Same source but get only half the channels

[amg131]

The Fool map:
http://www.tvfool.com/?option=com_wr...13494444629a73

shows channels 2.1 (CBS), 4.1 (NBC), 5.1 FOX, 7.1 (ABC), 11.1 (PIX), and 13.1 (PBS) all come from the same source 109 degrees. Only able to receive 7.1 and above; 2.1, 4.1 and 5.1 don't come in. (5.1 does at night). If they are all coming from the same source why is reception inconsistent?

Get all of them in the winter but 2.1 does break up at times.

My antenna is from radio shack and is similar to this one:
http://www.radioshack.com/product/in...32189_Antennas

Thanks

[signals unlimited]

How high is your antenna? What direction is your aim? Are there trees in your path?

Are you using an amplifier? What model amplifier? How many sets are hooked up?

List all of the channels that are going out.

[Electron]

The tvfool radar plot report shows the antenna height at 25 feet , thats Ok , however if the antenna were higher the many weak tv transmissions will most likely be stronger.

Make 2 more tvfool radar plot reports with antenna heights at 40 and 60 feet.

Is the antenna mounted at about 25 feet high??

Any big trees or structures that can reduce or block reception to the east/south/east??

Is the antenna aimed at about 115 degree magnetic compass.

Aim the antenna at about 115 degree magnetic compass for the reception of the Tv stations from WMBC-TV channel 18 at 92 degree magnetic compass to WNJB channel 8 at 162 degree magnetic compass.

Here is how to aim antennas , http://www.kyes.com/antenna/pointing/pointing.html.

How many Tv's are/will be connected??

Is there a amplifier installed??

If so , what make and model number??

Is it a radio shack amplifier??

To Test the reception.

Examen the antenna structure.

Connect a Known To Be Good matching transformer (balun) to the antenna.

Connect a Known To Be Good coax to the matching transformer.

Run the Known to be good coax through a open window or open door Direct to a Known To Good Tv.

Connect the Known to be good coax to the Tv.

No amplifiers , No splitters , No nothing.

Aim the antenna at about 115 degree magnetic compass.

Scan for channels.

It is the , Antenna , matching transformer , coax , Tv.

What is reception like now??

[amg131]

Thanks, it will take a couple of days to check out suggestions. Antenna is mounted on a pole at a roof peak; it clears remaining roof lines but there are trees some about 300 feet away.

There is only one TV. Sharp Aquos flat panel
Yes there is a Radio Shack amplifier which sems to be working fine. Had it for many years.

Will get a new transformer and see what happens. But if that was the problem, don't think the reception would be good on some channels and bad on others.

[Electron]

Examen the antenna structure.

Antenna , Known to be good matching transformer , Known to be good coax , Direct to the Tv through a open window or door.

No splitters , No amplifier , No nothing.

Aim the antenna at about 115 degree magnetic compass for the reception of the Tv stations from WMBC-TV channel 18 at 92 degree magnetic compass , to , WNJB channel 8 at about 162 degree magnetic compass.

Scan for channels.

What is reception like now??

[GroundUrMast]

Originally Posted by amg131

Thanks,
...

Will get a new transformer and see what happens. But if that was the problem, don't think the reception would be good on some channels and bad on others.

Water in the matching transformer can produce total failure, but often you'll have less dramatic and conclusive symptoms. This is an inexpensive trouble shooting step.

[ADTech]

If they are all coming from the same source why is reception inconsistent?

While it is correct in that all the stations mentioned transmit from the Empire State Building, there are some differences that that come into play that are outside that condition.

In NYC, channels 7, 11, & 13 transmit on those real operating channels. ALL of the other stations with channel numbers below 13 no longer utilize those channels which they used for their original analog broadcasts. In other words, they are now UHF stations, regardless of their original channel number.

UHF and VHF signals behave differently in several ways.

First, the shorter wavelengths of UHF signals do not bend as readily as do the longer VHF wavelengths, a process called diffraction (see http://en.wikipedia.org/wiki/Radio_p...on#Diffraction and http://www.hdtvprimer.com/ANTENNAS/g...ml#diffraction for discussion). This tends to adversely affect UHF far more than VHF.

Secondly, the water content in trees tends to have a greater amount of attenuation and scattering at UHF frequencies than at VHF frequencies. See http://www.hdtvprimer.com/ANTENNAS/glossaryR.html#trees and http://www.hdtvprimer.com/ANTENNAS/siting.html This problem is less in the winter when leaves are off the trees.

Based on your TVFool plot, it can be seen that you are in low-lying terrain relative to the signal path from NYC much like as is depicted in this image:


The conclusion would be then that the bulk of the possible signals from the ESB are going over your head with very little arriving at your antenna.

Best advice is to try a combination of several things for those UHF signals: High-gain antenna with suitable pre-amplifier, roof/tower as high as feasible, and to mount the antenna as far back from any trees as is possible.

I live is a similarly impaired location, about 20 miles outside St Louis, in a valley and am surrounded by trees. My TVFool plot suggests that a simple two or four bay UHF antenna should be fine, but, it took an 11' modified 91XG mounted 45' in the air plus a pre-amp to achieve reliable reception most of the time for most of the channels. Still, when a particular sycamore tree in our yard that is unavoidably in the signal path leafs out in the spring, I usually loose my local flea-powered PBS station until autumn. The wife won't let me cut it down so we just deal with it.

As always, YMMV.

Cheers!

[amg131]

Thanks, your reply explains a lot. The image provided is right on target. Was not aware that the stations had changed to UHF. I have some work to do but it is just too hot to be on the roof lately. Thanks again.