But it is your statement. 73 Gary K4FMX
> -----Original Message----- > From: [email protected] [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of Ron Wright > Sent: Sunday, September 02, 2007 6:46 AM > To: [email protected] > 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: [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. > > > > > > > > Yahoo! Groups Links > > >
