Re: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
Ron Wright, C'mon Ron, I asked to get a feel for the references used in your explanation of how coax has a lower freq limit, not a compilation of your library collection. It appears that when you get a specific question you cannot provide an answer to, you go into a rambling dialog about unrelated and useless subjects. How about sticking to the subject at hand without the superfluous, nonessential, redundant, fluff. I get the feeling that when you get a direct question you cannot or are unable to provide an answer to, you meander into an unrelated direction to distract the person asking. Or to get them to go away in disgust. From what I can see about the tough questions you are asked, your answers possibly lack any substance or credibility, and may even border on being defective. How about it now, just provide the books or technical references you have to buttress your comments so I can look in them also to see how you arrived at your conclusions. I too have an extensive library of technical documents and some of the ones you have mentioned and I'm interested in furthering my knowledge, If you cannot or will not provide the references, I will understand. Your credibility in the technical responses provided with reference to coax having a low freq cutoff will have just evaporated. What do you say Ron? Can you support your utterances with references? Or am I and all the others reading this dialog, are to believe you're just puffing? Again. 73 Allan Crites WA9ZZU Ron Wright [EMAIL PROTECTED] wrote: Allan, Well I think most on here do not quote their sources for many got info long time ago and from many sources. If you want a list of some of what I got...well ok: Reference Data for Radio Engineers, ITT (have had about 30 years so probably should update, but still the RF stuff is pretty good...also very good quick reference book). Antenna Analysis by Wolff (need to know Calculus for this one) Electronic Engineers Handbook, Fink (is very popular) Handbook of Engineering Fundamentals, Eshbach (got at garage sell for $2, about 1500 pages) Information Transmission Modulation , and Noise, Schwartz (was my college EE text book on information theory...had great professor. This give real good analyas of modulations such as TDMA, etc. Mostly uses Fourier Transform). Have about 50 others along with many not related to electronics, but Physics and Cheminstry and a bunch of other stuff. Also lots on transistor and ones I really like data books giving all that technical stuff on parts like ICs. I even still have a tube manual and a tube checker. Will not do many sweep tubes so cannot help you with a CB amp. However, I find most of these are good for reference. The real fun is coming up with stuff on ones own and maybe using reference for some of it. Einstin once said one does not have to remember much as long as one knows where to go and get it, hi. Of course with the internet books are kinda loosing out, but still fun to look at well the ones with lots of pictures. I hope you enjoyed this as much as I. 73, ron, n9ee/r From: allan crites [EMAIL PROTECTED] Date: 2007/09/03 Mon PM 04:09:58 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Ron , Aw c'mon Ron, dig out those equations from your library so we can all see where you're comming from. That way we can get an idea how much reference materials you really have and who and what they are. And just because your name is Wright doen't mean you're right all the time. Jesse also doesn't ever bother to quote the sources for his statements. I'm begining to wonder if you as well as he have any.  73 Allan Crites WA9ZZU Ron Wright [EMAIL PROTECTED] wrote: Gary, I gave the reason for the statement...measured with HP piece of test equipment. Was quick and to the point. I did not think I had to dig into my libary and dig out the equations. Same with stating an SWR...thought most would take a reading from a meter and not having to give the equations. I did not see you giving your basis for rejecting the statement, but then again I really did not expect it, hi. 73, ron, n9ee/r From: Gary Schafer [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 08:29:08 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers But it is your statement. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- [EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Sunday, September 02, 2007 6:46 AM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Gary, I don't know. Why don't you tell us. I don't know why gravity will pull me to the ground real fast if I jump off a bridge, but I have all the faith in the world it will. Einstin tried to explain it,
Re: RE: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
