Re: Topband: Problem with compression F connectors on Quad RG-6
On 5/7/2013 7:33 AM, Paul Christensen wrote: The standard drop cable is a bonded foil with single braid, it has been that way since the late 1970's. The current best grade is Brightwire by CommScope. Any good cable will far exceed FCC specs without a quad shield. It remained that way with Comcast ATT Broadband at least until 2002 when I left ATT corporate engineering, shortly after the merger. I doubt much has changed since then. Concerns are a bit different in the broadband world where downstream leakage must be minimized between 50 MHz - 1 GHz. The upstream path is in HF region, but no sane cable operator uses spectrum below about 10 MHz. The only services anywhere near that area of spectrum are used for data transponders and IPPV from the set-top box where modulation is almost always QPSK. Telephony and DOCSIS cable modem service is all relegated to an area above 20 MHz. In the Jacksonville Comcast system, it's now all above 30 MHz which was made possible through the use of tighter diplexer specs in the system amps and fiber-optic nodes. if you could see a spectrum analyzer display of the return path back at the headend, you would be amazed that the return path works at all. Any point of ingress results high levels of interference, most notably SWBC. I recall writing up a paper in the mid-'90s that predicted a need for better return path certification and an upward move of the lowest usable frequency to well above 20 MHz. I pointed to the 11-year sunspot cycle as an important driver. The non-ham engineers in our group didn't get it. But the CTO of MediaOne was a ham, and he did get it. The public did not know it, but there was a real fear between 1995 and 2000 that return path broadband technology would never work. When you consider all the points of potential failure, especially on a power-passing system, it truly is a miracle that it works at all. Consider this: The typical fiber-optic node services between 200-500 home passings. From the comfort of your living room, and with an RF signal generator, one can wipe out an entire service area when the return path frequencies of the system are known. This isn't theoretical, I demonstrated the impact to a sober group of engineers with an Eico generator. That potential still exists today. Concerning SANS connectors and wiring, I would take the lead from the cable operators. They cannot afford to have unreliable cables anywhere between the customer equipment and the headend or hub facilities. When you've got thousands of miles of cable plant and interfacing hardware, that becomes the most important piece in the network. If a router, modulator or fiber amp fails in the system, the fix is easy with money. But if you deploy bad cable and hardware into a system, you'll feel the pain a long time as it affects long-term service call volume, unhappy customers, and angry government leaders who generally hate the cable operators. Paul, W9AC About six months ago, our garbage truck hit the sagging telephone/CATV drops that serve my house and my neighbor's. It took several days to get a response from Time Warner despite the fact that the cable was hanging at neck level at times (we pulled it up the best we could only to see it get knocked down again by the various delivery trucks that come through the neighborhood). In any case, when Time Warner finally responded, I saved the discarded drop cable and took it up to my station in the desert north of here. I didn't pay close attention to it at the time, but this discussion got me to wondering what sort of shielding was used in that drop cable, so I retrieved some last time I was up there. This evening I took a close look at it. The drop cable is Times Fiber Communications (TFC/Amphenol) T10 Teledrop. It look like an RG6 (I didn't measure the diameter) paired with a messenger on one side and a telephone twisted pair on the other. The coax is tri-shield (bonded inner tape layer, braid, and outer tape layer). There also appears to be some sort of sticky flooding compound which may be TFC's Lifetime non-drip/non-leak flooding compound (see page 85 of the following): http://www.timesfiber.com/TFC_Cable_Book_III.pdf The other interesting information in the TFC Cable Book III is Technical Note 1025 Drop-Cable Transfer Impedance starting on page 70. What this note says is that you can't ignore cable aging due to flexure and corrosion when looking at shielding effectiveness. Comparing the shielding effectiveness at beginning of life (BOL) can yield vastly different conclusion compared with shielding effectiveness done on cable that has experienced significant environmental exposure. Quad shield seems to have been developed to address the problems that come from foil seam separation that occurs as the result of drop cable flexing. It's actually a pretty complicated trade space which may explain some of the lack of consensus in
Re: Topband: Problem with compression F connectors on Quad RG-6
Mike, Here's a link to an article on crimp UHF connectors with suppliers. It's from 2008 so the prices may have changed: http://www.eham.net/articles/19257 Today, you can get a crimp tool from a number of suppliers ranging from the low $30s and up. I have been using RF Industries UHF Crimp connectors with RG213 and LMR400 for years with excellent results. Make sure you have the correct connector for the coax you are using. I always solder the center conductor in the connector rather than crimping it. No more connector problems, no shorts or melted dielectric, etc. and much faster and easier to get it right. W3LPL and others have mentioned many times that the extra cost of the connectors is small compared to the cost of the entire installation and is worth it to reduce or eliminate a common point of failure. Les W2LK On 5/8/2013 6:16 PM, Michael Tope wrote: On 5/7/2013 7:55 PM, Tom W8JI wrote: LMR400 or any cable, in sensitive applications, requires a solid bond to the shield that carries the vast majority of return current. In the case of almost all cables on HF and higher, that is the innermost foil. Of course it is different at audio or lower frequencies. One common connector problem comes from not forcing the woven shield tight against the foil at the connector, or having the foil or woven shield tarnish or corrode. The path to the inside of the foil is out on the braid to an eventual contact point, then back on the outside of the foil to the foil edge. At the edge current can go inside. This is like adding 2X the length of the path to the connection point in overall shield connection path length. (Current can also get in across the edge of a longitudinal seam, if the seam's overlap is insulated. The problem with that is the seam can kill UHF performance.) If you solder to the shield of LMR400, and put it on a network analyzer and measure the stub characteristics, many times (not always) it will move around as the cable is flexed. This is because the soldering heat contracts the dielectric, releasing pressure between the braid overlay and the foil. Now you have a crummy connection that changes electrical length of the connection to the real shield. Even if you do things right, once the foil and braid develop an oxide layer the connection goes away. This can work its way out for several feet of cable length, really messing up a cable. This will not show with a single shield. Cables with foil have to be installed and treated correctly. The more layers you add, the more careful we must be. Since the extra layers are pretty much meaningless, the best practice is to avoid them. Use a good shield against the center and connect to it at the connector. Tom, I'll have to admit that I haven't given this much thought, but what you are saying about the foil to braid contact makes perfect sense. I do recall one friend who is a rabid VHF/UHF repeater builder complaining that LMR-400 has issues with IMD. Perhaps this is why. Can you recommend a source for a good LMR-400 crimp connectors and the corresponding installation tools? To date I've been soldering PL-259s on all the LMR-400 I've used as if it were regular single shield RG8. I haven't had any hard failures, but clearly there is some risk to doing this depending on the application. In fact I do recall some phantom inter-station QRM that would come and go when we had an SO2R setup running at W6UE some years back. Some of the coax used in that setup was LMR-400 with soldered PL-259s. 73, Mike W4EF. All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
