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 called TACMO. >> Due >> >> to the weight the wings kept falling off...well they were continously >> >> inspected and replaced before they fell off, but the aircraft was >> >> deffinitly over loaded. Had generators on all 4 engines to get the >> power >> >> they needed. Now that was a repeater. >> >> >> >> However, AC power distribution is not trying to radiate power, but >> >> transfer it with widly varing loads. Totally different engineering. >> >> >> >> At low frequencies such as 1 kHz little radiation takes place. Far >> less >> >> at 60 Hz. The EMF returns to the radiator, wire, before the next cycle >> >> can force it out. This is a problem in some applications, but since >> most >> >> do not want radiation it is not. >> >> >> >> 73, ron, n9ee/r >> >> >> >> >> >> >> >> >> >> >From: Gary Schafer <[EMAIL PROTECTED]> >> >> >Date: 2007/08/31 Fri PM 05:59:28 CDT >> >> >To: Repeater-Builder@yahoogroups.com >> >> >Subject: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers >> >> >> >> > >> >> >Are you sure that the impedance meter you used was speced for >> operation >> >> >below .5 MHz? >> >> > >> >> >Yes all capacitors have inductance. Lead length is particularly a >> >> problem. >> >> > >> >> >15 KHz can be treated as RF or audio it all depends on what transducer >> >> you >> >> >are using it to couple it with. Use a speaker and it is audio. Use an >> >> >antenna it is RF. All RF propagates the same on a transmission line. >> 15 >> >> KHz >> >> >or even 1 KHz propagates as RF just like any RF signal does through >> the >> >> air >> >> >and even thru the ground as in the case of low frequencies. Read about >> >> what >> >> >some of the VLF guys are doing. >> >> > >> >> >On a video cable remove the termination on the far end of the cable >> and >> >> look >> >> >at the reflected energy. It has the same effect at those frequencies >> as >> >> it >> >> >does at HF or VHF. >> >> > >> >> >Yes long runs of video cable can be a problem. Long runs of cable in >> the >> >> >catv industry have the same problems of frequency roll off. They call >> it >> >> >"tilt" and their amplifiers have compensation for cable attenuation in >> >> order >> >> >to make the system "flat". >> >> > >> >> >I have an HP signal level meter that measures RF from 10 Hz to 30 MHz. >> I >> >> can >> >> >feed an audio oscillator set to 1 KHz or 1 MHz into the same input as >> I >> >> feed >> >> >a 1 MHz RF generator into. The signal level meter handles it the same. >> >> Only >> >> >difference is the output impedance of the audio oscillator is 600 ohms >> >> >rather than 50 ohms. The instrument doesn't know or care if we want to >> >> call >> >> >it audio or RF. As far as it is concerned it treats it as RF. >> >> > >> >> >I have an audio amplifier that has just about a flat response from >> around >> >> 5 >> >> >Hz to 1 MHz. Is that an audio amplifier or an RF amplifier? :>) >> >> > >> >> >73 >> >> >Gary K4FMX >> >> > >> >> >> -----Original Message----- >> >> >> From: Repeater-Builder@yahoogroups.com [mailto:Repeater- >> >> >> [EMAIL PROTECTED] On Behalf Of Ron Wright >> >> >> Sent: Friday, August 31, 2007 7:12 AM >> >> >> To: Repeater-Builder@yahoogroups.com >> >> >> Subject: Re: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: >> Duplexers >> >> >> >> >> >> Gary, >> >> >> >> >> >> To measure the impedance of the RG59 I used an HP impedence meter >> which >> >> >> displayed Z and phase. I use to use it to determine where caps >> became >> >> >> resonant as a demo for many caps look inductive above a given freq. >> >> Mica >> >> >> caps did pretty good, but still hard to find a cap at 1000 pf that >> was >> >> a >> >> >> cap above 25 MHz. These become issues in bypass caps and also for >> >> >> resonant circuits trying to get higher Qs where the C is large. >> >> >> >> >> >> In a good lab one often has tons of test equipment for making >> >> >> measurements, even spectrum anal that go down to tenths of Hz and to >> >> many >> >> >> GHz. I've had the previdlege of working in such places and some was >> >> for >> >> >> my use in my work. >> >> >> >> >> >> I know RG59 is a most commonly used cable in video. However, one >> does >> >> not >> >> >> have to go far before it really affects video especially color where >> >> the >> >> >> phase is so important. Also the syncs get torn up so bad monitors >> >> loose >> >> >> sync on the veritical retrace and a portion of the picture is torn >> at >> >> the >> >> >> top. Many manufactures make line amps that not only compenstate for >> >> loss, >> >> >> but