From: Gary Schafer [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 09:07:18 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Isnât it interesting to note thatthe impedance goes UP at low frequencies but not by leaps and bounds. It goes up for the impedance is now more related to R and series L with the parallel C having little affect. The cable now is in series with the load. This is why we use transmission lines so as not to be part of the load, but to transfer power.  However you didnât say if the âRâresistance in the equations is DC resistance or AC resistance? The R is both AC and DC although skin effect can produce more R at higher frequency, but not much at 100 kHz. The beauty of R...same all the time unless one gets too much I then the R changes and sometimes get smoke.  If you also look in those Beldon papersyou will see that the âcharacteristic impedanceâ of coax is not aspecific number but rather an average number. The impedance swings all over theplace with change in frequency. There are many high and low swings in impedanceat specific frequencies. If you got characteristic impedance or just impedance swinging all over the place you got a problem. One does see slight bumps in cables like the big water pipe with flange connections due to they are most often air with donut type insulator. These insulators form a defferent dielectric and give some slight difference in characteristic impedance. When running 10s of kW they become a factor so applications like TV stations order specific lengths of this coax to null out these bumps. A continous length of hardline will have consistant impedance. I guess we were talking about wheather coax has a lower freq limit.  At low frequencies (or most any frequency)a coax cable does not start to exhibit coax cable (transmission line) propertiesuntil the length of the cable approaches 1/10 wavelength. Yes this means thatwith most common lengths of cable at audio frequencies for example, a piece ofcoax cable only looks like a piece of shielded cable with capacitance acrossit. But lengthen that same cable with the same frequency to 1/10 wave length ormore and the cable now looks like a transmission line. This same thing happens with powerdistribution lines. The long lines are transmission lines (appropriately named)and suffer from the same problems as any other transmission line includingstanding waves.  73 Gary K4FMX   From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd Sent: Sunday, September 02, 20074:10 PM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE:RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers  So to plug some numbersin: Say you have a cable with the following specs (50 ohm cable) Capacitance of 100.3 pF/m Inducatance of 251 nH/m Resistane of 0.164 ohms/m Shunt conductance of 12.8 mS/m Zo = sqrt [ (R + j 2 pi f L ) / (G  + j 2 pi f C ) ] at 100 Hz= 113 ohms at 1 Khz= 111 ohms at 10 Khz= 97 ohms at 100 Khz= 65 ohms at 1 Mhz= 52 ohms at 100 Mhz= 50 ohms at 1 Ghz= 50 ohms Proved.com Jesse On 9/2/07, RonWright [EMAIL PROTECTED]wrote: Jeff, I have plenty of text books here, oh well. All refer to impedance as Z andZ=R+jX or Z = magnitude and phase angle. A 500 Ohm resistor has an impedance of500 Ohms or 500+j0 or 500 0 deg phase. I think in Jesse's and my last posting you might see about the low and highfreq differences in coax. Maybe not. Oh well. Good discussion. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 12:12:51 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re:Duplexers Impedance refers to both R and X, resistance andreactance. Impedance affects all current flow, DC and AC. X affects AC only. Impedance is specific to AC. There's no such thing asimpedance at DC, only resistance. Look up in the definition of impedance in anyengineering text and you'll find that it only applies to AC. A cable's characteristic impedance is determined by the ratioof E to I when there are no reflections on the line. Reflections can onlyexist when the current being carried is varying, i.e. an AC waveform. A coaxial cable that has a 75 ohm characteristic impedancewill conduct steady-state DC at any E to I ratio, and will do so withoutreflection. The cable does not perform any transformation regardless of theload, unlike the AC case. No a coax will not function the same at 5 Hz as it doesat 2 meters. Why not? Evidently you have not had the previledge of workingwith equipment or engineers that allows one to look at someof these issues. Oh, I think have... --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. Ron Wright, N9EE
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This could be correct in that say a 50 Ohm coax at 10 MHz would be say 120 Ohms at 100 kHz or 90 Ohms at 50 kHz...freq dependent. There is still L and C. However, this would have to be for a specific design or application. It would affect wideband stuff like video and it does. I guess one could build different loads seperated by filters...not me, hi. As I said in the beginning coax has a upper and lower limit as far as characteristic impedance. 73, ron, n9ee/r From: Gary Schafer [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 08:41:54 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers I was wondering when someone was going to dredge that up from the Beldon papers. Good going Jesse. But that still doesn't mean or show that coax cable has a low frequency cutoff or that it stops looking like or acting like a coax cable at low frequencies. It tells us that other factors come into play at low frequencies. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- [EMAIL PROTECTED] On Behalf Of Jesse Lloyd Sent: Sunday, September 02, 2007 12:38 PM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Ok. Coax doesn't have an impedance at DC it has a resistance. Coax impedance is found by: Zo = sqrt [ (R +j 2 pi f L ) / (G + j 2 pi f c) ] where: f is frequency L is inductance C is capacitance R is the resistance G is shunt conductance in mhos caused by the dielectric j is of course the imaginary number At extreamly low frequencies 2 pi f L and 2 pi F c are small compared to R and G, So you can now rewight as: Zo= sqrt (R/G) once f gets large enough, R and G can be neglected so the equation then is: Zo= sqrt [j 2pi f L / j 2pi f L) or Zo = sqrt (L/C) So as you can see the equation for transmission lines involves f, therefor f does have an effect on imedance... Ron's right. Jesse On 9/2/07, Ron Wright [EMAIL PROTECTED] wrote: Jeff, Impedance refers to both R and X, resistance and reactance. Impedance affects all current flow, DC and AC. X affects AC only. Yes DC is steady state. Guess you can get the simple stuff. No a coax will not function the same at 5 Hz as it does at 2 meters. Evidently you have not had the previledge of working with equipment or engineers that allows one to look at some of these issues. Oh well. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] Date: 2007/09/02 Sun AM 09:01:03 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers The question is way off base. No one said one cannot carry DC or any other signal on coax. The question was what was the impedance of a coax at given frequencies. You said coax has a low-frequency cutoff. I'm asking about that specifically. I didn't ask about about impedance. At DC I can guarantee you RG59 is not 75 Ohms unless you got enough to get enough R and this is totally another discussion. Under steady-state conditions, yes, you'd be right. At DC, I would think you would agree one will not see RG59 being 75 Ohm at DC. At steady-state DC, there's no such thing as impedance, there's only resistance. By definition, impedance is the opposition to a varying electric current, i.e. it only applies when we're talking about AC. The same can be said at 1 Hz or 2 Hz or 5 Hz...etc. No, it can't. If you had a piece of cable long enough, it would behave the same way at 5 Hz as would a 100 foot piece of cable on 2m. There is a point at which it starts to propergate and does look like 75 Ohms. I think you might understand this. I'm not trying to rake you over the coals Ron, but I *am* trying to prove a point: there is no low-frequency cutoff for coaxial cable, period. You may experience (or even measure) behavior at very low frequencies when the cable is a small fraction of an electrical wavelength that might make you want to think otherwise, but it's not due to transmission line theory, math, or physics breaking down at some low-frequency cutoff. --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. Yahoo! Groups Links Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
One can see there becomes a point where the coax will not look like coax at low frequencies or atleast have a characteristic impedance of something other than it normal value. Most of this is true (although I don't know what you mean by coax will not look like coax), and I already acknowledged in a previous post that at sufficiently low frequencies and sufficiently short cable lengths (in terms of a fraction of a wavelength) that you may measure effects that seem to conflict with what you would expect to happen at higher frequencies and longer cable lengths. That's not what we're arguing. Or at least that's not what I'm arguing. I specifically was addressing your statement that all coax has a low-frequency cutoff, which it does NOT. Will a transmission line behave identically at all frequencies? Of course not, that's not new news, there are many things that affect a cable's behavior as frequency is varied. To put this to bed once and for all, can we at least agree that coax does not have a low-frequency cutoff? I'm sure there will be many audiophiles that will be happy to hear that their gold-plated oxygen-free litz-wire triple-shielded phono cables that they paid $100 for will continue to work into the subaudible range if we can just acknowledge this fact and move on. --- Jeff
Re: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
Hahaha a audiophiles... can sell them anything no need for real physics, just tell them that this device will make things sound better, back it up with a BS statment that doesn't apply, and charge them 100 bux. On 9/3/07, Jeff DePolo [EMAIL PROTECTED] wrote: One can see there becomes a point where the coax will not look like coax at low frequencies or atleast have a characteristic impedance of something other than it normal value. Most of this is true (although I don't know what you mean by coax will not look like coax), and I already acknowledged in a previous post that at sufficiently low frequencies and sufficiently short cable lengths (in terms of a fraction of a wavelength) that you may measure effects that seem to conflict with what you would expect to happen at higher frequencies and longer cable lengths. That's not what we're arguing. Or at least that's not what I'm arguing. I specifically was addressing your statement that all coax has a low-frequency cutoff, which it does NOT. Will a transmission line behave identically at all frequencies? Of course not, that's not new news, there are many things that affect a cable's behavior as frequency is varied. To put this to bed once and for all, can we at least agree that coax does not have a low-frequency cutoff? I'm sure there will be many audiophiles that will be happy to hear that their gold-plated oxygen-free litz-wire triple-shielded phono cables that they paid $100 for will continue to work into the subaudible range if we can just acknowledge this fact and move on. --- Jeff
