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improve S/N for AM car radio by a factor of 2...5...10?
Hi all,
I've looked on the web, but with very little success. I have never posted to this group before, so I apologize if my question is lame. I listen to the Bay Area's KGO 810 MHz a lot. Their transmitter is located in South San Fran Bay near the Dumbarton Bridge, and outpus 50 kW (that's what they say anyway). I am guessing, it's directed mostly at the Pacific coast line. I often listen while driving east on I-80 to Truckee/Tahoe for skiing and camping. Usually the signal fades substantially by the time I reach Sacramento - but it's still tolerable listening (by ear, S/N of ~3). By the time I reach Auburn it's essentially inaudible. Much better signal at night (~again, by ear, S/N improves by ~2). At night, I can sort of pick up words in truckee. Question: can I *substantially* improve the S/N - say, factor of 2/5/10 by installing a better car antenna, so that, say, I could listen in the Sierras day and night? I do not care if the antenna is huge/geeky_looking, my car is being driven into the ground anyway. I would be happy to make this a DIY project - to save on $ and learn about radio. What kind of specs should I look for? I.e. I don't want to go on the web and blindly buy an antenna advertised to "boost" your AM radio reception - I would want some numbers. I have limited knowledge in electronics, my background mostly is in biophysics and biochemistry. So if you steer me into the right direction I think I should be able figure it out. |
improve S/N for AM car radio by a factor of 2...5...10?
If you have mobile Internet try this:- http://wareseeker.com/Windows-Widget...player-1.2.zip... HTH Clive That's a good one. I am often in places with no cell reception. I originally discovered KGO when I lived in La Honda, CA - it was the only radio station I could easily pick up. No cell reception and no FM there. |
improve S/N for AM car radio by a factor of 2...5...10?
wrote in message ... Hi all, I've looked on the web, but with very little success. I have never posted to this group before, so I apologize if my question is lame. I listen to the Bay Area's KGO 810 MHz a lot. Their transmitter is located in South San Fran Bay near the Dumbarton Bridge, and outpus 50 kW (that's what they say anyway). I am guessing, it's directed mostly at the Pacific coast line. I often listen while driving east on I-80 to Truckee/Tahoe for skiing and camping. Usually the signal fades substantially by the time I reach Sacramento - but it's still tolerable listening (by ear, S/N of ~3). By the time I reach Auburn it's essentially inaudible. Much better signal at night (~again, by ear, S/N improves by ~2). At night, I can sort of pick up words in truckee. Question: can I *substantially* improve the S/N - say, factor of 2/5/10 by installing a better car antenna, so that, say, I could listen in the Sierras day and night? I do not care if the antenna is huge/geeky_looking, my car is being driven into the ground anyway. I would be happy to make this a DIY project - to save on $ and learn about radio. What kind of specs should I look for? I.e. I don't want to go on the web and blindly buy an antenna advertised to "boost" your AM radio reception - I would want some numbers. I have limited knowledge in electronics, my background mostly is in biophysics and biochemistry. So if you steer me into the right direction I think I should be able figure it out. Presumably you mean 810 kHz. What is the source of the noise? Noise generated in the receiver is usually insignificant in the medium-wave band. If the cause is other transmissions on the same and nearby frequencies you may not gain much by changing the antenna, but a receiver with better channel (IF) filtering may help if there is any contribution from adjacent channels. If the noise is coming from your car (does it improve when you park in a rural area) then you may need to improve the RF suppression of its circuitry (e.g. ignition if it's a petrol engined car). I expect you can work out what tests would be needed to locate the principal sources of the noise. Chris |
improve S/N for AM car radio by a factor of 2...5...10?
Presumably you mean 810 kHz. *What is the source of the noise? Noise generated in the receiver is usually insignificant in the medium-wave band. If the cause is other transmissions on the same and nearby frequencies you may not gain much by changing the antenna, but a receiver with better channel (IF) filtering may help if there is any contribution from adjacent channels. *If the noise is coming from your car (does it improve when you park in a rural area) then you may need to improve the RF suppression of its circuitry (e.g. ignition if it's a petrol engined car). I expect you can work out what tests would be needed to locate the principal sources of the noise. Chris Yes, KHz, sorry. The noise goes up several fold when I pass underneath bridges/pass big trucks, etc. Does this suggest that the noise is from other frequencies? |
improve S/N for AM car radio by a factor of 2...5...10?
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improve S/N for AM car radio by a factor of 2...5...10?
