power transmission lines and its effect on the MW tX

[rami.masadeh]

Gent:

There is one operator planning to install MW link on the same tower of the High voltage power lines, our ferquency for the MW is 6Ghz---38Ghz, and the voltage value on the lines 10Kv---43Kv, is there any effect on on our MW link if it is installed over these transmission lines???????

 

[flatulent]

There are two types of interactions. You are probably using high gain antennas and so the wires will probably not distort your radiation pattern as much as building reflections.

There will be a small magnetic field at the mains frequency. Your system should be in a metal box and this will greatly reduce the effects.

 

[biff44]

You will probably be ok, assuming your system is properly designed.

There will be all sorts of electrical noise. A whopping amount of 60 Hz noise, which might induce phase noise on the microwave oscillators (even with shielding). If it is a large data rate system, this is probably ok, as the receiver will lock onto the moving carrier frequency (modulated at 60 or 120 or 180 Hz) and ignore it. If it is a low data rate system (2kbps or so), you could have big problems. In any event, be prepared to filter out 60 Hz hum with some honkin big capacitors. Obviously, a 256 QAM system will be more sensitive than a 4 FSK system!

Power lines ROUTINELY get struck with lightning. The metal tower is not necessarily properly grounded to prevent that. So, if lightining strikes 2 miles away, you want to make sure your system is not fried. I would make sure that the enclosure is connected to earth ground. What are the details of the unit you are mounting on the tower? Is it self contained? If so, you will probably need to isolate thedigital input somehow to keep lightning voltages from blowing out your digital logic (a fiber optic feed would be ideal). At the least, I would make sure there are protection diodes on any inputs.

If the unit in the tower is RF only, and the digital portion is on the ground, then you will need an IF lightning supressor somewhere between the two units. These things have spark gap devices that short out high voltage pulses.

I have designed such protection schemes for backhaul radios in the past, so if you need design help, email me.