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: [email protected] >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: [email protected] [mailto:Repeater- >> [EMAIL PROTECTED] On Behalf Of Ron Wright >> Sent: Saturday, September 01, 2007 8:49 AM >> To: [email protected] >> 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: [email protected] >> >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: [email protected] [mailto:Repeater- >> >> [EMAIL PROTECTED] On Behalf Of Ron Wright >> >> Sent: Friday, August 31, 2007 7:12 AM >> >> To: [email protected] >> >> 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: [email protected] >> >> >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: [email protected] [mailto:Repeater- >> >> >> [EMAIL PROTECTED] On Behalf Of Ron Wright >> >> >> Sent: Thursday, August 30, 2007 10:48 AM >> >> >> To: [email protected] >> >> >> 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: [email protected] >> >> >> >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.