On Jan 19, 3:38*pm, Roy Lewallen wrote:
wrote: Yes, KHz, sorry. The noise goes up several fold when I pass underneath bridges/pass big trucks, etc. Does this suggest that the noise is from other frequencies? No. It means that the noise is coming from outside your car. Your antenna and radio can't tell the difference between this noise and the desired signal, so improving your antenna or increasing your receiver's sensitivity will simply increase the signal and noise in the same proportion. And because it's not coming from your own car, there's no way for you to reduce the noise. In other words, there's really nothing you can do to improve the S/N ratio in the presence of that noise. Roy Lewallen, W7EL increase the signal and noise in the same proportion. Is there anyway to "filter" the 810 frequency somehow? |
improve S/N for AM car radio by a factor of 2...5...10?
wrote in message ... On Jan 19, 3:38 pm, Roy Lewallen wrote: wrote: Yes, KHz, sorry. The noise goes up several fold when I pass underneath bridges/pass big trucks, etc. Does this suggest that the noise is from other frequencies? No. It means that the noise is coming from outside your car. Your antenna and radio can't tell the difference between this noise and the desired signal, so improving your antenna or increasing your receiver's sensitivity will simply increase the signal and noise in the same proportion. And because it's not coming from your own car, there's no way for you to reduce the noise. In other words, there's really nothing you can do to improve the S/N ratio in the presence of that noise. Roy Lewallen, W7EL increase the signal and noise in the same proportion. Is there anyway to "filter" the 810 frequency somehow? Hi Are you certain that the noise increases? I suspect the "signal" decreases. It is entirely possible that the antenna on your vehicle is inadequate. Car antennas are *not* simple. They do appear simple. They often appear to be a whip mounted above the fender. The way that fender whip is connected to the receiver is critical. Depending what type vehicle you have, the increase of sensitivity to 810 KHz could be to mount a stub atop the fender and connecting it to the receiver with a Low Capacity coax line. In addition, the receiver can be tuned at the place where the antenna connects to the first amplifer to maximize sensitivity to 810 KHz. Many new cars include an amplifier at the base of the antenna to increase sensitivity. Are you open to taking your car to a specialist to let them try to tune your "antenna" to your receiver? Jerry KD6JDJ |
improve S/N for AM car radio by a factor of 2...5...10?
wrote:
Presumably you mean 810 kHz. What is the source of the noise? Noise generated in the receiver is usually insignificant in the medium-wave band. If the cause is other transmissions on the same and nearby frequencies you may not gain much by changing the antenna, but a receiver with better channel (IF) filtering may help if there is any contribution from adjacent channels. If the noise is coming from your car (does it improve when you park in a rural area) then you may need to improve the RF suppression of its circuitry (e.g. ignition if it's a petrol engined car). I expect you can work out what tests would be needed to locate the principal sources of the noise. Chris Yes, KHz, sorry. The noise goes up several fold when I pass underneath bridges/pass big trucks, etc. Does this suggest that the noise is from other frequencies? Does it do this for KKOH as well? Try 780 and see if it exhibits similar behavior. If not, it's the KGO signal. They are pretty anemic to the East North East. http://www.fccinfo.com/CMDProEngine....49372&sHours=U |
improve S/N for AM car radio by a factor of 2...5...10?
On Mon, 19 Jan 2009 13:15:11 -0800 (PST),
wrote: I often listen while driving east on I-80 to Truckee/Tahoe for skiing and camping. Usually the signal fades substantially by the time I reach Sacramento - but it's still tolerable listening (by ear, S/N of ~3). Daytime coverage map: http://www.radio-locator.com/cgi-bin/pat?call=KGO&service=AM&status=L&hours=D 2.5, 0.5 and 0.15 mV/m contours. It still should be usable in Sacramento. Something is wrong. When you're in Sacramento, have some other driver try their vehicles AM radio on KGO and see if it's the same. If it's better, it's time to go shopping for a new radio or a new antenna system on your vehicle. In particular, try to find a real short wave radio with an ignition noise blanker, to use for the comparison. Also try it with the engine off and see if things improve. If all the other radios and conditions sound roughly the same, give up. Incidentally, there's usually an adjustable trimmer capacitor to tune the car antenna somewhere on the radio. It's usually hidden behind the volume or tuning dial (on older radios with dials) or right on the front panel on later model radios. Find a weak station and tune for maximum. Question: can I *substantially* improve the S/N - say, factor of 2/5/10 by installing a better car antenna, so that, say, I could listen in the Sierras day and night? No. Look at the map. You're in fringe-land in the Sierras. The only way that's going to work is if you get away from local noise sources (i.e. engines, get a decent antenna, and if propagation is in your favor). It's possible, but not guaranteed or reliable. Back when I was getting started in radio, I was a SWL (short wave listener) which included listening to distant AM broadcast stations. I could hear the world, but only at random times, not for very long, and certainly not with armchair listening quality. Strangely enough, some practice listening to a noisy AM station may actually improve the quality. I was out of radio for perhaps 15 years. When I dived back in, I couldn't understand anyone on the radio. It took about a month of listening to "tune" my ear so that I would mentally ignore the noise and interference. The same thing happened when I spent 10 years driving back and forth to Smog Angeles twice a month. I would listen to KSCO on the way. The more I listened, the better the station sounded. I do not care if the antenna is huge/geeky_looking, my car is being driven into the ground anyway. A big antenna may not help much. It will pickup more signal, but also more noise. The ratio of the signal to the noise will remain roughly constant, resulting in no net improvement. I have limited knowledge in electronics, my background mostly is in biophysics and biochemistry. So if you steer me into the right direction I think I should be able figure it out. You might look into satellite radio (XM/Sirius). They don't have KGO but might have equally useful or interesting programming. The nice part is that it works anywhere. On the other hand, if you don't need current listening, just have someone record a days worth of KGO in MP3 format, and play it on a cheap MP3 player. It may be a day late, but unless you're into the news, weather, traffic, or sports, it probably doesn't matter being a day late. Google Maps http://maps.google.com/maps?f=q&hl=en&q=37.52639,+-122.10056+(KGO-AM)&om=1 -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
improve S/N for AM car radio by a factor of 2...5...10?
