Will a stronger antenna help or hurt?

pointer · 3-Apr-2012, 2:51 AM

In the analysis

http://www.tvfool.com/?option=com_wr...267e94071d7e20

all the stations of interest to me are shown LOS from Mt. Wilson (where all the transmitters are). I can see it on a clear day east and slightly south, about 100 degrees, 25 miles away.

But pointing my antenna there, all the signals are too weak. We have to point our antenna east and slightly north, at about 70 degrees for usable signals. I think we're getting mostly bounce off the mountains rather than line of sight signal, or some combination. Apparently the analysis can't take this into account. I can't think of any other reasons.

Almost all the channels 2 through 62 are good. However, we're still getting dropouts on a few channels when atmospherics change with weather, like when we get very hot day. Rather than increased attenuation of a fixed path, this is probably due to the signal path changing. Then the apparent direction of the transmitter moves to the side of my antenna's beam, where the antenna's gain is less and the signal output diminishes.

The (virtual) channels that disappear frequently for long intervals are 22, 34, 52, 58. 58 is worst; KLCS (L.A. schools system) doesn't have the best equipment. I've heard that tuners have more trouble with its signals when they are weak. Channel 7 is odd because it fluctuates quickly while the others fade, even though the signal strength on the converter is at the low end of Good.

According to the analysis, 52 and 7 near the top of the list should be strong but but they're not adequate all the time. 58 is about halfway down the list, at the top of the red area, so it is definitely weak and comes and goes more often. I'm not interested in any of the stations further down in the red area.

I currently have Winegard's CA 7078 antenna and AP4700 amplifier, 4 way splitter, 75 to 100 ft of RG6 coax, 3 Digital Stream DTX 9950 digital converters, and a Samsung flat panel with built-in converter. Our antenna is 15 ft above our single story house, which puts it 35 ft above ground, just above the top of the hill across the street.

We need a stronger signal, so it would seem like a higher gain antenna is the obvious solution. However, a higher gain antenna would also have a narrower beamwidth. If the beamwidth of the new antenna is too narrow and the apparent direction of the transmitter shifts too much, it could even fall outside the antenna pattern. It looks like we're now pointing about 30 degrees north of line of sight. I can't guess how much the apparent position shifts with weather, but maybe you can. Probably not a lot, since only a few channels are affected. So, there's hope that the right combination of antenna gain and beamwidth could work.

The amplifier is making up for the transmission line loss of the cable and the splitter, and trying a stronger amplifier didn't help on the weakest channels. Clearly I need more signal output from the antenna.

Will any of the newer "digital TV" antennas solve the problem? Which one?

I've also thought about a really high gain antenna pointed LOS at 100 degrees, with a narrow enough beam to ignore the stronger signals at 80 degrees, but this sounds like fighting nature and doing it backwards. This would require a very large antenna, which would be a hazard in the high winds we experience here.

GroundUrMast · 3-Apr-2012, 6:45 AM

My first suspicion is that the AP4700 is overloaded. By turning away from Mt. Wilson you may be reducing the signal strength enough to get the AP4700 out of an overloaded condition. But now you are also aiming the antenna into some of the stronger multipath...

To test this theory, bypass the preamp (the mast mounted unit and the power insertion block) and any splitters using a known good coax directly from the antenna to one tuner that has signal metering. Now, starting with the antenna pointing straight at Mt Wilson, be sure to fine tune the aim of the antenna. Do you get a better signal?

I'm not convinced you need an amplifier at all. But if you do, it needs to be able to accommodate a large number of strong signals. If you have good signal from the antenna when feeding only one tuner and then loose some weaker signals after reinstalling the splitter, I'll be happy to suggest a high-input preamp or DA.

If you don't get a reliable signal at the antenna, an amplifier is not going to 'clean up' the poor signal. We would need to consider whether or not the existing antenna is damaged (another explanation for the aim point being displaced to the right of bore-sight), or do you need to consider a narrow beam-width antenna capable of rejecting multipath.

GroundUrMast · 3-Apr-2012, 7:03 AM

As an aside, rather than using an amplifier, I generally favor using a high gain antenna. (However, you're correct that when stations are widely separated, the narrow beam of a high gain antenna may make it undesirable.)

