Sunday, October 9, 2011

Antenna Testing At W8MDE

This weekend I decided to set up the KD8JHJ 40 Meter Vertical Antenna in the back yard and perform some testing.  Because I built this antenna during the past two years while I held my original call sign I've decided to refer to it by this name even though I now have a new amateur radio call sign.  

During my last testing sessions earlier this year I was unable to attain a good match anywhere near the 40 Meter band (7 MHz).  During this deployment I did one thing different and discovered why my initial efforts to establish resonance at 7 MHz failed.  Because space is limited in my backyard I used some 16' 6" radial wires I had made up for another project.  These radial wires I constructed with ring terminals at each end not only facilitating easy connection to the radial plate below the match box but also allowing me to anchor the other end of the radial wire to earth using a 8" steel spike.  Using this method I effectively connected the coax shield to ground thus completing the antenna circuit allowing the antenna to resonate in the 40 Meter band.

In past testing I secured the ends of the radials to plastic stakes using short lengths of poly antenna cord thinking that because the radials were elevated they did not need to make positive electrical contact with Earth.  Obviously a vertical antenna needs to work against ground.

I had the vertical up and down probably twenty times this weekend as I optimized the coil observing the SWR on my antenna analyzer as I added or removed turns from the loading coil.  Once I achieved the best looking curve I placed a length of heat shrink tube over the coil and sealed the upper end with black electrical tape.  I left the bottom end open so in case moisture does enter the coil area it can dry.

Match box and radial plate

Parallel shunt inductance coil to match the antenna to a 50 Ohm transmission line

I connected the other end of the feed line to my antenna switch and with my transmitter set to the CW mode I sent out CQ CQ CQ de W8MDE using Morse code.  For this initial transmitting test I set my power at 25 watts.  I was pleased to hear K9VON answering my call.  Ross, located in Peach Tree City, Georgia 517 miles away was copying my signal and reported a 359 RST.  Before my next transmission I increased power to 50 watts and Ross then reported 579 reception.  

Later at 7.032 MHz I heard the CQ calls of WA1HFF.  I answered this call and promptly received a 599 report from Steve in Springfield, Mass. 538 miles away.  I am very happy with these first two contacts using an antenna I made with my own two hands.  To learn Morse code and use it in radio communications is an achievement in it's own right but to do it with my homebrew antenna is icing on the proverbial cake.

For reception testing I tuned around the band and using the antenna switch I could easily compare signals heard between the 66 foot end fed wire and the vertical.  Most signals seemed to be about an S-unit less on the vertical versus the horizontal wire.  Not a big deal as I could easily copy all signals on either antenna.  Overall I am very pleased with the results of my first attempt at a high frequency radio antenna.

I don't have fancy antenna modeling software but using the MFJ-259B analyzer I can provide these figures which illustrate SWR curve.

7.180 MHz     1.2 SWR     7.292 MHz
7.129      1.3 SWR     7.308
7.090      1.4 SWR     7.353 
7.031      1.5 SWR     7.370 
6.889      2.0 SWR     7.485 

For additional information click on the "40 Meter Vertical" label below.


  1. Mike are you going to have these antennas available for us other hams? Does it need a radial system?

  2. Hello Norm, No it won't be me bringing this antenna to the market (too labor intensive to build) but it is a good design and surprising me the more I use it. Last night I worked a station in Texas -917 miles as the crow flies.

    The white wires in the pictures are the radials. They are elevated and slope down to the ground at about 30 degrees or so.

    73 Mike