Home |
Search |
Today's Posts |
#51
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
christofire wrote:
Could I suggest taking a look at one of the well regarded text books such as 'Antennas' by J. Kraus. The international 3rd edition is available at www.abebooks.com for about $22. There's no reason for any amateur radio operator who is serious about antennas not to have one. http://www.abebooks.com/servlet/Sear...ions&x=47&y=13 -- 73, Cecil http://www.w5dxp.com |
#53
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
christofire wrote:
I'm aware of issues involved in claiming generation of separate E or H fields, as has been described by Kabbary et al in their 'crossed-field antenna', but surely the issues concerning a receiving antenna are different? Those issues, and an acute sensitivity to them, are evidently at the root of the misunderstanding here. The oversensitivity perhaps caused confusion, irritation, defensiveness, and temporary blurry vision. Scientists at the MIT Radiation labs during World War II found that it was a simple matter to measure E and H individually. I imagine that it is still possible to do without having to perform the miracle of 'field separation'. ac6xg |
#54
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
Jim Kelley, AC6XG wrote:
"Scientists at the MIT Radiation Labs during World War ll found that it was a simple matter to measure E and H individually." Yes indeed. Two dircuits in separate shielded enclosures can be coupled with a coupling capacitor and only the E-field gets through. Similarly, two transformer windings separated by a Faraday shield are completely coupled magnetically and have no electrostatic coupling. I`ve worked in several broadcast stations and all towers were so coupled to avoid capacitive coupling which could give advantage to harmonic frequencies over the broadcast fundamental frequency. Best regards, Richaqrd Harrison, KB5WZI |
#55
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
|
#56
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
Richard Clark, KB7QHC wrote:
"Which field is chosen won`t mstter much----." Agreed as the fields trade the same energy back and forth on each cycle. Narrowing bandwidth is not the only way to reduce noise. Auto radios use non-directional antennas out of convenience. A desired signal can come from any direction. But, directivity can improve signal to noise ratio as it reduces noise from unwanted directions. An example is my Telefunken receiver which features a large horizontal ferrite rod antenna. This rod is rotatable in azimuth from a control on the front panel for best reception. This radio was designed for reception in a fixed location so azimuth change is needed only when changing stations. A ferrite rod antenna can be used anywhere to improve s/n ratio through its high directivity. It requires more inconvenience to reset when the direction of the vehicle changes and it needs to be mounted outside the shielded enclosure and equipped with a direction control, i.e. a rotator. MFJ among others sells such a ferrite rod antenna for the standard broadcast band. Aimed for best reception of KGO in San Francisco, it would discriminate against noise from most other directions. Best regards, Richard Harrison, KB5WZI |
#57
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 23, 7:37*am, Cecil Moore wrote:
I'm not saying that a coaxial loop is a "magnetic" antenna. I am saying that antennas do exist which respond primarily to the magnetic field and a ferrite rod antenna is one obvious example proven by rotating the ferrite rod in the presence of a vertically polarized signal. Note the polarization of a radiated plane wave is referenced to the E-field, not the H-field. -- 73, Cecil *http://www.w5dxp.com I had to ponder the loop for a while. Something kept bugging me, and it was mainly wondering about the pattern of say a small 1/10 wave loop, vs a large 1 wave loop. Both are diamonds. I was pretty sure I remembered them as having a different pattern, and I decided to model them to see. Well. I found out that even when I'm feeding the small diamond at the bottom corner, I'm still getting mostly all vertical polarization. So with the small vertical loop, I'm getting almost all vertical polarization, no matter where it is fed. With it fed on a side corner, which most would consider vertically fed, I have almost the same pattern, except it's even cleaner, with very little horizontal. Totally unlike the large loop which if I feed at the bottom, it's almost all horizontally polarized. So it seems my MW loops are still pretty much vertically polarized, even when fed at the bottom corner. So anyway, as far as the small loops, I'm not receiving cross polarized after all. I generally don't see much difference in operation between a ferrite loop antenna, and a wound solenoid loop with many turns for MW. And I did make a "PVC Tube" solenoid loop antenna once when I was messing around with them. But don't have it together now. But I seem to remember it acting basically the same as all the other versions. IE: the directivity was off it's ends. I'd have to make another one to compare tilting it vertical, vs horizontal. |
#58
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
wrote:
I'd have to make another one to compare tilting it vertical, vs horizontal. Again, I'm not talking about any loop in air. I'm only one example of a ferrite rod loop antenna as exists in AM radios. Those rods are mounted horizontal within the radio while the polarization of the transmitted signal is vertical. This was in response to the assertion that magnetic field antennas don't exist. A ferrite rod responds to the EM magnetic field whether there are any coils of wire on it or not. -- 73, Cecil http://www.w5dxp.com |
#59
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
Richard Harrison wrote:
MFJ among others sells such a ferrite rod antenna for the standard broadcast band. Richard, what's the MFJ part number? I can't locate it in the catalog. -- 73, Cecil http://www.w5dxp.com |
#60
|
|||
|
|||
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 25, 9:46*am, Cecil Moore wrote:
wrote: I'd have to make another one to compare tilting it vertical, vs horizontal. Again, I'm not talking about any loop in air. I'm only one example of a ferrite rod loop antenna as exists in AM radios. Those rods are mounted horizontal within the radio while the polarization of the transmitted signal is vertical. I realize that, but I guess you missed the point. The point being, I'm not so sure it wouldn't be responding to mostly vertical polarization no matter how the antenna was oriented, unless maybe it was flipped on it's side. The rods are mounted horizontal, but are receiving a vertical signal off the ends. You seem to imply a difference in pattern using a ferrite bar, vs not using one. I'm not so sure I agree with that without more checking. But like I say, I'd have to rig up some test dummies to refresh myself. But.. as I remember from the past versions I made, the ones I made with air cores seemed to act exactly the same as the ones with a ferrite bar as far as pattern. IE: both are bi-directional off each end and both are responding to a vertical signal. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Improve the Rec.Radio.Shortwave Newsgroup -by- Making On-Topic ... | Shortwave | |||
improve fm reception on transistor radio | Antenna | |||
5 Ways to Improve HD Radio Reception | Shortwave | |||
What are ferrite core chokes to improve radio reception? | Shortwave | |||
Realistic \ Radio Shack DX-200 improve audio mods | Shortwave |