Long wire ideal length

(1/5) > >>

Albert Scherer:
I am thinking of stringing a long wire antenna, then feeding it with 9913.  My plan is 80 and 40 meters, possibly 20, possibly 160, but mainly 80 and 40.  Is there a magical length?  Just run it as long as I can and use a tuner? or should it be mutiples of something.  I realize it wont be resonant on mutiple bans, but I do want it to work as good as it can.  I have found an 80 meter antenna does not work that well on 20, so maby it is becaue it is to long.  I have allways heard that you should be at least as long as the lowest band, so should it be 130 feet to be a quarter wave at 1.8Mhz?  What is the best length to use?

Jon M. Pollock:

Feeding a "long wire" is not necessarily simple. The feedpoint impedance varies WIDELY depending upon the frequency. Almost NEVER is it 50 ohms and a good match for coax. Secondly, there is a ton of misinformation about what is a "long wire". A 130 ft. piece of wire is a "long" piece of wire, but it is not a true "long wire" antenna. A REAL long wire antenna is typically several to many WAVE LENGTHS long and may have multiple wires. i.e. to exhibit serious gain and directivity a wire probably needs to be a minimum of about 6 half waves. This is a LONG antenna on 80 meters (800+ feet long)!! Obviously, it could be considerably shorter on, say, 20 M to acheive the required number of wave lengths.

In the real world a RANDOM WIRE antenna is more often than not called a "Long Wire" and usually these antennas need a tuning net work (i.e. a "Tuner") working against a pretty decent RF ground system to be efficient. A simple end fed wire is often (incorrectly) called a "long wire" and the impedance of this this type of antenna is RARELY 50 ohms.

I strongly suggest you pick up a copy of the ARRL Antenna Book and study the chapter on Long Wire antennas. They are a specialize type and there are several ways to feed them depending on the antenna configuration and band or bands you want to cover.

Respectfully, at this point probably the best single investment you could make in your station is to pick up a copy of the ARRL Antenna Book or other good reference and put in a little book time. Antennas are not complex, but they require some specific parameters to be met in order to accept RF power and radiate it efficiently. Matching a Random Wire or true Long Wire is much to complex for a quick paragraph on this website. You can often find a cheap older copy on Ebay and the info in there is just as good as a new book when it comes to antenna basic theory.

Good luck on your project.  73,  K0ZN

tom lish II:
go for a nice fan dipole,

Mike Brenza:
For it to be a "Long wire" antenna, it must be over 1 wavelength long... otherwise, it is considered a "random wire" antenna.
Length is not critical, the longer, the better.  But getting it as HIGH as practical is the most important trait.  On 160, 80, and even 40 meters, this can be the challenge!  1/2 wavelength high on 40 meters equates to about 66 feet.  Not many hams have that luxury!  They are great for fade-free reception!


Bob Lewis:
Let me expand a little on what K0ZN said. To work well the end of a random wire antenna must be connected directly to the tuner terminals. Using coax between the end of the wire and the tuner will result in some very high loss on most frequencies.

In addition, the tuner chassis must be connected to a good RF ground like a radial system, just like a vertical antenna. Failure to do this will result in RF inside the shack on the radio chassis, microphone, etc. It will result in inefficiency and can cause RFI problems into other household equipment like TV sets, phones, etc.

The bottom line is that a multi-band end-fed antenna is often not as easy to implement as it would first seem although it can work well if done properly.


[0] Message Index

[#] Next page