Im another who has been using the RF Industries tool for well over 20 years for both 50 Ohm and mostly CATV or Belden RG-11 foam. No failures or funny things happening. Carl KM1H Mike, Here's a link to an article on crimp UHF connectors with suppliers. It's from 2008 so the prices may have changed: http://www.eham.net/articles/19257 Today, you can get a crimp tool from a number of suppliers ranging from the low $30s and up. I have been using RF Industries UHF Crimp connectors with RG213 and LMR400 for years with excellent results. Make sure you have the correct connector for the coax you are using. I always solder the center conductor in the connector rather than crimping it. No more connector problems, no shorts or melted dielectric, etc. and much faster and easier to get it right. W3LPL and others have mentioned many times that the extra cost of the connectors is small compared to the cost of the entire installation and is worth it to reduce or eliminate a common point of failure. Les W2LK On 5/8/2013 6:16 PM, Michael Tope wrote: On 5/7/2013 7:55 PM, Tom W8JI wrote: LMR400 or any cable, in sensitive applications, requires a solid bond to the shield that carries the vast majority of return current. In the case of almost all cables on HF and higher, that is the innermost foil. Of course it is different at audio or lower frequencies. One common connector problem comes from not forcing the woven shield tight against the foil at the connector, or having the foil or woven shield tarnish or corrode. The path to the inside of the foil is out on the braid to an eventual contact point, then back on the outside of the foil to the foil edge. At the edge current can go inside. This is like adding 2X the length of the path to the connection point in overall shield connection path length. (Current can also get in across the edge of a longitudinal seam, if the seam's overlap is insulated. The problem with that is the seam can kill UHF performance.) If you solder to the shield of LMR400, and put it on a network analyzer and measure the stub characteristics, many times (not always) it will move around as the cable is flexed. This is because the soldering heat contracts the dielectric, releasing pressure between the braid overlay and the foil. Now you have a crummy connection that changes electrical length of the connection to the real shield. Even if you do things right, once the foil and braid develop an oxide layer the connection goes away. This can work its way out for several feet of cable length, really messing up a cable. This will not show with a single shield. Cables with foil have to be installed and treated correctly. The more layers you add, the more careful we must be. Since the extra layers are pretty much meaningless, the best practice is to avoid them. Use a good shield against the center and connect to it at the connector. Tom, I'll have to admit that I haven't given this much thought, but what you are saying about the foil to braid contact makes perfect sense. I do recall one friend who is a rabid VHF/UHF repeater builder complaining that LMR-400 has issues with IMD. Perhaps this is why. Can you recommend a source for a good LMR-400 crimp connectors and the corresponding installation tools? To date I've been soldering PL-259s on all the LMR-400 I've used as if it were regular single shield RG8. I haven't had any hard failures, but clearly there is some risk to doing this depending on the application. In fact I do recall some phantom inter-station QRM that would come and go when we had an SO2R setup running at W6UE some years back. Some of the coax used in that setup was LMR-400 with soldered PL-259s. 73, Mike W4EF. All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3162/5810 - Release Date: 05/09/13 All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
On 5/7/2013 7:55 PM, Tom W8JI wrote: LMR400 or any cable, in sensitive applications, requires a solid bond to the shield that carries the vast majority of return current. In the case of almost all cables on HF and higher, that is the innermost foil. Of course it is different at audio or lower frequencies. One common connector problem comes from not forcing the woven shield tight against the foil at the connector, or having the foil or woven shield tarnish or corrode. The path to the inside of the foil is out on the braid to an eventual contact point, then back on the outside of the foil to the foil edge. At the edge current can go inside. This is like adding 2X the length of the path to the connection point in overall shield connection path length. (Current can also get in across the edge of a longitudinal seam, if the seam's overlap is insulated. The problem with that is the seam can kill UHF performance.) If you solder to the shield of LMR400, and put it on a network analyzer and measure the stub characteristics, many times (not always) it will move around as the cable is flexed. This is because the soldering heat contracts the dielectric, releasing pressure between the braid overlay and the foil. Now you have a crummy connection that changes electrical length of the connection to the real shield. Even if you do things right, once the foil and braid develop an oxide layer the connection goes away. This can work its way out for several feet of cable length, really messing up a cable. This will not show with a single shield. Cables with foil have to be installed and treated correctly. The more layers you add, the more careful we must be. Since the extra layers are pretty much meaningless, the best practice is to avoid them. Use a good shield against the center and connect to it at the connector. Tom, I'll have to admit that I haven't given this much thought, but what you are saying about the foil to braid contact makes perfect sense. I do recall one friend who is a rabid VHF/UHF repeater builder complaining that LMR-400 has issues with IMD. Perhaps this is why. Can you recommend a source for a good LMR-400 crimp connectors and the corresponding installation tools? To date I've been soldering PL-259s on all the LMR-400 I've used as if it were regular single shield RG8. I haven't had any hard failures, but clearly there is some risk to doing this depending on the application. In fact I do recall some phantom inter-station QRM that would come and go when we had an SO2R setup running at W6UE some years back. Some of the coax used in that setup was LMR-400 with soldered PL-259s. 73, Mike W4EF. All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
CATV installers use almost 100% quad shield in order to keep the signals inside and not cause interfering leakage (egress); FCC specs are adamant about that. These specs go back to the 70's. In more recent years the cable also must keep local RFI (ingress) out. While they do use tape foil shield cables, CATV systems rarely use quad shield cables. As a matter of fact I just bought a bunch of drop cable from a CATV system, and it is all single foil single braid. This is true for the drop, which has a messenger strand, and the house wiring, which is identical without a messenger strand. In the late 70's and early 80's, I was system's engineer at a company that had dozens of small cable systems. We inherited some systems near an FM/AM station that had a second harmonic on a local TV channel video frequency. The former cable system operator had given up, after installing quad shield and all sorts of special cables. 100% of their problems were isolated power and CATV grounds, letting the AM signal loop through the system, and the quad shield developing poor connections letting the FM harmonic in. We ripped all that stuff out, and went with normal hardline and good quality drop cable, bonded the cable grounds to the entrance and breaker panels, and nearly 100% cured the system. We had dumpster load of special cable that was nothing but connector headaches. The standard drop cable is a bonded foil with single braid, it has been that way since the late 1970's. The current best grade is Brightwire by CommScope. Any good cable will far exceed FCC specs without a quad shield. Single-foil single-shield Brightwire has over 120 dB of external shield current to center conductor current isolation on 160 meters, and it gets better as you go up in frequency. I can't imagine anyone needing more than 80 dB isolation outside the house, and maybe 100 dB if it is in a noisy house. All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