On Mon, 19 Jan 2009 17:14:27 -0800, Jeff Liebermann
wrote: Daytime coverage map: http://www.radio-locator.com/cgi-bin/pat?call=KGO&service=AM&status=L&hours=D 2.5, 0.5 and 0.15 mV/m contours. It still should be usable in Sacramento. Something is wrong. Mo http://www.fcc.gov/fcc-bin/amq?list=0&facid=34471 http://www.fcc.gov/ftp/Bureaus/MB/Databases/AM_DA_patterns/249372-2649.pdf The antenna pattern is pretty much dead to the east and north-east. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
improve S/N for AM car radio by a factor of 2...5...10?
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improve S/N for AM car radio by a factor of 2...5...10?
wrote in message ... snip Question: can I *substantially* improve the S/N - say, factor of 2/5/10 by installing a better car antenna, so that, say, I could listen in the Sierras day and night? I do not care if the antenna is huge/geeky_looking, my car is being driven into the ground anyway. I would be happy to make this a DIY project - to save on $ and learn about radio. What kind of specs should I look for? I.e. I don't want to go on the web and blindly buy an antenna advertised to "boost" your AM radio reception - I would want some numbers. I have limited knowledge in electronics, my background mostly is in biophysics and biochemistry. So if you steer me into the right direction I think I should be able figure it out. I needed to abandon my van's fender-mount antenna because the shield ground broke and AM reception was pretty awful, with spark plug noise and assorted clicks and pops whenever I wasn't parked. I got a connector adapter which plugged into the antenna jack on the back of the radio. I connected a VHF magnetic mount ham radio antenna to it. I now have a cable running between the bucket seats and out the back door but I have really good AM/FM reception. On long trips, like across the southern deserts, I unscrew the standard element and replace it with a longer element (about 4') and AM reception is improved dramatically. The cable from the fender-mount antenna dangles inside the dashboard, unseen and unused. If you think you might tackle such a project, post again and I'll provide more details. Having a limited knowledge of electronics is not a problem; finding just the right parts is. "Sal" |
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 19, 7:14*pm, Jeff Liebermann wrote:
Daytime coverage map: http://www.radio-locator.com/cgi-bin/pat?call=KGO&service=AM&status=L... 2.5, 0.5 and 0.15 mV/m contours. *It still should be usable in Sacramento. *Something is wrong. Agree. The link below leads to an example of the noise on a weak, daytime AM signal received from WBBM, Chicago (50 kW non-D on 780 kHz) on a Sony ICF-2002 with its internal antenna, indoors in an urban location. The groundwave path from WBBM to the receiver is about 225 miles in length. According to the FCC propagation curves, WBBM has a daytime groundwave field intensity of about 0.14 mV/m for this path (probably less in an urban area). The noise in this MP3 clip maybe is tolerable for short-term listening, or if there is nothing better receivable. The recording was made Jan 10, 2009 at about 12:30 pm CST. http://www.datafilehost.com/download-18b37f18.html RF |
improve S/N for AM car radio by a factor of 2...5...10?
