[TowerTalk] Foam cables and velocty factor

[Robert Chudek]

Here's an update regarding the 160m inverted vee I am testing.

A few of you questioned the 2.3 Ohm reading I reported. Someone (who will remain nameless... but his call is AD3F) suggested the graphs look like there is a short at the feedpoint of the antenna. This never occurred to me because I never screw up installing PL259's.

But the light bulb went off in my head, I could measure the coax from the shack now that I had removed the balun. Shore-E-Nuff... 3 ohms of DC resistance! Mystery solved and a lesson learned: check your transmission line for continuity and no shorts prior to installation. It doesn't matter how many cables you have built over the years.

So I replaced that faulty PL259 connector (the one I installed perfect the first time) and ran the analyzer again. Much better!

I uploaded the final PDF's into the 160m folder on http://chudek.aberon.net for your viewing pleasure. They have the 160m-3- designations in the filenames.

So what values am I getting now? I'm glad you asked that question...

1) There are 1.1:1 vswr and 0 Ohms reactance between 1665 and 1695 KHz.
2) There are minimum phase angle (-21 Ohms) and minimum reactance (-12 deg) at 1800 KHz.
3) There are 2.1:1 vswr and -7 Ohms reactance at 1830 KHz, my target frequency.
4) The lowest impedance shows 23 ohms at 1850 KHz. 

I have two questions:

a) Where in the spectrum is this 248 foot hunk of wire resonant anyway!?
    i) 1680 KHz (no reactance),
   ii) 1800 KHz (minimum reactance & phase)
  iii) 1850 KHz (minimum resistance),
  iv) can't be determined from the data, or
   v) depends on what the word "resonant" is.

b) What will provide the best "performance" for this wire at 1830 KHz?
    i) Build a 2:1 matching device for the feedpoint,
   ii) Trim the legs shorter to move the minimum vswr to 1830 KHz,
  iii) Adjust the coax length to move the minimum vswr, or
  iv) depends on what the word "performance" is.

My 160m antenna objective is to provide the best match for my amplifier and radiate the most signal into the air (not heat the wires).

You know, as simple as this seemed to me in the beginning, I am starting to think it IS rocket science! I am going to review that 5 pound antenna book over there on the shelf. It's dark outside now and it's going to snow tomorrow.

73 de Bob - K0RC