AT&T U-verse issues in related to Amateur Ham Radio operation

Transcription

1 AT&T U-verse issues in related to Amateur Ham Radio operation HF operation interferences the U-verse modem vdsl utilizing MHz over twisted pair

2 At NN5T, U-verse modem loses the system synchronization resulted in NO SERVICE to all TV, internet and phone land-line if any RF on 80/75 meter band is detected above 50 Watts on SSB/CW, worse on continuous carrier like RTTY Throughout the trouble-shooting, unplugging all output connections, adding AC line filter, or clip-on ferrite core(s) onto CAT5 DSL input line did not help. It cannot be the long-term solution due to the heat, but temporary wrapping the modem around completely with aluminum foil did not help either. Temporary setup the 12V battery operation condition of the modem without cord, no change. Therefore RF is coming into the modem through DSL input --- sure DSL is RF and the interference is happening at DSL input. Adding much ferrite, or typical RF bypass caps like 0.01uF onto the CAT5 line not only reduces the 80/75 meter RF but also effecting to the DSL signal, these cannot be applied to the improvement.

3 Per G3TXQ site, I can create perfect 100Ω shielded-balanced line with two RG-58 by connecting the shield at the both end to replace existing CAT5 line on U-verse. The predicted Zo for Twin Feed using lengths of RG-58 (3.3mm braid, 4.8mm jacket) is between 64 Ohms and 110 Ohms, depending on what proportion of the field is contained within the PVC jacket. I measured the Zo as 73 Ohms and the Velocity Factor as 0.66, suggesting that the effective Dielectric Constant is about 2.3 (compared to 3 for PVC alone). But RG-58 is not an ideal choice: PVC makes a relatively lossy RF dielectric, and there is some evidence that manufacturers load their PVC jackets with carbon to make them more UV stable. There are better choices. A comment by KD7NM pointed me in the direction of RG-400. It is a similar size to RG-58 but its Flourinated Ethylene Propylene (FEP) jacket makes a better RF dielectric. It is much less lossy than PVC, and although its Dielectric Constant is lower at 2.1 this is offset by the jacket being thinner. The photograph on the right shows a cross section of an experimental length of Twin Feed formed by placing two lengths of RG-400 inside heatshrink tubing. The predicted Zo for Twin Feed using lengths of RG-400 (3.9mm braid, 4.9mm jacket) is between 58 Ohms and 84 Ohms, depending on what proportion of the field is contained within the FEP jacket. I measured the Zo as 68 Ohms and the Velocity Factor as 0.79, suggesting that the effective Dielectric Constant is about 1.6 (compared to 2.1 for FEP alone). Interestingly the ratio of the effective Dielectric Constant to the jacket Dielectric Constant is exactly the same as for the RG-58 case - a result we might have anticipated because the geometries are very similar. Although the Zo is not as low as the target 50 Ohms, this Twin Feed would be acceptable for the HexBeam application. Stripping the jacket from one of the cables would further reduce the Zo to about 58 Ohms Given that the air surrounding the jackets forms a significant part of the total dielectric, we might expect that any water on the jackets could affect the characteristics of the cable. I took a short length of the "twin RG-400", placed a load resistor across one end, and measured the input impedance with the cable dry: it was 104 Ohms. I then sprayed the cable with water. The impedance immediately dropped by 30 Ohms to 74 Ohms. As it dried out the impedance slowly climbed - after 5 hours it had reached 98 Ohms and it finally recovered to 104 Ohms after 12 hours.

4 Then the second-thought, I called AT&T U-verse Specialist I explained the situation and they agreed to replace existing CAT5 line with shielded CAT6 from where DSL is coming up from ground by twisted pair to the modem for free.

5 See where to locate, note old A/B cables for Time Warner is no longer used.

6 See the great grounding to the shield and all other unused CAT6 wires are also grounded.

7 In order to maintain the flexibility at the modem-end, the tech installed the RJ-11 connector and spliced with normal telephone extension cord (though it marked as DATA CABLE). Guess what, the RF interference was occurring as before. I insisted to install RJ-11 jack directory onto the CAT6 cable.

8 With this modification, now I can transmit 600 Watts plus on 80/75 meters without any problem (and did not cost a penny). If you want AT&T but afraid this kind of interference, you can talk with AT&T techs.