Richard Fry wrote:
On Jan 19, 7:14 pm, Jeff Liebermann wrote: Daytime coverage map: http://www.radio-locator.com/cgi-bin/pat?call=KGO&service=AM&status=L... 2.5, 0.5 and 0.15 mV/m contours. It still should be usable in Sacramento. Something is wrong. Agree. The link below leads to an example of the noise on a weak, daytime AM signal received from WBBM, Chicago (50 kW non-D on 780 kHz) on a Sony ICF-2002 with its internal antenna, indoors in an urban location. The groundwave path from WBBM to the receiver is about 225 miles in length. According to the FCC propagation curves, WBBM has a daytime groundwave field intensity of about 0.14 mV/m for this path (probably less in an urban area). In this situation a Select-A-Tenna will work wonders. No good for a car radio, however. http://www.old-fashioned-values.com/...ct-a-tenna.htm |
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 20, 7:58*am, Dave wrote:
Richard Fry wrote: On Jan 19, 7:14 pm, Jeff Liebermann wrote: Daytime coverage map: http://www.radio-locator.com/cgi-bin/pat?call=KGO&service=AM&status=L... 2.5, 0.5 and 0.15 mV/m contours. *It still should be usable in Sacramento. *Something is wrong. Agree. *The link below leads to an example of the noise on a weak, daytime AM signal received from WBBM, Chicago (50 kW non-D on 780 kHz) on a Sony ICF-2002 with its internal antenna, indoors in an urban location. *The groundwave path from WBBM to the receiver is about 225 miles in length. *According to the FCC propagation curves, WBBM has a daytime groundwave field intensity of about 0.14 mV/m for this path (probably less in an urban area). In this situation a Select-A-Tenna will work wonders. *No good for a car radio, however. http://www.old-fashioned-values.com/...enna_improve-a... On a lot of AM auto radios the SN ratio really stinks and an external preamp especially one with some preselection can really help. As previously stated on radios with adequate sigal to noise ratio adding a preamp just makes things worse. Jimmie |
improve S/N for AM car radio by a factor of 2...5...10?
I got a connector adapter which plugged into the antenna jack on the back
of the radio. I connected a VHF magnetic mount ham radio antenna to it. I now have a cable running between the bucket seats and out the back door but I have really good AM/FM reception. On long trips, like across the southern deserts, I unscrew the standard element and replace it with a longer element (about 4') and AM reception is improved dramatically. The cable from the fender-mount antenna dangles inside the dashboard, unseen and unused. I have done the same thing with a spare 2 meter 5/8 whip (without the base matching coil) on the roof with excellent results. The length is little longer than stock. I used to own an older European car that had a 3 section whip that was nearly 5' long fully extended and I wish I could find another. A 102" CB whip will do better on AM (although less optimal for FM). There used to be CB/AM/FM splitters for truckers, but I don't know how well they work. The stock whip is far short considering the wavelength, so the longest you can get on the car will only improve the capture area. As mentioned, you will notice a peak if you adjust the trimmer in the radio to your new antenna. They are usually peaked for 1300 kc anyway, so that might be something to toy with first if you don't mind sacrificing the high end of the band. An HF antenna with tuner would be the best you could do. In the campsite, you can clip a longwire on and throw it in the trees. |
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 20, 11:29*am, JIMMIE wrote:
On a lot of AM auto radios the SN ratio really stinks and an external preamp especially one with some preselection can really help. As previously stated on radios with adequate sigal to noise ratio adding a preamp just makes things worse. Jimmie I wouldn't say that. Most all the auto AM radios I've had were quite good. Always plenty of sensitivity as long as the antenna was functioning correctly. The current car I'm driving "Corolla" uses a small helically wound antenna, which is at the rear of the roof. It's pretty short overall, and I still have plenty of sensitivity. The daytime is the best time to check that, and I've never had any trouble receiving out of town stations. And if I tune to an open frequency, I hear background atmospheric noise, so any increase in sensitivity is pretty much useless. I've had older Delco radios in cars and the AM was excellent on those. If the OP can hear background noise when tuned to an empty frequency, and not have it sound "dead", adding more pre-amp is unlikely to help. I think the main culprit in this case is propagation, and the pattern of the array, and unfortunately, I think he's basically out of luck. Normally you would probably be able to hear the ground wave out to at least 200-300 miles in the daytime, but that assumes a fairly stout signal. If the pattern is away from that direction, even the ground wave possibilities start to look kind of bleak. If an auto AM radio does not have enough sensitivity, it usually means there is something wrong with it, or the antenna. Most as they come from the factory have more than enough. |
improve S/N for AM car radio by a factor of 2...5...10?
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improve S/N for AM car radio by a factor of 2...5...10?
Dave wrote:
wrote: On Jan 20, 11:29 am, JIMMIE wrote: The current car I'm driving "Corolla" uses a small helically wound antenna, which is at the rear of the roof. It's pretty short overall, and I still have plenty of sensitivity. Newer cars have active antennas. The helical on some antennas is for wind noise. |
improve S/N for AM car radio by a factor of 2...5...10?
I can speak from an experience I had.
