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#21
February 20th 07, 03:13 AM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Mon, 19 Feb 2007 12:43:12 -0800, Frank Gilliland
wrote: +++On Mon, 19 Feb 2007 19:12:33 GMT, james wrote +++in : +++ +++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland wrote: +++ ++++++Conjugate match is needed for maximum power transfer. ++++++ ++++++ ++++++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is ++++++when the impedances are complex, which isn't always the case. +++*********** +++ +++I have found that it is rare in the real world that impeadances are +++not complex. Outside transimission lines, there is little that is not +++complex. +++ +++ +++You just said that resistors have complex impedance and transmission +++lines are flat. +++ ************ No I did not. Besides Resistors can have complex impedances depending upon constrtuctinand frequency in which they are used. +++ +++ Then again when you conjugate match, the imaginary part of +++the complex impedances is nulified and you are then left with the real +++part. +++ +++ +++Reactances don't just disappear. They create a current between the +++source and load that must be assessed to see if it is going to cause +++any problems. Sometimes it doesn't and sometimes it does. +++ +++ *********** I did not say they disappeared. At resonance the conjugate match causes the net reactance to be zero. Thus nulify. The reactance are always there. james |
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#22
February 20th 07, 06:52 AM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Tue, 20 Feb 2007 03:13:52 GMT, james wrote
in : On Mon, 19 Feb 2007 12:43:12 -0800, Frank Gilliland wrote: +++On Mon, 19 Feb 2007 19:12:33 GMT, james wrote +++in : +++ +++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland wrote: +++ ++++++Conjugate match is needed for maximum power transfer. ++++++ ++++++ ++++++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is ++++++when the impedances are complex, which isn't always the case. +++*********** +++ +++I have found that it is rare in the real world that impeadances are +++not complex. Outside transimission lines, there is little that is not +++complex. +++ +++ +++You just said that resistors have complex impedance and transmission +++lines are flat. +++ ************ No I did not. Go back and read your own words again. Besides Resistors can have complex impedances depending upon constrtuctinand frequency in which they are used. When a resistor is used at its intended frequency, any reactance is insignificant. If it wasn't then it would be called an 'inductor' or 'capacitor'. +++ +++ Then again when you conjugate match, the imaginary part of +++the complex impedances is nulified and you are then left with the real +++part. +++ +++ +++Reactances don't just disappear. They create a current between the +++source and load that must be assessed to see if it is going to cause +++any problems. Sometimes it doesn't and sometimes it does. +++ +++ *********** I did not say they disappeared. At resonance the conjugate match causes the net reactance to be zero. Thus nulify. The reactance are always there. Notwithstanding the fact that the non-reactive component of impedance changes at or near resonance, maximum power transfer (due to matched impedances) occurs regardless of whether those impedances are reactive or not. Hence "impedance match" instead of the more limited "conjugate match". As for your assertion that non-reactive impedances are rare in the "real world", maybe you should describe -your- "real world" and how it differs from the rest of reality. |
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#23
February 20th 07, 06:52 PM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Mon, 19 Feb 2007 22:52:40 -0800, Frank Gilliland
wrote: +++Notwithstanding the fact that the non-reactive component of impedance +++changes at or near resonance, maximum power transfer (due to matched +++impedances) occurs regardless of whether those impedances are reactive +++or not. Hence "impedance match" instead of the more limited "conjugate +++match". As for your assertion that non-reactive impedances are rare in +++the "real world", maybe you should describe -your- "real world" and +++how it differs from the rest of reality. ********** I am not saying that the real portion of impendances are rare. I am saying that pure resistance is but a subset of complex impedance. Pure resistance is where the reactive part of the complex impedance is zero. In the real world no component has a "zero" reactive component as does it not have zero resistive part. In conjugate matching, the nodal point where the output of the transform network terminates with the load will have a net reactance of zero. The real part is still there. It does not go away. The net real part should be half that of the real part of the load. All components have complex impedances. In cases where frequency of operation is well below the self resonance frequency, discrete passive components can be thought of as purely resistive or purely reactive dending on construction of the passive part. That be whether it is a resistor or a capacitor or inductor. Non passive components have complex impedances. All the above is valid only when you are dealing with time varying signals. Complex impedance has no definition when dealing with a non time varying signal(ie. DC). james |
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#24
February 20th 07, 07:10 PM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Feb 17, 1:59 am, "Pete KE9OA" wrote:
Another eBay special that "worked perfectly". It doesn't matter if I put in an external audio source from an audio oscillator or a microphone. I've tried three good microphones, and have the same problem. When I first key the mic, Tx audio is fine, but it quickly, almost abruptly fades after about 2 seconds. Has anybody seen this problem? Pete It certainly could be many things... but what you describe would lead me to replace the high power audio IC. I'm assuming that it has one... and uses a high-level modulation scheme. I have seen these fail in the way you have described. I believe what happens there is that the internal die has somehow lost contact with the heat sink... and therefor heats rapidly... sending semiconductors within the IC all over the bias map. This IC is normally failrly cheap, available, and is usually easy to replce. Hope that helps... www.telstar-electronics.com |
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#25