Antenna gain is better than amplifier gain. Antenna gain increases net signal to noise ratio at the tuner. Antenna gain often reduces the amount of multipath versus direct path signal which also improves the quality of the signal delivered to the tuner.

Amplifiers add noise and distortion which reduces the net SNR. Amplifiers do nothing to reduce the effects of multipath either.

GroundUrMast · 3-Apr-2012, 7:20 AM

Are there any unused splitter ports?

Is there more than one splitter in the system?

How much coax is used between the antenna and splitter?

How much coax is used to run from the splitter to the most distant tuner?

Electron · 3-Apr-2012, 8:22 AM

The housing on the CA7078 has the matching transformer that connects the antenna metal receiving elements to the coax connection. Check out the housing/transformer the connections inside and the coax connection. I recommend remove All of the preamplifier , the outside part and the inside parts so you are not tempted to connect the preamplifier. Then after checking out the matching transformer on the CA7078 , run one known to be good coax from the CA7078 through a open window or door direct to the tv that has a built in Digital Broadcast Tuner , what is the reception like now?? The Tv stations that are in the direction that you are receiving have a spread of about 25 degrees. The CA7078 has a wide forward beam width. The http://www.winegarddirect.com , HD7698P , has a narrower beam width that will cover the 25 degree spread. The HD7698P antenna has more gain then the CA7078 so the HD7698P antenna will supply more signal to the Tv's with out a preamplifier. A distribution amplifier CM3414 can be used if needed.

pointer · 4-Apr-2012, 1:02 AM

System Design Questions

Are there any unused splitter ports?
no

Is there more than one splitter in the system?
no -- only one, 4 outputs

How much coax is used between the antenna and splitter?
from antenna and preamp to splitter -- 40 ft

How much coax is used to run from the splitter to the most distant tuner?
50 ft
_________________

GroundUrMast · 4-Apr-2012, 1:34 AM

Thanks for that information.

Will you be testing the system as suggested?

pointer · 4-Apr-2012, 5:55 AM

Will you be testing the system as suggested?

Yes

pointer · 27-Jun-2012, 5:14 AM

Sorry for the delay in responding. There are some very good reasons, but let's not clutter up this discussion.

I tested as you suggested. Components are all OK. One straight-in short coax with no splitter and no amplifier supplies most of the desired channels OK, but weak channels 22, 34, 52, 58. 58 (58 is worst) are still weak.

Also, I put a 3db attenuator in front of the amplifier and lost most of the good signals. It's a weak signal problem because of the 4-way split, not an amplifier overload. Note that the AP4700 amplifier is UHF only, to avoid overload by VHF in this area.

It's interesting that Ch 7 breaks up a lot when the 3 converter boxes' signal strength indicators are a little bit into the green whereas the other good channels work fine at that signal strength. Maybe interference? In addition, our Samsung flat panel TV (with an internal converter) has never responded to Ch 58 while the other converter boxes captured it OK. A Winegard consultant said that it has a poor internal converter that requires stronger signals in order to work properly. (Isn't that nice of Winegard to help out?)

Three months ago, pointing the antenna at 80 degrees was necessary because pointing at 100 degrees, straight at Mt. Wilson, was too weak for all the channels.

Weather conditions have changed substantially since then. Now I receive all the desired channels by pointing at almost 100 degrees, with the amplifier and 4 way splitter in place. This is still marginal because turning the antenna only +- 5 degrees loses the weakest, ch 58, even though the CA7078 antenna is pretty broad beam. Surprisingly, the Samsung is capturing Ch 58 now, for the first time. Signals are definitely stronger now.

This suggests that the multipath has shifted dramatically. Since I'm now pointing a little North of straight on to Mt. Wilson, I think I'm getting mainly direct and still a little multipath. Electron, you mentioned, "The Tv stations that are in the direction that you are receiving have a spread of about 25 degrees." But looking at Mt. Wilson from my house, all of it only looks like 10 degrees, which offers hope that a higher gain antenna might avert the multipath change that will surely recur when the weather changes again. If it's 25 degrees, it looks like I'm stuck.