I needed better reception on a car radio because I lived in a rural area. This was years ago but might still apply I installed a full height 1/4 wave cb whip antenna. I ran the same coax that came with the original antenna. My radio had a tuning capacitor in the back of it. I peaked for maximum signal. Voila, it was much better. If there is no tuning capacitor in the back of your radio, I suspect this fix will not work at all. wrote: Hi all, I've looked on the web, but with very little success. I have never posted to this group before, so I apologize if my question is lame. I listen to the Bay Area's KGO 810 MHz a lot. Their transmitter is located in South San Fran Bay near the Dumbarton Bridge, and outpus 50 kW (that's what they say anyway). I am guessing, it's directed mostly at the Pacific coast line. I often listen while driving east on I-80 to Truckee/Tahoe for skiing and camping. Usually the signal fades substantially by the time I reach Sacramento - but it's still tolerable listening (by ear, S/N of ~3). By the time I reach Auburn it's essentially inaudible. Much better signal at night (~again, by ear, S/N improves by ~2). At night, I can sort of pick up words in truckee. Question: can I *substantially* improve the S/N - say, factor of 2/5/10 by installing a better car antenna, so that, say, I could listen in the Sierras day and night? I do not care if the antenna is huge/geeky_looking, my car is being driven into the ground anyway. I would be happy to make this a DIY project - to save on $ and learn about radio. What kind of specs should I look for? I.e. I don't want to go on the web and blindly buy an antenna advertised to "boost" your AM radio reception - I would want some numbers. I have limited knowledge in electronics, my background mostly is in biophysics and biochemistry. So if you steer me into the right direction I think I should be able figure it out. |
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 20, 8:30*pm, Dave wrote:
wrote: On Jan 20, 11:29 am, JIMMIE wrote: The current car I'm driving "Corolla" uses a small helically wound antenna, which is at the rear of the roof. It's pretty short overall, and I still have plenty of sensitivity. Newer cars have active antennas. I don't think mine is, but I'm not sure. It's basically the same setup as any other antenna, just the whip is shorter, and helically wound, I suppose for tuning purposes. I guess it's about 15 or so inches long. I'd have to measure it. Of course, it also functions for FM too. |
improve S/N for AM car radio by a factor of 2...5...10?
"Michael" ha scritto nel messaggio . .. is no tuning capacitor in the back of your radio, I suspect this fix will not work at all. Nobody prevent you to add it externally, i think. BTW... curious to know if any ferrite antenna or 2x ferrite antennas in a sort of cross-coupled way mounted in a waterproof container perform better than whips. I goggled, but can't find a gain table for ferrite antennas vs. dipole, or a medium dBI gain (negative, i suppose) for ferrite antennas mounted into the commons consumer radios. Chris, -.-. --.- |
improve S/N for AM car radio by a factor of 2...5...10?
"-.-. --.-" wrote in message ... "Michael" ha scritto nel messaggio . .. is no tuning capacitor in the back of your radio, I suspect this fix will not work at all. Nobody prevent you to add it externally, i think. BTW... curious to know if any ferrite antenna or 2x ferrite antennas in a sort of cross-coupled way mounted in a waterproof container perform better than whips. I goggled, but can't find a gain table for ferrite antennas vs. dipole, or a medium dBI gain (negative, i suppose) for ferrite antennas mounted into the commons consumer radios. Chris, -.-. --.- Amongst several other factors, it depends how you combine the signals from two crossed ferrite rods/coils - simple in-phase addition of their signals won't yield a radiation pattern that is omni-directional in the horizontal plane. Magnetic antennas are sometimes considered beneficial for mobile reception of medium/lomg-wave signals because they can be made insensitive to electric fields, and evidence can be found of greater fluctuation of the electric field of the wanted signal vs. the magnetic component. Also, some forms of interference are found to present stronger electric fields than magnetic ones. However, obtaining the requisite omni pattern isn't trivial. Chris |
improve S/N for AM car radio by a factor of 2...5...10?
christofire wrote:
Magnetic antennas are sometimes considered beneficial for mobile reception of medium/lomg-wave signals because they can be made insensitive to electric fields, ... A magnetic antenna was used in all of the California 75m mobile antenna shootouts that I attended. I was told it was to keep the close-by human bodies from having an effect on the strength of the received signals. Which leads me to a question: Most of us OFs have witnessed the effects of human bodies on analog VHF TV signals being received using rabbit ears. If we used "magnetic rabbit ears", would the problem go away? Is it only the electric field that varies when an EM signal passes through a non-magnetic medium like a human body - or a tree? -- 73, Cecil http://www.w5dxp.com |
improve S/N for AM car radio by a factor of 2...5...10?
