Hi Bruce "We know that limiting the noise pick up from more directions of an antenna we can usually hear better"
Agree, actually the directivity of the receiving antenna is the only place you can increase signal to noise ratio. More RDF means more directivity (3D) resulting better signal to noise ratio. All electronic devices add noise at output. No amplifier is perfect. Passive devices ahead of the preamplifier add noise impacting directly on the Noise Figure of the system. 2 db cable loss, 1.5 db filter insertion loss add up to 3.5 db on the total Noise Figure. Whatever you do adjusting the radio you are reducing degradation of the signal noise from the signal coming from the antenna, including adjusting the bandwidth of the receiver. Reducing RF gain reduce the degradation and the signal to noise ratio at the speaker is improved. The issue with RDF or directivity is that we have many antennas on 160. The one we know, our TX antenna, and sometimes six or twelve other antennas fort 160m that we don’t know about it. All these antennas interact with you receiving antenna and your ground at the station near the receiver. 2 wave length on 160m is over 500ft. AM broadcast station detune cell phone towers miles away for the same reason. Just because you can’t measure the deterioration of the patter of you beverage or any fixed receiving antenna, does not mean it is a working as it shows on the paper. EZNEC can simulate the interaction, you just need to all "all your 160m antennas". Antennas you don’t know you have for 160m. 1- That 120 ft of coax for your 6m Yagi 2- The triband feed line 3- Rotor cable 150ft with not a single ground, connected to your control box and right into the ground of your station combining from the AC line 4- The wiring in you r house. 5 -\,,, 6 ... and on and on and on. 7- elevated radials, ... 8- low dipoles with no choke!! ... Any 100Ft of wire is a very good vertical for 160m. If you live near a city the level of energy captured by this "antenna" is huge, and what we do with that? , we connected it to our station ground with a #14 wire ... at the station. Right next to the radio!!! All these "antennas" as well the TX antenna must be detuned for 160, believe or not, it is the true for any vertical receiving antenna. For vertical receiving antennas the reduction in noise is 12 to 24 db, for horizontal receiving antennas, it is 6 or 8 db. Narrow filter, like the one I use ahead of my preamplifier, 0.2db insertion loss and 40KHz BW does help to reduce reciprocal noise and unload the radio from the energy from outside the band. I visited several station during 2016, I found signals above +10 dBm coming from the TX antenna, and leaking everywhere into the radio. That's a lot of RF energy. 10 mW.. of garbage.. Agree again with you about the narrow filter front end. Happy Holidays! 73 JC N4IS This concept is very important -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of K1FZ-Bruce Sent: Thursday, December 22, 2016 3:42 PM To: Topband <topband@contesting.com> Subject: Topband: "Thinking out loud" We know that limiting the noise pick up from more directions of an antenna we can usually hear better. We also know if we limit the noise from a receiver IF we can hear less noise, and better yet, if we have a roofing filter earlier in the receiver we can eliminate even more noise in relationship to the wanted signals. What if we take it a step further, could we limit the band-with of the antenna signal with a crystal lattice for 160 meters before the receiver. Years ago I played around with a single crystal at the input of an old tube type receiver. It was remarkable what I could hear on 40 meters, on what seemed to be one frequency. 73 Bruce-k1fz http://www.qsl.net/k1fz/beverage_antenna.html _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
