[LakelandARC] Re: Can someone help Jim with this?

[Bill]

Chet,

A balun is recommended for the Cobra Ultra-lite. This is a note that I just sent to Rich.

Also, make sure you log on to your Yahoo account frequently, just to work the kinks out. The more you use it, the better. 


Note just sent to Rich:

      Rich,



      The current balun is recommended for the Cobra UltraLite antenna. http://www.k1jek.com/



      Jim has decided to go with the Junior, primarily do to space limitations. This antenna is similar to a center fed dipole and is fed by ladder line, hence the need for the balun. Prices for the 160-10, 80-10, and 40-6 are similar. Getting a 144 foot antenna on a 100 foot lot is more problematic. :-)



      Here is an excerpt from the site's FAQ



      Do I Need a Tuner?

      All Cobras require a tuner. In most installations, the auto-tuner built into your transceiver should provide sufficient tuning range. Because the Cobra presents a balanced load, we recommend installing a 4:1 current-style balun at the station end of the feedline (many external tuners provide a built-in balun)

      .

      Jim has done his homework on this antenna. He visited two hams who are using them, and got some hands on with one at Julian's (W4VCO) shack. 



      This simple question was a great opportunity to do a little research for myself. I have two antennas, both dipoles, one with, and one without a balun. The one that was store-bought, with came with a balun, the other was a home brew that didn't require one. I have little in-depth knowledge of balun design, but do know that sometimes they are not needed, and in some cases make things worse when they are used. 



      In Jim's case he is feeding with a ladder line, balanced, and needs to go to coax, unbalanced. Why a 4:1 I don't know. On the surface of things, the Cobra looks like a folded dipole made from three wire ladder line. 



      Bill



      PS This might be a topic for Chet, but not at April's meeting




  ----- Original Message ----- 
  From: chestercarruth at yahoo.com [LakelandARC] 
  To: LakelandARC at yahoogroups.com 
  Sent: Sunday, January 25, 2015 9:43 PM
  Subject: [LakelandARC] Re: Can someone help Jim with this?


    

  My first question is: Why do you need a balun? Second question: Why are you buying a dipole?

  I can provide the wire you need for a simple but very effective dipole antenna. The impedance will be in the range of 35-75 ohms which will work just fine into a 50 ohm coax with no balun. A folded dipole will be a higher impedance, requiring impedance matching by some means, not necessarily a balun.

  Bear in mind that the dipole antenna, folded or not, will resonate at only one frequency and that is where you would get a good match to 50 ohm coax. As you change frequency, the impedance will change and become either inductive or capacitive, depending on which way you move. You can change frequency a fair amount, depending on the band, and get by with the tuner in your radio......... The "KISS" method works very well.

  "KISS" = Keep It Short and Simple........ no balun, no store bought antennas, just string up a resonant length of wire for the dipole and feed it directly with coax........... Good Luck!!



  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lakelandarc.org/pipermail/cq-lakelandarc.org/attachments/20150126/61fb785f/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/x-ygp-stripped
Size: 141 bytes
Desc: not available
URL: <http://lists.lakelandarc.org/pipermail/cq-lakelandarc.org/attachments/20150126/61fb785f/attachment.bin>