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al coax
hi
I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious |
al coax
On Mar 25, 4:19 am, ml wrote:
hi I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious Skin effect means that the RF current is only being carried in a very, very thin layer, so one can silver plate the inside of the aluminum shield and the outside of the center conductor. At 100 MHz skin depth for copper or silver is a bit more than 6 microns (0.25 mil), so it doesn't take a very thick layer. |
al coax
On 25 Mar, 06:44, wrote:
On Mar 25, 4:19 am, ml wrote: hi I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious Skin effect means that the RF current is only being carried in a very, very thin layer, so one can silver plate the inside of the aluminum shield and the outside of the center conductor. At 100 MHz skin depth for copper or silver is a bit more than 6 microns (0.25 mil), so it doesn't take a very thick layer. I had some 1/2" diameter stuff once that laid on the ground prior to entering the house. A year or so later and the sheathing turned to dust. You may see some used for cable t.v. about 1 " diameter, these use air as a dialectric and moisture can get in. All aluminum forms dislike bending and easily kinks and do not straighten out easily. Personaly I would avoid aluminum for transmission lines. Art |
al coax
Aluminum has good conductivity. Before the corrugated
copper lines became popular Times Wire made an Alumafoam cable with an aluminum sheath for many years. We still have some runs in service at several of my work locations.. Pete |
al coax
Uncle Peter wrote:
Aluminum has good conductivity. Before the corrugated copper lines became popular Times Wire made an Alumafoam cable with an aluminum sheath for many years. We still have some runs in service at several of my work locations.. Aluminum is used extensively in cable TV coax. -- 73, Cecil http://www.w5dxp.com |
al coax
On 25 Mar, 17:38, Cecil Moore wrote:
Uncle Peter wrote: Aluminum has good conductivity. Before the corrugated copper lines became popular Times Wire made an Alumafoam cable with an aluminum sheath for many years. We still have some runs in service at several of my work locations.. Aluminum is used extensively in cable TV coax. -- 73, Cecil http://www.w5dxp.com That is correct Cecil but they are using a insulator instead of air because of moisture getting in. The coax is also covered with plasic which with the inside insulation makes it less liable to kink or attack by ground alkali or moisture. Actually some of the older air insulated coax did not have a plastic covering but these were changed out when HDTV entered the mix. The air filled coax makes useful parts for antennas, you apply a voltage to the inner wire and the heat allows the spacers to soften and separate from the outer aluminum. The outer aluminum tubing is thicker than the norm so it can be put into use in several ways. Couplings are hard to get unless you manage to get some when the coax is changed out, the center wire is solid so it is not as easy to join as corregated copper types which are tubular in form allowing for a conductive rod to be pushed into the joining ends and then sliding a copper tube over the outer corregation before soldering Art |
al coax
I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious Actually, the loss characteristics of solid jacket heliax depends much more on the dielectric material, physical diameter, and the size of the center conductor, than it does on the jacket material. Also, aluminum is a pretty good conductor anyway. Ed K7AAT |
al coax
Ed wrote:
I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious Actually, the loss characteristics of solid jacket heliax depends much more on the dielectric material, physical diameter, and the size of the center conductor, than it does on the jacket material. Also, aluminum is a pretty good conductor anyway. In order of importance, the size of the centre conductor contributes most to losses, followed by the outer shield and the dielectric. This is simply because the centre conductor is smallest. It carries the same current as the shield; but the current *density* on the centre conductor is several times higher. RF current flows only on the surfaces - the outside of the centre conductor, and the inside of the shield - so it works out that the resistive losses are proportional to diameter-squared. Because losses in the shield are much less important, a small increase due to using aluminium will have almost no effect on the overall cable losses. The problems with aluminium-shielded coax are almost entirely about corrosion. Dielectric losses don't come into this at all, because they are only a small part of the overall cable loss (at least, for frequencies up through UHF). "Low-loss foam" is simply marketing guff. When someone designs a lower-loss version of a standard cable, it has to start with a larger centre conductor - because that is the only change that *really* makes a difference. A foamed or semi-airspaced dielectric is something the designer was *forced* to use, to keep the same characteristic impedance. It is technically true that the dielectric losses are a little bit lower than for the same solid material; but dielectric losses aren't important anyway, so using foam makes almost no difference to the overall cable loss. The designer knows that... but at some stage the message switches over to "low-loss foam", because that's what the managers, the company, the industry and its victXXXXcustomers expect to hear. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
al coax
On 26 Mar, 00:40, Ian White GM3SEK wrote:
Ed wrote: I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious Actually, the loss characteristics of solid jacket heliax depends much more on the dielectric material, physical diameter, and the size of the center conductor, than it does on the jacket material. Also, aluminum is a pretty good conductor anyway. In order of importance, the size of the centre conductor contributes most to losses, followed by the outer shield and the dielectric. This is simply because the centre conductor is smallest. It carries the same current as the shield; but the current *density* on the centre conductor is several times higher. RF current flows only on the surfaces - the outside of the centre conductor, and the inside of the shield - so it works out that the resistive losses are proportional to diameter-squared. Because losses in the shield are much less important, a small increase due to using aluminium will have almost no effect on the overall cable losses. The problems with aluminium-shielded coax are almost entirely about corrosion. Dielectric losses don't come into this at all, because they are only a small part of the overall cable loss (at least, for frequencies up through UHF). "Low-loss foam" is simply marketing guff. When someone designs a lower-loss version of a standard cable, it has to start with a larger centre conductor - because that is the only change that *really* makes a difference. A foamed or semi-airspaced dielectric is something the designer was *forced* to use, to keep the same characteristic impedance. It is technically true that the dielectric losses are a little bit lower than for the same solid material; but dielectric losses aren't important anyway, so using foam makes almost no difference to the overall cable loss. The designer knows that... but at some stage the message switches over to "low-loss foam", because that's what the managers, the company, the industry and its victXXXXcustomers expect to hear. I disagree. The cable companies are changing out to foam filled cable for good reason even if it is expensive.When a joint allows moisture in it accumulates and cables that hang between poles sag such that water collects at the center. This accumulation does make a difference and the only correction is to replace that section.Fortunately the foam used in cables are 'closed cell' which prevents moisture seeping in. Art -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)http://www.ifwtech.co.uk/g3sek- Hide quoted text - - Show quoted text - |
al coax
It is technically true that the dielectric losses are a little bit lower than for the same solid material; but dielectric losses aren't important anyway, so using foam makes almost no difference to the overall cable loss. While I have no disagreement with everything else Ian stated, I do take some exception to the above comment about foam. Just take a look at RG-8 for example. With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Ed K7AAT |
al coax
Ed wrote:
While I have no disagreement with everything else Ian stated, I do take some exception to the above comment about foam. Just take a look at RG-8 for example. With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Significance is in the eye of the beholder. At 400 MHz, RG-8 foam seems to have a loss advantage over ordinary RG-8 of ~2 dB per 100 feet. At 10 MHz, it is ~0.2 dB. Is that significant? -- 73, Cecil http://www.w5dxp.com |
al coax
On 26 Mar 2007 17:01:36 GMT, Ed
wrote: With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Hi Ed, Actually, all other aspects do not remain the same when you go from one dielectric to the other. The size of the inner conductor changes, and with it so does loss. The loss is in the conductor, not the dielectric. 73's Richard Clark, KB7QHC |
al coax
"ml" wrote in message ... hi I've seen recently that some companies such as andrews etc are now offering different coax and hardline with al outer shielding they advertise lower cost, and lighter weight then copper , ok i get that but then they say the rf spec's are 'the same' so i ponder how do they do that i would think copper would have better spec's ? obviously i am missing something obvious I think you are referring to the Times Microwave LMR cables. The LMR240 is sort of a low loss RG8X, and the LMR400 is a low loss RG213. These cables are made like RG6 in that there is 100% foil coverage bonded to the inner dielectric with normally a tinned copper braid over it. The aluminum versions of these replace the copper braid with aluminum braid. They claim the loss is the same because the bonded foil is the same. The only problem I see is soldering to the aluminum braid, and I suspect crimp on connectors will be easier to install. You can still solder the center conductor. Check out www.timesmicrowave.com BTW, the LMR240UF makes for great patch cords. It has a stranded center conductor. 1/4 inch cable that is rated at 1500W. The LMR240 without the UF suffix has a solid center conductor, costs about half as much, and I use it for longer runs below 30 MHz. Haven't seen any of the aluminum stuff yet. Tam/WB2TT |
al coax
Ed wrote:
It is technically true that the dielectric losses are a little bit lower than for the same solid material; but dielectric losses aren't important anyway, so using foam makes almost no difference to the overall cable loss. While I have no disagreement with everything else Ian stated, I do take some exception to the above comment about foam. Just take a look at RG-8 for example. With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Detailed specifications, please? It is impossible to change only the dielectric and have literally "all other aspects remaining the same". If you want to keep the same characteristic impedance, at least one more thing has to be changed - either the centre conductor diameter or the shield diameter (or possibly both). -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
