[TowerTalk] Elementary feedline loss question

Grant Saviers grants2 at pacbell.net
Fri Apr 4 14:31:02 EDT 2014

Perhaps a less error prone way to measure loss is to use your 
transmitter, dummy load, and SWR/power meter.  I put the power meter at 
the transmitter and set the power level on the SWR meter.  Then move it 
to the load end and measure again.  Then

db loss = 10 log(Pout/Pin)

Your rig is more accurate in freq than the MFJ and the same power meter 
and load are used to take out those variables.  Also works for freq. 
where the MFJ won't go.

I've measured various vintage RG8's 12 to 20 YOA and found near original 
spec loss, although some of it was MIL-SPEC quality.  I then tape on the 
cable the date, measurement freq, and loss for future reference.

Grant KZ1W

On 4/4/2014 6:53 AM, Pete Smith N4ZR wrote:
> If I terminate a long 50-ohm coaxial cable with a 50-ohm dummy load, 
> and put an MFJ-259B on the other end, and it reads R=56, X=0 at a 
> given frequency, what is the mathematical relationship between the 
> measured R (leaving calibration out of it, for now) and the loss in dB?

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