Some things you can try to combat TI:
1. The problem is not always TI related. Therefore, check your dish alignment and make sure you can track the satellite arc. Adjust the skew, elevation and azimuth settings one at a time and check to see if performance improves.
2. Change the illumination pattern of your feed. A feed which over-illuminates the parabola will detect more TI because of the larger side lobes. A feed which under-illuminates will have significantly smaller side lobes and therefore detect less TI. To under-illuminate your dish, simply move the scalar ring further up the throat of the LNB. You can also remove the scalar ring altogether for extreme under-illumination.
3. Try using an anti-TI feed. For small amounts of TI outside the C-band range of frequencies, these bandpass filters work quite well. If the TI occurs inside the range of C-band frequencies (e.g. future 5G), you will likely need a notch filter. These are expensive and will also wipe out any transponder at the center frequency of the notch filter. However, they will restore the rest of the C-band frequency range. The company Microwave Filters makes them, but expect to pay a small fortune to purchase one.
4. Add motorized skew or motorized declination control (or both) to your dish. When you change the skew or declination of your dish, you are effectively rotating the radiation plot. This slight rotation can cause the TI power to fall on a null point between two side lobes, or at a point where lower amounts of TI power will be detected. I can confirm to you that this trick works remarkably well. In the one direction of rotation the TI noise increases, but in the other direction, it attenuates. The only downside is that your C/N ratio will drop a bit because the satellite signal is being detected off-axis. For example, when detecting an on-axis satellite signal, you may have a C/N of 12 dB but significant amounts of TI make reception impossible. After rotating the feed or changing the declination, the new C/N may only be 10 dB but the transponder locks fine.
5. Change the location of your dish. Try installing behind a structure like a building which will shield your antenna from TI. If this isn't possible, consider digging out a bunker and installing the dish partially below ground. You will also get the added advantage of protection from high winds. Finally, consider building wire-mesh TI screens or a Faraday cage to protect your dish from strong levels of TI.
6. Lastly, consider upgrading to a larger dish. Larger dishes have smaller side lobes and therefore "see" much less TI. Upgrading to a larger dish is equivalent to adding a shroud around a smaller dish, with the added advantage of more gain. That's why I'm not a big fan of shrouds.
TI is mostly a big city problem. If you are a TV or radio station and your 10' dish gets hit with a ton of 5G TI one of these days, you may consider upgrading to a 12', 13.5' or 15'. Below, a fully motorized Az-El-Skew antenna for TV/Radio stations, cable companies, military and astronomy applications, etc. Only available in sizes 12' and up.
Last edited by tek2000
on Mon Aug 12, 2019 8:05 am, edited 1 time in total.
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