Re: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
Allan, Well I think most on here do not quote their sources for many got info long time ago and from many sources. If you want a list of some of what I got...well ok: Reference Data for Radio Engineers, ITT (have had about 30 years so probably should update, but still the RF stuff is pretty good...also very good quick reference book). Antenna Analysis by Wolff (need to know Calculus for this one) Electronic Engineers Handbook, Fink (is very popular) Handbook of Engineering Fundamentals, Eshbach (got at garage sell for $2, about 1500 pages) Information Transmission Modulation , and Noise, Schwartz (was my college EE text book on information theory...had great professor. This give real good analyas of modulations such as TDMA, etc. Mostly uses Fourier Transform). Have about 50 others along with many not related to electronics, but Physics and Cheminstry and a bunch of other stuff. Also lots on transistor and ones I really like data books giving all that technical stuff on parts like ICs. I even still have a tube manual and a tube checker. Will not do many sweep tubes so cannot help you with a CB amp. However, I find most of these are good for reference. The real fun is coming up with stuff on ones own and maybe using reference for some of it. Einstin once said one does not have to remember much as long as one knows where to go and get it, hi. Of course with the internet books are kinda loosing out, but still fun to look at well the ones with lots of pictures. I hope you enjoyed this as much as I. 73, ron, n9ee/r From: allan crites [EMAIL PROTECTED] Date: 2007/09/03 Mon PM 04:09:58 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Ron , Aw c'mon Ron, dig out those equations from your library so we can all see where you're comming from. That way we can get an idea how much reference materials you really have and who and what they are. And just because your name is Wright doen't mean you're right all the time. Jesse also doesn't ever bother to quote the sources for his statements. I'm begining to wonder if you as well as he have any.  73 Allan Crites WA9ZZU Ron Wright [EMAIL PROTECTED] wrote: Gary, I gave the reason for the statement...measured with HP piece of test equipment. Was quick and to the point. I did not think I had to dig into my libary and dig out the equations. Same with stating an SWR...thought most would take a reading from a meter and not having to give the equations. I did not see you giving your basis for rejecting the statement, but then again I really did not expect it, hi. 73, ron, n9ee/r From: Gary Schafer [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 08:29:08 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers But it is your statement. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- [EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Sunday, September 02, 2007 6:46 AM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Gary, I don't know. Why don't you tell us. I don't know why gravity will pull me to the ground real fast if I jump off a bridge, but I have all the faith in the world it will. Einstin tried to explain it, but died before he got the results. Taking the word of good test equipment is a good engineering approach. Doing the math, I am sure I have here somewhere, and I am sure the defferential equations would take a while probably starting with Maxwell's, but as with gravity if you know it does what it does I use it. These discussions can at times go no where, hi. 73, ron, n9ee/r From: Gary Schafer [EMAIL PROTECTED] Date: 2007/09/01 Sat PM 08:48:03 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Ron, Maybe you could tell us why coax cable has a lower frequency limit? You claim that it does but have not explained why or how. Why does the impedance change significantly at lower frequencies? 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- [EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Saturday, September 01, 2007 8:49 AM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Gary, Yes the HP meter was spec'd to go below below 0.5 MHz, it went down to 100 kHz. I don't know where the confusion is...all coax and feedline has a upper and lower freq limit. Might try to learn something about this. I know about low freq RF. Worked on a Navy program that used 18 kHz, a C130 aircraft with 30,000 ft of wire hung out the back as a platform to talk to surmerged submarines. Ran over 250 kW. It was
Re: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
