I purchased a 1:64 scale Baron from JRY online, and used 20.1 meters of silver-plated PTFE wire (approximately 1.5 square) to create the antenna. I mounted it between the roof of my building and the opposite building. Due to the distance, the antenna was approximately 1 meter away from the opposite building's roof, while the Baron was about 80cm to 1 meter away from my building's roof. I used standard 50-3 coaxial cable to run along the metal water pipes in the building (there is a row of water pipes leading to each house, and I hid the coaxial cable between the pipes and the exterior wall to prevent it from being discovered). After entering the building, I measured the SWR using a frequency meter. The SWR was slightly higher than 2.7 at 28MHz, but remained between 1.1 and 1.3 at 7MHz, 14MHz, and 21MHz.
The radio used was a Yaesu PMR-171. The first time I powered it on, around 6:00 PM, I noticed very high background noise. The signals on 7 MHz and 14 MHz were S9+, while the 21 MHz was S9+20.
The second test was at 3:00 AM. At this time, the noise on 7 MHz had decreased to S3-S4, and the 21 MHz was around S5. However, I could only hear a few local HAMs using FT8 CQ on 21 MHz, but not any other signals.
I tested it again at noon today, and found that the background noise had returned to S9+20 levels across all bands.
Initially, I suspected that the close proximity of the antenna to the building was causing the problem. However, after consulting with Mr. JRY, I learned that the antenna's proximity to the building does not significantly affect the receiver's noise level. I also browsed hellocq and found similar posts where users reported high noise levels when using a direct-to-base station setup. These users suggested trying an air-borne balun, but my attempts did not yield significant improvements. Currently, I have ordered a magnetic loop and plan to wind a choke coil myself on the feed line side of the radio to see if it helps. However, I am not holding out much hope.
I was hoping to get some advice from you all. Are there any other suggestions you have?
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