varied freq response and some for sync...the better ones do sync >> >> also. >> >> >> The vertical sync is at about 60 Hz and horiz at 15734 Hz which is >> in >> >> the >> >> >> audio freq where the signal is not really propergating like in RF. >> >> Many >> >> >> things change. Of course for a run of couple hundred feet this is >> not >> >> a >> >> >> problem, but long runs it becomes one. >> >> >> >> >> >> 73, ron, n9ee/r >> >> >> >> >> >> >> >> >> >> >> >> >From: Gary Schafer <[EMAIL PROTECTED]> >> >> >> >Date: 2007/08/30 Thu PM 07:39:21 CDT >> >> >> >To: Repeater-Builder@yahoogroups.com >> >> >> >Subject: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers >> >> >> >> >> >> > >> >> >> >I wonder what you were using to measure the impedance of the cable >> >> with >> >> >> >below .5 MHz? >> >> >> >Some cable especially rg59 types have copper clad steel center >> >> >> conductors. >> >> >> >If the copper clad is very thin low frequencies can penetrate the >> >> copper >> >> >> >clad and get into the steel where the loss can go up substantially. >> If >> >> >> you >> >> >> >are using that cable to transform an impedance the additional lose >> can >> >> >> make >> >> >> >the impedance transformation something other than expected. The >> >> impedance >> >> >> >will be closer to the characteristic impedance of the cable rather >> >> than >> >> >> the >> >> >> >expected transformation impedance. >> >> >> >But to have the characteristic impedance fall apart at .5 MHz would >> be >> >> a >> >> >> >mystery. 75 ohm cable is used extensively in video base band >> >> applications >> >> >> >where flat low frequency response is needed. >> >> >> > >> >> >> >73 >> >> >> >Gary K4FMX >> >> >> > >> >> >> >> -----Original Message----- >> >> >> >> From: Repeater-Builder@yahoogroups.com [mailto:Repeater- >> >> >> >> [EMAIL PROTECTED] On Behalf Of Ron Wright >> >> >> >> Sent: Thursday, August 30, 2007 10:48 AM >> >> >> >> To: Repeater-Builder@yahoogroups.com >> >> >> >> Subject: Re: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers >> >> >> >> >> >> >> >> Gary, >> >> >> >> >> >> >> >> I've measured RG59 cable terminated into a 75 Ohm resistive load >> >> with a >> >> >> >> variable freq impedance meter. We found the coax stopped being >> 75 >> >> Ohms >> >> >> >> below about 0.5 MHz. The cable manufacture also verified this. >> >> Other >> >> >> >> engineers in our department knew of this as well. >> >> >> >> >> >> >> >> We were designing security systems using video and the vertical >> and >> >> >> >> harizonal sync signals became very distored over long, 2500 ft. >> RG59 >> >> >> >> cables and this was the major reason. We had to design circuits >> >> that >> >> >> >> corrected this, but the cable had the problem. >> >> >> >> >> >> >> >> I am sure different RG59 cables have different low freq >> bandwidths. >> >> >> RG11 >> >> >> >> would also be different as well as cable TV cable. >> >> >> >> >> >> >> >> All coax has a lower and upper frequency range. Since we deal >> with >> >> >> radio >> >> >> >> this is not much of a factor until one gets real low or GHz >> levels. >> >> >> >> >> >> >> >> Coax also has the problem of a upper freq limit due to it's outer >> >> >> shield >> >> >> >> becomes large enough to act as wave guide. One will see upper >> freq >> >> >> specs >> >> >> >> will be lower the larger cable. >> >> >> >> >> >> >> >> 73, ron, n9ee/r >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >From: Gary Schafer <[EMAIL PROTECTED]> >> >> >> >> >Date: 2007/08/29 Wed PM 09:23:57 CDT >> >> >> >> >To: Repeater-Builder@yahoogroups.com >> >> >> >> >Subject: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers >> >> >> >> >> >> >> >> >> >> >> >> >As far as bandwidth goes,,, where do you get this .5 MHz for >> rg59 >> >> >> cable >> >> >> >> as a >> >> >> >> >lower limit? >> >> >> >> > >> >> >> >> >Open wire lines begin to radiate as frequency is increased to >> the >> >> >> point >> >> >> >> >where the line spacing becomes an appreciable portion of a wave >> >> length >> >> >> >> due >> >> >> >> >to the time it takes for propagation of fields between wires. >> >> >> >> > >> >> >> >> >73 >> >> >> >> >Gary K4FMX >> >> >> >> > >> >> >> >> >> >> >> >> >> >> >> >> 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. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> Yahoo! Groups Links >> >> >> >> >> >> >> >> >> >> >> > >> >> > >> >> >> >> >> >> 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. >> >> >> >> >> >> >> >> Yahoo! Groups Links >> >> >> > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
