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Receiving Loop Antenna Question
On Jan 26, 5:22*pm, "Dave" wrote:
"christofire" wrote in message ... I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; and be glad that you don't understand it! *its pure bafflegab, unless you really like magical levitating diamagnetic neutrinos that hop off the antenna to make em waves. David Your accusations doesn't bother me. After all, you got a degree by memorising the books without checking from first principles for yourself. Choosing from a,b,c or d is a similar short cut for education without the application of personal intelligence It would be suicidal for any student to not parrot phrases and teachings ennunciated by their professor. He is the one who reads your work and determines whether you have earned a degree or not, thus conformity is a requirement. When you stated that statics has no place with respect to radiation or words to that effect it was understandable for me as the aproach that I ventured is not covered in any of the books presently being published. The point that all should know is that you cannot build a castle on sand, or in other words, all theories must rest on a sound foundation or findings and since your degree was obtained by being a follower your reaction to that which is not in compliance with the books of the day is perfectly understandable Take care Art Unwin KB9MZ.......xg (uk) |
Receiving Loop Antenna Question
On Jan 26, 2:40*pm, Art Unwin wrote:
On Jan 26, 1:59*pm, "christofire" wrote: "Art Unwin" wrote in message .... On Jan 26, 12:16 pm, "christofire" wrote: "Art Unwin" wrote in message 8 Chris First of all thank you very much for the effort that you placed in your response. It really what I expected from you after reading your profile ie the anbsence of derision. Now I am not fully convinced with your response as the rest of the newsgroup already suspect Coming from a different direction with respect to mathematics, when adding a timevarying field to a Gaussian field it equates in every way to the laws of Maxwell. Both of these laws I consider as an absolute truth. The above therefore states that the presence of particles is undeniable in the generation of RF communication. Because of the specificity of a state of equilibrium in a Gaussian field the following can be stated. A radiator or array can be any size, shape or varied elevation ..............AS LONG AS IT IS IN A STATE OF EQUILIBRIUM From the above ground rules which is confirmed by Maxwells laws the single winding of a wire is NOT in equilibrium unless the lumped properties are cancelled which leaves a structure that is in equilibrium ala wire that is conductive and with no other properties other that he addition of distributed loads that are common from a conductor. Your response is based on the generation of fields without which the radiator cannot receive by incoming waves from a transmitter, Where as my response is based on the basis of particles impinging on a receive antenna to create oscillation. The biggest difference is the interpretation of a tank circuit( a circuit in equilibrium) where in *the perfect case of zero friction your aproach would define this operation as a zero tx/rc element My interpretation is that it cannot be zero friction even if the distributed components were friction free because of the presence of particles, which must be impelled by force to another radiator to create oscillation. So to sum up *Your aproach is from dissipating fields to provide communication and mine is from non dissipating fields that dislodge particles as it rotates to and from the distributed loads using both as energy retainers.. As I have stated before, this is a presently a widely known method in a macro *re enactment of salvage processes *that sorts materials by directional magnetic field thrusts provided by eddy fields I do need more time to study your response to see the difference between the field aproach and the particle aproach tho with my present circumstances I may not be able to determine. Again, thankyou for your gentlemanly response, a rarity in this particular newsgroup. Regards Art You're welcome. I can't say I understand much of what you've written above but I'm sure there are often many ways to visualise the same physical process; the wave/particle duality of EM radiation being one often spoken about. *For this case, I wrote from the viewpoint of the work reported in a large number of text books: the set of principles that's passed on at universities and has been used to design the vast majority of antennas that have been used since the discovery of radio. *I'm not aware of any successful antenna designs, operating lower than EHF, based on a particle theory of electromagnetic radiation. *However I am aware of a few unsuccessful designs (e.g. the 'crossed-field antenna') for which the creators have purported to re-write the known (wave) theory of radiation. I know it's generally bad to generalise (!) but it seems clear to me, and probably many others, that antennas based on well-documented, well-understood, theory are always a safer bet! *They certainly are in (most lines of) business where cost matters - but perhaps not in amateur circles where different motives apply. Chris Understood I have an applied patent that is on the net somewhere that goes thru these same motions to obtain an array inequilibrim whbich are then displayed via the AO pro program whiuch confirms the equilibrium theoryn that is obtained by the Gaussian field aproach on Maxwells laws. On the same patent request I provided an analysis of a verticle dipole which for maximum gain is tipped with reference to earth. The tipping force is the weak force or the eddy field I spoke of which is not included in programs associated with planar forms that are based on intercoupling coupling. The same aproach can also be applied using the equilibrium requirement as I proposed earlier. The only problem I can see in using MOM programs is the validity of close spaced conduntors where it is possible to conceive of interfering eddy currents not impinging upon particles, but it terms of receiving there is nothing to prevent the impact of particles on the radiator. At present my tower antenna is made of circularly wound wires in both