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pwmac(at)sisna.com
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 Posted: Sun Apr 29, 2012 3:46 am Post subject: Radio Coax |
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Is there physics to the comment below?
I happened to pick up the comment on a jeep forum where the guys buy an antenna with a stock length of coax and don't have the ability to change the length.
Apperciate any comments. Thanks, Paul
DO NOT coil your antenna coax lead or let it cross over itself, to get the best reception and transmission from your radio. I have now tried this and found significant increases for both. Run your lead around the seat, around the roof, or whatever you have to do to prevent crossover of the lead, next to itself. You will find much improvement in your reception.
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Sun Apr 29, 2012 4:23 am Post subject: Radio Coax |
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At 06:39 AM 4/29/2012, you wrote:
Is there physics to the comment below?
I happened to pick up the comment on a jeep forum where the guys buy an antenna with a stock length of coax and don't have the ability to change the length.
Apperciate any comments. Thanks, Paul
DO NOT coil your antenna coax lead or let it cross over itself, to get the best reception and transmission from your radio. I have now tried this and found significant increases for both. Run your lead around the seat, around the roof, or whatever you have to do to prevent crossover of the lead, next to itself. You will find much improvement in your reception.
No validity to this idea at all. This narration suggests that there are things going on OUTSIDE the coaxial feedline that can have an effect on things that go on INSIDE the feedline. In fact, the very nature of an idealized feedline (low SWR and artful construction) calls for keeping all good things in and bad things out.
When I worked at Boeing there was an analog computer associated with the terrain avoidance radar that had perhaps a dozen coax cables of critical length running between a couple of the black boxes. The lengths were adjusted on installation to achieve the desired performance. It took about three shifts to get this thing tuned up and had a system MTBF on the order of 10 hours.
During a tune up procedure in the airplane, we could count on going to the lab with two or three circuit cards. But the point to be made here is after they were all measured and verified for performance NOT bundled, the last chore was to coil them up and string tie them into a neat and secure installation. No shifts in performance of the radar was experienced or expected for having repositioned the coax cables.
We don't often see "too long" cables in a TC aircraft. They are cut to ideal installed length on installation. But the idea that system performance would suffer because the feedlines are coiled or 'cross over themselves' is bogus.
If the writer had some demonstrable variations in performance due to feedline positioning, there was something seriously wrong with the installation and the feedline was acting more like a piece of wire than a coax cable.
Bob . . . [quote][b]
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pwmac(at)sisna.com
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| Posted: Sun Apr 29, 2012 7:11 am Post subject: Radio Coax |
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Thanks for your input
Paul
=========
At 06:22 AM 4/29/2012, you wrote:
[quote]At 06:39 AM 4/29/2012, you wrote:
Is there physics to the comment below?
I happened to pick up the comment on a jeep forum where the guys buy an antenna with a stock length of coax and don't have the ability to change the length.
Apperciate any comments. Thanks, Paul
DO NOT coil your antenna coax lead or let it cross over itself, to get the best reception and transmission from your radio. I have now tried this and found significant increases for both. Run your lead around the seat, around the roof, or whatever you have to do to prevent crossover of the lead, next to itself. You will find much improvement in your reception.
No validity to this idea at all. This narration suggests that there are things going on OUTSIDE the coaxial feedline that can have an effect on things that go on INSIDE the feedline. In fact, the very nature of an idealized feedline (low SWR and artful construction) calls for keeping all good things in and bad things out. When I worked at Boeing there was an analog computer associated with the terrain avoidance radar that had perhaps a dozen coax cables of critical length running between a couple of the black boxes. The lengths were adjusted on installation to achieve the desired performance. It took about three shifts to get this thing tuned up and had a system MTBF on the order of 10 hours. During a tune up procedure in the airplane, we could count on going to the lab with two or three circuit cards. But the point to be made here is after they were all measured and verified for performance NOT bundled, the last chore was to coil them up and string tie them into a neat and secure installation. No shifts in performance of the radar was experienced or expected for having repositioned the coax cables. We don't often see "too long" cables in a TC aircraft. They are cut to ideal installed length on installation. But the idea that system performance would suffer because the feedlines are coiled or 'cross over themselves' is bogus. If the writer had some demonstrable variations in performance due to feedline positioning, there was something seriously wrong with the installation and the feedline was acting more like a piece of wire than a coax cable.
Bob . . .
[b]
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john.maccallum(at)bigpond
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| Posted: Mon Apr 30, 2012 12:42 am Post subject: Radio Coax |
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Hi Paul,
Coaxial cable can be run next to metal objects and coiled. In fact under some circumstances coiling it is beneficial, such as if you want to make a
Transmission line choke Balun, strain relief or water isolation.
You can’t do that with a Balanced Line Feeder such as the old 300 ohm TV ribbon, which may be where the idea of not crossing over
Itself came from.
Sometimes you can get into trouble with odd ¼ wave multiples of the frequency you are working at causing the impedance of the Antenna
and Transmission line together to be something other than it should be. This results in a high SWR but this requires a reasonably big miss match
of the Antenna’s fed point impedance and the Transmission Lines Characteristic Impedance (50 ohms).
So get yourself an SWR meter, check the SWR and if it’s less than 2.5 to 1 you will be ok.
Cheers
John MacCallum
VH-DUU
RV10 #41016
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of paul wilson
Sent: Sunday, 29 April 2012 9:39 PM
To: aeroelectric-list(at)matronics.com
Subject: Radio Coax
Is there physics to the comment below?
I happened to pick up the comment on a jeep forum where the guys buy an antenna with a stock length of coax and don't have the ability to change the length.
Apperciate any comments. Thanks, Paul
DO NOT coil your antenna coax lead or let it cross over itself, to get the best reception and transmission from your radio. I have now tried this and found significant increases for both. Run your lead around the seat, around the roof, or whatever you have to do to prevent crossover of the lead, next to itself. You will find much improvement in your reception. | Quote: | | http://www.matronics.com/Navigator?AeroElectric-List |
0123456789
[quote][b]
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pwmac(at)sisna.com
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| Posted: Mon Apr 30, 2012 6:47 am Post subject: Radio Coax |
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Hi John,
Interesting comments. I will pass them along. I wondered where the no ant coil vs coil came from.
For my various rigs I use SWRs, cheapy one for CB and another pricy one for the VHF setups. My SWRs are great due to my significant effort. I now have one of Bobs low ohm devices and will work thru all my grounds and feeds to see what I find. Should be fun and informative.
I know my discussion was for off road rigs, but I hope the airplane guys dont mind. Seems applicable to any radio install.
Thanks, Paul
===========
At 02:39 AM 4/30/2012, John MacCallum wrote:
[quote]Hi Paul,
Coaxial cable can be run next to metal objects and coiled. In fact under some circumstances coiling it is beneficial, such as if you want to make a
Transmission line choke Balun, strain relief or water isolation.
You can’t do that with a Balanced Line Feeder such as the old 300 ohm TV ribbon, which may be where the idea of not crossing over
Itself came from.
Sometimes you can get into trouble with odd ¼ wave multiples of the frequency you are working at causing the impedance of the Antenna
and Transmission line together to be something other than it should be. This results in a high SWR but this requires a reasonably big miss match
of the Antenna’s fed point impedance and the Transmission Lines Characteristic Impedance (50 ohms).
So get yourself an SWR meter, check the SWR and if it’s less than 2.5 to 1 you will be ok.
Cheers
John MacCallum
VH-DUU
RV10 #41016
From: owner-aeroelectric-list-server(at)matronics.com [ mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of paul wilson
Sent: Sunday, 29 April 2012 9:39 PM
To: aeroelectric-list(at)matronics.com
Subject: Radio Coax
Is there physics to the comment below?
I happened to pick up the comment on a jeep forum where the guys buy an antenna with a stock length of coax and don't have the ability to change the length.
Apperciate any comments. Thanks, Paul
DO NOT coil your antenna coax lead or let it cross over itself, to get the best reception and transmission from your radio. I have now tried this and found significant increases for both. Run your lead around the seat, around the roof, or whatever you have to do to prevent crossover of the lead, next to itself. You will find much improvement in your reception.
[b]
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