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Old 14-Sep-2010, 4:57 PM   #1
geobrick
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Help with channels 7 and 36 in LA

I'm getting every channel emanating from Mt Wilson in Los Angeles except for channels 36 (KNBC) and 7 (KABC) which are marginal.

I'm doing this with an attic mounted antenna because of home owner association restrictions. The antenna is a 10 year old radio shack VHF/FM/UHF model that's about 101" long. I donít know the model #. I also added a CM-7777 pre-amp to help with the cable runs and splitter downstream. With the amp, I got a few more channels. I'm 52 miles away and according to the report below, I'm at 1edge for most of the channels.

The TV fool report is here:

http://www.tvfool.com/?option=com_wr...a36269f1ab38e5

Before I invest a lot more time and money, I wanted to make sure the signal was getting into the attic. I confirmed I can get KABC (real channel 7) but itís more consistent at night. KNBC (real channel 36) was more difficult but I finally got a signal. It drifts in and out randomly (stays for several minutes and cuts out for several minutes). All the other Los Angeles stations seem to work fine. Iím even getting the Santa Barbara channels when the antenna is pointed east towards LA even though the signals are 210 degrees apart and theyíre 60 miles away (but theyíre LOS).

I have easy access to the east side of the attic (itís a wall not a roof when pointing east). Among the typical attic problems are a cement tile roof and a stucco wall (I assume with a 1Ēx1Ē or so metal mesh in one of the stucco layers. Even so, I still get every channel except the two mentioned.

Iím considering the following and would appreciate any opinions or other solutions. 1) I can replace my existing antenna with a Winegard 7697P or 2) get an CM 4228HD and combine it through the CM7777 with my existing antenna.

Any thoughts?
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Old 14-Sep-2010, 7:19 PM   #2
mtownsend
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Ahh. It's clear now that there really is some terrain blockage causing your "1Edge" diffraction. This makes your signals fairly weak (in the "red" zone on your signal list). I hope you will consider going with a rooftop antenna for stations in this range because you're probably losing quite a bit of signal just because the antenna is inside the attic.

I understand that a lot of HOA policies try to scare people out of using an outdoor antenna, but you should probably read up on the FCC's OTA reception devices rule (http://www.fcc.gov/mb/facts/otard.html). This is a federally issued policy that basically says that everyone (except for a few special exceptions) has the right to install an antenna for the purposes of OTA reception. Since it is a federal rule, it carries the legal force to supersede any landlord, HOA, city, county, or state regulations that might try to limit your right to exercise this right. Some HOAs are actually aware of this rule but conveniently forget to mention it to the residents, and for anyone not aware of this rule, the FCC link is a good place to start.

I do not advocate creating friction between yourself and your HOA, but sometimes it helps just to know that the law is on your side in this particular case.



If you are able to move your existing antenna or get a similar new antenna on the roof, I suspect that your reception will improve considerably.

If you decide to stick with an attic antenna, then you will need to go with an even bigger antenna to compensate for the building loss and added interference from being indoors. I'm not sure if you have enough room in your attic for a channel 7-69 antenna like the Winegard HD7698P.
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Old 14-Sep-2010, 9:22 PM   #3
John Candle
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Tv Reception

Every one is aware of the law except , guess what , The Home Owners.
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Old 14-Sep-2010, 10:54 PM   #4
geobrick
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Originally Posted by mtownsend View Post
I'm not sure if you have enough room in your attic for a channel 7-69 antenna like the Winegard HD7698P.
Thanks for the reply. I'd prefer the attic method for now because everything comes in great except the two channels (7 and 36).

I'm pretty sure I can fit the HD7697P but not the HD7698P. Is it worth a try? They have a 7697P at Fry's Electronics for $80. Is it worth a try?
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Old 15-Sep-2010, 12:29 AM   #5
mtownsend
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The HD7697P is roughly half-way in between your current antenna and the HD7698P in terms of performance (a guess based on approximate size and design of your current antenna). You will probably gain about 1-2 dB with the HD7697P and another 1-2 dB if you go with the HD7698P.

More antenna gain means more margin to deal with whatever is causing instability on your two missing channels. Whether or not that's good enough to make channels 7 and 36 stable is uncertain.

Indoor environments have many more random variables (blockage, reflection, noise, etc.) than an outdoor environment, so that makes it very hard to say if any given setup is "good enough". We have no way of really knowing how close you are to the breaking point on these channels and how much more margin you need to make them stable. You won't know until you try it.

If you do someday go with a rooftop antenna, you are much more likely to succeed.
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Old 15-Sep-2010, 1:41 AM   #6
geobrick
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Originally Posted by mtownsend View Post
Ahh. It's clear now that there really is some terrain blockage causing your "1Edge" diffraction. This makes your signals fairly weak (in the "red" zone on your signal list).
True the chart shows 1Edge diffraction but in my post in a different section, I questioned how accurate this is.

When I click on KNBC on the report I provided above, I get a Transmitter Profile Detail chart showing my home is in a blue area (it's hard to see the detail). It shows the blockage comes from some high terrain about 1/10th of the distance from my house towards the transmitter (I know you say the terrain scale is exaggerated).