"Cecil Moore" wrote in message ... christofire wrote: Magnetic antennas are sometimes considered beneficial for mobile reception of medium/lomg-wave signals because they can be made insensitive to electric fields, ... A magnetic antenna was used in all of the California 75m mobile antenna shootouts that I attended. I was told it was to keep the close-by human bodies from having an effect on the strength of the received signals. Which leads me to a question: Most of us OFs have witnessed the effects of human bodies on analog VHF TV signals being received using rabbit ears. If we used "magnetic rabbit ears", would the problem go away? Is it only the electric field that varies when an EM signal passes through a non-magnetic medium like a human body - or a tree? -- 73, Cecil http://www.w5dxp.com I understand it becomes increasingly difficult to create a purely-magnetic antenna as the frequency rises, and ferrite with the required properties becomes progressively more expensive! Some VHF pagers used ferrite rods, and one or two-turn coils. Screened one-turn loops are used in the short-wave bands, by some amateurs as well as by the military (e.g. British Royal Navy). Chris |
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 21, 12:12*pm, "christofire" wrote:
I understand it becomes increasingly difficult to create a purely-magnetic antenna as the frequency rises, and ferrite with the required properties becomes progressively more expensive! *Some VHF pagers used ferrite rods, and one or two-turn coils. *Screened one-turn loops are used in the short-wave bands, by some amateurs as well as by the military (e.g. British Royal Navy). Chris The way I look at it, there is no such thing as a "magnetic" antenna. As an example, some call shielded single turn loops "magnetic" antennas. They claim special properties such as lower noise reception. But this is not the case. They receive the same s/n ratio as any other single turn loop. The only advantage the shield provides is inherently good balance. Good balance improves the depth of the nulls. But you can construct plain wire single turn loops to have just as good balance if you use good construction. I've side by side compared the two, and came to the conclusion most of the theories about shielded or so called magnetic loops to basically be a myth. |
improve S/N for AM car radio by a factor of 2...5...10?
wrote:
The way I look at it, there is no such thing as a "magnetic" antenna. Given that a transmitting dipole and a receiving dipole transfer maximum signal when oriented in the same plane, how does one explain a ferrite loop antenna receiving maximum signal in a plane orthogonal to the transmitting dipole? -- 73, Cecil http://www.w5dxp.com |
improve S/N for AM car radio by a factor of 2...5...10?
"Cecil Moore" wrote in message ... wrote: The way I look at it, there is no such thing as a "magnetic" antenna. Given that a transmitting dipole and a receiving dipole transfer maximum signal when oriented in the same plane, how does one explain a ferrite loop antenna receiving maximum signal in a plane orthogonal to the transmitting dipole? -- 73, Cecil http://www.w5dxp.com Ampere's circuital law and the well-known 'right-hand rule'. Chris |
improve S/N for AM car radio by a factor of 2...5...10?
wrote in message ... On Jan 21, 12:12 pm, "christofire" wrote: I understand it becomes increasingly difficult to create a purely-magnetic antenna as the frequency rises, and ferrite with the required properties becomes progressively more expensive! Some VHF pagers used ferrite rods, and one or two-turn coils. Screened one-turn loops are used in the short-wave bands, by some amateurs as well as by the military (e.g. British Royal Navy). Chris The way I look at it, there is no such thing as a "magnetic" antenna. As an example, some call shielded single turn loops "magnetic" antennas. They claim special properties such as lower noise reception. But this is not the case. They receive the same s/n ratio as any other single turn loop. The only advantage the shield provides is inherently good balance. Good balance improves the depth of the nulls. But you can construct plain wire single turn loops to have just as good balance if you use good construction. I've side by side compared the two, and came to the conclusion most of the theories about shielded or so called magnetic loops to basically be a myth. I believe the issue is that if an open loop isn't perfectly balanced then it will respond to an electric field, acting as a monopole. Then, when the loop is oriented so the magnetic field of a signal should be in one of its nulls, the cancellation may be incomplete because of sensivity to the electric field component of that signal. Screening the loop overcomes this effect so it could be claimed that screening improves the balance, although this isn't what's really happening. With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal and to record their strengths at different locations. This can reveal significant differences on account of building and electrical clutter, but only if the loop is adequately screened. No myth! Chris |
improve S/N for AM car radio by a factor of 2...5...10?
On Thu, 22 Jan 2009 01:06:28 -0000, "christofire"
wrote: With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal and to record their strengths at different locations. This can reveal significant differences on account of building and electrical clutter, but only if the loop is adequately screened. No myth! What you describe is a direction finding system with a general antenna that can be switched in to sniff for a transmitter to take a bearing on. A commonplace design for this application. The loops are no more screened than any other, and careful observation of their construction details would reveal the necessary break in the screen which serves for balance only. Any claims to magnetic field separation are, as Mark well put it, a myth. The only way you could achieve this separation is by traveling at the speed of light with your antenna in that magnetic field, at its 90 degree peak to the electric field null. This reduces the topic from the status of myth to that of absurd. 73's Richard Clark, KB7QHC |
improve S/N for AM car radio by a factor of 2...5...10?