Comments, please.

GroundUrMast · 27-Jun-2012, 8:25 AM

I gather the CA7078 has been in place for several years at this point? A small amount of corrosion, particularly at the connection between the antenna phasing lines and the matching transformer could produce low signal output, skewed pattern & intermittent symptoms affected by changes in temperature or humidity.

@Electron mentioned the Winegard HD7698P earlier, and in your situation it makes sense to consider using one. I honestly believe you should be able to gather enough signal out of the air... with no amplifier at all.

Before you do that though, a less expensive upgrade can be tried. Add an FM trap. You can find them at Radio Shack, Cat. No. 15-024. You may find it helps with real CH 7 and possibly others. It needs to install between the antenna and the preamp. (The second harmonic of KCRW-FM, 89.9MHz lands in the top end of real CH-7's bandwidth. {89.9 * 2 = 179.8}... Real CH-7 is 174 to 180 MHz.) If you replace the antenna, the addition of the FM trap is still prudent.

pointer · 28-Jun-2012, 6:10 AM

I appreciate your previous reply. It's well reasoned and I followed up. I'm concerned about 25 degree spread of the stations; all of Mt. Wilson looks like less than 10 degrees from here. If so, then perhaps a higher gain unit in that series of antennas might do a better job of eliminating multipath as well as get a stronger signal.

Could you please explain how you get 25 degrees? What do you think of a higher gain (than HD7698P ) antenna in this situation?

Electron · 28-Jun-2012, 6:52 AM

pointer , your core group of tv stations is from KVEA UHF channel 39 at 91 degree magnetic compass to KVMO UHF channel 23 at 113 degree magnetic compass.
A spread of about 22 degrees.

With the HD7698P antenna aimed at about 105 degrees magnetic compass the HD7698P antenna should also receive KWJD-LP UHF 22 or is it UHF 25 ??

And thats if KWJD is transmitting , http://en.wikipedia.org/wiki/KWJD-LP.

Of the antennas , HD7694P , HD7695P , HD7696P , HD7697P , HD7698P , the HD7698P is the highest gain antenna.

Electron · 28-Jun-2012, 7:29 AM

If you will like to go after K39GY VHF channel 2 or is it UHF 39. That is the same as KHIZ-DT UHF 44 , KHIZ is received at your location. These channels may be transmitting Analog not Digital.
http://en.wikipedia.org/wiki/K39GY

And KVTU-LP 3 , http://en.wikipedia.org/wiki/KMCA-LP , that is most likely transmitting as Analog channel 3 but might change to a UHF channel.

And KLAU-LP VHF channel 5 , that is most likely UHF Analog channel 45. http://en.wikipedia.org/wiki/KLAU-LP

Then install a HD7084P ALL channel antenna.

All channel antennas receive All the channels that way All the channels are covered.

I say install a HD7084P All channel antenna and be done with it.

Aim the HD7084P antenna at about 105 degree magnetic compass.

Electron · 28-Jun-2012, 11:31 AM

Some times I refrain from recommending a All channel antenna.

The reason is a All channel antenna that receives all the channels including VHF low band channels 2 thru 6 , along with , VHF high band channels 7 thru 13 , and UHF band channels 14 thru 69.

The VHF low band 2 thru 6 channels part of the antenna , like iron to a magnet , brings on bumpy road comments from other advisors that Do Not like the VHF low band.

This happens over and over again.

Sometimes I do not recommend a All band antenna to avoid the bumpy road comments and plowing the field over and over again. Some other advisors insist on causing trouble.

There are no bumpy road comments , about weak signal strength UHF channels , it is , if you get'em you get'em , and if not , then what can be done to get em.

There are no bumpy road comments , about weak signal strength VHF high band channels. From other advisors.

The last time I checked , The HD7084P is Less money then the HD7698P at http://www.solidsignal.com

The HD7698P antenna is Longer then the HD7084P antenna but not as wide.

The HD7084P is wider the HD7698P antenna but not as long.

The HD7084P ALL band antenna receive ALL the Tv channels , VHF low band 2 thru 6 , VHF high band 7 thru 13 , UHF band 14 thru 69.

