Antenna - Theory .com: The Antenna Site

Antenna Basics Antenna Types Smith Charts Antenna Measurements

antenna-theory.com :: View topic - Old VHF/UHF combo antennas
antenna-theory.com Forum Index antenna-theory.com
Antenna Theory
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Old VHF/UHF combo antennas

 
Post new topic   Reply to topic    antenna-theory.com Forum Index -> Questions Related to Antenna Theory
View previous topic :: View next topic  
Author Message
Maury Markowitz
Antenna-Theory.com Newbie


Joined: 07 Oct 2015
Posts: 1

PostPosted: Wed Oct 07, 2015 8:33 pm    Post subject: Old VHF/UHF combo antennas Reply with quote

I was walking around the neighbourhood admiring all the old TV antennas still up there with broken dipoles, rusted rotors and cut-off wiring.

But then I got to wondering. Reading the classic on merging antennas:

http://www.hdtvprimer.com/antennas/merging.html

The basic rule seems to be that you're going to lose 1/2 of your signal if you combine.

But it seems these antennas did just that, I can convince myself I see two feed lines, one from the VHF and one from the UHF portions. I suspect they didn't lose 1/2 of the signal?

What is the obvious thing that I'm missing here?
Back to top
View user's profile Send private message
admin
Site Admin


Joined: 03 Jan 2007
Posts: 204

PostPosted: Thu Oct 08, 2015 5:50 pm    Post subject: merging antennas Reply with quote

The problem is you don't know the phase of the signals coming down the transmission line. They could be in phase, 180 degrees out of phase, 90 degrees out of phase, whatever.

If signals add in phase, the power adds directly. If 180 degrees out of phase, powers subtract. Everything else is vector summation.

If you add antenna signals, it will likely add for some frequencies and subtract for others, which is why it can be a bit more complicated than you would expect.
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    antenna-theory.com Forum Index -> Questions Related to Antenna Theory All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group