[TowerTalk] Importance of feed line length

[David Robbins]

feedline length is very important... if it isn't long enough to reach the radio it won't work... anything more is a waste of money.

Sep 9, 2012 09:05:26 PM, powdermnky007 at hotmail.com wrote:

Hi everyone,
I've been doing research to determine how important feed line length is. I've been reading up on this off and on for the last few weeks. I'm currently studying to get my ham license and am very excited about it. I built my first antenna this weekend. A 1/4 wave vertical on 2m, just to see what I could hear. It was a rewarding experience!

I've seen much talk on feed line length and found some very convincing article, but then I seem to find others that contradict them. I have read lots of posts from this forum and this seems to be one of the most knowledgeable places on the internet. Once I get my general license I am planning on setting up an inverted v on 80m. Just when I thought I had figured out the feed line length issue, I learned about cable velocity factor and how common mode current travel at much higher speeds down the feed lines than the actual signals going to the antenna. That really blew my mind! 

My 80m antenna will not be very high off the ground, so it will be a NVIS. I will be using a common mode choke as per Jim Brown's document "A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing". Which was the most informative document on the internet about chokes, and what led me here. I will go with a 50 ohm feed line because my antenna will be between 8 & 15 feet off the ground, and probably an inverted v. I know 50 ohms will match an inverted v better. 

I'm trying my best here to not sound totally ignorant, but if any one knows the answer I would appreciate it greatly! I look forward to your answer!
Thank you,
Justin 


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