Re: [Elecraft] OT: pwr rating of RG6, etc
The myths have been busted 30 years ago. I Recommend reading Walt Maxwell's Reflections or his series of articles in QST in the early 70's. Or you can just go to his website w2du.com and read the SWT Mythbuster in action. Russ, N3CO - Original Message - From: Peter Howson [EMAIL PROTECTED] Perhaps we should send this to the mythbusters and see if thay can blow it away!! Anyway, I am now going to browse my RadCom back numbers for a revision session. 73 Peter GM8GAX K2 #04027 ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] OT: pwr rating of RG6, etc
Top banders use RG6 all the time and run full bore (and then some) through it. At 1 Mhz, it is rated at 4kw. If you're only interested in 100 watts output (you didn't say what frequency you operate), you're good to go with RG6 up to 1GHz. The white stuff is so cheap, you can replace it every 5 years if you want to be conservative with concerns about UV deterioration. http://www.therfc.com/powerrat.htm de Doug KR2Q PS...you can always paint black coax using exterior paint. Mine gets painted for free every time the house is repainted. LOL ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
RG6 is 75 ohm cable. Why would you buy a great radio and worry about performance,then go use the wrong cable. You start out at a 1.5:1 swr. Idon't get it. kf4yox - Original Message - From: DOUGLAS ZWIEBEL [EMAIL PROTECTED] To: elecraft@mailman.qth.net Sent: Tuesday, November 13, 2007 6:28 AM Subject: [Elecraft] OT: pwr rating of RG6, etc Top banders use RG6 all the time and run full bore (and then some) through it. At 1 Mhz, it is rated at 4kw. If you're only interested in 100 watts output (you didn't say what frequency you operate), you're good to go with RG6 up to 1GHz. The white stuff is so cheap, you can replace it every 5 years if you want to be conservative with concerns about UV deterioration. http://www.therfc.com/powerrat.htm de Doug KR2Q PS...you can always paint black coax using exterior paint. Mine gets painted for free every time the house is repainted. LOL ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
You use it because of 2 characteristics. 1) It has lower loss than an equal physical size 50 ohm cable - and that is true even considering the added loss due to mismatch. 2) It is conviently available and inexpensive. Considering the added loss due to a 1.5 SWR, look at the charts. If the matched line loss is 2 dB, the loss when the SWR is 1.5 is only 2.1 dB. Even if the matched line loss is 10 dB, having an SWR of 1.5 adds only 0.2 dB to the total loss. A 1.5 SWR is insignificant when considering line loss, especially at HF. The facts do not support the popular view that an SWR any higher than 1.0 is a bad thing. In most cases, a transmission line SWR of 2.0 or below will work fine. Now, there is another part to consider - the feedpoint impedance at the output of a transceiver may have to be transformed to something closer to 50 ohms for proper, full power operation of the PA - but that is the job of a tuner, it has nothing to do with feedline loss beyond the tuner. Unfortunately, these two parameters get mixed together and the result is 'numerical soup'. 73, Don W3FPR Samuel Strongin wrote: RG6 is 75 ohm cable. Why would you buy a great radio and worry about performance,then go use the wrong cable. You start out at a 1.5:1 swr. Idon't get it. kf4yox ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
-Original Message- From: Samuel Strongin [EMAIL PROTECTED] RG6 is 75 ohm cable. Why would you buy a great radio and worry about performance,then go use the wrong cable. You start out at a 1.5:1 swr. Because RG-6 may not be the wrong cable, and the SWR may not be 1.5 to 1. IMHO, the question of what cable to use requires evaluating the entire antenna/transmission line *system* and taking all the issues into account. Depending on the antenna impedance, frequency, length of line and comparison coax, RG-6 might be lower loss than 50 ohm line (say, RG-58 or even RG-8X). For example, suppose I had a wire dipole at a height such that the feedpoint Z was 75 ohms, and it needed a long feedline to reach the shack. Feed it with RG-6 and the SWR on the line will be 1:1. All I need to do is match that 75 ohms to 50 ohms at the shack, which can be done with an unun or the ATU in the rig. With 50 ohm cable the load SWR will be 1.5 to 1, and I'll probably still need to match it at the shack end - but the shack-end Z can be anything inside the 1.5 to 1 SWR circle on the Smith Chart. Depending on the line used, the loss with 50 ohm cable may be greater, too. 73 de Jim, N2EY Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
I have a great idea don't use the proper cable at all just use the cheapest piece of junk and try to justify it. The fact of the matter 1.5 does matter.For example Icom radios fold back when seeing a swr of 1.5 to one. CHEAP is not a reason to use something yes it will work so what. Is it the proper cable to use no. Rg6 gives you a starting loss at 1.5. Rg 59 will work to on 75 meters it will even handle some power would I use it No. Good luck using the wrong cable. We don't have pi networks any more. Solid state devices want to see the proper load. They arn't rated 50-75 ohms. Yes it will work so will a coat hanger with a tuner as antenna. - Original Message - From: Don Wilhelm [EMAIL PROTECTED] To: Samuel Strongin [EMAIL PROTECTED] Cc: DOUGLAS ZWIEBEL [EMAIL PROTECTED]; elecraft@mailman.qth.net Sent: Tuesday, November 13, 2007 9:10 AM Subject: Re: [Elecraft] OT: pwr rating of RG6, etc You use it because of 2 characteristics. 