To see where this hill or mountain was, I followed the Google maps terrain view along the path towards the transmitters on Mt Wilson. Those transmitters are at close to 6000' in altitude. My house is at 1000' altitude. At 53 miles the effect of the earth's curvature would be about 35 feet. (53mx8"). I found a 1400' hill about 20,000 feet from my house along the path to the transmitters. That hill appears to be just enough to cause the 1edge effect. So it seems the charts are accurate. To get full LOS Id need the antenna to be at 340 feet.

Last edited by geobrick; 15-Sep-2010 at 5:48 AM.
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Old 15-Sep-2010, 2:26 AM   #7
John Candle
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Tv Reception

Tip the front of the antenna Up so the length of the antenna is in line with the tv signal as the signal is being bent over the hill. The bending effect of the signal is known as diffraction.

Last edited by John Candle; 15-Sep-2010 at 2:28 AM.
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Old 15-Sep-2010, 5:47 AM   #8
geobrick
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Originally Posted by John Candle View Post
Tip the front of the antenna Up so the length of the antenna is in line with the tv signal as the signal is being bent over the hill. The bending effect of the signal is known as diffraction.
Thanks. I'll try that and report back.
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Old 15-Sep-2010, 6:03 PM   #9
mtownsend
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Originally Posted by geobrick View Post
the chart shows 1Edge diffraction but in my post in a different section, I questioned how accurate this is.
Just to give you a visual of what's going on, here's a bird's eye view of the coverage map for KOCE (Mt. Wilson) around your neighborhood.


In these coverage maps, red, yellow, and green represent very strong signals while cyan, blue, and purple represent weaker signals.

If you look a bit below where the transmitter is shown, you can see how the Burbank hills casts a shadow across Burbank itself. Anyone close to the base of the hills is deep in the shadows and will get less signal than people farther away because the radio waves cannot bend at steep angles.



In your area, something similar is happening. However, since you are further from the transmitter, the shadows tend to be much longer. It looks like your entire valley is still "in the shadows" of the local hills, and no one has a line-of-sight shot at the signal until you start to climb the hills to the west of your location.

KOCE is on channel 50, which is a high UHF station. High frequencies cannot bend as sharply as lower frequencies, so if you were to look at other channels (lower UHF channels and VHF channels), you would see more signal getting down into the shadows due to better diffraction.
Attached Images
File Type: jpg KOCE.jpg (278.6 KB, 993 views)
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Old 16-Sep-2010, 5:07 AM   #10
geobrick
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Very cool view. Thanks for posting it. Is that Google Earth?

I"m in the dark blue area near where it says Casa Conejo.

I tried tilting the antenna up as suggested above but I still can't get channels 7 and 36.

However, I am getting signal strengths in the low 90s for many of the chennels that were in the 70s and 80s before (those numbers are according to the Tivax converter box hooked up to a portable DVD player that I'm using in the attic to get real time feedback when I move the antenna).

I'm making some progress. I'll try the 7697P next. We'll see how that does.
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Old 16-Sep-2010, 6:04 AM   #11
mtownsend
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Yes, that is a screen capture from Google Earth.

You can download coverage maps for transmitters in your neighborhood from here: http://www.tvfool.com/index.php?opti...ask=view&id=15
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Old 23-Mar-2013, 8:51 PM   #12
geobrick
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Bought the HD7698P

I finally got around to buying a Winegard HD7698P. The signal strength improved on everything but I still can't get KNBC (real channel 36). I get all the other channels I want. Even KABC is now strong enough to be consistent. The transmitters are all pretty close together so it's hard to figure out why KNBC is being blocked yet KCBS (real channel 44) is fine even though the NM on KCBS is lower than KNBC (2.1 vs 8.2).

I'll play a little more with pointing (maybe I'll try tilting it up like I tried with the old antenna).

This is the Report:
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Old 24-Mar-2013, 7:27 AM   #13
GroundUrMast
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Have you ever 'tested' reception with the antenna outside, clear of the various impairments of roof and building construction? As already mentioned, your HOA does not have standing to create or enforce rules that prohibit you from using an antenna. http://www.fcc.gov/guides/over-air-r...n-devices-rule

Your report strongly suggests that you'll need to avoid artificial obstructions if you're going to have success.
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Old 24-Mar-2013, 8:39 AM   #14
geobrick
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Originally Posted by GroundUrMast View Post
Have you ever 'tested' reception with the antenna outside, clear of the various impairments of roof and building construction? As already mentioned, your HOA does not have standing to create or enforce rules that prohibit you from using an antenna. http://www.fcc.gov/guides/over-air-r...n-devices-rule

Your report strongly suggests that you'll need to avoid artificial obstructions if you're going to have success.
I don't really want to put it outside even if the law allows it. I didn't try it outside but I was tempted to do it just to see if I could get KNBC while it was outside the attic. I didn't do it because whether I got it or not, I'd have to take it apart to put it in the attic anyway. I decided to skip that and just put it in the attic.

