Coaxial Cable Leakage

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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.

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, or just to illustate the amount of ingress through this type of coaxial cable shield.

Building Entrance (old pictures)

 

Building Entrance Panel

 

 

Test Conditions

200 watts transmitter power. Cable terminated in 75 ohms. Signal levels are measured at receiver. Antennas used were my most distant beverage antenna group approximately 2500 feet (one half mile) from my transmitting antennas. "dBm" values below for RX antenna dBm are the values with actual transmission line losses included.

160 Meters

Transmitting Antenna Strongest RX antenna signal level of transmitter in dBm Weakest case RX antenna signal level of transmitter in dBm Terminated RX feedline  level dBm
1/2 wave dipole, 130 ft high, immediately above and parallel to receiving antenna 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 Strongest RX antenna signal
from TX in dBm		 Weakest TX signal from
RX antenna in dBm		 Terminated RX feedline level dBm
Low 80M dipole parallel and 40 ft
above receiving antenna coax		 -43 -52 -45.5
High 80M dipole 155 feet above coax (parallel to RX feedline) -34.5 -55 -56
High 80M dipole 150 feet above coax (right angle to RX feedline) -26.5 -36.5 -44

There are only two cases where signal ingress can exceed signal level from the beverages that are loacted one half mile away. Both cases are where a low dipole is mounted right above and parallel to the feedline. In these cases, the feedlines from the low dipole test antennas also paralleled the F11 receiving antenna feedline for at least 200 feet in the same bundle.

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

 

Conclusion

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. All of the signal will be from the receiving antennas and not leakage through the coax shield. 

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