1) It has lower loss than an equal physical size 50 ohm cable - and that is true even considering the added loss due to mismatch. 2) It is conviently available and inexpensive. Considering the added loss due to a 1.5 SWR, look at the charts. If the matched line loss is 2 dB, the loss when the SWR is 1.5 is only 2.1 dB. Even if the matched line loss is 10 dB, having an SWR of 1.5 adds only 0.2 dB to the total loss. A 1.5 SWR is insignificant when considering line loss, especially at HF. The facts do not support the popular view that an SWR any higher than 1.0 is a bad thing. In most cases, a transmission line SWR of 2.0 or below will work fine. Now, there is another part to consider - the feedpoint impedance at the output of a transceiver may have to be transformed to something closer to 50 ohms for proper, full power operation of the PA - but that is the job of a tuner, it has nothing to do with feedline loss beyond the tuner. Unfortunately, these two parameters get mixed together and the result is 'numerical soup'. 73, Don W3FPR Samuel Strongin wrote: RG6 is 75 ohm cable. Why would you buy a great radio and worry about performance,then go use the wrong cable. You start out at a 1.5:1 swr. Idon't get it. kf4yox ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
Samuel, Because a radio is poorly made and starts shutting back at an swr of 1.5:1 does not mean that the coax cable is not efficiently transferring the power to the antenna. Many superstations use 75 ohm hardline obtained from cable companies and those stations get out just fine, ok they get out better than fine. Radio shack used to sell some RG-8 cable that was cheap. The braid, if you were lucky, covered 50 percent of the dielectric. There is cheap coax out there. I have purchased 1000's of feet of RG-6U at Home depot and it is high quality belden cable. SWR is not loss. SWR is a standing wave ratio. Just because you have 50 ohm coax does not mean that you have 50 ohms at the end of that coax. An SWR of 1:1 does not guarantee that you have maximized the power transfer from the rig to the antenna. If just means that the rig is seeing a 50 ohm load. You can cut a piece of coax at a particular length that will make a poorly matched antenna fool the radio into thinking there is a good match. The SWR will be low but the antenna will not work very well. On 11/13/07 8:16 AM, Samuel Strongin [EMAIL PROTECTED] wrote: I have a great idea don't use the proper cable at all just use the cheapest piece of junk and try to justify it. The fact of the matter 1.5 does matter.For example Icom radios fold back when seeing a swr of 1.5 to one. CHEAP is not a reason to use something yes it will work so what. Is it the proper cable to use no. Rg6 gives you a starting loss at 1.5. Rg 59 will work to on 75 meters it will even handle some power would I use it No. Good luck using the wrong cable. We don't have pi networks any more. Solid state devices want to see the proper load. They arn't rated 50-75 ohms. Yes it will work so will a coat hanger with a tuner as antenna. - Original Message - From: Don Wilhelm [EMAIL PROTECTED] To: Samuel Strongin [EMAIL PROTECTED] Cc: DOUGLAS ZWIEBEL [EMAIL PROTECTED]; elecraft@mailman.qth.net Sent: Tuesday, November 13, 2007 9:10 AM Subject: Re: [Elecraft] OT: pwr rating of RG6, etc You use it because of 2 characteristics. 1) It has lower loss than an equal physical size 50 ohm cable - and that is true even considering the added loss due to mismatch. 2) It is conviently available and inexpensive. Considering the added loss due to a 1.5 SWR, look at the charts. If the matched line loss is 2 dB, the loss when the SWR is 1.5 is only 2.1 dB. Even if the matched line loss is 10 dB, having an SWR of 1.5 adds only 0.2 dB to the total loss. A 1.5 SWR is insignificant when considering line loss, especially at HF. The facts do not support the popular view that an SWR any higher than 1.0 is a bad thing. In most cases, a transmission line SWR of 2.0 or below will work fine. Now, there is another part to consider - the feedpoint impedance at the output of a transceiver may have to be transformed to something closer to 50 ohms for proper, full power operation of the PA - but that is the job of a tuner, it has nothing to do with feedline loss beyond the tuner. Unfortunately, these two parameters get mixed together and the result is 'numerical soup'. 73, Don W3FPR Samuel Strongin wrote: RG6 is 75 ohm cable. Why would you buy a great radio and worry about performance,then go use the wrong cable. You start out at a 1.5:1 swr. Idon't get it. kf4yox ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
A couple of points: 1 -- While the feedline might have a 1.5:1 swr, a tuner at the rig can allow the rig to see it as 1.0:1. 2 -- If the feedpoint of the antenna has an impedance close to 75 ohms, RG-6 would be the _correct_ feedline to use. (Correct meaning best match to the antenna and lowest voltage peaks on the feedline while transmitting.) 3 -- Just because an Icom box does something does not make it right. 4 -- If you need a pi-network, BUILD ONE! There is nothing sacred about 50ohms. After all the impedance of free space is about 377ohms. 50ohms is just the impedance that the K3 wants to see at its feedpoint for best power transfer. Mark ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] OT: pwr rating of RG6, etc
