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coax length
- Thread starter wewjr71
- Start date
I realize this is an old thread, yet I want to re-ask the question with some alternative points of view; none of them my own. I haven't developed my point of view on this, and I am trying to learn.
Which is, in your opinion, true?
View 1. Because radio waves are tuned wavelengths of energy, we have to take into account the coax cable length. Therefore, here is how to figure out your true 1/2-wave:
492 x (Velocity Factor) / Frequency (MHz) and cut the coax in multiples of 1 whole wavelength - the stated formula x two (2) to the closest shortest usable length to the antenna adapter.
View 2. For 11 meter operation, use these figures to set up your antenna and coax. For base stations. Cut your RG-8/U coax in multiples of 11 feet. For example.. if you need 50 feet of coax to reach your antenna, use 55 feet instead. 11 X 5 = 55. Or 11 feet multiplied by 5 multiples equals 55 feet total. If you need 37 feet, use 44 feet instead.
11 X 4 = 44. What ever length you need, go to the next highest length that can be divided evenly by 11. Include all jumper cables in that length. Jumper cables should be cut to 6, 9, or 12 feet. Never less than 6 feet, or more than 12 feet. Example. . . If you need 55 feet of coax to reach your antenna, and you want to add a meter in the line. Use 49 feet of coax from the antenna to your meter, and 6 feet from your meter to your radio. 49 + 6 = 55.
For set up on 11 meters in your automobile, use RG-8X or RG MINI coax. Do the same as I instructed for base station installations, except this time cut your RG-8X to 20 feet minimum. Do not use less than 20 feet. Even if you only need 1/2 of that length, still use 20 feet. The extra coax can be coiled up and put in the trunk or under the seat. If it is possible, try to coil the extra coax as close to the antenna as you can get it. If not, the trunk or under the seat is good. It will not cause any problems. A length shorter than 20 feet can cause RF feedback, because of the antenna being so close to the radio. Also, mobile antennas are usually 1/4 wave or less.
View 3. The the length of coax does not matter at all.The ONLY proper length to use is whatever it takes to reach from the antenna connector to the radio connector
I am in search of something more than a personal assumption either way. I want the best tx/rx I can afford to purchase and put together, and for now it isn't more than Belden RG58U. I need to know that I am doing as well as I can on my setup.
Which is, in your opinion, true?
View 1. Because radio waves are tuned wavelengths of energy, we have to take into account the coax cable length. Therefore, here is how to figure out your true 1/2-wave:
492 x (Velocity Factor) / Frequency (MHz) and cut the coax in multiples of 1 whole wavelength - the stated formula x two (2) to the closest shortest usable length to the antenna adapter.
View 2. For 11 meter operation, use these figures to set up your antenna and coax. For base stations. Cut your RG-8/U coax in multiples of 11 feet. For example.. if you need 50 feet of coax to reach your antenna, use 55 feet instead. 11 X 5 = 55. Or 11 feet multiplied by 5 multiples equals 55 feet total. If you need 37 feet, use 44 feet instead.
11 X 4 = 44. What ever length you need, go to the next highest length that can be divided evenly by 11. Include all jumper cables in that length. Jumper cables should be cut to 6, 9, or 12 feet. Never less than 6 feet, or more than 12 feet. Example. . . If you need 55 feet of coax to reach your antenna, and you want to add a meter in the line. Use 49 feet of coax from the antenna to your meter, and 6 feet from your meter to your radio. 49 + 6 = 55.
For set up on 11 meters in your automobile, use RG-8X or RG MINI coax. Do the same as I instructed for base station installations, except this time cut your RG-8X to 20 feet minimum. Do not use less than 20 feet. Even if you only need 1/2 of that length, still use 20 feet. The extra coax can be coiled up and put in the trunk or under the seat. If it is possible, try to coil the extra coax as close to the antenna as you can get it. If not, the trunk or under the seat is good. It will not cause any problems. A length shorter than 20 feet can cause RF feedback, because of the antenna being so close to the radio. Also, mobile antennas are usually 1/4 wave or less.