Jesse, You got it, well said. If you take a simple 100 ft piece of 1/4 superflex a typical value for its C=2400pf, L=6 uH and R=570 Ohm. At 5 Hz the Ls and Cs mean little compared to the R. At 10 MHz Ls and Cs mean a lot compared to the R. One can see there becomes a point where the coax will not look like coax at low frequencies or atleast have a characteristic impedance of something other than it normal value. I did this about 30 years ago for RG59, but cannot remember the numbers for some reason, hi. 73, ron, n9ee/r From: Jesse Lloyd [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 12:38:28 CDT To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Ok. Coax doesn't have an impedance at DC it has a resistance. Coax impedance is found by: Zo = sqrt [ (R +j 2 pi f L ) / (G + j 2 pi f c) ] where: f is frequency L is inductance C is capacitance R is the resistance G is shunt conductance in mhos caused by the dielectric j is of course the imaginary number At extreamly low frequencies 2 pi f L and 2 pi F c are small compared to R and G, So you can now rewight as: Zo= sqrt (R/G) once f gets large enough, R and G can be neglected so the equation then is: Zo= sqrt [j 2pi f L / j 2pi f L) or Zo = sqrt (L/C) So as you can see the equation for transmission lines involves f, therefor f does have an effect on imedance... Ron's right. Jesse On 9/2/07, Ron Wright [EMAIL PROTECTED] wrote: Jeff, Impedance refers to both R and X, resistance and reactance. Impedance affects all current flow, DC and AC. X affects AC only. Yes DC is steady state. Guess you can get the simple stuff. No a coax will not function the same at 5 Hz as it does at 2 meters. Evidently you have not had the previledge of working with equipment or engineers that allows one to look at some of these issues. Oh well. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] Date: 2007/09/02 Sun AM 09:01:03 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers The question is way off base. No one said one cannot carry DC or any other signal on coax. The question was what was the impedance of a coax at given frequencies. You said coax has a low-frequency cutoff. I'm asking about that specifically. I didn't ask about about impedance. At DC I can guarantee you RG59 is not 75 Ohms unless you got enough to get enough R and this is totally another discussion. Under steady-state conditions, yes, you'd be right. At DC, I would think you would agree one will not see RG59 being 75 Ohm at DC. At steady-state DC, there's no such thing as impedance, there's only resistance. By definition, impedance is the opposition to a varying electric current, i.e. it only applies when we're talking about AC. The same can be said at 1 Hz or 2 Hz or 5 Hz...etc. No, it can't. If you had a piece of cable long enough, it would behave the same way at 5 Hz as would a 100 foot piece of cable on 2m. There is a point at which it starts to propergate and does look like 75 Ohms. I think you might understand this. I'm not trying to rake you over the coals Ron, but I *am* trying to prove a point: there is no low-frequency cutoff for coaxial cable, period. You may experience (or even measure) behavior at very low frequencies when the cable is a small fraction of an electrical wavelength that might make you want to think otherwise, but it's not due to transmission line theory, math, or physics breaking down at some low-frequency cutoff. --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
Jeff, I have plenty of text books here, oh well. All refer to impedance as Z and Z=R+jX or Z = magnitude and phase angle. A 500 Ohm resistor has an impedance of 500 Ohms or 500+j0 or 500 0 deg phase. I think in Jesse's and my last posting you might see about the low and high freq differences in coax. Maybe not. Oh well. Good discussion. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] Date: 2007/09/02 Sun PM 12:12:51 CDT To: Repeater-Builder@yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Impedance refers to both R and X, resistance and reactance. Impedance affects all current flow, DC and AC. X affects AC only. Impedance is specific to AC. There's no such thing as impedance at DC, only resistance. Look up in the definition of impedance in any engineering text and you'll find that it only applies to AC. A cable's characteristic impedance is determined by the ratio of E to I when there are no reflections on the line. Reflections can only exist when the current being carried is varying, i.e. an AC waveform. A coaxial cable that has a 75 ohm characteristic impedance will conduct steady-state DC at any E to I ratio, and will do so without reflection. The cable does not perform any transformation regardless of the load, unlike the AC case. No a coax will not function the same at 5 Hz as it does at 2 meters. Why not? Evidently you have not had the previledge of working with equipment or engineers that allows one to look at some of these issues. Oh, I think have... --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