On Jan 21, 3:11*pm, Cecil Moore wrote:
wrote: The way I look at it, there is no such thing as a "magnetic" antenna. Given that a transmitting dipole and a receiving dipole transfer maximum signal when oriented in the same plane, how does one explain a ferrite loop antenna receiving maximum signal in a plane orthogonal to the transmitting dipole? -- 73, Cecil *http://www.w5dxp.com I'm not sure without looking into it, but I notice this with both shielded, and unshielded loops. As an example, my 44 inch per side 5 turn diamond loop prefers to be fed horizontally vs vertically when receiving MW stations which use a vertical transmit antenna. IE: I feed it at the middle lowest corner. If I feed it at a side corner, which would be vertically fed, I seem to remember it not working near as well. Do you consider an open small loop "unshielded" a "magnetic" antenna? Some do, but I tend not to. They act the same as the shielded loops that many seem to call "magnetic" antennas. The ability to respond to mostly the magnetic field vs the electric field only pertains to the very near field within about 1/10 wavelength. Within 1 wavelength they often respond more to the electrical wave. In the far field they should respond to both fields the same as any other antenna. Or this is my current understanding anyway.. :/ So using any type of "magnetic" antenna for the OP's purpose would seem to be a waste of time unless they are trying to reduce noise pickup that is within 1/10 of a wavelength away. I know myself that these small loops are still quite capable of picking up local noise, just like most any other antenna. The only advantage are the sharp nulls which you use to get rid of said noise. If your mobile tests were within 1/10 of a wave, maybe it makes more sense. But I'm not sure if I can see any advantage to trying to receive a far field signal vs any other antenna unless the nulls are useful. |
improve S/N for AM car radio by a factor of 2...5...10?
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improve S/N for AM car radio by a factor of 2...5...10?
"Richard Clark" wrote in message ... On Thu, 22 Jan 2009 01:06:28 -0000, "christofire" wrote: With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal and to record their strengths at different locations. This can reveal significant differences on account of building and electrical clutter, but only if the loop is adequately screened. No myth! What you describe is a direction finding system with a general antenna that can be switched in to sniff for a transmitter to take a bearing on. A commonplace design for this application. No, the loops were commutated in order to provide an omni-direction pattern in the horizontal plane and the receiver was switched between the loops and whip to measure H and E. This was used to establish for medium and long-wave broadcasting stations (in the UK) the field strength and receivability on ferrite-rod antennas. The loops are no more screened than any other, and careful observation of their construction details would reveal the necessary break in the screen which serves for balance only. The loop has to be split at some point to prevent it acting as a shorted turn - the splits were at the top in this case. Any claims to magnetic field separation are, as Mark well put it, a myth. The only way you could achieve this separation is by traveling at the speed of light with your antenna in that magnetic field, at its 90 degree peak to the electric field null. In a normal single, plane-polarised, far-field TEM radio wave the peaks of E and H occur at the same places and the same times, and the nulls of E and H occur at the same places and the same times. The peaks of both correspond to the peaks of current in the transmitting antenna by which they were generated, and the nulls of both correspond to the zero-crossings of the current. If you believe something is radiated in the far field when the current in the antenna is zero I would be intrigued to hear an explanation. This reduces the topic from the status of myth to that of absurd. You're entitled to your opinion. Chris 73's Richard Clark, KB7QHC |
improve S/N for AM car radio by a factor of 2...5...10?
wrote:
On Jan 21, 3:11 pm, Cecil Moore wrote: Given that a transmitting dipole and a receiving dipole transfer maximum signal when oriented in the same plane, how does one explain a ferrite loop antenna receiving maximum signal in a plane orthogonal to the transmitting dipole? I'm not sure without looking into it, but I notice this with both shielded, and unshielded loops. I'm not talking about coaxial loops. I'm talking about coils of wire wrapped around a ferrite rod typical of AM radios. Seems pretty obvious it is responding to the magnetic field when it needs to be at right angles to the transmitting monopole (or dipole). -- 73, Cecil http://www.w5dxp.com |
improve S/N for AM car radio by a factor of 2...5...10?
On Thu, 22 Jan 2009 10:19:14 -0000, "christofire"
wrote: "Richard Clark" wrote in message .. . On Thu, 22 Jan 2009 01:06:28 -0000, "christofire" wrote: With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal and to record their strengths at different locations. This can reveal significant differences on account of building and electrical clutter, but only if the loop is adequately screened. No myth! What you describe is a direction finding system with a general antenna that can be switched in to sniff for a transmitter to take a bearing on. A commonplace design for this application. No, the loops were commutated in order to provide an omni-direction pattern in the horizontal plane and the receiver was switched between the loops and whip to measure H and E. This was used to establish for medium and long-wave broadcasting stations (in the UK) the field strength and receivability on ferrite-rod antennas. The description you offer in rebuttal says nothing of field separation. The commutation discussion imparts nothing to the physical relationship of the wave. The remainder of the description doesn't actually describe any physical/geometric relationship to the wave at all. Physics in the UK are not different from the rest of the world. The loops are no more screened than any other, and careful observation of their construction details would reveal the necessary break in the screen which serves for balance only. The loop has to be split at some point to prevent it acting as a shorted turn - the splits were at the top in this case. This, too, is merely conventional design then. You haven't described anything out of the ordinary, and the ordinary (spanning centuries) has not shown the attributes you describe as field separation. You're entitled to your opinion. As are you, but this isn't rec.radio.amateur.antenna.polls and you haven't gone beyond unsubstantiated claims. If the necessity of proof for your claims were set aside, Nature still demands that noise and signal still arrive by the same mechanism and any invention that separates fields must apply them equally to both sources - returning us to the conventional observation that S/N hasn't changed one bit. The net result of this is that you have provided unsubstantiated claims for an useless invention. Any value it may have comes by conventional means. 73's Richard Clark, KB7QHC |
improve S/N for AM car radio by a factor of 2...5...10?