View 3. The the length of coax does not matter at all.The ONLY proper length to use is whatever it takes to reach from the antenna connector to the radio connector
I am in search of something more than a personal assumption either way. I want the best tx/rx I can afford to purchase and put together, and for now it isn't more than Belden RG58U. I need to know that I am doing as well as I can on my setup.
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Ok, guys, this is a well worn out horse, but not yet dead to the uninitiated. Spare me and post something to validate your point of view...
View #1 on my previous post had some science, the next two (2) views had only someones' say-so. If the views are valid, where lies the science, and whose science is genuine???
Thanks for your patience.
View #1 on my previous post had some science, the next two (2) views had only someones' say-so. If the views are valid, where lies the science, and whose science is genuine???
Thanks for your patience.
OK.
Belden 9913F Flex or LMR-400 Flex is best. Cost quite a bit more than RG58U - though. To be honest with you, the ONLY time I would use RG58 is to a mobile base load antenna - and only because I would have to. Unless I was using a steel whip.
For a base station, I have Belden 8237 that I am about to retire. I'm gonna get some Belden 9913 Flex. At/around the 30Mhz range, the quality of coax becomes an issue. If you use a 144-48Mhz radio, it becomes a must have situation - unless it is a short-length run. Short, as in less than 50 feet.
By the way, it is a good idea too use the shortest length of coax that you can for a base antenna, as there is loss in all cable. A 1db loss on a 100 ft cable run means that you have lost 20% of the power of the radio to the antenna. As far as determining what multiples are used, generally ODD number multipliers are preferred.
the key here is properly tuned antenna. many fixed antennas on the market do not qualify as antennas because half of them are missing, as in the case of the A99 and the Imax antennas which offer the "other half of the antenna" as an option. voltage/current standing wave ratio has been shown to be affected by the length of the line under these conditions because the line is resonant. the manufacturers depend on common-mode current travelling on the outside of the line to replace the other missing half of the antenna unless of course you know all of this and spring for the other half of the antenna or fabricate some reasonable facsimile. the outer shield of the feedline behaves as a counterpoise, the missing elevated radial system. but then once this is remedied we have another problem, a balanced antenna and an unbalanced feedline, more on that later.
standing waves on the line occur whenever the load and the lines' characteristic impedances do not match, assuming that the source and the line input are matched. the problem with solid state transmitters is that the amount of incident power produced is dependent on a minimum amount of reflection from the load to produce maximum power output. as reflected power at the load increases because of the mismatch the transmitter makes less power available to the line because the mismatch at the load is seen at the transmitter input and power output is reduced.
non-resonant lines:
a transmission line is non-resonant when it is terminated in an impedance that is equal to the characteristic impedance of the line. changing the length of non-resonant transmission lines does not change the impedance at the input. It can be 50 feet or 100 feet, but the input impedance will remain unchanged. the only degrading factor will be the loss of the line as the length increases.
resonant lines:
when a transmission line is terminated by an impedance that is not equal to the characteristic impedance of the line, it is said to be resonant. the length of a resonant transmission line is critical. changing the length of the line will change the impedance of the line, looking from the source. when an antenna impedance is other than the characteristic impedance of the transmission line, the line length can be adjusted to present a better matching impedance at the output of the transmitter. there are multiple resonant frequencies for any system supporting standing waves.
therefore, if the load matches the characteristic impedance of the line then the length of the feedline (except for line losses) has absolutely no effect on the voltage standing wave ratio.
conversely, if the load does NOT match the characteristic impedance of the feedline then the line is resonant and line length has an effect on the position of nodes and antinodes up and down the entire length of the line and because of this there are a range of impedance values present up and down the line anywhere from 33-75 ohms for a measured load vswr of 1.5:1 and for a line with a characteristic impedance of 50 ohms and the selection of terminating points along the line affects the voltage standing wave ratio of the line. the higher the vswr measured at the load the wider the range of available impedances. when standing waves are present, (the qualifier that Cebik left out) every length of feedline is a matching transformer. ~Cebik~
any length that reaches from point a to point b is the exception, not the rule.
of course there are many methods by which the problem can be mitigated and there's the rub. key to understanding all of this is realizing that "all power delivered to the load is radiated, regardless of mismatch." the only dissipative loss incurred is due to the repeated process of reflection and re-reflection from the load and back to the transmitter (line loss) during every cycle at the frequency in use. in the relatively short lines that we use for most mobile installations the loss is miniscule at best. the real reduction in available power is the direct result of the mismatch that exists between the transmitter (source) and the line input.
in the case of solid state transmitters the match between the output of the transmitter and the input to the line is in many cases more important than the match between the line and the load. we can disregard the load mismatch and instead see to it that the input to the line closely matches the transmitter output and we can use the knowledge of the presence and placement of these nodes and antinotes along the line to do this as long as we're dealing with a resonant transmission line, a line with a characteristic impedance that does not match the load.
it is these standing waves and their presence on the line that creates these nodes and antinodes along with the associated range of available impedances up and down the line. we can use these standing waves to our advantage in instances where the degree of mismatch at the load can be isolated from the transmitter input end of the line by terminating the line at such a length that provides an impedance at the input to the line that closely if not almost exactly matches the output impedance of the transmitter, solving the problem of the reduction of transmitter power output which is the real problem encountered when attempting to deliver all available power to the load.
http://www.firecommunications.com/mismatch.txt
http://www.allaboutcircuits.com/vol_2/chpt_14/6.html
standing waves on the line occur whenever the load and the lines' characteristic impedances do not match, assuming that the source and the line input are matched. the problem with solid state transmitters is that the amount of incident power produced is dependent on a minimum amount of reflection from the load to produce maximum power output. as reflected power at the load increases because of the mismatch the transmitter makes less power available to the line because the mismatch at the load is seen at the transmitter input and power output is reduced.
non-resonant lines:
a transmission line is non-resonant when it is terminated in an impedance that is equal to the characteristic impedance of the line. changing the length of non-resonant transmission lines does not change the impedance at the input. It can be 50 feet or 100 feet, but the input impedance will remain unchanged. the only degrading factor will be the loss of the line as the length increases.
resonant lines:
when a transmission line is terminated by an impedance that is not equal to the characteristic impedance of the line, it is said to be resonant. the length of a resonant transmission line is critical. changing the length of the line will change the impedance of the line, looking from the source. when an antenna impedance is other than the characteristic impedance of the transmission line, the line length can be adjusted to present a better matching impedance at the output of the transmitter. there are multiple resonant frequencies for any system supporting standing waves.
therefore, if the load matches the characteristic impedance of the line then the length of the feedline (except for line losses) has absolutely no effect on the voltage standing wave ratio.
conversely, if the load does NOT match the characteristic impedance of the feedline then the line is resonant and line length has an effect on the position of nodes and antinodes up and down the entire length of the line and because of this there are a range of impedance values present up and down the line anywhere from 33-75 ohms for a measured load vswr of 1.5:1 and for a line with a characteristic impedance of 50 ohms and the selection of terminating points along the line affects the voltage standing wave ratio of the line. the higher the vswr measured at the load the wider the range of available impedances. when standing waves are present, (the qualifier that Cebik left out) every length of feedline is a matching transformer. ~Cebik~
any length that reaches from point a to point b is the exception, not the rule.
of course there are many methods by which the problem can be mitigated and there's the rub. key to understanding all of this is realizing that "all power delivered to the load is radiated, regardless of mismatch." the only dissipative loss incurred is due to the repeated process of reflection and re-reflection from the load and back to the transmitter (line loss) during every cycle at the frequency in use. in the relatively short lines that we use for most mobile installations the loss is miniscule at best. the real reduction in available power is the direct result of the mismatch that exists between the transmitter (source) and the line input.
in the case of solid state transmitters the match between the output of the transmitter and the input to the line is in many cases more important than the match between the line and the load. we can disregard the load mismatch and instead see to it that the input to the line closely matches the transmitter output and we can use the knowledge of the presence and placement of these nodes and antinotes along the line to do this as long as we're dealing with a resonant transmission line, a line with a characteristic impedance that does not match the load.
it is these standing waves and their presence on the line that creates these nodes and antinodes along with the associated range of available impedances up and down the line. we can use these standing waves to our advantage in instances where the degree of mismatch at the load can be isolated from the transmitter input end of the line by terminating the line at such a length that provides an impedance at the input to the line that closely if not almost exactly matches the output impedance of the transmitter, solving the problem of the reduction of transmitter power output which is the real problem encountered when attempting to deliver all available power to the load.
http://www.firecommunications.com/mismatch.txt
http://www.allaboutcircuits.com/vol_2/chpt_14/6.html
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Thanks, Rob KI6USW, for the tip on good coax.
If I understand you correctly, freecell, the length of line comes into play primarily as a function of correcting the poorer properties of an inferior antenna (as in the case of an A99), and in that case it would be advised to use lengths representative of the frequency one desired to operate on. On the other hand, if a superior (you said complete) antenna were in use, then the need to use the antenna feed line in the function of matching impedances is negated because of the inherent match of the system from transmitter to load.
Is there a complete antenna at the 27mhz range?
If I understand you correctly, freecell, the length of line comes into play primarily as a function of correcting the poorer properties of an inferior antenna (as in the case of an A99), and in that case it would be advised to use lengths representative of the frequency one desired to operate on. On the other hand, if a superior (you said complete) antenna were in use, then the need to use the antenna feed line in the function of matching impedances is negated because of the inherent match of the system from transmitter to load.
Is there a complete antenna at the 27mhz range?
the feedline length only becomes a factor or has an effect on vswr at the line input (source, transmitter) when the load (antenna) impedance DOES NOT MATCH the characteristic impedance (50 ohms) of the feedline. if the line and the antenna are both 50 ohms then line length has no effect on vswr, not at the input, not at the load, not anywhere.
in addition, any line that is an ELECTRICAL (not physical) 1/4 wavelength long INVERTS impedance while any line that is an ELECTRICAL (not physical) 1/2 wavelength long repeats impedance, both respectively from one end of the line to the other. the 1/4 wave line can be extended in odd multiples for additional physical length if and when needed and likewise the 1/2 wave line can be extended in either odd or even multiples without disturbing the electrical characteristics of either of the two lines.
a tuned electrical 1/4 wave line for channel 19 using feedline with a velocity factor of .78 (foam) would be 7.058 feet or 7' and .696 inches (3/4") and a tuned electrical 1/2 wave line for the same channel using the same velocity factor would be 14.116' or 14' and 1.392 inches (1.5") respectively, close enough for antenna engineering work.
where some of you guys got the lengths mentioned previously in this thread is beyond me.
"Is there a complete antenna at the 27mhz range?"
if you're buying an A99, Imax or similiar antenna just make sure you get all of the parts. where these antennas and others like them are concerned the ground plane kit is not an option if you want a complete antenna, unless of course you plan on operating it at ground level or fabricating your own radial system like i mentioned earlier.
p.s. the only thing beaten to death in this thread is the statement, "this question has been beaten to death."
in addition, any line that is an ELECTRICAL (not physical) 1/4 wavelength long INVERTS impedance while any line that is an ELECTRICAL (not physical) 1/2 wavelength long repeats impedance, both respectively from one end of the line to the other. the 1/4 wave line can be extended in odd multiples for additional physical length if and when needed and likewise the 1/2 wave line can be extended in either odd or even multiples without disturbing the electrical characteristics of either of the two lines.
a tuned electrical 1/4 wave line for channel 19 using feedline with a velocity factor of .78 (foam) would be 7.058 feet or 7' and .696 inches (3/4") and a tuned electrical 1/2 wave line for the same channel using the same velocity factor would be 14.116' or 14' and 1.392 inches (1.5") respectively, close enough for antenna engineering work.
where some of you guys got the lengths mentioned previously in this thread is beyond me.
"Is there a complete antenna at the 27mhz range?"
if you're buying an A99, Imax or similiar antenna just make sure you get all of the parts. where these antennas and others like them are concerned the ground plane kit is not an option if you want a complete antenna, unless of course you plan on operating it at ground level or fabricating your own radial system like i mentioned earlier.
p.s. the only thing beaten to death in this thread is the statement, "this question has been beaten to death."
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Any recommendations on cable for a mobile installation?
OK.
Belden 9913F Flex or LMR-400 Flex is best. Cost quite a bit more than RG58U - though. To be honest with you, the ONLY time I would use RG58 is to a mobile base load antenna - and only because I would have to. Unless I was using a steel whip.
For a base station, I have Belden 8237 that I am about to retire. I'm gonna get some Belden 9913 Flex. At/around the 30Mhz range, the quality of coax becomes an issue. If you use a 144-48Mhz radio, it becomes a must have situation - unless it is a short-length run. Short, as in less than 50 feet.
By the way, it is a good idea too use the shortest length of coax that you can for a base antenna, as there is loss in all cable. A 1db loss on a 100 ft cable run means that you have lost 20% of the power of the radio to the antenna. As far as determining what multiples are used, generally ODD number multipliers are preferred.
Well, most of the major makers of good mobile antenna supplies good coax with their unit. WIlson, K-40 and so on use pretty high quality RG58 and is usually 18 ft long. Not such a big deal because it is relatively short. If I were to use a 102" steel whip (doesn't come with coax), I would use the 9913 Flex because a short piece would be cheap and offer no resistance/capacitance/loss. That's me building in a little overkill and insurance if I decude to run a heater. In a short feed, it doen't really matter that much. When it is longer - greater than 50 ft on your base station radio - it will cut into your antenna output.
Cars offer different problems, in that where the antenna is mounted will affect the directionality of RF propagation. Put it on the bumper on either end of the car, and the opposite front corner will have the best directioality of wave propagation. Putting it in the center of the roof will radiate equally front and back, while the side to side will be weaker. The vehicle becomes the ground plane to the radio waves coming off of the antenna; so it is anything but uniform.
Keeping common mode current in control can be an issue. If someone in the vehicle has a laptop or is watching a DVD, it could creat problems. Using a ferrite bobbin on the power wires in to your radio is just good practice is cheap and effective. Coiling coax near the antenna itself is the best way to choke it out. Setting the SWR to its lowest will help eliminate any standing waves that can affact many kinds of elelctronics that one has in your wheels.
Here's a good find on the choke/ferrite:
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
Hi Rob,
Thank you for the advice. I am aware of antenna placement being a factor and that was my next question.
Maybe if I describe my vehicle / setup you can help steer me in the right direction. I would greatly appreciate that.
I have a modified 1997 Lexus LX-450 which is basically a Toyota Land Cruiser. The vehicle has been heavily modified for serious Expedition Off-Road travel. The mods that I believe relate to my radio install are as follows:
* Dual Odyssey Deep Cycle Battery Setup with Aux Battery directly feeding Radio / Amp
* ARB Heavy Steel Front Bumper / Winch with Antenna Mounts - (Front Left & Right)
* Kaymar Heavy Steel Rear Bumper with Tire Carrier / Jerry Can Holder & Antenna Mount - (Can mount Rear Left, Center, or Right)
* African Outback full length Roof Rack
I want to stay away from installing an antenna on the roof for a varierty of reasons. Height being the maion issue as I travel off-road a lot and the antenna is too vulnerable at that height. Also, I use my Roof Rack for travel sometimes and may want to install a Roof Top Tent for more serious expeditions. This pretty much eliminates the roof alltogether for any antenna installation.
Therfore, I am looking for 2nd best position on the vehcile. I can mount the antenna center rear of the vehicle on the Tire Carrier ... there is an antenna mount in this location.
However, I am looking for best performance so I had the following idea.
Can I possibly mount two antennas ... one front right and one rear left ... one each on the front aand rear bumpers ... and run them in a co-phase setup? Would this make sense?
If not, I would go with the center rear location as it gives me the most height and is closest to center of the vehicle. I believe this would be a better option than a front corner location on the front bumper.
Also, from reading this thread ... contrary to what I was told .... I see it does not matter what length the cable is from my amp to the antenna ... albeit perhaps it does in a co-phase setup?
How about the cable lenght from the radio to the amp? Does this need to be in increments of 3 feet as I was told? For example 3 feet, 6 feet, or 9 feet would be OK but diferent lengths would not be OK?
Last question. Can you recommend a high quality, small, easy to read, accurate, professional SWR / Power Meter that I can use to setup my Antenna (SWR) keep in-line for moitoring power & modulation? I need something that will go from 1 watt to 500 watts. I realize I may need a switchable power scale to get any accuracy and resolution for such a wide range.
I am a serious audiophile and audio performance is critical to me. I am horrified by the thought of overmodulation and want the cleanest sounding on-air audio I can get. Price is no object so I want the best possible setup with the best performance and best sound quality I can get.
With that said, I am running PROPERLY tuned Magnum Radios ... meaning they were not touched by hacks .... that were setup for proper swing (4 to 1) and best quality audio without overdriving the unit I have an S-680 and and S-9 with an original Powerstick Antenna and a knock-off Powerstick 2 with a Cobra XL-500 Amps - (I have 9 of them ... it is a long sad story). Here is a link to the amp.
Cobra XL500 LINEAR Amplifier
Any assistance you can provide would be greatly appreciated. I got left hanging by the last shop I purchased all these items from (who will go unamed) and got ripped off to boot ... they never shipped some of the products I paid for and refuse to take or return calls.
I really need some assitance so I am hoping you can steer me in teh right direction. I am willing to hire somebody in my area to do the install as well if you know of anyone in the northeast that is good.
Thank you for the advice. I am aware of antenna placement being a factor and that was my next question.
Maybe if I describe my vehicle / setup you can help steer me in the right direction. I would greatly appreciate that.
I have a modified 1997 Lexus LX-450 which is basically a Toyota Land Cruiser. The vehicle has been heavily modified for serious Expedition Off-Road travel. The mods that I believe relate to my radio install are as follows:
* Dual Odyssey Deep Cycle Battery Setup with Aux Battery directly feeding Radio / Amp
* ARB Heavy Steel Front Bumper / Winch with Antenna Mounts - (Front Left & Right)
* Kaymar Heavy Steel Rear Bumper with Tire Carrier / Jerry Can Holder & Antenna Mount - (Can mount Rear Left, Center, or Right)
* African Outback full length Roof Rack
I want to stay away from installing an antenna on the roof for a varierty of reasons. Height being the maion issue as I travel off-road a lot and the antenna is too vulnerable at that height. Also, I use my Roof Rack for travel sometimes and may want to install a Roof Top Tent for more serious expeditions. This pretty much eliminates the roof alltogether for any antenna installation.
Therfore, I am looking for 2nd best position on the vehcile. I can mount the antenna center rear of the vehicle on the Tire Carrier ... there is an antenna mount in this location.
However, I am looking for best performance so I had the following idea.
Can I possibly mount two antennas ... one front right and one rear left ... one each on the front aand rear bumpers ... and run them in a co-phase setup? Would this make sense?
If not, I would go with the center rear location as it gives me the most height and is closest to center of the vehicle. I believe this would be a better option than a front corner location on the front bumper.
Also, from reading this thread ... contrary to what I was told .... I see it does not matter what length the cable is from my amp to the antenna ... albeit perhaps it does in a co-phase setup?
How about the cable lenght from the radio to the amp? Does this need to be in increments of 3 feet as I was told? For example 3 feet, 6 feet, or 9 feet would be OK but diferent lengths would not be OK?
Last question. Can you recommend a high quality, small, easy to read, accurate, professional SWR / Power Meter that I can use to setup my Antenna (SWR) keep in-line for moitoring power & modulation? I need something that will go from 1 watt to 500 watts. I realize I may need a switchable power scale to get any accuracy and resolution for such a wide range.
I am a serious audiophile and audio performance is critical to me. I am horrified by the thought of overmodulation and want the cleanest sounding on-air audio I can get. Price is no object so I want the best possible setup with the best performance and best sound quality I can get.
With that said, I am running PROPERLY tuned Magnum Radios ... meaning they were not touched by hacks .... that were setup for proper swing (4 to 1) and best quality audio without overdriving the unit I have an S-680 and and S-9 with an original Powerstick Antenna and a knock-off Powerstick 2 with a Cobra XL-500 Amps - (I have 9 of them ... it is a long sad story). Here is a link to the amp.
Cobra XL500 LINEAR Amplifier
Any assistance you can provide would be greatly appreciated. I got left hanging by the last shop I purchased all these items from (who will go unamed) and got ripped off to boot ... they never shipped some of the products I paid for and refuse to take or return calls.
I really need some assitance so I am hoping you can steer me in teh right direction. I am willing to hire somebody in my area to do the install as well if you know of anyone in the northeast that is good.
Well, most of the major makers of good mobile antenna supplies good coax with their unit. WIlson, K-40 and so on use pretty high quality RG58 and is usually 18 ft long. Not such a big deal because it is relatively short. If I were to use a 102" steel whip (doesn't come with coax), I would use the 9913 Flex because a short piece would be cheap and offer no resistance/capacitance/loss. That's me building in a little overkill and insurance if I decude to run a heater. In a short feed, it doen't really matter that much. When it is longer - greater than 50 ft on your base station radio - it will cut into your antenna output.
Cars offer different problems, in that where the antenna is mounted will affect the directionality of RF propagation. Put it on the bumper on either end of the car, and the opposite front corner will have the best directioality of wave propagation. Putting it in the center of the roof will radiate equally front and back, while the side to side will be weaker. The vehicle becomes the ground plane to the radio waves coming off of the antenna; so it is anything but uniform.
Keeping common mode current in control can be an issue. If someone in the vehicle has a laptop or is watching a DVD, it could creat problems. Using a ferrite bobbin on the power wires in to your radio is just good practice is cheap and effective. Coiling coax near the antenna itself is the best way to choke it out. Setting the SWR to its lowest will help eliminate any standing waves that can affact many kinds of elelctronics that one has in your wheels.
Here's a good find on the choke/ferrite:
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
Do you have a link to a place where I can purchase 9913 Flex cable? I get like 14 Belden Part Numbers with "9913" when I search for it.
Where can I purchase the ferrite chokes and if I decide to coil wore by the antenna how much should I coil and how close to the antenna?
Thanks again for your help..!!
Where can I purchase the ferrite chokes and if I decide to coil wore by the antenna how much should I coil and how close to the antenna?
Thanks again for your help..!!
- If I were to use a 102" steel whip (doesn't come with coax), I would use the 9913 Flex because a short piece would be cheap and offer no resistance/capacitance/loss. That's me building in a little overkill and insurance if I decide to run a heater.
Using a ferrite bobbin on the power wires in to your radio is just good practice is cheap and effective. Coiling coax near the antenna itself is the best way to choke it out.
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
B
BOOTY MONSTER
Guest
heres some reviews by pork butts , aka hams . lol
http://www.eham.net/reviews/products/7
the belden 9913F7 , lmr-400 and davis bury flex are all look to be good coax IMO .
Search Results:
Davis RF - Amateur Products, Coax Cable
Times Microwave - LMR Wireless Products
when buying coax id steer clear of the knock off name-alikes .
http://www.eham.net/reviews/products/7
the belden 9913F7 , lmr-400 and davis bury flex are all look to be good coax IMO .
Search Results:
Davis RF - Amateur Products, Coax Cable
Times Microwave - LMR Wireless Products
when buying coax id steer clear of the knock off name-alikes .