Author Topic: What is a RANDOM LENGTH WIRE?  (Read 4959 times)

Offline Carl

  • Mr HamTastic!
  • Forum Veteran
  • *********
  • Posts: 13105
  • Karma: 714
  • COW?...No ,I haven't seen your cow.
What is a RANDOM LENGTH WIRE?
« on: July 31, 2015, 08:33:03 AM »
Many times I am asked about random length wire as a Ham antenna and I must answer that RANDON does not mean ANY LENGTH as random actually means NOT RESONANT in this reference(as an antenna). So a random wire antenna actually is a specific length so as to avoid resonance problems that an antenna tuner can not tune for our use. An antenna does not need to be a specific length to be effective,but most are specific length so as to use them without a MATCHER or TUNER on specific bands...the tuner is only to match the antenna impedance to the 50 ohm radio output to avoid damage to the radio.

The antenna tuner does NOT TUNE THE ANTENNA ,but matches the antenna to the impedance that the radio needs, older TUBE radios had final PA tune that was ,in effect,an antenna tuner and the tubes could take a lot more mismatch abuse. So all we really do is make the radio happy with what wire etc we connect....so when an antenna advertises it will work all bands with an external tuner...about all it is saying is "This $500 aluminum wonder is as good as a $3 piece of wire"  ::)

Wire is easy to find and often FREE (my current antenna was an old extension cord from a trash can) and easy to use. If you only plan to use ONE Ham band ,then by all means cut a dipole...knowing  a dipole is good on ONE BAND ,but I like to use several bands and though several dipoles can be fed from one balun (transformer for radio)  this is not so easy to put into use for home or temporary use.

Enter the random wire ...ONE WIRE to work most,or all,of the Ham bands ,with a auto or manual antenna tuner at it's heart and easy and fast to deploy as a travel antenna or spare (after the storm) antenna that needs only ONE support and will even work just tossed across bushes as a very effective NVIS antenna for better close in communications (a high antenna is good for distant stations BUT a low antenna is best for near use and acceptable distant communications)

I use a W3EDP or ZEP antenna and here is a thread on the subject and a photo ...looks and is EASY to make.





Here is the earlier thread about the antenna and Canadian Prepper's experiments with it:


http://thesurvivalpodcast.com/forum/index.php?topic=53436.0



Here is a random ,or NOT SO RANDOM length chart to chose which length and bands you want to cover.

http://udel.edu/~mm/ham/randomWire/

Also note that the antenna tune is effected by the feed line length and nearby metal and other conductors (even Trees conduct RF)



So with a balun and auto tuner this ZEP,W3EDP,or so called random wire will perform well with just one wire ,for all HF bands within it's cut length.

  I know ,it is a bit complicated when it is not so random ,but this is mostly due to solid state radios verses the radios of old.




Offline Saint-TyR

  • Survivor
  • ***
  • Posts: 107
  • Karma: 3
    • Ruby Lane Farm
Re: What is a RANDOM LENGTH WIRE?
« Reply #1 on: July 31, 2015, 03:17:18 PM »
Great read! Thank you for the post... I have a GV5R antenna right now strung up high between to oaks, which I tend to get nervous during storms. I have been thinking about stepping off the ledge to make my home brew antenna as a back up but more as a new learned HAM skill. I might have to add this one to my list.

Stay Safe!

Offline Carl

  • Mr HamTastic!
  • Forum Veteran
  • *********
  • Posts: 13105
  • Karma: 714
  • COW?...No ,I haven't seen your cow.
Re: What is a RANDOM LENGTH WIRE?
« Reply #2 on: July 31, 2015, 03:58:40 PM »
Great read! Thank you for the post... I have a GV5R antenna right now strung up high between to oaks, which I tend to get nervous during storms. I have been thinking about stepping off the ledge to make my home brew antenna as a back up but more as a new learned HAM skill. I might have to add this one to my list.

Stay Safe!

If you read the ZEP thread linked in the above ,you will read of on man's experiments as he built what I described to him and his results and trials to make it perfect for his use.Canadian Prepper did some great experiments with the ZEP/W3EDP antenna.

Offline Smurf Hunter

  • Survival Veteran
  • ********
  • Posts: 7171
  • Karma: 333
Re: What is a RANDOM LENGTH WIRE?
« Reply #3 on: August 01, 2015, 01:22:25 AM »
Good excuse to buy another balun.

Would you suggest 4:1 ?

Offline Carl

  • Mr HamTastic!
  • Forum Veteran
  • *********
  • Posts: 13105
  • Karma: 714
  • COW?...No ,I haven't seen your cow.
Re: What is a RANDOM LENGTH WIRE?
« Reply #4 on: August 01, 2015, 04:58:26 AM »
Good excuse to buy another balun.

Would you suggest 4:1 ?

Yes the 4 to 1 is great with most external antenna tuners as external tuners have a 10 to 1 or so tuning range....
For use with internal tuners which most often have a 3 to 1 range ,the 9 to 1 balun will give somewhat better tuning range
but (I have read) at a cost to performance,efficiency.

It is my opinion,after testing both CURRENT and VOLTAGE baluns that a CURRENT BALUN is a better device for antenna performance with non-resonant wire antennas like the ZEP or W3EDP discussed in the original post.
You can read the short story of both types here:

http://www.dxengineering.com/techarticles/balunsandfeedlinechokes/baluns-choosing-the-correct-balun

And I will add that there are a couple of good ,inexpensive options that I have used and had good service from and they can be found at many dealers but I include links from AMAZON..NOTE that voltage or current balun BOTH WORK ,CURRENT is my preference ...but either will work and few people will notice the subtle differences between them..BE AWARE THAT HIGH VOLTAGES CAN CAUSE FIRE WHEN ANTENNA ENDS ARE CLOSE OR TOUCHING COMBUSTIBLES...the insulators are used for a reason on antennas.

voltage balun  http://www.amazon.com/Jetstream-JTBAL41-Voltage-Antenna-3-5-30/dp/B00RU6PDI6/ref=sr_1_65?s=electronics&ie=UTF8&qid=1438426838&sr=1-65&keywords=balun

current balun  http://www.amazon.com/MFJ-Enterprises-Original-MFJ-913-Balun/dp/B00OU5KEDO/ref=sr_1_15?s=electronics&ie=UTF8&qid=1438426783&sr=1-15&keywords=balun

Molded option that I like   http://www.amazon.com/Jetstream-4-1-Balun/dp/B00I3ROVFM/ref=sr_1_23?s=electronics&ie=UTF8&qid=1438426783&sr=1-23&keywords=balun

Nine to one baluns are available from many Ham radio shops and I have very little exposure to them so I can't suggest one as better than another.
« Last Edit: August 01, 2015, 05:23:02 AM by Carl »

Offline Carl

  • Mr HamTastic!
  • Forum Veteran
  • *********
  • Posts: 13105
  • Karma: 714
  • COW?...No ,I haven't seen your cow.
Re: What is a RANDOM LENGTH WIRE?
« Reply #5 on: August 01, 2015, 10:46:50 AM »
I did come up with a good definition of random length wire:

A random length wire( antenna ) is a length in which NO HALF WAVELENGTH OF ANY COVERED BAND EXIST.


 :popcorn: :popcorn: :popcorn: :popcorn: :popcorn:  I get popcorn for making it that simple.