Same tower, 4 channels, mixed reception

bbaker73

DTVUSA Member
#1
I lose CBS channel 30 frequently, especially in the clear daytime. There are 3 other channels that appear to come from the same tower. 2 of them are always stable, 1 is stable most of the time, but CBS if very sketchy.

Looking at rabbitears.info, they appear to be on the same tower, so I'm wondering what might cause 30 to not tune well? Power, frequency? (not just one tv tuner either, i have 4 tv's)

WBZ CBS 30 (bad channel) RabbitEars.Info
WGBX PBS 43 (good most of time) RabbitEars.Info
WCVB ABC 20 (I think pretty stable) RabbitEars.Info
WGBH PBS 19 (ALWAYS STABLE) RabbitEars.Info

I pull in WFXT Fox fine. It's 1 degree different from the above, and according to tvfool should be a weaker signal.

Just weird and it bothers me :)

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=8e03c8409f1ad5
 
Last edited:
#2
Without digging too deep into it. Differences in transmit antenna directivity, transmit antenna height above ground, transmit antenna polarity ( horizontal or elliptical). ERP and TPO doesn't tell you which direction the signal is being radiated.
Steve
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#3
bbaker,

Digital TV signals arrive at your antenna something like a stack of pancakes and the trick is to locate your antenna in the center of one of the pancakes, not in the gap between them. So, try raising or lowering your antenna a foot or two and there may be an improvement in your reception. The challenge, is to find the right height where all of your channels appear at the same height level. Here is a link to a terrific website that does a good job explaining RF propagation: Siting the antenna

Jim
 

bbaker73

DTVUSA Member
#4
Thanks guys. Just a quick question you can answer in simple terms (I'm not that technical you've probably noticed by now). Would combining another HDB91X with my current one provide much if any gain to make a difference on this week channel or am I just asking for trouble? Problem is, it would have to be a vertical stack at about 15' apart. I cannot take my 20' mast down easily or safely to put a 2nd one any closer to the one that is at the top of the mast, so I would have to mount it low enough I can reach and estimate the cable length and try to get them similar to combine before the preamp.

I came across this UHF Vertical Stacked A-D 91XG but all the tech data doesn't mean much to me except it seems at 5-8' apart is better.

Worth trying?
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#5
bbaker,

Your antenna survey reports WBZ as a 2-edge signal that barely reaches you, so you are sniffing for vapors and the best answer is higher antenna height, as hard as that may be to make happen.

Personally, I wouldn't add a second antenna for the minor amount of gain - if any gain - at such a low height. You can get as much or more gain by raising your existing antenna into the next 'pancake' layer as I mentioned above and is described on the website link: even a foot or two change (up or down) can make a major difference sometimes.

On the other hand, you will never know unless you try and the second antenna's location may be superior, in spite of being lower. If you buy a second antenna test it alone, not connected to the existing antenna to determine the best height for it, then combine them making certain they are pointed precisely the same direction.

Jim
 

bbaker73

DTVUSA Member
#6
Thanks Jim. I was finally able to get some assistance while I was on the roof and someone else watching the tv and tweak the antennae closer to WBZ magnitude. I did see an increase in signal in it and the other major broadcasters, ABC, Fox, NBC from the same tower vicinity. So WBZ CBS is more stable now, on the contrary, on the same tower WGBX is now not stable, reverse from previous. Must me a variance in how the different antennas on the same tower bounce around the 2Edge to reach me. But I'll take the increase in the major stations, most of WGBX is similar to WENH and WGBH that I have no problem with.

I'm still trying to decide what to do with my buddy in the other thread http://www.dtvusaforum.com/dtv-hdtv...ion/77490-hd-stacker-vs-winegard-hd7698p.html but if I end up getting him a 91x, i may test stacking it here before I install it there.
 
#7
About all I can do is to reference you to the HDTV Primer web site. I find the site a bit difficult to navigate so I took time to look up a few pages that apply here.
Copied from HDTV Primer.
If the combiner is 90% efficient then a 2.5 dB gain is seen.
If the antennas point in different directions, there is a 3.5 dB loss at the combiner.
If the antennas point in the same direction, there is a 2.5 dB gain at the combiner.
Stacking multiple antennas
A 16-Bay UHF Antenna
Merging feedlines
There is a lot of very good information on that site.
Steve
 
Top