Tom's comments sparked a question. (No pun intended). Does the SNR of the targeted noise source vs. other signals on the sense antenna, matter in this application?
Art NK8X ᐧ On Sun, Nov 1, 2015 at 12:07 PM, Tom W8JI <w...@w8ji.com> wrote: > I have an intermittent RFI issue that comes from a subdivision about a 1/4 >> mile away. To combat the noise I have been trying to use my ANC4 and I >> built a sense antenna out of an 80m hamstick that I put 20 feet in the air >> yesterday for a trial to cancel the noise on 80m (cheap and easy >> experiment). The location of the sense antenna is at the corner of my lot >> as close to the subdivision that I can get. The design is the hamstick as >> a vertical element and two 102 inch whips as elevated radials. >> >> > 102 inch whips would not be an effective counterpoise unless one or both: > > 1.) The whips were loaded to resonance with a high Q coil, at which point > it would be a single frequency counterpoise and still require a good > feedline choke > > 2.) The feedline had a much high common mode impedance than the common > point impedance of the whips > > Without the above, the coax shield is mostly the antenna...not the > Hamstick. You would have been much better off with a ground rod. > > > The noise is s9 on my 1/4 wave 80m vertical and 160m inverted L. This is >> a multi band vertical with wires for 40m, 80m & 160m. I also have other >> antennas such as a 160m 2wl long loop and a trapped dipole. What is >> interesting is that the noise is significantly less on the loop and the >> dipole. I attribute this to the noise being vertically polarized based on >> my research on the internet. Also this sense antenna is roughly 150ft away >> from the vertical antenna. >> >> > That actual reason for that is the earth acts like a short circuit and > attenuates any horizontally polarized ground wave. > > The low horizontal antennas also have very poor ground wave response. > > This combines to make horizontally polarized antennas less sensitive to > distant ground wave noise. > > The issue is the level of the sense antenna noise is significantly less >> than the vertical and I am not able to find a null point that makes a >> difference. I can however use the loop antenna and I have enough signal >> with the hamstick experiment to get a null as the received level of noise >> on the loop is significantly less. So I believe I need more receive gain >> on the sense antenna. >> >> So with the above in mind, is there a low cost pre-amp that I could use >> on the sense antenna to boost the signal? Or what other ideas are there >> for a sense antenna. I don’t want to put up another 1/4 wave antenna for >> sensing. I have read where folks suggest putting 50 ft leg dipole at 5 ft >> above the ground for 80m & 40m but I think the noise is vertically >> polarized and this wont do much but I could be wrong and have been wrong >> before. >> >> > I would build a ground mounted vertical sense antenna with amplifier, use > a ground rod as a ground, and decouple the coax near the sense antenna. A > simple J310 source follower amplifier on a 102 inch whip would have a ton > of signal level. > > 73 Tom > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband