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This page give measurements of leakage into a 3000-foot long coaxial line. This line is CommScope dual-shield F11 (RG-11 style) cable. It consists of a single 100% foil shield with a single 60% coverage aluminum braid overlay.

My intention is to install remote antennas that are nulled for transmitter signal level, allowing duplex operation during contests. A separate receiving antenna and receiver can be used to find new multipliers while making contacts on the main radio. An operator can  be tuning the band listening for new multipliers or contacts on an omni-directional receiver antenna while the main radio used for contacts is transmitting.

The purpose of this test was to see if cable shield leakage of the transmitted signal would exceed signal level picked up by Beverages.  This data should be useful in other applications.

Building Entrance

 

Building Entrance Panel

 

 

200 watts transmitter power. Cable terminated in 75 ohms. FS measured at receiver. Antennas used were my most distant beverage group approximately 2500 feet (one half mile) from my transmitting antennas. In order to eliminate cable leakage as a factor in signal level from Beverages, the signal was measured at the Beverages. The dB value for RX antennas below is that value with actual transmission line losses included.

160 Meters

Antenna Worse-case  RX antenna dBm Best-case RX antenna dBm Terminated line dBm
Low dipole 130 ft high right above coax -25 -41 -38
High Dipole 300 feet high above coax -23 -39 -57
Vertical 200ft high 350 ft from coax -14.5 -34.5 -44

80 Meters

Antenna Worse-case  RX antenna dBm Best-case RX antenna dBm Terminated line dBm
Low dipole 40 ft high right above coax -43 -52 -45.5
High Dipole 155 feet high above coax (parallel) -34.5 -55 -56
High Dipole 150 feet above coax (right angle) -26.5 -36.5 -44

There are only two cases where signal ingress can exceed signal level from the Beverages one half mile away. Both cases are where a low dipole is mounted right above the feedline. In these cases the feedlines from the low dipoles also parallel the F11 receiver feedline for at least 200 feet with very little physical separation.

160 Meters

Antenna Worse case Headroom
Low dipole above receiver feedline -3dB
High Dipole above receiver feedline +18dB
Vertical Omni +9.5dB

80 Meters

Antenna Worse case Headroom
Low dipole 40 ft above receiver feedline and parallel with feedline -6.5dB
High Dipole155 ft  above receiver feedline (and right angle to Beverages) +1dB
High dipole 150 ft above receiver feedline and right angles to feedline (broadside to Beverages) +7.5dB

 

Even with Beverages 1/2 mile from the transmitter, there are very few cases where signal ingress into the coax exceeds the signal level from the Beverages. The only cases of failure were when low dipoles parallel to the feedline were excited and compared to a Beverage with a deep null towards the transmitting antenna. This data assumes good coaxial connections. Common mode chokes were not used in this test.

Certainly for any Beverage installation closer than 1/2 mile to transmitting antennas feedline ingress will not be a problem.

 

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