help with random wire antenna length?

I don't know anything about short wave but what I have been told. And I don't understand that ether. What I need is a random wire antenna that I can clip to my SW so as to pick up 20, 40, and 60M bands equally well. Can anyone tell me the proper length to do that? I was told I need to stay away from 1/2 waves. though I don't understand why. those 3 bands are all I need to be concerned with... Any help would be appreciated.

 

Ben, I haven't been long in the game of ground/marine comms but done some in my career, did recently get my Extra license, my forte is wideband (tropo/satcom/microwave) but BTPost is telling you the correct thing to do. It sounds like someone is telling not to use a half-wave antenna maybe because it does generate more harmonics but your not transmitting either so...anyway in your case with a simple SW receiver - well - don't get excited about it. What you want to do is capture as much of the signal as possible and BTPost solution is truly simple AND elegant. In fact, I just purchase a SW myself (ETON Satellit) and intend to do exactly as he suggested...been scratching my head today because I want to get more signal but it's 16F outside so don't want to screw about too much, something field expedient... Nevertheless, if you want to cut your antenna to length the formula is as follows:

468 / frequency in Mhz = total length in feet for a half wave dipole.
If you want a quarter wave then it is 234/freq or divide the above by 2.

A couple of other formulas you will need are below. Put them in your pocket for later:
Wavelength = 300 / Frequency
and
Frequency = 300 / wavelength
so
20 meters = 15 Mhz
40 meters = 7.5 Mhz
60 meters = 5 Mhz

EDIT: And, if you can't do 200 feet of wire then do what you can. Let us know how it turns out.

EDIT: Here is a simple article about building a shortwave antenna...keep it simple:
Build a Multiband Shortwave Antenna - Simple Shortwave Antennas for Shortwave Radios!

 

I am not transmitting at all. Only receiving. Also don't know if it matters, But the long wire will run north/ south. I'm looking for the best length to pick up all signals in the 20, 40, and 60 meter bands. But no other signals matter. length of antenna does not matter, just the "Best" all around length for the purpose. I have a rather cheep SW that can pick up those bands. And I want to make sure I can pick up any transmission in those bands if required. I have tried to do some reading and research to understand the subject. But for certain medical reasons, I'm finding I want to shoot my comp.

 

Xmit'ing on a wire antenna the strongest signal will be in a figure 8 with the lobes broadside to the wire, not off the ends. I suppose rcv'ing would be similar. You could consider a beverage antenna. They are typically low enough to service on foot. But are directional and fixed.

 

Re; My post above. Beverage antennas are made of wire, not empty beverage containers.

 

Back in the day when I was in the 'green machine' and we were using A510 HF radios....the aerial grounding point became the platoon urinal ...it seemed to work ok.


A510

 

Thank you that helps

Thank you all for your help. Its much appreciated

 

The question has been answered but it's worth pointing out that there is something of a debate in the radio community as to how long a random wire should be. Some will advise to avoid exact resonance on any one band, or their harmonics. There are a lot of theories out there.

IMHO, if you are purposely constructing a random wire antenna to be a certain length, or to avoid a certain length, then it's not really "random," is it?

My advice is to get enough copper in the air to catch a decent signal, at least fifty feet or more if you can, and don't sweat the details. If you go over 100 feet it won't hurt anything but there are diminishing returns.

@ghrit 's reply is right on.

 

All three bands you listed are in the amateur spectrum. Order "Receiving antennas for amateur radio" - 0789 ($24.95) from the ARRL. Even if the frequencies you want to pull in aren't HAM, the numbers in this book should help you find ideas to try. While you're on the phone to ARRL, check into getting your license.