KR2Q penned: Top banders use RG6 all the time and run full bore (and then some) through it. At 1 Mhz, it is rated at 4kw. Doug, where did you find that spec? From what I know, most flavors of RG6 lack the voltage rating to instill confidence in putting a lot of power down the line. Yes, topbanders use tons of it, but as long inexpensive receive-only Beverage feedlines. 73, Barry N1EU ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
At 10:16 AM 11/13/2007, Samuel Strongin wrote... just use the cheapest piece of junk and try to justify it. The fact of the matter 1.5 does matter.For example Icom radios fold back when seeing a swr of 1.5 to one. Remind me to never buy an Icom. Who would want a radio which can't be used with a simple dipole having a 72 ohm characteristic impedance? There's gotta be a huge market out there for a 1.5:1 balun, which no one is filling. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
Actually, I've found Icoms to be much more tolerant of SWR issues then Yaesu. When you consider that most (90% or more?) recent rigs have built in antenna tuners that can match up to 150 ohms minimum, the idea of 72 VS: 52 seems trivially unimportant. Mike S wrote: At 10:16 AM 11/13/2007, Samuel Strongin wrote... just use the cheapest piece of junk and try to justify it. The fact of the matter 1.5 does matter.For example Icom radios fold back when seeing a swr of 1.5 to one. Remind me to never buy an Icom. Who would want a radio which can't be used with a simple dipole having a 72 ohm characteristic impedance? There's gotta be a huge market out there for a 1.5:1 balun, which no one is filling. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
I have been following this thread and find it very interesting, particularly as a Mechanical Engineer I have to read it slowly but may I comment -- 1, I don't know the details of Icom's protection system, but the ones I have seen sense reflected power, well actually it will be the voltage detected at the sensor against an assumed impedance of 50 ohms (50+j0). The actual SWR at which the protection will come into play will be a function of feedline impedance (which will, in practice, have a reactive element), feedline losses, antenna impedance and efficiency. -- If it's a problem - just add a few feet of coax!! 2, It shows an underlying belief in SWR as the be all and end all of antenna systems. 3, Many years ago now I had the opportunity to visit the main Naval transmitting station in the UK. Utilising frequencies from VLF to VHF their antenna systems were out of this world. But the majority were fed with 600 ohm open line across many kilometres of open ground. I recall one of our guys asking about SWR. The station chief just shrugged. One of the main HF transmitters was opened for maintenance and contained a large number of 4CX250 valves connected in parallel - not the easiest valve to run. So what should we be doing; as an instructor I see and hear a hell of a lot of myths about SWR and do try to correct them within my own understanding of the subject. But I do have to hand it to those who fully understand the subject and who take the time to explain it at the level of our examination system, which cannot be easy. Perhaps we should send this to the mythbusters and see if thay can blow it away!! Anyway, I am now going to browse my RadCom back numbers for a revision session. 73 Peter GM8GAX K2 #04027 P.S. My Mechanical Engineering comment was to give you Electronic and Radio Engineers a little laugh. I can read as fast as you, any slowing down now is due to age, eye sight etc. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] OT: pwr rating of RG6, etc
Peter (and interested others), You might want to peruse the article Antennas, Transmission Lines, and Tuners at my website http://w3fpr.qrpradio.com. The article tries to flatten several myths in terms that should be understood by most hams - no math, but I believe a good explanation of principles. 73, Don W3FPR Peter Howson wrote: I have been following this thread and find it very interesting, particularly as a Mechanical Engineer I have to read it slowly but may I comment -- 1, I don't know the details of Icom's protection system, but the ones I have seen sense reflected power, well actually it will be the voltage detected at the sensor against an assumed impedance of 50 ohms (50+j0). The actual SWR at which the protection will come into play will be a function of feedline impedance (which will, in practice, have a reactive element), feedline losses, antenna impedance and efficiency. -- If it's a problem - just add a few feet of coax!! 2, It shows an underlying belief in SWR as the be all and end all of antenna systems. 3, Many years ago now I had the opportunity to visit the main Naval transmitting station in the UK. Utilising frequencies from VLF to VHF their antenna systems were out of this world. But the majority were fed with 600 ohm open line across many kilometres of open ground. I recall one of our guys asking about SWR. The station chief just shrugged. One of the main HF transmitters was opened for maintenance and contained a large number of 4CX250 valves connected in parallel - not the easiest valve to run. So what should we be doing; as an instructor I see and hear a hell of a lot of myths about SWR and do try to correct them within my own understanding of the subject. But I do have to hand it to those who fully understand the subject and who take the time to explain it at the level of our examination system, which cannot be easy. Perhaps we should send this to the mythbusters and see if thay can blow it away!! ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
