[Antennas] Homemade HD Antenna

[Terry Conboy]

On 2009-03-16 6:48 AM, Phil Florig W9IXX wrote:
> Hi all,
>
> Thinking some may be interested in watching this:
>
> http://www.metacafe.com/watch/762088/coat_hanger_hdtv_antenna_better_than_store_bought_amazing/
>
> Wonder if this has been modeled by anyone....
>   
It's an attempt at a stacked pair of Lazy-H's that should have about 11 
dBi gain in free space (bidirectional).  The normal design has 1/2 
wavelength between the elements, with 1 wavelength (or sometimes 1.25 
wl) elements.

The design in the video uses 5.75 inch element spacing, which is 1/2 wl 
at 1026 MHz.  The ~15.5 inch (14" plus feeder spacing) elements are 1.25 
wl at 952 MHz.

This is well above the UHF TV band, which now covers from 470 MHz to 698 
MHz. (The UHF TV band now consists of only channels 14-51, since all the 
higher UHF channels have been re-allocated to emergency services or 
cellular).  And there are (or will be) many DTV channels in the VHF 
band, too.

I built an EZNEC model using the dimensions given in the video, and on 
the horizon in free space, it has about 1 dBi gain at 470, 7.5 dBi at 
527, 8.7 dBi at 584, 9.1 dBi at 641, and 9.6 dBi at 698.  The best match 
to 300 ohms is at 476 MHz (SWR 1.4:1) and it's over 5:1 from 524 MHz to 
698 MHz.  (At 1000 MHz, the SWR is 1.3:1 and the gain is 11.5 dBi).

Increasing the element spacing to 10 inches (1/2 wl at 590 MHz) and the 
element wire lengths to 10 inches (20 inches folded in half with 4 inch 
tip spacing) makes a better UHF TV antenna, with a minimum of 9.8 dBi 
gain at the band edges.

It's quite amazing that tossing this in the corner behind the TV gives a 
good picture.  I guess that's a testament to how robust digital TV is!

73, Terry N6RY