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So to plug some numbers in: Say you have a cable with the following specs (50 ohm cable) Capacitance of 100.3 pF/m Inducatance of 251 nH/m Resistane of 0.164 ohms/m Shunt conductance of 12.8 mS/m Zo = sqrt [ (R + j 2 pi f L ) / (G + j 2 pi f C ) ] at 100 Hz= 113 ohms at 1 Khz= 111 ohms at 10 Khz= 97 ohms at 100 Khz= 65 ohms at 1 Mhz= 52 ohms at 100 Mhz= 50 ohms at 1 Ghz= 50 ohms Proved.com Jesse On 9/2/07, Ron Wright [EMAIL PROTECTED] wrote: Jeff, I have plenty of text books here, oh well. All refer to impedance as Z and Z=R+jX or Z = magnitude and phase angle. A 500 Ohm resistor has an impedance of 500 Ohms or 500+j0 or 500 0 deg phase. I think in Jesse's and my last posting you might see about the low and high freq differences in coax. Maybe not. Oh well. Good discussion. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] jeff%40depolo.net Date: 2007/09/02 Sun PM 12:12:51 CDT To: Repeater-Builder@yahoogroups.com Repeater-Builder%40yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Impedance refers to both R and X, resistance and reactance. Impedance affects all current flow, DC and AC. X affects AC only. Impedance is specific to AC. There's no such thing as impedance at DC, only resistance. Look up in the definition of impedance in any engineering text and you'll find that it only applies to AC. A cable's characteristic impedance is determined by the ratio of E to I when there are no reflections on the line. Reflections can only exist when the current being carried is varying, i.e. an AC waveform. A coaxial cable that has a 75 ohm characteristic impedance will conduct steady-state DC at any E to I ratio, and will do so without reflection. The cable does not perform any transformation regardless of the load, unlike the AC case. No a coax will not function the same at 5 Hz as it does at 2 meters. Why not? Evidently you have not had the previledge of working with equipment or engineers that allows one to look at some of these issues. Oh, I think have... --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers
Isn't it interesting to note that the impedance goes UP at low frequencies but not by leaps and bounds. However you didn't say if the R resistance in the equations is DC resistance or AC resistance? If you also look in those Beldon papers you will see that the characteristic impedance of coax is not a specific number but rather an average number. The impedance swings all over the place with change in frequency. There are many high and low swings in impedance at specific frequencies. At low frequencies (or most any frequency) a coax cable does not start to exhibit coax cable (transmission line) properties until the length of the cable approaches 1/10 wavelength. Yes this means that with most common lengths of cable at audio frequencies for example, a piece of coax cable only looks like a piece of shielded cable with capacitance across it. But lengthen that same cable with the same frequency to 1/10 wave length or more and the cable now looks like a transmission line. This same thing happens with power distribution lines. The long lines are transmission lines (appropriately named) and suffer from the same problems as any other transmission line including standing waves. 73 Gary K4FMX _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd Sent: Sunday, September 02, 2007 4:10 PM To: Repeater-Builder@yahoogroups.com Subject: Re: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers So to plug some numbers in: Say you have a cable with the following specs (50 ohm cable) Capacitance of 100.3 pF/m Inducatance of 251 nH/m Resistane of 0.164 ohms/m Shunt conductance of 12.8 mS/m Zo = sqrt [ (R + j 2 pi f L ) / (G + j 2 pi f C ) ] at 100 Hz= 113 ohms at 1 Khz= 111 ohms at 10 Khz= 97 ohms at 100 Khz= 65 ohms at 1 Mhz= 52 ohms at 100 Mhz= 50 ohms at 1 Ghz= 50 ohms Proved.com Jesse On 9/2/07, Ron Wright [EMAIL PROTECTED] wrote: Jeff, I have plenty of text books here, oh well. All refer to impedance as Z and Z=R+jX or Z = magnitude and phase angle. A 500 Ohm resistor has an impedance of 500 Ohms or 500+j0 or 500 0 deg phase. I think in Jesse's and my last posting you might see about the low and high freq differences in coax. Maybe not. Oh well. Good discussion. 73, ron, n9ee/r From: Jeff DePolo [EMAIL PROTECTED] mailto:jeff%40depolo.net Date: 2007/09/02 Sun PM 12:12:51 CDT To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers Impedance refers to both R and X, resistance and reactance. Impedance affects all current flow, DC and AC. X affects AC only. Impedance is specific to AC. There's no such thing as impedance at DC, only resistance. Look up in the definition of impedance in any engineering text and you'll find that it only applies to AC. A cable's characteristic impedance is determined by the ratio of E to I when there are no reflections on the line. Reflections can only exist when the current being carried is varying, i.e. an AC waveform. A coaxial cable that has a 75 ohm characteristic impedance will conduct steady-state DC at any E to I ratio, and will do so without reflection. The cable does not perform any transformation regardless of the load, unlike the AC case. No a coax will not function the same at 5 Hz as it does at 2 meters. Why not? Evidently you have not had the previledge of working with equipment or engineers that allows one to look at some of these issues. Oh, I think have... --- Jeff Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