What role does skin effect have in this situation - at 1.8 MHz? Skin depth isolates the outside and inside, virtually nothing passes through a conductor wall that is several skin depths thick. This is true for both the magnetic field and the electric field, and why shielded loops are a misnomer. Look at this link http://www.w8ji.com/skindepth.htm Current in the center has to be matched by current on the inside of the closest shield. Current always can get into the center three ways: 1.) The shield can be so thin it doesn't isolate the outside and inside, but then that would not be a good shield 2.) Current spills over an edge 3.) There is a direct connection to the inside If we study connectors with an accurate picture of what current has to do (current, the magnetic field, nor the electric field can NOT go through a wall several skin depths thick), we can spot potential issues with shield connections. We don't have to have a connection to the side if there is an edge to spill over that is right at the same connection spot. What we do not want is the edge to be inches from the connection point. For example, a braid overlay on top of foil that has a poor electrical and pressure connection to the foil is not a good connection point. This is why LMR400 is problematic when the braid is soldered to a PL-259. The very same cable is great with a crimp connector, if the cable is clean (not tarnished or corroded) inside. 73 Tom All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
The standard drop cable is a bonded foil with single braid, it has been that way since the late 1970's. The current best grade is Brightwire by CommScope. Any good cable will far exceed FCC specs without a quad shield. It remained that way with Comcast ATT Broadband at least until 2002 when I left ATT corporate engineering, shortly after the merger. I doubt much has changed since then. Concerns are a bit different in the broadband world where downstream leakage must be minimized between 50 MHz - 1 GHz. The upstream path is in HF region, but no sane cable operator uses spectrum below about 10 MHz. The only services anywhere near that area of spectrum are used for data transponders and IPPV from the set-top box where modulation is almost always QPSK. Telephony and DOCSIS cable modem service is all relegated to an area above 20 MHz. In the Jacksonville Comcast system, it's now all above 30 MHz which was made possible through the use of tighter diplexer specs in the system amps and fiber-optic nodes. if you could see a spectrum analyzer display of the return path back at the headend, you would be amazed that the return path works at all. Any point of ingress results high levels of interference, most notably SWBC. I recall writing up a paper in the mid-'90s that predicted a need for better return path certification and an upward move of the lowest usable frequency to well above 20 MHz. I pointed to the 11-year sunspot cycle as an important driver. The non-ham engineers in our group didn't get it. But the CTO of MediaOne was a ham, and he did get it. The public did not know it, but there was a real fear between 1995 and 2000 that return path broadband technology would never work. When you consider all the points of potential failure, especially on a power-passing system, it truly is a miracle that it works at all. Consider this: The typical fiber-optic node services between 200-500 home passings. From the comfort of your living room, and with an RF signal generator, one can wipe out an entire service area when the return path frequencies of the system are known. This isn't theoretical, I demonstrated the impact to a sober group of engineers with an Eico generator. That potential still exists today. Concerning SANS connectors and wiring, I would take the lead from the cable operators. They cannot afford to have unreliable cables anywhere between the customer equipment and the headend or hub facilities. When you've got thousands of miles of cable plant and interfacing hardware, that becomes the most important piece in the network. If a router, modulator or fiber amp fails in the system, the fix is easy with money. But if you deploy bad cable and hardware into a system, you'll feel the pain a long time as it affects long-term service call volume, unhappy customers, and angry government leaders who generally hate the cable operators. Paul, W9AC All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
Improper connector installation plagues many ham stations, not only with RG-6 CATV connectors but with all types of coaxial connectors. An improperly installed connector is an invitation to RFI ingress and equipment damage. At transmit power levels, an improperly installed connector can cause equipment damage. If you're not confident in your connector installation skills, its worth a few dollars to have them professionally installed. Quad cable connector installation requires skills and patience. Compounding the problem, hams often use connectors that are not intended for use with quad RG-6. Quad cable connector installation involves five specific steps, each performed carefully and correctly: 1. Use an RG-6 stripping tool to remove the jacket. Inspect the braid wires to be sure none of the wires are damaged. Never use a knife to remove the jacket, inevitably it will damage the fragile braid wires no matter how careful you are. 2. Carefully fold back only the outer braid and spread the braid wires evenly around the circumference of the cable jacket. Verify that no wires are broken. All of the braid wires should lay flat over the jacket, should not be more than 1/4 inch long, and should not be bunched up. 3. Remove the foil tape between the two braid shields. Do not use a knife to assist in foil tape removal. This step is time consuming and often ignored. The connector will be very difficult to install if the foil tape is not removed. If somehow you manage to force the connector onto the cable with the foil tape in place, the connector will be intermittent and unreliable. 4. Carefully fold back the inner braid and spread the braid wires evenly around the circumference of the cable jacket. Verify that no wires are broken. All of the braid wires should lay flat over the jacket, should not be more than 1/4 inch long, and should not be bunched up. 5. Install the proper connector for quad shield cable. Be sure the connector is fully seated. If you need to use great force to mate the connector something is wrong, either you used the wrong connector or the cable was improperly prepared . If somehow you manage to force the connector onto the cable, the connector will be intermittent and unreliable. Improper connector installation is so pervasive in the cable TV industry that CommScope prepared an illustrated paper on improper connector installation. http://docs.commscope.com/Public/ImproperQuadPrep.pdf 73 Frank W3LPL - Original Message - From: Paul Christensen w...@arrl.net To: topband topband@contesting.com Sent: Tuesday, May 7, 2013 3:33:00 PM Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 The standard drop cable is a bonded foil with single braid, it has been that way since the late 1970's. The current best grade is Brightwire by CommScope. Any good cable will far exceed FCC specs without a quad shield. It remained that way with Comcast ATT Broadband at least until 2002 when I left ATT corporate engineering, shortly after the merger. I doubt much has changed since then. Concerns are a bit different in the broadband world where downstream leakage must be minimized between 50 MHz - 1 GHz. The upstream path is in HF region, but no sane cable operator uses spectrum below about 10 MHz. The only services anywhere near that area of spectrum are used for data transponders and IPPV from the set-top box where modulation is almost always QPSK. Telephony and DOCSIS cable modem service is all relegated to an area above 20 MHz. In the Jacksonville Comcast system, it's now all above 30 MHz which was made possible through the use of tighter diplexer specs in the system amps and fiber-optic nodes. if you could see a spectrum analyzer display of the return path back at the headend, you would be amazed that the return path works at all. Any point of ingress results high levels of interference, most notably SWBC. I recall writing up a paper in the mid-'90s that predicted a need for better return path certification and an upward move of the lowest usable frequency to well above 20 MHz. I pointed to the 11-year sunspot cycle as an important driver. The non-ham engineers in our group didn't get it. But the CTO of MediaOne was a ham, and he did get it. The public did not know it, but there was a real fear between 1995 and 2000 that return path broadband technology would never work. When you consider all the points of potential failure, especially on a power-passing system, it truly is a miracle that it works at all. Consider this: The typical fiber-optic node services between 200-500 home passings. From the comfort of your living room, and with an RF signal generator, one can wipe out an entire service area when the return path frequencies of the system are known. This isn't theoretical, I demonstrated the impact to a sober group of engineers with an Eico generator. That potential still
Re: Topband: Problem with compression F connectors on Quad RG-6
- Original Message - From: Tom W8JI w...@w8ji.com To: topband topband@contesting.com Sent: Tuesday, May 07, 2013 9:48 AM Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 CATV installers use almost 100% quad shield in order to keep the signals inside and not cause interfering leakage (egress); FCC specs are adamant about that. These specs go back to the 70's. In more recent years the cable also must keep local RFI (ingress) out. While they do use tape foil shield cables, CATV systems rarely use quad shield cables. As a matter of fact I just bought a bunch of drop cable from a CATV system, and it is all single foil single braid. This is true for the drop, which has a messenger strand, and the house wiring, which is identical without a messenger strand. In the late 70's and early 80's, I was system's engineer at a company that had dozens of small cable systems. We inherited some systems near an FM/AM station that had a second harmonic on a local TV channel video frequency. The former cable system operator had given up, after installing quad shield and all sorts of special cables. 100% of their problems were isolated power and CATV grounds, letting the AM signal loop through the system, and the quad shield developing poor connections letting the FM harmonic in. We ripped all that stuff out, and went with normal hardline and good quality drop cable, bonded the cable grounds to the entrance and breaker panels, and nearly 100% cured the system. We had dumpster load of special cable that was nothing but connector headaches. The standard drop cable is a bonded foil with single braid, it has been that way since the late 1970's. The current best grade is Brightwire by CommScope. Any good cable will far exceed FCC specs without a quad shield. Single-foil single-shield Brightwire has over 120 dB of external shield current to center conductor current isolation on 160 meters, and it gets better as you go up in frequency. I can't imagine anyone needing more than 80 dB isolation outside the house, and maybe 100 dB if it is in a noisy house. Around here Comcast installers use TFC T-10 quad shield. Ive also seen PPC trishield used for satellite. As you can easily see they list their cables by RF noise enviroment from low for standard dual shield, medium-moderate for premium dual shield, plus high for trishield and quad for severe with these last 2 also rated for 2 way use. http://www.timesfiber.com/TFC_Cable_Book_III.pdf Go to Page 36 Dont let ANYONE tell you that the shielding type isnt important. In the 80's I was an engineering manager for Wang Labs broadband networking RD department and one of my responsibilities was qualifying all cable related components for outdoor and indoor use for moderate to severe RF enviroments which included nuclear carriers and plants, plus oil refineries. There was a measurable difference between dual and quad shield as well as percent of braid coverage. These cables plus connectors were tested in the screen room in the Tempest group. Tempest was a DOD/CIA Top Secret program tasked to minimize electronic signal ingress and egress from spies and saboteurs. Since I had maintained my TS Crypto clearance as a USN Reservist and as an engineering tech and an engineer for Sanders Associates who was a leader in Tempest technology, I had full access to the testing. I have also applied that knowledge at home for ham and consumer products ever since. It was Tempest starting in the mid 70's that gave me an understanding of ferrites for RFI, etc and that was applied to Wangs network as well as at home where I continue to do mortal battle with noise generators and common mode. Carl KM1H All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
But if you deploy bad cable and hardware into a system, you'll feel the pain a long time as it affects long-term service call volume, unhappy customers, and angry government leaders who generally hate the cable operators. Paul, W9AC I started the Cable Committee here and led it thru many negotiations and problems with various CATV outfits over 25 years. The current group along with Comcast have maintained an excellent relationship but it took lots of training of committee members who did not have a tech backround and beating on cable company reps who would try anything to claim innocence or double talk their way around contract, and technical issues (much like what happens on some ham forums (-; It was a nice compliment when other towns sent their members here to get edumecated. Carl KM1H All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
On 5/7/2013 9:23 AM, donov...@starpower.net wrote: 3. Remove the foil tape between the two braid shields. Do not use a knife to assist in foil tape removal. This step is time consuming and often ignored. The connector will be very difficult to install if the foil tape is not removed. If somehow you manage to force the connector onto the cable with the foil tape in place, the connector will be intermittent and unreliable. This is the key issue with these things. I find that I simply cannot tear the foil with my bare hands, on account of the fact that it is not foil, but rather plastic (probably mylar) with an evaporated or sputtered metal coating. I have resorted to using a very small pair of diagonal cutters to cut the foil. Any other suggestions? Rick N6RK All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
You've been watching over my shoulder, Rick. Mis dos centavos de Milt, N5IA -Original Message- From: Richard (Rick) Karlquist Sent: Tuesday, May 07, 2013 3:27 PM To: donov...@starpower.net Cc: PVRC ; topband Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 On 5/7/2013 9:23 AM, donov...@starpower.net wrote: 3. Remove the foil tape between the two braid shields. Do not use a knife to assist in foil tape removal. This step is time consuming and often ignored. The connector will be very difficult to install if the foil tape is not removed. If somehow you manage to force the connector onto the cable with the foil tape in place, the connector will be intermittent and unreliable. This is the key issue with these things. I find that I simply cannot tear the foil with my bare hands, on account of the fact that it is not foil, but rather plastic (probably mylar) with an evaporated or sputtered metal coating. I have resorted to using a very small pair of diagonal cutters to cut the foil. Any other suggestions? Rick N6RK All good topband ops know how to put up a beverage at night. _ Topband Reflector - No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.3272 / Virus Database: 3162/6306 - Release Date: 05/07/13 All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
The way that you are doing it it exactly the way that Belden recommends doing it in their 3' 37 video on YouTube (the video recommended here on May 5 by Paul, W9AC). I forget the exact URL, but it's easy to find. Belden has several similar videos on YouTube for other types of coax and connectors; the video you want is the one that's 3' 37 long. That foil with the blue Mylar coating between the braids HAS to be removed. The other foil, the one that's bonded to the outside of the dielectric, is NOT removed. 73, Mike www.w0btu.com On Tue, May 7, 2013 at 5:27 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: 3. Remove the foil tape between the two braid shields. Do not use a knife to assist in foil tape removal. This step is time consuming and often ignored. ... This is the key issue with these things. I find that I simply cannot tear the foil with my bare hands, on account of the fact that it is not foil, but rather plastic (probably mylar) with an evaporated or sputtered metal coating. I have resorted to using a very small pair of diagonal cutters to cut the foil. Any other suggestions? All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
This is the YouTube video Mike referred to: https://www.youtube.com/watch?v=kN1yUBp2CzI 73 Frank W3LPL - Original Message - From: Mike Waters mikew...@gmail.com To: topband topband@contesting.com Sent: Tuesday, May 7, 2013 11:49:06 PM Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 The way that you are doing it it exactly the way that Belden recommends doing it in their 3' 37 video on YouTube (the video recommended here on May 5 by Paul, W9AC). I forget the exact URL, but it's easy to find. Belden has several similar videos on YouTube for other types of coax and connectors; the video you want is the one that's 3' 37 long. That foil with the blue Mylar coating between the braids HAS to be removed. The other foil, the one that's bonded to the outside of the dielectric, is NOT removed. 73, Mike www.w0btu.com On Tue, May 7, 2013 at 5:27 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: 3. Remove the foil tape between the two braid shields. Do not use a knife to assist in foil tape removal. This step is time consuming and often ignored. ... This is the key issue with these things. I find that I simply cannot tear the foil with my bare hands, on account of the fact that it is not foil, but rather plastic (probably mylar) with an evaporated or sputtered metal coating. I have resorted to using a very small pair of diagonal cutters to cut the foil. Any other suggestions? All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
I'm interested in your comment about LMR400 and soldered braids, Tom. I understand the point about shield current flowing on the insde of the foil or braid closest to the center conductor, but if the shield connection is faulty, oxidized, or has high resistance, then it seems to me the outer braid (presumed to be soldered to the PL259) would carry a potion of the return current. It would be an interesting physics problem to work out the relative return currents carried by a coaxial cable with two concentric shields, each having non-zero resistivity, or a thickness comparable or thinner than the skin depth.. I don't recall the skin depth at 1.8MHz, but my guess is it's probably longer than the thickness of the coating on aluminized mylar. I don't know what the foil thickness is on LMR400. 2 MHz skin depth of copper is .0018 inches. 2 MHz skin depth of aluminum is .0023 inches. The LMR400 type cable I have is about .006-.008 foil. I chemically stripped the foil off, and the foil was two wraps thick around the cable. LMR400 or any cable, in sensitive applications, requires a solid bond to the shield that carries the vast majority of return current. In the case of almost all cables on HF and higher, that is the innermost foil. Of course it is different at audio or lower frequencies. One common connector problem comes from not forcing the woven shield tight against the foil at the connector, or having the foil or woven shield tarnish or corrode. The path to the inside of the foil is out on the braid to an eventual contact point, then back on the outside of the foil to the foil edge. At the edge current can go inside. This is like adding 2X the length of the path to the connection point in overall shield connection path length. (Current can also get in across the edge of a longitudinal seam, if the seam's overlap is insulated. The problem with that is the seam can kill UHF performance.) If you solder to the shield of LMR400, and put it on a network analyzer and measure the stub characteristics, many times (not always) it will move around as the cable is flexed. This is because the soldering heat contracts the dielectric, releasing pressure between the braid overlay and the foil. Now you have a crummy connection that changes electrical length of the connection to the real shield. Even if you do things right, once the foil and braid develop an oxide layer the connection goes away. This can work its way out for several feet of cable length, really messing up a cable. This will not show with a single shield. Cables with foil have to be installed and treated correctly. The more layers you add, the more careful we must be. Since the extra layers are pretty much meaningless, the best practice is to avoid them. Use a good shield against the center and connect to it at the connector. I also wonder about the ability of a thin foil shield to carry Amps of RF without appreciable loss! RF flows on the surfaces nearest opposing (differential) current flow. You have the small outer surface area of the center conductor carrying the same current as all of that wide area of the foil. The shield has a great deal of surface area compared to the center. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
Back on the subject of RG-6, Ideal specifies folding back the top layer of braid, cutting off the first foil layer, then folding back the second layer of braid. The trouble is that on my cable, the second foil layer is mylar, aluminized on the outside. On the one hand this means good contact between the aluminum layer and the inner braid, but when you put on the connector it folds the inner mylar back, exposing the dielectric and putting the blue mylar side up over at least part of the circumference. I can see that in a worst case situation that could insulate the inner aluminized mylar from the connector, but don't know if it would really matter since the inner braid is folded back and making a good compression connection both to the inner foil and to the connector shell. What role does skin effect have in this situation - at 1.8 MHz? 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 5/5/2013 11:08 PM, Tom W8JI wrote: How about folding the shields back a little? I think that's a superior way of doing it as opposed to cutting them all flush with the jacket. Be careful doing that or using any non-approved assembly method, or using improper connectors. Many cables (I'm not sure exactly what percentage, but I saw a lot of them) aluminize mylar to form the foil shield. You can usually see the mylar on close inspection, it often is blue or a blue tint. This insulates one side of the foil. The shield that must have the best integrity at connectors is the shield just outside to the center conductor. Nearly all shield current in on the inside of that shield. If you do not get a good solid connection to the INSIDE wall of that shield, the cable will have all sorts of issues. It doesn't matter how solid outside shield connections are, because the innermost surface of the innermost shield does all of the real work. The inner wall connection can be, and usually is, by conduction across the cut end of the shield. Say the inner shield is mylar on the dielectric side, or bonded to the dielectric. The bare outside contacts the braid with pressure. The current just travels across the cut end edge (a very short path) to the inside of the inner shield. If you do something to miss that good solid end connection to the inner foil edge, like folding a mylar shield over so blue side is out, the connection is by stray coupling over what can be a pretty long length of cable, adding many feet to the shield connection path.Or you might have no connection at all. I generally avoid quad shield, because the extra layers are unnecessary and can often cause connection problems. This is especially true outside with lightning and age. I asked a question here some months ago about