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ON4DD

Joined: Sat, Aug 2nd 2014, 09:58 Roles: N/A Moderates: N/A

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Topic Created Posts Views Last Activity
Cable loss higher than expected Jun 17th 2018, 10:54 2 1,551 on 26/5/19
Power measurements, what am I doing wrong? May 15th 2017, 04:40 4 2,966 on 15/5/17

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Topic Author Posted On
Cable loss higher than expected ON4DD on 17/6/18
Dear,

I am testing a long cable run (about 90m). This cable has been used outside in rather harsh environments at times.

I've set up my VNA with the correct values (velocity factor,...) and the distance to fault is correct when I just connect one side to the RF out connector (S11).
However, the datasheet specifies 25.8dB loss per 100m at 1Ghz, but I am measuring 43dB loss (S21).
DC resistance of the center conductor and shield is according to the manufacturer specifications for that length. There is no (measurable) DC loss between shield and center. Capacitance is defined at 56pF/m, I measured 5.82nF which seems to correct.

I am wondering if this could be caused by:
- possible moisture in the foam PE dielectric
- other reasons?

Anything I might be missing?
Thank you,

Dieter ON4DD
Power measurements, what am I doing wrong? ON4DD on 15/5/17
Dear Zack,

Thank you very much.
That makes sense and confirms the other measurements.
So... I should have my doubts about the signal generator then, correct?

Regards,
Dieter
Power measurements, what am I doing wrong? ON4DD on 15/5/17
I have tried to combine a few measurement methods on a signal coming from a signal generator.
They don't really seem to agree on the measured power, so I guess I might be making some measurement/thought mistakes.

Source:
Signal generator: TTi TGR2050, 100MHz, 0dBm out
Cable: know good Ecoflex 10 cable

Measurements:
1. Tektronix TDS 5054 500MHz scope
Terminated in 50 ohms, measured Vpp=0.261V
Power: P=U²/R, adds up to 1.36mW or 1.34dBm

2. Rohde&Schwarz FSL Spectrum analyser
RBW and VBW set to 300Hz, span 10kHz
Peak power: -7.63dBm

3. Rohde&Schwarz URY millivoltmeter with RF sensing head
Terminated in 50ohms load
-7.67dBm
PEP: -7.53dBm

Seems I am not measuring correctly, or my understanding isn't deep enough.
What am I doing wrong?

Regards,

Dieter
ON4DD

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