February 21st 07, 01:58 AM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
"Telstar Electronics" wrote in message oups.com... On Feb 17, 1:59 am, "Pete KE9OA" wrote: Another eBay special that "worked perfectly". It doesn't matter if I put in an external audio source from an audio oscillator or a microphone. I've tried three good microphones, and have the same problem. When I first key the mic, Tx audio is fine, but it quickly, almost abruptly fades after about 2 seconds. Has anybody seen this problem? Pete It certainly could be many things... but what you describe would lead me to replace the high power audio IC. I'm assuming that it has one... and uses a high-level modulation scheme. I have seen these fail in the way you have described. I believe what happens there is that the internal die has somehow lost contact with the heat sink... and therefor heats rapidly... sending semiconductors within the IC all over the bias map. This IC is normally failrly cheap, available, and is usually easy to replce. Hope that helps... You don't think it might be caused by him not having at least 9 square feet of ground plane? Posted Via Usenet.com Premium Usenet Newsgroup Services ---------------------------------------------------------- ** SPEED ** RETENTION ** COMPLETION ** ANONYMITY ** ---------------------------------------------------------- http://www.usenet.com |
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#26
February 21st 07, 05:46 AM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Tue, 20 Feb 2007 18:52:07 GMT, james wrote
in : On Mon, 19 Feb 2007 22:52:40 -0800, Frank Gilliland wrote: +++Notwithstanding the fact that the non-reactive component of impedance +++changes at or near resonance, maximum power transfer (due to matched +++impedances) occurs regardless of whether those impedances are reactive +++or not. Hence "impedance match" instead of the more limited "conjugate +++match". As for your assertion that non-reactive impedances are rare in +++the "real world", maybe you should describe -your- "real world" and +++how it differs from the rest of reality. ********** I am not saying that the real portion of impendances are rare. I am saying that pure resistance is but a subset of complex impedance. Pure resistance is where the reactive part of the complex impedance is zero. In the real world no component has a "zero" reactive component as does it not have zero resistive part. Well, in my "real world" there are many components with reactances so small as to be insignificant and are therefore ignored. In conjugate matching, the nodal point where the output of the transform network terminates with the load will have a net reactance of zero. The real part is still there. It does not go away. Okay.... The net real part should be half that of the real part of the load. Huh? All components have complex impedances. In cases where frequency of operation is well below the self resonance frequency, discrete passive components can be thought of as purely resistive or purely reactive dending on construction of the passive part. That be whether it is a resistor or a capacitor or inductor. Thank you. And I should add that it is more often the case where an intended reactive component is measured for resistive impedance than an intended resistive component is measured for reactive impedance. Non passive components have complex impedances. Not necessarily, for the very same reasons mentioned above. All the above is valid only when you are dealing with time varying signals. Complex impedance has no definition when dealing with a non time varying signal(ie. DC). For all practical purposes, true. But you are still ignoring the fact that a conjugate match is nothing more than an impedance match using a conjugate impedance, which is often not necessary. Just because some comp resistors -- or even the wires or PCB traces -- in an audio amp or power supply may have a very slight inductive reactance doesn't mean you waste your time trying to load them all with sub-pF caps. That's why, here in the real world, the term "impedance match" is used to include any necessary conjugate match that may (or may not) be necessary, and why you don't hear the term "resistance match" used very often (i.e, never). |
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#27
February 21st 07, 08:03 PM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Tue, 20 Feb 2007 21:46:57 -0800, Frank Gilliland
wrote: +++But you are still ignoring the fact that a conjugate match is nothing +++more than an impedance match using a conjugate impedance, which is +++often not necessary. ********** True Sometimes it is the easiest and cheapest method though james |
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#28
February 21st 07, 10:38 PM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Wed, 21 Feb 2007 20:03:02 GMT, james wrote
in : On Tue, 20 Feb 2007 21:46:57 -0800, Frank Gilliland wrote: +++But you are still ignoring the fact that a conjugate match is nothing +++more than an impedance match using a conjugate impedance, which is +++often not necessary. ********** True Sometimes it is the easiest and cheapest method though I tend to disagree with that, too, but I'll drop it because it could revive the great coax length debate..... AARGGHHH!!! |
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#29
February 22nd 07, 12:21 AM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
Frank Gilliland wrote:
I'll drop it because it could revive the great coax length debate..... AARGGHHH!!! NOoooo! |
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#30
February 22nd 07, 02:25 PM
posted to rec.radio.cb
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Cobra 2010 loses Tx audio
On Wed, 21 Feb 2007 14:38:38 -0800, Frank Gilliland
wrote: +++On Wed, 21 Feb 2007 20:03:02 GMT, james wrote +++in : +++ +++On Tue, 20 Feb 2007 21:46:57 -0800, Frank Gilliland wrote: +++ ++++++But you are still ignoring the fact that a conjugate match is nothing ++++++more than an impedance match using a conjugate impedance, which is ++++++often not necessary. +++********** +++ +++True +++ +++Sometimes it is the easiest and cheapest method though +++ +++ +++I tend to disagree with that, too, but I'll drop it because it could +++revive the great coax length debate..... AARGGHHH!!! +++ ************ I use conjugate matches with active devices and crystal filters. In that aspect they are easier and cheaper. james |
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