectangular ones for single polarisation. Thus, the only way to is to make cicular waveguide by itself. Sounds not impossible since one needs metal pipe with specific diameter and two flanges. Here there are detailed issues I would like to ask:

- Standard internal diameter of circular Ku waveguide is 19 mm but the nearest I can find is 20mm (22mm external) copper which would result in a mismatch bettwen the LNB and feed. Is such mismatch important/critical?
 
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