Antenna Coax Cable Question

[DanW]

Does the length of the coax cable have an effect on transmission or reception, or even SWR?  

 

[axorlov]

1 hour ago, DanW said:

Does the length of the coax cable have an effect on transmission or reception, or even SWR?  

 

Cables have loss. The bigger the loss along the run of the cable, the less signal goes out and comes in. Also, the more the loss the better the SWR. The longer the cable, the bigger the loss.

Coax loss chart: https://www.w4rp.com/ref/coax.html
Coax loss calculator: https://www.qsl.net/co8tw/Coax_Calculator.htm

There are number of thread here discussing cables, loss, SWR, whatnot.

[mbrun]

Does the length of the coax cable have an effect on transmission or reception, or even SWR?  
 

Good Day Dan.

Yes, the length of cable does have an effect on both transmission and reception equally. As does air, trees, buildings, antennas, hills and other medium that reside between two radios that are trying to communicate. In effect, power is lost/consumed as it travels through any medium.

Yes, cable can effect SWR. If the cable is damaged or the connectors are poor quality or mate poorly the cable assembly can cause an elevated SWR, whereas a good cable assembly that is particularly long and otherwise has excessive loss can make the SWR misleadingly low.


Michael
WRHS965
KE8PLM

[phottomatt]

Can I assume then that the SWR should be tested after installation? If I'm testing the SWR for my Jeep setup I should do it after running the cable and installing the antenna in the intended location?

[SteveC7010]

1 hour ago, phottomatt said:

Can I assume then that the SWR should be tested after installation? If I'm testing the SWR for my Jeep setup I should do it after running the cable and installing the antenna in the intended location?

Correct. The SWR has to be checked with antenna and coax in their installed configuration. Otherwise you may get an inaccurate measurement. 

[WyoJoe]

You can also test as you go. For example, install the antenna and test it, then install the coax and test it, then, if you have adapters, lightning arresters, or anything else to add, install those and test again. The purpose of doing this would be to ensure nothing you add to your antenna system causes any problems along the way.

Your most important reading, though, will be the final one, where the antenna system connects to the radio. If you had any flaky readings along the way, hopefully you would have made any necessary corrections, so the final reading should be good (or the last thing you added could be causing a problem).

Overall, though, you want to check the antenna system as a whole. The test as you go suggestion is mostly to help rule out problems as you're building the antenna system.

[phottomatt]

Deleted

Wrong antenna

[PACNWComms]

Power out and SWR should also be checked from time to time, or if something changes in your equipment. With anything that moves, vehicles, vessels and aircraft, movement leads to wear and failure. I have had many state that their radio "just quit working" only to find a broken connector on a cable, damaged or missing antenna, or corrosion that has worn a cable. A good rule of thumb is to check coax (and antenna and radio) by placing a meter in line and testing once a year at least. In many commercial/municipal/government uses, this is required and spelled out in contracts, and is a compliance issue.