Questions about antenna basics

DRBComm

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Dec 18, 2015
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Post Falls, ID
I'm a new amateur licensee and really enjoying the hobby so far. I am learning as much as possible so I can get the most out of what I am doing and have a few questions that I have not found answers for elsewhere. I'm currently a Technician and studying now for my General so I can get into HF. But for now, my questions are currently directed toward VHF and UHF since that is where I am at right now. Here are my antenna related questions so far...

1. I've read that some antennas which are very good at reception over wide bandwidths are generally not good for transmission on the same frequencies. i.e. a Discone antenna is great for use with a scanner receiving a wide range of frequencies but not the best choice for transmission. What I would like to know is what is a good resource that explains why this is the case? Or if anyone wants to answer it here, that would be great as well.

2. My next question is with regard to different lengths of antennas. I found a great thread at 1/4, 1/2, 5/8 wave?? but it starts to get over my head a bit right now. My question is a bit more general about the the 5/8 wave vs. 1/2 wave vs. 1/4 wave, etc. I understand that a 1/2 wave antenna is half the length of a 'full wave' antenna but what I am wondering is if any of those lengths could be used for any particular frequency that matches the wavelength? I hope that makes sense. In other words, a properly tuned antenna for 144.480 MHz would have a 81.75 in. antenna but could I use a 40.87 in. antenna as a 1/2 wavelength and get the same results? Is 40.87 in. automatically tuned for 144.480 MHz?

I'm doing my best to phrase my questions as a 'new guy' so please be patient if I am mis-using some of the terminology.
 

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W0JOG

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Oct 30, 2020
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The American Radio Relay League, ARRL, the fraternity of amateur radio operators, has an excellently founded series of books on the principals of the hobby. Their Handbook should be in every ham's library. Their book on the fundamentals of antennas and some types you can build yousrelf also is recommended reading. What you ask are the fundamentals of rf energy and how it moves thrugh and reacts to various substances. Reading and building from scratch are your best ways to learn, if you want to really pursue the hobby. That, and seeking out an Elmer to help you along. A local club should have some one who is interested in helping you.

That's what all of us Old Timers did. Maybe too out of date for the age of Instant Gratification??
 

AK9R

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I will tackle question #1. For receive purposes, covering a broad range of frequencies is often a primary goal. If your monitoring targets use a wide range of frequencies, then a broadband antenna, like a discone, can be a plus. But, these broadband antennas typically have little or no gain. This is generally not a problem for receive, but having gain while transmitting can extend the range of your transmitted signal. The end result is that while a discone might be great for a scanner listener who monitors all sorts of frequencies, a discone isn't so good for an amateur radio operator who transmits in limited segment of the spectrum.
 

chief21

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Each antenna wavelength has different properties... both good and bad. Generally, full-wavelength antennas are not used. For HF, half-wavelength antennas are probably the most common. For vertical antennas at VHF and UHF, quarter-wavelength sizes are usually the best compromise of practicality and function.
 
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