We seem to be limiting ourselves to the worst or best possible feedline commonly used for CB? I have no problem with using better then needed quality, but honestly, LMR-400 is overkill for this application.
Loss info on different cables below taken from here, and using 27.185MhZ for the frequency.
RG-58, 1.2 dB or 23.7% loss over 50 feet.
RG-8X, 0.9 dB or 19.3% loss over 50 feet.
LMR-240, 0.6 dB or 13.6% loss over 50 feet.
RG-213, 0.5 dB or 10.8% loss over 50 feet.
LMR-400, 0.3dB or 7.2% loss over 50 feet.
This information comes with some qualifiers, the data was taken from Times Microwave's site, they make high quality coax. Feedline of the same type from another manufacturer is not necessarily up to the above specs, and if it is the crap that comes from Radio Shack or a Chinese company expect it to be much worse...
To put losses in perspective, a remote unit with a radio and a properly calibrated s-meter will barely notice the difference between the RG-58 and the LMR-400, if they notice it at all. A one s-unit drop would require a 75% (or 6 dB) loss in power to achieve, and the amount of difference in the above cables at said length and frequency aren't even close to that. The difference with the above cables at said frequency and length will be less than 1/4 of an s-unit on the recieve station.
Something else to consider in relation to feedline losses is the apparent SWR of the antenna at the far end of the feedline. Losses in a feedline only make the SWR on the far end appear better then it actually is. The more losses you have the better your SWR appears to be. If you have enough losses in your feedline it will hide a tuning (or other potential) problem with the antenna itself. A tuning problem hidden behind feed line losses can have as much of an effect on antenna system losses as the losses in the feedline. For an example, a thread that shows the SWR differences using RG-58AU coax over 100 feet can be found here.
You would be surprised at how often when someone upgrades their feedline they see a higher SWR and think the new feedline is the cause of their problem, when in reality their antenna was never tuned as well as it could/should have been in the first place.
The DB
Loss info on different cables below taken from here, and using 27.185MhZ for the frequency.
RG-58, 1.2 dB or 23.7% loss over 50 feet.
RG-8X, 0.9 dB or 19.3% loss over 50 feet.
LMR-240, 0.6 dB or 13.6% loss over 50 feet.
RG-213, 0.5 dB or 10.8% loss over 50 feet.
LMR-400, 0.3dB or 7.2% loss over 50 feet.
This information comes with some qualifiers, the data was taken from Times Microwave's site, they make high quality coax. Feedline of the same type from another manufacturer is not necessarily up to the above specs, and if it is the crap that comes from Radio Shack or a Chinese company expect it to be much worse...
To put losses in perspective, a remote unit with a radio and a properly calibrated s-meter will barely notice the difference between the RG-58 and the LMR-400, if they notice it at all. A one s-unit drop would require a 75% (or 6 dB) loss in power to achieve, and the amount of difference in the above cables at said length and frequency aren't even close to that. The difference with the above cables at said frequency and length will be less than 1/4 of an s-unit on the recieve station.
Something else to consider in relation to feedline losses is the apparent SWR of the antenna at the far end of the feedline. Losses in a feedline only make the SWR on the far end appear better then it actually is. The more losses you have the better your SWR appears to be. If you have enough losses in your feedline it will hide a tuning (or other potential) problem with the antenna itself. A tuning problem hidden behind feed line losses can have as much of an effect on antenna system losses as the losses in the feedline. For an example, a thread that shows the SWR differences using RG-58AU coax over 100 feet can be found here.
You would be surprised at how often when someone upgrades their feedline they see a higher SWR and think the new feedline is the cause of their problem, when in reality their antenna was never tuned as well as it could/should have been in the first place.
The DB