whether or not that should be done or not on my flooded quad-shield F-6 (the CATV alum. shield version of RG-6) that I use for my Beverages and to feed my inverted-L. Some people said absolutely not! and others said absolutely they should!. People do all sorts of strange things with shields. With copper braid, aluminum braid, or solid aluminum foil (not aluminized mylar) you can do almost anything at HF and get away with it. I see people fold the shield back over RG-8 and screw the connector over it! Just because it works in some cases, that doesn't mean it is a good idea. One cable that is really misused is LMR400. If you solder to the braid on LMR400, you set yourself up for shield connection problems. This is because the inner foil, and that is the real shield, often moves away from the braid and makes a sloppy connection. Sometimes wiggling the cable will make the electrical length of the cable change, and shield integrity is all over the place, when the cable is soldered. This generally won't hurt with dipoles, but it can with critical applications. Crimps actually make a better connection. Since folding them back is the only way of being sure that the braids are all making contact with the shell of the F connector, I now fold the shields back a little in my snap-and-seal F connectors. How can that hurt anything? I think it's a better way to do it. I would always use the correct connector, and install the connectors the way the connector and cable manufacturer say. They usually know more about their products than we do. :-) It is a bad idea to improve installation instructions without understanding the product in precise detail. How many people do you think understand the issue caused by overlaying a foil shield with braid, and soldering to the braid? 73 Tom All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
How about folding the shields back a little? I think that's a superior way of doing it as opposed to cutting them all flush with the jacket. Be careful doing that or using any non-approved assembly method, or using improper connectors. Many cables (I'm not sure exactly what percentage, but I saw a lot of them) aluminize mylar to form the foil shield. You can usually see the mylar on close inspection, it often is blue or a blue tint. This insulates one side of the foil. The shield that must have the best integrity at connectors is the shield just outside to the center conductor. Nearly all shield current in on the inside of that shield. If you do not get a good solid connection to the INSIDE wall of that shield, the cable will have all sorts of issues. It doesn't matter how solid outside shield connections are, because the innermost surface of the innermost shield does all of the real work. The inner wall connection can be, and usually is, by conduction across the cut end of the shield. Say the inner shield is mylar on the dielectric side, or bonded to the dielectric. The bare outside contacts the braid with pressure. The current just travels across the cut end edge (a very short path) to the inside of the inner shield. If you do something to miss that good solid end connection to the inner foil edge, like folding a mylar shield over so blue side is out, the connection is by stray coupling over what can be a pretty long length of cable, adding many feet to the shield connection path.Or you might have no connection at all. I generally avoid quad shield, because the extra layers are unnecessary and can often cause connection problems. This is especially true outside with lightning and age. I asked a question here some months ago about whether or not that should be done or not on my flooded quad-shield F-6 (the CATV alum. shield version of RG-6) that I use for my Beverages and to feed my inverted-L. Some people said absolutely not! and others said absolutely they should!. People do all sorts of strange things with shields. With copper braid, aluminum braid, or solid aluminum foil (not aluminized mylar) you can do almost anything at HF and get away with it. I see people fold the shield back over RG-8 and screw the connector over it! Just because it works in some cases, that doesn't mean it is a good idea. One cable that is really misused is LMR400. If you solder to the braid on LMR400, you set yourself up for shield connection problems. This is because the inner foil, and that is the real shield, often moves away from the braid and makes a sloppy connection. Sometimes wiggling the cable will make the electrical length of the cable change, and shield integrity is all over the place, when the cable is soldered. This generally won't hurt with dipoles, but it can with critical applications. Crimps actually make a better connection. Since folding them back is the only way of being sure that the braids are all making contact with the shell of the F connector, I now fold the shields back a little in my snap-and-seal F connectors. How can that hurt anything? I think it's a better way to do it. I would always use the correct connector, and install the connectors the way the connector and cable manufacturer say. They usually know more about their products than we do. :-) It is a bad idea to improve installation instructions without understanding the product in precise detail. How many people do you think understand the issue caused by overlaying a foil shield with braid, and soldering to the braid? 73 Tom CATV installers use almost 100% quad shield in order to keep the signals inside and not cause interfering leakage (egress); FCC specs are adamant about that. These specs go back to the 70's. In more recent years the cable also must keep local RFI (ingress) out. For topband Id suspect that the foil thickness is so thin that some skin depth currents are on the outside. The foil is BONDED to the foam dielectric and is not supposed to be folded back; I dont know where that misinformation originated. Id suggest actually reading the connector manufacturers and major installation professionals cable prep instructions and all the ones Ive seen specifically states to NOT fold back that foil. For QS the outer braid is folded back, the next layer is the outer foil and that is removed, and then the inner braid is folded back. The inner foil goes thru the connector tube and both braids go between the outer and inner tubes. Carl KM1H All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
How about folding the shields back a little? I think that's a superior way of doing it as opposed to cutting them all flush with the jacket. I asked a question here some months ago about whether or not that should be done or not on my flooded quad-shield F-6 (the CATV alum. shield version of RG-6) that I use for my Beverages and to feed my inverted-L. Some people said absolutely not! and others said absolutely they should!. Since folding them back is the only way of being sure that the braids are all making contact with the shell of the F connector, I now fold the shields back a little in my snap-and-seal F connectors. How can that hurt anything? I think it's a better way to do it. BTW, I run the legal limit through my F-6 and F connectors on 160. :-) I know others do, too. They don't even get warm. 73, Mike www.w0btu.com All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
On 5/4/2013 2:07 PM, Pete Smith N4ZR wrote: I'm having a repeated weird problem with compression F connectors on quad-shield RG6. When I connect a short length (say 4 feet) of cable to my MFJ-259B, I would expect R650. Instead, when I wiggle the coax, occasionally I see the display change to R=0 and X= several hundred ohms at 1.8 MHz. This makes no sense to me - the R implies ashort, but where's all the X coming from? The problem seems to vary with the same connector and different PL-259 to F adapters, which makes me wonder what might be happening inside the adapters, but I can't imagine anything producing this result. I have also been unsuccessful in detecting a short using a simple DC multimeter. I;'m wondering if I should go through my RX antennas and replace all the F connectors and particularly the F to 259 adapters with something else, but what? BNCs? Anyone have any wisdom? I never have problems with F connectors. I buy quality Belden RG-6/U Quad Shield from ACK Radio in Atlanta as well as the right F connectors, and use a quality compression tool. There are several F connector sizes. The right one goes on the cable rather easily if it is stripped properly... All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
