Topband: 160m polarization and elevation angles

[Steve Ireland]

Hi Jim

The omission of  the words ‘inverted vee’ in front of ‘dipole’ for Tom W8JI’s antenna up 300 feet high was a slip of the keyboard at my end! I used to work Tom regularly back when he had the antenna up and helped him with comparative signal reports. 

When he was doing signal comparisons, Tom never used to name the particular antenna he was using at any one time, so as to remove the possibility of any psychological bias that might occur if the station he was working happened to favour a particular type of antenna.  Each antenna Tom used was only referred to as ‘Antenna 1’ or ‘Antenna 2’ and he told me he also used to switch the designations around.

As you say, an inverted-vee dipole is definitely inferior to a flat-top dipole. From memory, I recall John ON4UN found by modelling that a 90 degree inverted vee in the broadside direction was around 1 to 1.5dB down on a flat top dipole at the same height as the inverted vee’s apex – and the radiation angle of the latter was slightly higher, owing to average height of the latter being less. 

While 1 to 1.5dB might not mean much on the upper bands, on noisy 160m it might make the difference in being above (or below) the noise at a DX station. 

All that being said, my main point was that a combination of latitude (reasonable high) and low soil conductivity in south-west VK6 mean that the losses of predominantly vertically polarised antennas are such that a predominantly horizontally-polarised antenna is better.  My present inverted-vee dipole has its apex at 90 feet, but I’d swap it like a shot for a flat-top at 90’ if the yard-size here allowed.  

Vy 73

Steve, VK6VZ (also G3ZZD and VY2LF)

##  W8JI  never had a dipole up  300 ft.   He had an inverted  VEE    up  300 ft.  I believe the enclosed angle was far less than 90 degrees. 
You require  2 x 300  ft towers to string up a 160m dipole at  a height of 300 ft.  W8JI  only had  1 x  300 ft tower at the time.  
  Tom,  N6BT is adamant that a rotary dipole  will outperform an inverted vee  by 6 db, with the apex of the Vee  at the same height as the rotary  dipole. 
N6BT  also claimed the  rotary dipole would have a 14 db  FS.... on DX signals. 

##  Years ago,  I heard these 2  fellows on from Oregon. One of them had up his new  F12  160m  rotary dipole,  mounted on top of his  120 ft tower. 
This  160m rotary dipole  was aprx 102 ft long, and used  LL wires both  above..and below the main trunk section.  The fellow was using a MFJ-259
at the time, and those things  wont work below  1800 khz.   The rotary dipole was resonant below  1800 khz.    They finally got it sorted out..and resonated it 
at the low end of 160m band.   2:1  SWR BW  was aprx   18 khz.  IE:  + /-  9 khz..   Relays  have to be used to  switch band segments about.   
The very 1st  DX station he worked was a  4X4  on CW..... go figure.   Trying to work  EU  from the west coast  on  160M is a tough nut to crack. 

##  If using an inverted vee..and say oriented N-S..... then move the legs  so they are now  E-W,   I never saw any difference, minor at best, but that was on 80m,
and also 40m..... and in both cases, the re-orientation of the legs was done fairly quickly.   I believe the baluns I used at the time were flaky at best...  BN-86  junk. 

##  Other than the fellow in ORE,  I never heard about anybody else using a loaded rotary dipole on 160m.   I have heard several rotary dipoles on both 80m  and also 40m.
The 80m rotary dipoles that I have heard on the air  had pretty substantial signals if oriented broadside in my direction.   When the bands were lousy, and signals were weak, the
fellows with the 80m rotary dipoles were  way ahead of the fellows with the inverted vees.     I never did find out what the RX noise level was like with the 160m  rotary   dipole 
in Ore.  

Jim   VE7RF   


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