the cw and ccw direction, again based on the equilibrium finding, where the antenna is a travelling wave form that is end fed which allows for smaller volume antennas to those presently known. Everything revolves around the extended Gaussion theorem which equates to Maxwell's laws with the addition of particles within a boundary in equilibrium. Break that association down then all of mine falls apart. I will place a dual wound helix on my page in the next couple of days that is produced via the AOP Minninec program for antennas by Beasely so that you can see it for your self. It will not be completely accurate as such an arrangement requires many more point calculations than I have available to me. Will be at hospital all day tomorrow so please be patient on my page issue. Best regards Art ok Chris I have to get ready for an operation early tomorrow so I collected some stuff from the past and just put it into a package for my son to post for me. It will at least give you some stuff to look at until I get back. The important thing to remember is all other polarizations are always 3db down from 'max gain' and with only one circular direction with horiz and vert. The object is to choose the polarization required which you are aiming for to get the purest of radiation which helps in the reflected signal when searching for weather abnormalities at airports such as wind shear with minimum distortion. Sorry I could not plan the offering so I have not vetted what is posted See....,. http://users.sdsc.edu/~unwin/ Best regards Art unwin KB9MZ.......xg (uk) |
Receiving Loop Antenna Question
What about ribbon cable? I've got a fair length of ribbon cable
(something like 25 wires - the sort used in PCs to connect hard drives and the like) put away for a rainy-day loop antenna project. While I could make one large loop using all 25 wires for the really low frequencies, I'll almost certainly cut it up and make several smaller loops with fewer wires for the higher frequencies. -- Ian- Hide quoted text - Hello Ian, I have used 16 core ribbon cable, with each core connected in series for an AM broadcast band loop antenna. It was about 1 metre long in circumference which gave me a total length of 16 metres. I used a cheap tuning variable capacitor with a switch which connected another capacitor to increase the total capacitance so I could tune down to the bottom of the AM band. It is coupled through the internal ferrite antenna in the radio. On my main tuner in the house, it has connections for an antenna on the back, so I made another ribbon cable loop antenna and put a single wire with it as a pick up wire. Each end of the pick up wire is connected to the antenna inputs on the tuner. I have made four of them. They are easily made, not too fiddly and they work well. Cheers Max |
Receiving Loop Antenna Question
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Receiving Loop Antenna Question
On Wed, 28 Jan 2009 13:03:45 -0000, "christofire"
wrote: My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Hi All, The strong signal issue goes well beyond the possibility of conduction. When you think about a voltage controlled capacitor, you have to account for the effects of the voltage of the signal you are tuning (and those you are not tuning). The BB212 application is found characterized for signal levels less than 100mV (typically far less). Why? A half volt signal level at the terminals of the device (taking the BB212 for example) biased at 1V will swing the capacitance 100pF above and below where it would be thought to be tuned. Of course, correspondingly smaller signals have correspondingly smaller swings - it all depends on how much you can tolerate. This swing is also a problem for PIN diodes used as voltage variable attenuators. 73's Richard Clark, KB7QHC |
Receiving Loop Antenna Question
In message , Richard Clark
writes On Wed, 28 Jan 2009 13:03:45 -0000, "christofire" wrote: My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Thanks for the advice, however...... Hi All, The strong signal issue goes well beyond the possibility of conduction. When you think about a voltage controlled capacitor, you have to account for the effects of the voltage of the signal you are tuning (and those you are not tuning). The BB212 application is found characterized for signal levels less than 100mV (typically far less). Why? A half volt signal level (that's surely one hell of an RF signal?) at the terminals of the device (taking the BB212 for example) biased at 1V will swing the capacitance 100pF above and below where it would be thought to be tuned. Of course, correspondingly smaller signals have correspondingly smaller swings - it all depends on how much you can tolerate. Varicap diodes will always suffer from having their capacitance modulated by an RF signal impressed upon them. However, they do seem to work well enough - even when the RF level is pretty high (which must be the case especially with varicap-tuned oscillators - ie most VCOs and PLL systems). Presumably, the effect of this modulation will be to generate intermodulation products. In VCOs, this will simply appear as harmonics of the oscillator signal (which you would get anyway - even with a conventional tuning capacitor). Where multiple-frequency signals are present (like you have with the receiving loop), the most apparent effect of the modulation of the diode capacity will appear as crossmodulation and other nasties on the other signals in the passband. However, as varicaps ARE used for the tuning of the input of receiver RF stages, how do they 'get away with it'? This swing is also a problem for PIN diodes used as voltage variable attenuators. My understanding of things is that the effectiveness of PIN diodes relies on them having a very poor performance at RF (especially at VHF and UHF). In attenuator circuits, they are forward biassed, and the DC current passing through them varies their RF resistance. However, the charges flowing through the junction are so 'sluggish' that they don't react to the rapidly-changing RF voltages. There is therefore negligible modulation of the RF resistance by the RF signals passing though them. -- Ian |
Receiving Loop Antenna Question
