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Measuring RF Loss - Antenna System


Paul F

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I tried to measure the loss through a 4-way splitter. But I'm getting odd results. I'm measuring a loss of about 5db which doesn't make sense.

 

I am connecting an LPDA to the input of the splitter. I connect an Anritsu spectrum analyzer to the output. Some distance away is a transmitter. All connections and cables are 50 ohm. The coax is RG-316. The other 3 outputs are not terminated. Is this why I'm getting odd results? Do I need to terminate the other outputs? I don't have a way to terminate the other outputs at the moment.

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Yes. I just did a with/without splitter comparison.

 

14 hours ago, Patrick Farrell said:

A 4 way split should be a 6 dB loss. I'd say "about 5 dB" is within the margin of error with the imprecise method of a receive antenna and transmitter some distance away.

I hear you. I was expecting to see about 7 db loss with connections and maybe poor splitter design. So 5db just doesn't make sense to me. The Anristu constantly recalibrates itself, so I'm assuming while actual power levels may not be accurate, the relative accuracy from reading to reading should be spot on.

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A perfect splitter would have 6 dB of loss with all ports terminated. A good, real world splitter will have 6.5 to 7 dB of loss with all ports terminated. If your splitter were terminated at all ports you would see the expected loss. Your 5 dB is probably dead on for unterminated ports.

Best Regards,

Larry Fisher

 

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On 10/23/2020 at 4:07 PM, drpro said:

A reliable method, but costly would be a spectrum analyzer with a tracking generator along with a return loss bridge.  For most of what we do really not necessary.

 

Not intending to be fastidious, but you don't need a directional bridge if you just want to measure the total loss through the splitter. :)

 

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1 hour ago, BAB414 said:

Should I be terminating unused ports in an active splitter to minimize loss?

It's not worth the effort or cost. You probably will have less loss with unterminated ports, active or passive, though the difference is almost unmeasurable and will make no difference in real world performance. 

Best Regards,

Larry Fisher 

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2 hours ago, LarryF said:

It's not worth the effort or cost. You probably will have less loss with unterminated ports, active or passive, though the difference is almost unmeasurable and will make no difference in real world performance. 

Best Regards,

Larry Fisher 

Thank you as always Larry.

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