al coax
Ian White GM3SEK wrote in
: Ed wrote: .... While I have no disagreement with everything else Ian stated, I do take some exception to the above comment about foam. Just take a look at RG-8 for example. With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Detailed specifications, please? It is impossible to change only the dielectric and have literally "all other aspects remaining the same". If you want to keep the same characteristic impedance, at least one more thing has to be changed - either the centre conductor diameter or the shield diameter (or possibly both). There is a market for lower loss cables that are of similar dimensions to existing cables like RG213 and RG58. In my experience there are a range of cables with the same outside conductor dimensions, foam dielectric and a effectively larger inner conductor. It is often stated that the foam dielectric give the cable its lower loss, whereas the mechanism at HF is that for the same sized outer conductor, the lower permittivity of the foam dielectric requires a larger centre conductor for same Zo. For example, the k1, k2 factors for a loss=k1*f^0.5+k2*f model for two dimensionally similar cables a Belden 8262 (RG58C/U): 1.30e-5, 2.95e-10 Times Microwave LMR195: 1.17e-5, 1.54e-11 k1 is proportional to copper loss, and k2 is proportional to dielectric loss. Looking at LMR195, the reduced loss at 10MHz is almost entirely due to the reduced copper loss. It is not until about 2GHz that the dielectric loss in RG58 equals the copper loss. The message to carry away is that an 'RG8 foam' cable may be manufactured with the same diameter dielectic and braid, but use a larger inner conductor. Connector compatibility might be more about compatibiility with the inner conductor than the connector body. Owen |
al coax
"Tam/WB2TT" wrote in
: BTW, the LMR240UF makes for great patch cords. It has a stranded center conductor. 1/4 inch cable that is rated at 1500W. The LMR240 From the spec sheet, the average power rating at 30MHz is 1240W. I assume that is with VSWR=1, so that a further derating is required for mismatch. For example, at VSWR=2, the heating at a current maximum is nearly double that for a flat line, so the power rating might be more like 620W with VSWR=2. Of course, in SSB telephony, the average power is very low and the cable is probably limited by voltage breakdown at peaks, specified as 5.6kW for LMR240UF. Owen |
al coax
"Owen Duffy" wrote in message ... "Tam/WB2TT" wrote in : BTW, the LMR240UF makes for great patch cords. It has a stranded center conductor. 1/4 inch cable that is rated at 1500W. The LMR240 From the spec sheet, the average power rating at 30MHz is 1240W. I assume that is with VSWR=1, so that a further derating is required for mismatch. For example, at VSWR=2, the heating at a current maximum is nearly double that for a flat line, so the power rating might be more like 620W with VSWR=2. Of course, in SSB telephony, the average power is very low and the cable is probably limited by voltage breakdown at peaks, specified as 5.6kW for LMR240UF. Owen Something happened to my cut and paste. The 1500W was supposed to refer to the non UF. Tam/WB2TT |
al coax
Ed wrote: While I have no disagreement with everything else Ian stated, I do take some exception to the above comment about foam. Just take a look at RG-8 for example. With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Significance is in the eye of the beholder. At 400 MHz, RG-8 foam seems to have a loss advantage over ordinary RG-8 of ~2 dB per 100 feet. At 10 MHz, it is ~0.2 dB. Is that significant? Actually, significance is based on the frequency of operation, as you just indicated. Since the original poster was talking about an aluminum jacketed heliax, I assumed the pertinent frequencies to be at least VHF, if not higher; which would make the difference between the foam dielectric RG-8 and solid dielectric RG-8 signifacant! Ed |
al coax
Richard Clark wrote in
: On 26 Mar 2007 17:01:36 GMT, Ed wrote: With all other aspects of it remaining the same, there certainly is a significant difference in loss figures when the dielectric is changed from solid to foam. Hi Ed, Actually, all other aspects do not remain the same when you go from one dielectric to the other. The size of the inner conductor changes, and with it so does loss. The loss is in the conductor, not the dielectric. 73's Richard Clark, KB7QHC I will eat my words! My previous experience has apparently been comparing apples and oranges. I just compared Belden 9913 with 9914... the only real difference between these two being one has a solid dielectric and the other a foam dielectric.... the loss differences were basically non-existant! Sorry for all the bother! Ed K7AAT |
al coax
Ed wrote:
Actually, significance is based on the frequency of operation, as you just indicated. Since the original poster was talking about an aluminum jacketed heliax, I assumed the pertinent frequencies to be at least VHF, if not higher; which would make the difference between the foam dielectric RG-8 and solid dielectric RG-8 signifacant! I'm moving to a new QTH and have only kept up with this thread sporadically. I have now gathered that the point is that it's not the foam per se that has the largest effect, but the larger center conductor required to bring the impedance back to 50 ohms. Consider the fact that the 9913 center conductor is #10 while the RG-213 center conductor is #12. -- 73, Cecil http://www.w5dxp.com |
al coax
Cecil Moore wrote:
Ed wrote: Actually, significance is based on the frequency of operation, as you just indicated. Since the original poster was talking about an aluminum jacketed heliax, I assumed the pertinent frequencies to be at least VHF, if not higher; which would make the difference between the foam dielectric RG-8 and solid dielectric RG-8 signifacant! I'm moving to a new QTH and have only kept up with this thread sporadically. I have now gathered that the point is that it's not the foam per se that has the largest effect, but the larger center conductor required to bring the impedance back to 50 ohms. From the designer's point of view, it was the other way around: centre conductor first, dielectric constant second. The boss says: "We want a lower-loss coax, in the same outline as RG213 and still 50 ohms." Starting from RG213, the first thing the designer does is increase the diameter of the centre conductor, because that's where most of the losses come from. He now has a lower-loss solid polyethylene cable that will fit an RG213 connector body, but has an impedance of around 40 ohms. Consider the fact that the 9913 center conductor is #10 while the RG-213 center conductor is #12. Just so. To bring the impedance back up to 50 ohms, the designer then has to reduce the dielectric constant, by using either foam dielectric or a semi-airspaced construction such as 9913. The losses do reduce a little more in the second step, but not much. As I said yesterday, the third step is that Marketing gets hold of it... and that's where it all turns into foam. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
al coax
"Tam/WB2TT" wrote in message . .. "Owen Duffy" wrote in message ... "Tam/WB2TT" wrote in : BTW, the LMR240UF makes for great patch cords. It has a stranded center conductor. 1/4 inch cable that is rated at 1500W. The LMR240 From the spec sheet, the average power rating at 30MHz is 1240W. I assume that is with VSWR=1, so that a further derating is required for mismatch. For example, at VSWR=2, the heating at a current maximum is nearly double that for a flat line, so the power rating might be more like 620W with VSWR=2. Of course, in SSB telephony, the average power is very low and the cable is probably limited by voltage breakdown at peaks, specified as 5.6kW for LMR240UF. Owen Something happened to my cut and paste. The 1500W was supposed to refer to the non UF. Tam/WB2TT Found some Tables of loss and power handling for various cables. At 30 MHz: LMR240 has a max power of 1490W, compared to RG213 of 1800W. LMR240 has a loss of 1.3 DB, compared to RG213 of 1.2 DB. Not a whole lot of difference, but the 213 has about 3X the cross section area. The LMR240 has 90 DB shielding, the 213 is not specified. I assume that these were specified under the same conditions. It is interesting that at 900 MHz, the LMR240 has less loss than RG213. Compared to RG8X, the 240 has 4 times the power handling capacity. Tam |
tnx al coax
In article . com,
"art" wrote: On 26 Mar, 00:40, Ian White GM3SEK wrote: Ed wrote: just wanted to say thanks to the many posters , i learned alot about coax in general and thanks to a few posters i somehow 'got it'... and started to see why a little al where the cu used to be like for like didn't make as dramatic a diff as my untrained gut assumed it would, dunno why i was so bothered by it bad assumption thanks for all the facts , from what i learned unless i can see that the outer jacket is soooo much better about keeping the elements out i'd be concerned about using al but for inside runs it could save alot of money and be just as good usually the smallest coax i use is like lmr600/cinta600 and some other variants some are all copper some are plated i use it for both hf and naturally 2m/440 for higher i use lmr900 or heliax 1" it's very heavy 100ft to roof 100ft indoor runs stiff and $$ so naturally i was attracted to the al coax but didn't want to suffer losses or other al related problems if corrosian is the the big killer i ponder even say for a indoor 2ft al patch cable, how long that would last say compared to a coax copper equivlant , i have really really old patch cables that still measure good i'll be interested to see some real world long term testing of this stuff but seems to be sexy thanks everybody |
tnx al coax
"ml" wrote in message ... In article . com, "art" wrote: On 26 Mar, 00:40, Ian White GM3SEK wrote: Ed wrote: just wanted to say thanks to the many posters , i learned alot about coax in general and thanks to a few posters i somehow 'got it'... and started to see why a little al where the cu used to be like for like didn't make as dramatic a diff as my untrained gut assumed it would, dunno why i was so bothered by it bad assumption thanks for all the facts , from what i learned unless i can see that the outer jacket is soooo much better about keeping the elements out i'd be concerned about using al but for inside runs it could save alot of money and be just as good usually the smallest coax i use is like lmr600/cinta600 and some other variants some are all copper some are plated i use it for both hf and naturally 2m/440 for higher i use lmr900 or heliax 1" it's very heavy 100ft to roof 100ft indoor runs stiff and $$ so naturally i was attracted to the al coax but didn't want to suffer losses or other al related problems if corrosian is the the big killer i ponder even say for a indoor 2ft al patch cable, how long that would last say compared to a coax copper equivlant , i have really really old patch cables that still measure good i'll be interested to see some real world long term testing of this stuff but seems to be sexy thanks everybody I have some al that has been up since summer 1990 with no problems. It has actually held up better than the run of RG213 I put up the following year. |
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