"Richard Clark" wrote in message ... On Wed, 28 Jan 2009 13:03:45 -0000, "christofire" wrote: My next question is about using varicap diodes to tune the loop. Most designs use a conventional capacitor, but a varicap would enable the loop to be located (say) in the loft, and the tuning varied from the shack downstairs. Is this technology worth perusing (ie Googling)? Or has it been found to be a waste of time? Varicaps are fine and you will find devices containing pairs like the BB212, specifically intended for tuning domestic receivers. They're used in all the modern radios that are digitally controlled. The trick is to use them in balanced pairs so strong signals don't push a single diode into conduction. Hi All, The strong signal issue goes well beyond the possibility of conduction. When you think about a voltage controlled capacitor, you have to account for the effects of the voltage of the signal you are tuning (and those you are not tuning). The BB212 application is found characterized for signal levels less than 100mV (typically far less). Why? A half volt signal level at the terminals of the device (taking the BB212 for example) biased at 1V will swing the capacitance 100pF above and below where it would be thought to be tuned. Of course, correspondingly smaller signals have correspondingly smaller swings - it all depends on how much you can tolerate. This swing is also a problem for PIN diodes used as voltage variable attenuators. 73's Richard Clark, KB7QHC Hi Richard I made a capacitator rotator for my 6 foot AM loop using a hobby shop servo to rotate the air variable cap. It works quite well and the components are affordable. The 3 section air capacitor allowed the use of each section by switching to the appropriate section with a TO-5 relay. That is Brute Force to tune an AM loop, but sure makes sense and uses affordable parts. Jerry KD6JDJ |
Receiving Loop Antenna Question
On Wed, 28 Jan 2009 20:12:15 +0000, Ian Jackson
wrote: Thanks for the advice, however...... Why? A half volt signal level (that's surely one hell of an RF signal?) I can see you don't know what environment you are living in. That, or you live out in a pastoral setting and the house has no significant RF contribution. Most of the world is urbanized and folks live within short distances of large transmitters. Varicap diodes will always suffer from having their capacitance modulated by an RF signal impressed upon them. However, they do seem to work well enough - even when the RF level is pretty high (which must be the case especially with varicap-tuned oscillators - ie most VCOs and PLL systems). You don't put the Varicap into the high level part of the circuit. This is obvious from the outset. Presumably, the effect of this modulation will be to generate intermodulation products. In VCOs, this will simply appear as harmonics of the oscillator signal (which you would get anyway - even with a conventional tuning capacitor). A conventional cap (and a conventional inductor, much less) will not contribute harmonics because it is linear. Harmonics comes from nonlinear components added by the circuit (partial conduction of an active component that aids in the oscillation). Where multiple-frequency signals are present (like you have with the receiving loop), the most apparent effect of the modulation of the diode capacity will appear as crossmodulation and other nasties on the other signals in the passband. However, as varicaps ARE used for the tuning of the input of receiver RF stages, how do they 'get away with it'? They don't if you are in such an environment. Again, if you don't know your environment, then it's all a crap shoot. There is no "getting away with it." The alternative is that the designer of a product fully anticipated these issues and purposely chose a design that minimized the effect of accidental contributions. Not all designers are up to speed on the topic. The web is full of reported failed projects that do not take bias Z and filtering into consideration. This swing is also a problem for PIN diodes used as voltage variable attenuators. My understanding of things is that the effectiveness of PIN diodes relies on them having a very poor performance at RF (especially at VHF and UHF). In attenuator circuits, they are forward biassed, and the DC current passing through them varies their RF resistance. However, the charges flowing through the junction are so 'sluggish' that they don't react to the rapidly-changing RF voltages. There is therefore negligible modulation of the RF resistance by the RF signals passing though them. Poor performance when a PIN diode is first and foremost a diode for RF and microwave applications? Only if you are using it for the wrong reason (like using a 1N23 for 120V 60HZ power rectification). PIN diodes are used as resistors and switches, not rectifiers. Further, don't confuse the switch application as meaning fast turn-off in the pico-to-subnanoseconds. Speed is relative to the application of signal path steering where 100s of nanoseconds is more than adequate. Consult: http://www.ieee.li/pdf/pin_diode_handbook.pdf 73's Richard Clark, KB7QHC |
Receiving Loop Antenna Question
On Wed, 28 Jan 2009 20:19:20 GMT, "Jerry"
wrote: Hi Richard I made a capacitator rotator for my 6 foot AM loop using a hobby shop servo to rotate the air variable cap. It works quite well and the components are affordable. The 3 section air capacitor allowed the use of each section by switching to the appropriate section with a TO-5 relay. That is Brute Force to tune an AM loop, but sure makes sense and uses affordable parts. Jerry KD6JDJ Hi Jerry, You have certain advantages over most of the correspondents here. You are something of a gear head, you know where to find things, you know how to put them together, and you actually do it. When I was a kid, I had the same bent, but my resources were from government surplus when you needed 400Hz 26V supplies (or other such oddities). It was back in the 60s when I started experimenting with Varicaps except they were 1N23 style diodes sold for their Varicap properties (which comes free with almost any diode); the real Varicaps sold for far too much for my allowance. Wasn't much tuning ratio back then either - about 3:1 to 5:1 - today's have more range than most air caps. 73's Richard Clark, KB7QHC |
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