Grouping Log Periodic Antennas

I'm having problem making a group of four log periodic TV antennas covering VHF-H and UHF band. The problem is that reception is much worse than it is with only one log periodic. Antennas are pointed in the same direction and mounted on top of each other with 20 inch distance between adjacent antennas. I connected them together via coax cables of the same length to ensure zero phase shift between signals. Here is how I see the problem, in common point (where cables of each antenna are connected together) impedance is 75/4 ohm unbalanced and needs to be matched to a 75 ohm coax. cable connecting antennas and TV. I used simple 1:4 transformer that is sometimes used for matching folded 300 ohm dipole to a 75 ohm coax. ( one coil on a ferrite core with the third connection in the middle). I connected common point to the middle connection of transformer, one of the external connections to the ground and the second one to the coax. cable feed. I guess that might be the problem. Can such type of transformer be used for matching two unbalanced ends as it is in this case? Is problem maybe something else?
Thanks!

 

[VEBill]

Here is a potentially useful link:

http://www.tvantenna.com/support/tutorials/combining.html

Good luck.

 

[jbartos]

Suggestion: Check this software

http://courses.ece.uiuc.edu/ece354/NEC/NWS_USER.pdf

 

[nbucska]

Of course you have problem. How can you connect 4 broadband
antennas maintaining 2n*PI phaseshift for the whole band ? .

Besides this you should transform the impedances or at least
connect them parallel-series -- this needs only baluns --
if you can solve the phase shift problem.

I suggest stay with only one high gain antenna or
add the signals after preamplifiers with variable
phase-shift perhaps with closed loop control.

The paralleling of preAMP-s would reduce their noise, too

Other : The distance between the antennas should be
AT LEAST the longest wavelength -- or you should
calculate (????? ) their interaction.
<nbucska@pcperipherals.com>

 

[jbartos]

Suggestion: Visit

http://doityourself.com/electric/tvanten.htm

(addresses filters)

http://www.mcibroadcast.com/article_12.html

http://www.tcibr.com/PDFs/900.pdf

etc. for more info