Richard Clark wrote:
On Thu, 22 Jan 2009 10:19:14 -0000, "christofire" wrote: "Richard Clark" wrote in message ... On Thu, 22 Jan 2009 01:06:28 -0000, "christofire" wrote: With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal and to record their strengths at different locations. This can reveal significant differences on account of building and electrical clutter, but only if the loop is adequately screened. No myth! What you describe is a direction finding system with a general antenna that can be switched in to sniff for a transmitter to take a bearing on. A commonplace design for this application. No, the loops were commutated in order to provide an omni-direction pattern in the horizontal plane and the receiver was switched between the loops and whip to measure H and E. This was used to establish for medium and long-wave broadcasting stations (in the UK) the field strength and receivability on ferrite-rod antennas. The description you offer in rebuttal says nothing of field separation. The commutation discussion imparts nothing to the physical relationship of the wave. The remainder of the description doesn't actually describe any physical/geometric relationship to the wave at all. Physics in the UK are not different from the rest of the world. The loops are no more screened than any other, and careful observation of their construction details would reveal the necessary break in the screen which serves for balance only. The loop has to be split at some point to prevent it acting as a shorted turn - the splits were at the top in this case. This, too, is merely conventional design then. You haven't described anything out of the ordinary, and the ordinary (spanning centuries) has not shown the attributes you describe as field separation. You're entitled to your opinion. As are you, but this isn't rec.radio.amateur.antenna.polls and you haven't gone beyond unsubstantiated claims. If the necessity of proof for your claims were set aside, Nature still demands that noise and signal still arrive by the same mechanism and any invention that separates fields must apply them equally to both sources - returning us to the conventional observation that S/N hasn't changed one bit. The net result of this is that you have provided unsubstantiated claims for an useless invention. Any value it may have comes by conventional means. 73's Richard Clark, KB7QHC Hi Richard, Are your powers of perception waning by any chance? Your correspondent deserves more credit than you're allowing him. As far as I've seen in this thread, you're the only one talking about 'field delamination' or such things. As you said, what he is talking about is purely conventional. And clever. That you apparently don't completely understand what he is saying is no fault of his. 73, ac6xg |
improve S/N for AM car radio by a factor of 2...5...10?
On Thu, 22 Jan 2009 11:18:03 -0800, Jim Kelley
wrote: Are your powers of perception waning by any chance? Your correspondent deserves more credit than you're allowing him. As far as I've seen in this thread, you're the only one talking about 'field delamination' or such things. Perhaps you powers of perception did not perceive this: On Thu, 22 Jan 2009 01:06:28 -0000, "christofire" wrote: With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal Returning to your complaint: That you apparently don't completely understand what he is saying is no fault of his. As christofire's quote above is his and not mine, and neither you nor he has explained it, my comprehension is not tested beyond what his unconventional statement has offered. If he cannot explain it, then the fault is not with me. Challenging blank assertions is not unusual here. Perhaps you mis-perceived: On Thu, 22 Jan 2009 01:06:28 -0000, "christofire" wrote: The way I look at it, there is no such thing as a "magnetic" antenna. because, in fact due to christofire's poor quotation practice, this statement is Mark's and one that I fully concur with and stated so. 73's Richard Clark, KB7QHC |
improve S/N for AM car radio by a factor of 2...5...10?
Richard Clark wrote:
On Thu, 22 Jan 2009 11:18:03 -0800, Jim Kelley wrote: Are your powers of perception waning by any chance? Your correspondent deserves more credit than you're allowing him. As far as I've seen in this thread, you're the only one talking about 'field delamination' or such things. Perhaps you powers of perception did not perceive this: On Thu, 22 Jan 2009 01:06:28 -0000, "christofire" wrote: With a pair of screened loops and a whip it is possible to receive separately the magnetic and electric fields associated with a radio signal I perceive that the quote says nothing about "field separation" - whatever that is. Since it's a term that you employed, perhaps you can explain what you mean by it and clear up the whole thing. Thanks, ac6xg |
improve S/N for AM car radio by a factor of 2...5...10?
On Thu, 22 Jan 2009 13:43:19 -0800, Jim Kelley
wrote: separately the magnetic and electric fields associated with a radio signal I perceive that the quote says nothing about "field separation" - Now that is getting "précis." 73's Richard Clark, KB7QHC |
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