Vertical Doublet Antenna for Tight Spaces, bands 20-10m (40-10m)

I wanted to write about the most succesful apartment antenna I have used thus far. It is the vertical doublet. A vertical doublet is a symmetrical antenna which is basically a dipole on some frequency fed with a low loss open feeder line. The feeder line section tunes the antenna.

The antenna has given me excellent results on the bands and it really shines on 10m where it is a full wave vertical dipole. The radiation angle for maximum gain is around 12 degrees on 10m. The most distant operator I have heard on 10m was some guy near Los Angeles during sunset in Finland. The most distant QSO was to Arkansas. On 10m the DX operators have commented that the antenna really does work for low angle radiation and testing with the locals also confirms it.

By playing with a model in MMANA you can see how adjusting the two variables which are 1) radiating wire length 2) open feeder length change the tuning. I have managed to tune the antenna so that on 10m and 17m it does not need a tuner. My setup is following:

RADIO--TUNER---COAX----1:1BALUN===450 Ohm line, 6.6 m or so===5m wire up, 4.7 m wire down


The structure looks like the letter T which is tilted 90 degrees to the side. The lower wire facing the earth needs to be a little shorter than the wire facing the sky because it couples to the earth and thus gets the antenna a bit out of balance. The feed line must be routed in a 90 degree angle so that it does not interact with the radiating elements. The coax cable between the balun and tuner should be as short as possible but the open feeder should start a couple of meters away from any structure to decrease noise pick up.  I will post the antenna model for MMANA below.

*
14.15
***Wires***
5
0.0,    0.0,    0.02,   0.0,    0.0,    5.12,   8.000e-04,      -1
0.0,    0.0,    0.0,    0.0,    0.0,    -5.01,  8.000e-04,      -1
0.0,    0.0,    0.0,    0.0,    7.85,   0.0,    8.000e-04,      -1
0.0,    0.0,    0.02,   0.0,    7.85,   0.02,   8.000e-04,      -1
0.0,    7.85,   0.0,    0.0,    7.85,   0.02,   8.000e-04,      -1
***Source***
1,      0
w5c,    0.0,    1.0
***Load***
0,      0
***Segmentation***
800,    80,     2.0,    2
***G/H/M/R/AzEl/X***
2,      5.2,    0,      50.0,   120,    60,     0.0


A link to the model here: http://koti.kapsi.fi/~mortal/vert_doublet.maa