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-   -   Newbie wants to combine antenna (http://forum.tvfool.com/showthread.php?t=1125)

piki 29-Dec-2010 11:33 PM

Newbie wants to combine antenna
 
Hi all,

I'm new here and I could find the info I needed in my searches, so here is my question.

First off, here is my signal sheet:
http://www.tvfool.com/?option=com_wr...da32e8ed1c7e2f

I just got an HD tv and I assembled a DIY coat hanger antenna. I installed the antenna in the attic and the signal I receive is satisfactory, I seem to be able to receive up to 75 miles. But my problem is, there are two directions that broadcast the channel I would like to watch. My main direction would be 280 degree mag (about 13 miles) since it offers the french channel, but there is also the 175 degree mag (about 75 miles) that offers the US channel.

I assembled a second coat hanger antenna, but now is there a way to combine them both to receive all the signals?

Or would an omnidirectional antenna fit my need (100+ degree span with 75+ miles distance)?


Thanks
Piki

John Candle 30-Dec-2010 12:39 AM

Tv Antennas and Reception
 
The signal sheet is not the correct one , has no information.

piki 30-Dec-2010 10:20 AM

Oops, I don't know what happen to my signal sheet. Here's a new one.

http://www.tvfool.com/?option=com_wr...da320d2f2ed740

Piki

John Candle 30-Dec-2010 11:55 AM

Tv Antennas and Reception
 
The best way is to run a coax from each antenna to the Tv location and connect the two coax to a Remote control A/B antenna switch. With the A/B switch there will be no interaction between the between the two antennas. If you use a two way splitter in reverse then some of the signal will go to the other antenna and not to the Tv. And cross talk of the antennas will happen with a two way splitter in reverse. If a isolation type combiner is used some signal strength will be lost in the combiner. . An A/B switch is the best.

piki 30-Dec-2010 12:15 PM

Thanks for the quick response John.

I guess an omnidirectional antenna is not a good option?

ADTech 30-Dec-2010 3:12 PM

Omni-directional antennas tend to pick up equally poorly in all directions. They are rarely effective beyond 25 miles and are useless if you're in a multi-path environment.

Use either the A-B switch or a rotor for best results.

Directional antennas that are at right angles to each other are sometimes more likely to be successfully combined using a simple reversed splitter. It will take some trial and error to see if you can avoid multi-path or phase cancellation problems along with the additional insertion loss of the splitter.

piki 30-Dec-2010 3:29 PM

Ok thanks, I'll forget about hte omnidirectional option.

I did try to connect both antenna to a simple two-way splitter in reverse but one of my cable was longer than the other and I was receiving very poor signal. But they weren't at a right angle but close since they were at ~100 degree. I guess I'll have to try with same length cable.

Since the signals I'm interested in are 280 degree and 175 degree, I tried setting the antenna at 230 degree but the signal was poor. I was going to ask how wide does a unidirectional antenna can cover, but I guess it depends on the antenna, right?.

If I put a reflective board behind each antenna, will it help to block behind the board signal?

John Candle 30-Dec-2010 6:05 PM

Tv Antennas and Reception
 
The Antennacraft 4 bay UHF U-4000 antenna is a typical 4 bay UHF antenna for about 35 dollars. . Winegard , ChannelMaster , AntennasDirect , also make them. There are also 8 Bay UHF antennas. Notice the -> UHF <- that keeps appearing. UHF = channels 14 thru 69 , VHF high = channels 7 thru 13 , VHF low = channels 2 thru 6 . . VHF high and VHF low are not in the UHF channels.

John Candle 30-Dec-2010 6:15 PM

Tv Antennas and Reception
 
As a learning experience go ahead and try every thing else.

ADTech 30-Dec-2010 6:29 PM

Quote:

I was going to ask how wide does a unidirectional antenna can cover, but I guess it depends on the antenna, right?.
Yagis and 8-bays typically have a -3dB beamwidth of between 15 and 45 degrees depending on the design. 4-Bays typically are between 40 and 60 degrees beamwidth. Beamwidth is a function of the directivity of the antenna, that is, how directional it is. A narrower beamwidth would tend to be the highest gain and would usually be best for either fringe signals or environments where multi-path must be controlled, ie, mountainous areas where reflected signals are a greater problem.

Quote:

If I put a reflective board behind each antenna, will it help to block behind the board signal?
Yes. However, it might be necessary to play with the distance between the barrier and the antenna's elements to prevent unintended reflections from interfering with the reception of the desired signal(s).

piki 30-Dec-2010 7:34 PM

Thanks guys for the answers.
I'll go to bed a more educated man tonight.

All that's left as John suggested is to make some test.

One last question: Is there an advantage of using a commercial made 4-bay (or 8-bay) antenna instead of using my homemade coat hanger (4 bowtie) antenna?


Piki

Tower Guy 30-Dec-2010 7:51 PM

Quote:

Originally Posted by piki (Post 4874)

One last question: Is there an advantage of using a commercial made 4-bay (or 8-bay) antenna instead of using my homemade coat hanger (4 bowtie) antenna?


Piki

The commercial bow tie antennas have reflectors, which reduces multipath. Your design may not use a reflector, so combining two of them becomes harder.

piki 30-Dec-2010 8:25 PM

Thank for the quick answer.

I guess I'll have to try out different scenarios, it going to be a science project with the kids.

A lot of fun is expected in the next few days, the antenna is in the attic and the TV is in the basement.

Piki


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