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Cable Loss Measurement - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


robh001
 Post subject: Cable Loss Measurement
Posted: Mon Jan 28, 2008 11:31 am 
 
Lieutenant
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Joined: Mon Jan 28, 2008 11:25 am
Posts: 2
Hi,

If I wanted to find the attenuation of a cable at 1.6Ghz how would I go about this. What equipment would I need. Is there a realtively inexpensive way to do this.

Thanks for any help,
Rob


 
   
 
IR
 Post subject:
Posted: Mon Jan 28, 2008 12:03 pm 
 
Site Admin
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Joined: Mon Jun 27, 2005 2:02 pm
Posts: 406
Location: Germany
Hello robh001,

You will need eith 1 of the following setups:

1. Vector Network Analyzer (VNA) - more expensive.

You should calibrate the VNA - insertion loss calibration would be enough (Through standard only) at 1.6GHz. Following that, connect the measured cable between the VNA's ports and measure S21. The result is the insertion loss of the cable.

2. A Signal generator and power meter - less expensive.

Calibrate the power meter. Se the frequency of the power meter to 1.6GHz, Then connect the measured cable on one side to the signal generator and on the other side to the power meter. Set the signal generator for frequency of 1.6GHz and output power of 0dBm and read the power, the result is the insertion loss (In absolute value).


 
   
 
robh001
 Post subject:
Posted: Tue Jan 29, 2008 11:35 am 
 
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Joined: Mon Jan 28, 2008 11:25 am
Posts: 2
Thanks IR,

The second way sounds more cost effective, if I was to get a signal generator to go to 1Ghz, how could I check the loss at 1.6Ghz,
is there a way of check a few different values, and then apply to a formula?

Thanks again,
Rob


 
   
 
nubbage
 Post subject:
Posted: Tue Jan 29, 2008 12:20 pm 
 
General
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Joined: Fri Feb 17, 2006 12:07 pm
Posts: 268
Location: London UK
Hi Rob
Sure: plot the loss from about 800MHz to 1GHz in 50MHz intervals, then draw a graph leaving enough space at the right-hand side to extend the curve to 1.6GHz.
Then extrapolate the values out to 1.6GHz. Cables generally have a smooth well-behaved curve so this approach is quite accurate. However, it becomes much less accurate as you approach the frequency where the first cylindrical waveguide mode can form.
I have a formula for cable loss somewhere. I will see if I can dig it out.






Posted  11/12/2012

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