I am experimenting a bit with TDR (time domain reflectometry) and for it I am generating a square wave with up to 10kHz and a rise time of about 1-2ns.

Now I would like to put that thing to use and see if I can figure out more about some cable tv cables in a house where there seems to be signal reflection issues.

Unfortunately I can not disconnect all the TVs that are connected, so while my measurements may disturb reception, they may not be so high as to damage the TV set (or any other receiving device, or amplifiers).

While I can find lots of anecdotal descriptions that suggest the limit to be anywhere between 100mVpp and 1Vpp when I look at some professional TDR test equipment, their test signal level is specified to be 6V. However their signal is specified as a "half sine pulse" and not a square wave, and I have no idea if the higher frequency content of my square wave at such high levels will be any more harmful, considering the device is most likely coupled via a small capacitance to the tv cable.

So what is a likely safe level for such a square wave, and why is that so (e.g. because regulations require it, all industry amplifiers accept at least xVpp etc.) ?

  • \$\begingroup\$ Time domain Reflectometry? \$\endgroup\$ – Andy aka Jan 26 '16 at 10:33
  • \$\begingroup\$ @Andyaka: yes, you think I should write it out? \$\endgroup\$ – PlasmaHH Jan 26 '16 at 10:34
  • \$\begingroup\$ Yeah I reckon so and can you make it clear about the specific port on the TV that might be affected. \$\endgroup\$ – Andy aka Jan 26 '16 at 10:35
  • \$\begingroup\$ @Andyaka: not so sure what you mean by that, all TVs I have ever seen only have one port where you plug in the cable tv cable \$\endgroup\$ – PlasmaHH Jan 26 '16 at 10:37
  • \$\begingroup\$ Ah I missed the "cable (TV cable)" part. I still use antenna sockets at my house (out in the sticks). \$\endgroup\$ – Andy aka Jan 26 '16 at 10:42

100dBuV is about the most signal you want to see on an antenna cable.

That comes out as 100mV RMS

This is not because the units are interchangeable. they're not. it's a coincidence.

so 141mV peak should not harm any equipment.

DiSEqC uses 22kHz (sine) at up-to 900mV peak-to-peak, but unlike your square-wave there's no RF component to that signal, so the receiver circuitry won't be effected.


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