I'm not sure the attic is the problem though. I know it's not the ideal place for it, but I'm getting every other channel with good signal strength. They all come from practically the same location on Mt. Wilson so why is KNBC bad but KCBS good? KCBS has the lower NM value yet still gets into the attic with plenty of strength.

I'm going to try some things later today and see what happens. I'll take the converter box up there and connect it to a monitor so I can see the changes in signal strength as I move the antenna.

By the way, your user name, "GroundURMast", is that a recommendation that improves performance or is it a safety thing?

Last edited by geobrick; 24-Mar-2013 at 8:43 AM. Reason: added the question about grounding masts.
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Old 24-Mar-2013, 9:46 AM   #15
GroundUrMast
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By the way, your user name, "GroundURMast", is that a recommendation that improves performance or is it a safety thing?
Safety first... Best practice. When your antenna system is grounded correctly, you protect the tuner from static discharge damage and you also would expect to be able to conduct enough current to ground to be able to trip a circuit breaker if power from a branch circuit accidentally contacted a part of the antenna system. (A nail driven through power and coax... Christmas light cord frayed... etc.)

I've heard arguments for grounding based on 'reduction of interference'. The technical support for that theory holds up in the LF, MF & HF bands where wave lengths are long and so the antenna down-lead is often a small fraction of a wave length. If so, grounding the down-lead shield can effectively reduce RF voltage on the outside of the coax and thus reduce the possibility that the coax shield would act as an unintended antenna element.

In the VHF and UHF bands, wavelengths are much shorter, so grounding the coax shield does not provide a continuous low impedance along the full length of the coax (presuming it's more than a few inches long... in fact just 1/4 wavelength from the ground point (presuming it's an effective RF ground) you will find a very high impedance point where a high RF voltage could be present despite the ground just inches away. The bottom line is, an antenna is connected to the coax... the antenna is going to receive interference if it's present and couple it to the coax.

http://forum.tvfool.com/showthread.php?t=901
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Old 25-Mar-2013, 4:54 AM   #16
geobrick
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I played with the position a little bit today but I made it worse (lost KABC).

I moved the whole antenna closer to the east wall (where the old one was) and it made things worse. My theory is that the signal may pass through the cement roof tiles easier than passing through the stucco wall.
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Old 25-Mar-2013, 5:25 AM   #17
teleview
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Attics and indoor reception Are Not a reception friendly environment and Never Will Be a reception friendly environment.

Signal attenuation , electric/electronic interference , multipath/reflections-signals bouncing all around in the attic/indoors.

Stucko is held in place with stucko ->Wire<- , The stucko ->Wire<- does a good job of blocking Tv reception.

Concrete roof tiles do a good job of reducing and blocking Tv reception.

Install the antenna ->Above The Peak Of The Roof<- in such a manner that reception is not blocked by the roof and house in the directions of reception.

It is best to install antennas in such a manner the antenna has the least amount to no amount of obstructions of any type or kind in the directions of reception including your own roof and house.

Here is the Federal Antenna Law that says Yes you can install antennas -Above The Roof- so as to have Reliable Reception.

http://www.fcc.gov/mb/facts/otard.html.

The Federal Antenna Law over rules and makes null and void , All , Hoa's/Aho's , housing coven-nuts , dead restricted housing , crazy neigh-boors , city , county , state , governments , and any other antenna haters no matter how they dress them selfs up to appear other then what they are --Nuts.

Last edited by teleview; 26-Mar-2013 at 7:11 AM.
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Old 25-Mar-2013, 12:41 PM   #18
No static at all
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If the antenna must stay in the attic, get it as high as possible. Touching the rafters or plywood is fine & may be required to receive the troublesome KNBC signal. I have my antennas suspended with short pieces of coax between the rafters to aid in mounting as high as possible. It really makes a difference with weak TV & FM signals.

If you must stay inside, I would consider augmenting the 7698 with a 91XG for UHF. The more compact 91XG can fit in tight areas of the attic where KNBC might be a bit stronger, but no guarantees. The 91XG can also be assembled without the center section making it even more compact with only a slight reduction in signal gethering ability.

Of course mounting outside would be much better, but you already know that.

The 7698 is extremely difficult/nearly impossbile to re-fold. You will need 2 flathead screwdrivers & lots of patience. Having a 2nd person to help will make things a lot easier.

It would be nice to have a sticky thread dedicated to warning people not to use the 7xxxp line of antennas if they must mount in the attic.
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Old 25-Mar-2013, 4:32 PM   #19
geobrick
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Thanks. I plan to move it back to where the signals were stronger and then play with it to see if I get KNBC. I know the stucco has that mesh imbedded in it and that could be acting like a shield. If that doesn't work, I'll look into the 91XG.

The signal strength I was getting for all the other stations wasn't marginal. According to the signal strength meter on the Tivox converter I was using in the attic, the unamplified signal on most channels was well into normal area and KCBS was in the green area (upper third of the scale). I think things are fairly good in the attic considering how much signal can be lost or scattered in there.
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