FIGHTING RECEIVER NOISE
In 2011, I installed an 80m OCFD near my house, with about 90 ft. of coax running back to the house.
The antenna was only about 25 ft. away from the house. The initial coax, 50 ft. of LMR-240, was connected to 40 ft. of RG8X through an RF-Choke (a Radio Works Line-Isolator, model TG3).
About 2 years later we replaced all of the incandescent light bulbs in the house with newer technology, including two 4.5-Watt LED lamps on the operating desk. For the first 7 years, the noise level on 80m had always been about S2.
Here is a sketch of the 80m OCFD installation:
The coax rand down the pole until a height of about 3m (abt. 10 ft.), then ran horizontally to the house, where it continued along the ground, around the patio, and into the shack.
Then one day my antenna ceased working. Its SWR was sky-high. As it turned out, the RF-Choke (outside) had died.
In order to get back on the air immediately, I replaced the RF choke with a double-female PL connector. The antenna worked perfectly well again, but the noise level on 80m rose to S7, making it difficult to copy many stations.
By switching devices on and off, I traced the source of the noise to the two LED lamps on my desk. One of them was generating 2 S-Units of noise, the other was generating 3 S-Units of noise; (together 5 S-Units).
I inserted a Maxwell RF Choke between the coax in the shack and the transceiver. The noise level dropped back to S2, the same as it had always been.
I then removed this choke and replaced the double-female connector outside between the two pieces of coax with it. The noise level remained at S2. Switching the LED lamps on or off made no difference in the receiver’s noise level.
Curious: although the source of the noise was sitting on the operating desk, right next to the radio, a choke in the coax 40 ft. away was suppressing it completely.
I make no attempt to explain how that is possible. I only want to point out how important it is to use an RF Choke in the coax transmission line near the house.
CONCLUSION: ALWAYS use an RF Choke in the transmission line, near the house.