The HD7698P antenna is designed to receive , VHF high band 7 thru 13 and UHF band 14 thru 69.
Not VHF low band 2 thru 6.

signals unlimited · 28-Jun-2012, 12:48 PM

If the OP is asking for a channel that is low VHF and I know that an all channel antenna or a low V yagi is the only way to receive that channel/channels, then and only will I recommend it. After all it is not we that recommend the antennas who purchase, install, and look at the antenna on there homes for years. It's the OP. Not politics.. just good common sense!

Electron · 28-Jun-2012, 3:42 PM

KVTU , Analog channel 3 at 30.6 NM(dB) noise margin signal strength.

And is LOS = Line Of Sight.

And is a Close 25.5 miles away.

Will be received with a All band antenna.

And if KVTU were transmitting a digital signal on channel 3 with a 30.6 NM(dB) noise margin signal strength.

And LOS = Line of Sight at the same Close 25.5 miles away.

The channel 3 digital signal would be received.

Most of the time the question askers do not know what to ask for.

That is why we are here , to help them ask the correct questions and find the correct answers.

Not keep MUM about certain information because the question asker does not know what to ask.

And to my own shame , sometimes I do not say any thing because I Know there is a bumpy road ahead from past experience , time after time , plowing the same field over and over again.

And receiving a bumpy ride from other advisors.

Did any other advisors even bother to look any of this up??

Or is MUM the word??

signals unlimited · 28-Jun-2012, 4:08 PM

So if this asker is interested in analog 3 (probably never to be digital), he (or she) has been educated and can decide on the antenna. Why is this low V thing such an issue for........ ?

Electron · 28-Jun-2012, 5:54 PM

I Quote from else where on this question askers post.

"If the OP is asking for a channel that is low VHF"

"and I know that an all channel or a low V yagi is the only way to receive that channel/channels" ,

", then and only will I recommend it."

This is not the first time - >If the OP is asking for a channel that is low VHF <- or words to that effect has appeared here at tvfool , I suspect it will not be the last.

And I agree , Why is this low V thing such an issue for ......... ? and others.

I do more then my best to present the options to the question askers because many question askers do not know what questions to ask and what channels are available to receive.

pointer · 28-Jun-2012, 8:15 PM

Wow! That's a lot to digest. Let me simplify by listing the few channels I want:
2.1 KCBS
4.1 KNBC
5.1 KTLA
7.1 KABC
9.1 KCAL
11.1 KTTV
13.1 KCOP
28.1 KCET
34.1 KMEX
50.1 KOCE
52.1 KVEA
56.1 KDOC
58.1 KLCS
not channels 3,6,8,10,12.
no analog stations.

I don't think any of these are in the low VHF band. Correct?

Perhaps these are closer together than the comprehensive lists in the replies above. I don't have a map of transmitter locations for determining the angles. Is there a website?

In the Predicted Channel Availability (Current) chart, all are in the green except KLCS, which is in the yellow. However, KLCS is one that I really want.
Oddly, my wife's favorite 34.1 is very weak (maybe due to terrain?), even though it's listed high up in the green.

Indeed, many of these stations provide abundant signal, but some don't. KLCS is, of course, the weakest. It barely shows up when I take a TV and converter up on the roof with only about 15 feet of cable from antenna straight to converter. It has no hope of reaching through the 4 way divider and 75 to 100 ft of RG6 coax into the house without an amplifier.

The AP4700 amplifier has an FM trap in it, and it's turned on. Nevertheless, I added the Radio Shack FM trap. I can't find any insertion loss spec for it, but 34.1 comes and goes more frequently now.

Thanks for all your interest.

Electron · 29-Jun-2012, 3:28 AM

You will spend about the same amount of money with HD7084P installation and the HD7698P installation.

Might as well go for the whole taco.

The HD7084P.

There is no such antenna that receives only the channels that you are interested in receiving.

KLCS Real UHF channel 41 not Virtual (58.1) will be most likely received buy both the HD7698P and HD7084P.

Tvfool lists both the REAL channels that are received and the Virtual channels.

The REAL channels are what is transmitted and received.

http://forum.tvfool.com/showthread.php?t=9455