Home |
Search |
Today's Posts |
#22
![]() |
|||
|
|||
![]()
Hello Richard,
What a curious defense for magnetic antennas's noise immunity. Where did I mention that this relates to noise immunity? I only tried to point you to a misconception regarding the use of the 2*D^2/lambda formula. [start quote] The traditional half-wave dipole antenna that exhibits the traditional usage for distinguishing between near and far: 2 40 /80 = 40 meters a smaller quarter-wave dipole antenna 2 20 /80 = 10 meters a tenth wave dipole antenna 2 8 /80 = 1.6 meters a fortieth wave dipole antenna 2 2 /80 = 10 centimeters Let's see where discussion follows in this regard. [end quote] You want to believe us that a usable antenna with size=2m and lambda=80m satisfies far field conditions at 10 cm, I really hope I understood you wrong. However, the magnetic antenna is not immune from the reactive fields of noise emitters that are very much larger than any loop discussed here. It is the field of the emitter that is important. I thought I would wait and see if anyone cottoned on to that aspect of the discussion. If we proceed with the assumption (repeated here): The dominant reactive field from a small "magnetic" loop or "electric" antenna at lambda=80m extends to somewhat more then 10cm, think of about 5m. Though the far fields may be similar, the reactive fields are completely different in orientation, strength and E/H ratio. See for example the link posted earlier: http://www.conformity.com/past/0102reflections.html This will result in complete different coupling to conductors present in the reactive field zone. When using reciprocity, this will also affect the coupling from noise current in the conductors towards the antenna. So I can't follow your statement below: wimpie: Smaller loop size does not result in smaller reactive field zone. then the magnetic antenna is doomed to noise in the same sense as an electric antenna is. Of course I agree with you for the case the noise source extends over large distance. What antenna is better, you cannot say beforehand and is food for the experimenter (as I mentioned earlier). This topic becomes lengthy. Do you think that it will result in better statements from other people on there websites (that was the subject of my first contribution)? The second part was just to show that the 3% claim for a 4 m loop (circumference) at 80m isn't bad. I have real doubts about it, so I decided to send PM to Norbert some days ago to setup a more constructive discussion. With kind regards, Wim PA3DJS www.tetech.nl |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
SBS-1 - information. Does anyone have any experience with ? | Scanner | |||
Material of wi does it affect a loop antenna's performance? | Antenna | |||
Magnetic Loop !!! | Antenna | |||
Dipole vs. Delta loop vs. Quad loop -pratical experience | Antenna |