Mike, I rarely recommend YouTube videos, but Belden has produced a 3' 37 second video promoting their ProSNS line of Snap-N-Seal F connectors. This list is tightly run, or I would otherwise post a link. Just run a search for Belden ProSNS. At 2 minutes into the video, the Belden rep does exactly as you described. However, in the Belden product, a plastic guide tube helps to transition the prepared cable end into the connector. After full insertion, the guide tube pops out of the assembly and is discarded. That feature probably qualifies as one of those flash of genius novelty ideas that separates this product from the others and gets awarded a patent! Other YouTube videos show a similar braid flaring, especially when using quad-shield. But be suspicious of any information that does not come from the product's vendor. I would also carefully evaluate any similar Snap-N-Seal knock-off product from Asia. In quantities, these connectors are inexpensive enough to purchase from well-known industrial suppliers. Paul, W9AC - Original Message - From: Mike Waters mikew...@gmail.com To: topband topband@contesting.com Sent: Saturday, May 04, 2013 11:12 PM Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 How about folding the shields back a little? I think that's a superior way of doing it as opposed to cutting them all flush with the jacket. I asked a question here some months ago about whether or not that should be done or not on my flooded quad-shield F-6 (the CATV alum. shield version of RG-6) that I use for my Beverages and to feed my inverted-L. Some people said absolutely not! and others said absolutely they should!. Since folding them back is the only way of being sure that the braids are all making contact with the shell of the F connector, I now fold the shields back a little in my snap-and-seal F connectors. How can that hurt anything? I think it's a better way to do it. BTW, I run the legal limit through my F-6 and F connectors on 160. :-) I know others do, too. They don't even get warm. 73, Mike www.w0btu.com All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
Very interesting, Jim - I have been using Ideal connectors from Home Depot, and they have no color band at all (nor do they have decent instructions for installing). I will try to find some of the black-banded ones (I have red-banded ones for RG-59). 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 5/4/2013 11:13 PM, Jim Garland wrote: I'm sure most of you know this already, but there are different compression F-connectors for ordinary RG6 and for quad-shield RG6. I use Ideal brand connectors with matching compression tool, and there is a color-coded band for the two types of cables (blue for RG6 and black for quad-shield). It is not always easy to find the installation instructions, but for quad shield especially, it is very important to follow the directions so as to make sure the multiple aluminum foil and braided shields make appropriate contact at the connector, just as Tom cautions. 73, Jim W8ZR -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Saturday, May 04, 2013 6:08 PM To: Topband@contesting.com Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 I'm having a repeated weird problem with compression F connectors on quad-shield RG6. When I connect a short length (say 4 feet) of cable to my MFJ-259B, I would expect R650. Instead, when I wiggle the coax, occasionally I see the display change to R=0 and X= several hundred ohms at 1.8 MHz. This makes no sense to me - the R implies ashort, but where's all the X coming from? R doesn't come from a short, it comes from no loss resistance, or more correctly very low loss resistance. It sounds like the connector you have is not contacting all the shields. This is typical for mismatched connectors and cable, or improperly manufactured cables. It could be somewhere else also, but I've seen this before with quad shield. That's why I avoid it. The problem seems to vary with the same connector and different PL-259 to F adapters, which makes me wonder what might be happening inside the adapters, but I can't imagine anything producing this result. I have also been unsuccessful in detecting a short using a simple DC multimeter. Remember how RF current flows. It flows on the outside of cables, unless it has a connection path to the inner shield. If you have cable with Mylar on the inside of one or more shield layers, and a connector that only contacts the outside of the outer shield, the inner shields that carry nearly all of the desired transmission line currents will be insulated and isolated from the shield at the connector. Every shield has to be contacted at the connector, or at least the inner shield does. This might not be it, but it is a common issue with quad shield. Dual shield is much more forgiving of connectors. You'll never detect the leakage in dual shield in outside runs. If you have nasty common mode problems, a thicker shield will help. It is also just as simple to add a few dozen or few hundred ohms of common mode choking to regular dual shield cables and knock down CM ingress to levels that cannot be noticed. I;'m wondering if I should go through my RX antennas and replace all the F connectors and particularly the F to 259 adapters with something else, but what? BNCs? BNC's are worse yet, as a general rule. They rely on spring pressure for the shield path. Look into a type match error between the cable you have and the connectors, or a connector installation error. 73 Tom All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
Hi Pete, The Ideal blue-banded connectors for RG6 are part number #89-055, and the black-banded ones for quad shield are #89-056. They both use compression tool #30-603. 73, Jim W8ZR -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Pete Smith N4ZR Sent: Sunday, May 05, 2013 1:39 PM To: Topband@contesting.com Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 Very interesting, Jim - I have been using Ideal connectors from Home Depot, and they have no color band at all (nor do they have decent instructions for installing). I will try to find some of the black-banded ones (I have red-banded ones for RG-59). 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 5/4/2013 11:13 PM, Jim Garland wrote: I'm sure most of you know this already, but there are different compression F-connectors for ordinary RG6 and for quad-shield RG6. I use Ideal brand connectors with matching compression tool, and there is a color-coded band for the two types of cables (blue for RG6 and black for quad-shield). It is not always easy to find the installation instructions, but for quad shield especially, it is very important to follow the directions so as to make sure the multiple aluminum foil and braided shields make appropriate contact at the connector, just as Tom cautions. 73, Jim W8ZR -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Saturday, May 04, 2013 6:08 PM To: Topband@contesting.com Subject: Re: Topband: Problem with compression F connectors on Quad RG-6 I'm having a repeated weird problem with compression F connectors on quad-shield RG6. When I connect a short length (say 4 feet) of cable to my MFJ-259B, I would expect R650. Instead, when I wiggle the coax, occasionally I see the display change to R=0 and X= several hundred ohms at 1.8 MHz. This makes no sense to me - the R implies ashort, but where's all the X coming from? R doesn't come from a short, it comes from no loss resistance, or more correctly very low loss resistance. It sounds like the connector you have is not contacting all the shields. This is typical for mismatched connectors and cable, or improperly manufactured cables. It could be somewhere else also, but I've seen this before with quad shield. That's why I avoid it. The problem seems to vary with the same connector and different PL-259 to F adapters, which makes me wonder what might be happening inside the adapters, but I can't imagine anything producing this result. I have also been unsuccessful in detecting a short using a simple DC multimeter. Remember how RF current flows. It flows on the outside of cables, unless it has a connection path to the inner shield. If you have cable with Mylar on the inside of one or more shield layers, and a connector that only contacts the outside of the outer shield, the inner shields that carry nearly all of the desired transmission line currents will be insulated and isolated from the shield at the connector. Every shield has to be contacted at the connector, or at least the inner shield does. This might not be it, but it is a common issue with quad shield. Dual shield is much more forgiving of connectors. You'll never detect the leakage in dual shield in outside runs. If you have nasty common mode problems, a thicker shield will help. It is also just as simple to add a few dozen or few hundred ohms of common mode choking to regular dual shield cables and knock down CM ingress to levels that cannot be noticed. I;'m wondering if I should go through my RX antennas and replace all the F connectors and particularly the F to 259 adapters with something else, but what? BNCs? BNC's are worse yet, as a general rule. They rely on spring pressure for the shield path. Look into a type match error between the cable you have and the connectors, or a connector installation error. 