1/2" LDF line losses

[KF4LZA]

I have a system that was on a piece of 35 foot LDF 1/2". I moved the antenna and had to increase the line to 100 ft. The specs say a 1.5 dB loss at 450 MHz @ 100 ft. Out of the duplexer I am getting 87w. At the antenna feed point I am getting 87w still, however since adding more line I have noticed attenuation of the TX signal in the field. Where it was 9+ over out to about 5 miles it has decreased to 3.5 mi. The question is, even though there is no output decrease at the antenna feed point should I assume there is still attenuation of the transmit getting into the antenna? The hieght of the antenna hasn't changed nor the output of the PA; only the length of cable.

[Tom in D.C.]

Something about your figures doesn't add up right.
If you have 87 watts out of the duplexer into 100
feet of coax then it's theoretically impossible to have
87 watts at the other end of the coax, unless the
reading is a combination of forward and reflected
power. Is it possible that your feedline is resonant
at or near your transmit frequency?

[KF4LZA]

you're 100% correct. when i hooked the bird between the hardline at the antenna feed point and put the antenna as the load instead of the dummy load it showed about 70 watts which is exactly the amount of signal attenuation expected for 100 feet of 1/2 LDF so it goes to show that sometimes the ratio of coax to resonant freq can fool a meter. I have already ordered 7/8 LDF as replacement.


thanks