73 Tom All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
How about folding the shields back a little? I think that's a superior way of doing it as opposed to cutting them all flush with the jacket. Be careful doing that or using any non-approved assembly method, or using improper connectors. Many cables (I'm not sure exactly what percentage, but I saw a lot of them) aluminize mylar to form the foil shield. You can usually see the mylar on close inspection, it often is blue or a blue tint. This insulates one side of the foil. The shield that must have the best integrity at connectors is the shield just outside to the center conductor. Nearly all shield current in on the inside of that shield. If you do not get a good solid connection to the INSIDE wall of that shield, the cable will have all sorts of issues. It doesn't matter how solid outside shield connections are, because the innermost surface of the innermost shield does all of the real work. The inner wall connection can be, and usually is, by conduction across the cut end of the shield. Say the inner shield is mylar on the dielectric side, or bonded to the dielectric. The bare outside contacts the braid with pressure. The current just travels across the cut end edge (a very short path) to the inside of the inner shield. If you do something to miss that good solid end connection to the inner foil edge, like folding a mylar shield over so blue side is out, the connection is by stray coupling over what can be a pretty long length of cable, adding many feet to the shield connection path.Or you might have no connection at all. I generally avoid quad shield, because the extra layers are unnecessary and can often cause connection problems. This is especially true outside with lightning and age. I asked a question here some months ago about whether or not that should be done or not on my flooded quad-shield F-6 (the CATV alum. shield version of RG-6) that I use for my Beverages and to feed my inverted-L. Some people said absolutely not! and others said absolutely they should!. People do all sorts of strange things with shields. With copper braid, aluminum braid, or solid aluminum foil (not aluminized mylar) you can do almost anything at HF and get away with it. I see people fold the shield back over RG-8 and screw the connector over it! Just because it works in some cases, that doesn't mean it is a good idea. One cable that is really misused is LMR400. If you solder to the braid on LMR400, you set yourself up for shield connection problems. This is because the inner foil, and that is the real shield, often moves away from the braid and makes a sloppy connection. Sometimes wiggling the cable will make the electrical length of the cable change, and shield integrity is all over the place, when the cable is soldered. This generally won't hurt with dipoles, but it can with critical applications. Crimps actually make a better connection. Since folding them back is the only way of being sure that the braids are all making contact with the shell of the F connector, I now fold the shields back a little in my snap-and-seal F connectors. How can that hurt anything? I think it's a better way to do it. I would always use the correct connector, and install the connectors the way the connector and cable manufacturer say. They usually know more about their products than we do. :-) It is a bad idea to improve installation instructions without understanding the product in precise detail. How many people do you think understand the issue caused by overlaying a foil shield with braid, and soldering to the braid? 73 Tom All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Topband: Problem with compression F connectors on Quad RG-6
I'm having a repeated weird problem with compression F connectors on quad-shield RG6. When I connect a short length (say 4 feet) of cable to my MFJ-259B, I would expect R650. Instead, when I wiggle the coax, occasionally I see the display change to R=0 and X= several hundred ohms at 1.8 MHz. This makes no sense to me - the R implies ashort, but where's all the X coming from? The problem seems to vary with the same connector and different PL-259 to F adapters, which makes me wonder what might be happening inside the adapters, but I can't imagine anything producing this result. I have also been unsuccessful in detecting a short using a simple DC multimeter. I;'m wondering if I should go through my RX antennas and replace all the F connectors and particularly the F to 259 adapters with something else, but what? BNCs? Anyone have any wisdom? -- 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
Re: Topband: Problem with compression F connectors on Quad RG-6
I'm having a repeated weird problem with compression F connectors on quad-shield RG6. When I connect a short length (say 4 feet) of cable to my MFJ-259B, I would expect R650. Instead, when I wiggle the coax, occasionally I see the display change to R=0 and X= several hundred ohms at 1.8 MHz. This makes no sense to me - the R implies ashort, but where's all the X coming from? R doesn't come from a short, it comes from no loss resistance, or more correctly very low loss resistance. It sounds like the connector you have is not contacting all the shields. This is typical for mismatched connectors and cable, or improperly manufactured cables. It could be somewhere else also, but I've seen this before with quad shield. That's why I avoid it. The problem seems to vary with the same connector and different PL-259 to F adapters, which makes me wonder what might be happening inside the adapters, but I can't imagine anything producing this result. I have also been unsuccessful in detecting a short using a simple DC multimeter. Remember how RF current flows. It flows on the outside of cables, unless it has a connection path to the inner shield. If you have cable with Mylar on the inside of one or more shield layers, and a connector that only contacts the outside of the outer shield, the inner shields that carry nearly all of the desired transmission line currents will be insulated and isolated from the shield at the connector. Every shield has to be contacted at the connector, or at least the inner shield does. This might not be it, but it is a common issue with quad shield. Dual shield is much more forgiving of connectors. You'll never detect the leakage in dual shield in outside runs. If you have nasty common mode problems, a thicker shield will help. It is also just as simple to add a few dozen or few hundred ohms of common mode choking to regular dual shield cables and knock down CM ingress to levels that cannot be noticed. I;'m wondering if I should go through my RX antennas and replace all the F connectors and particularly the F to 259 adapters with something else, but what? BNCs? BNC's are worse yet, as a general rule. They rely on spring pressure for the shield path. Look into a type match error between the cable you have and the connectors, or a connector installation error. 73 Tom All good topband ops know fine whiskey is a daylight beverage. _ Topband Reflector
