I'm swallowing my pride

[youngclarkh]

I thought I could figure this out on my own but it turns out I need help. So here goes....

I live in Tucson, Arizona at the base of a mountain. Here is my map:

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3dda325aff295b70

The transmitter I am interested in is the one that is only 9.1 miles away on top of the mountain. I guess I don't have line of site because it comes up in the Yellow zone at '2Edge'. The channels of interest to me are 9, 25, 23, 32, 30. It would seem I could have success with a simple UHF directional.

I have tried a large All Band UHF-VHF-FM antenna that I am pointing at 7 degrees true north. It looks exactly like the one in this link, second from the left on bottom row.

http://www.kyes.com/antenna/pointing/pointing.html

I still get nothing from the transmitter 9.1 miles away.

Please advise.

[Tower Guy]

II still get nothing from the transmitter 9.1 miles away.



Do you get none of the signals from 7 degrees, or everything but KGUN?

Two possibilities,

1. Excessive multipath due to the rugged terrain. The solution would be an antenna with more directivity.

2. FM interference from KMXZ and KRQQ. These stations are half the frequency of channel 9 and about 28 db stronger. That's normally not a problem unless you have a preamplifier or distribution amplifier that is overloaded by the strong FM stations. If you have such an amp, replace it with a Winegard AP4700. That amplifier bypasses VHF and amplifies UHF only.

[youngclarkh]

I am not using an amplifier so I suspect the multi path due to rugged terrain is more likely the issue. The antenna I am using seems like it has directivity. What specific antenna do you suggest?

The reason I don't use an amplifier is that the transmitter is only 9 miles away. Is that false logic?

[Tower Guy]

I am not using an amplifier so I suspect the multi path due to rugged terrain is more likely the issue. The antenna I am using seems like it has directivity. What specific antenna do you suggest?

The reason I don't use an amplifier is that the transmitter is only 9 miles away. Is that false logic?

I would not use an amplifier either.

If you're having trouble with the UHF stations from 9.1 miles away the 91XG is the right antenna. You can either tilt the antenna up a few degrees above the top of the ridge (7.4°) to the north of you, or find a spot with clear ground in front of the antenna and lower the antenna to about 3' off the ground. Play with the height and aiming until all the UHF stations are reliable. If you're having trouble with the VHF station, KGUN; either a Y10-7-13 or YA1713 are good choices. The optimum height for the VHF antenna will be about 7'. Use a UVSJ to add the antennas together.

I derived the height recommendations by calculating the angle to the nearest ridge using google maps and trigonometry and then determine the optimum antenna height to steer the beam upwards at the desired angle using EZNEC.

[Tower Guy]

One more thought, you could try your existing antenna at about 7' high. That's the optimum height for VHF, and the UHF signal would peak on the second lobe at the same height.

Here's one example of how lowering the antenna made a difference.

http://www.hdtvexpert.com/?p=134

[youngclarkh]

The 91xg sounds like it is for deep fringe areas requiring great distance. Why would it be appropriate for a tower only 9 miles away?

[Tower Guy]

The 91xg sounds like it is for deep fringe areas requiring great distance. Why would it be appropriate for a tower only 9 miles away?

The very narrow beam of the antenna will pick up more signal from the TV station while simultaneously rejecting bounces off the mountains arriving from other directions.

What did analog signals from that location look like before the analog shutdown? I'd assume that there were numerous ghosts. bounces=ghosts=multipath

The other option would be to try for reflected signal instead of a direct signal. For you that would mean aiming at about 80 °.

[youngclarkh]

You are correct. The analog was awful awful. I have had to use Dish or Directtv over the years. But I really want to not rely on them anymore. I hope this works. Your advise means a lot to me!

I don't know how I can put the antenna only 7' off the ground as i am on the roof, so I will attempt to tilt it just above the top of the first ridge at 7 degrees from true north.

I see I can get the antenna online. I wish I could find it locally so I can return it if it doesn't solve my dilemma.

[ADTech]

You are deeply shadowed by the bulk of the terrain. I've found that TVFool's forecasts tend to be over-optimistic when you're so close to the intervening terrain obstacle.

The 91XG is about the best choice for your location for the UHF stations (relatively) overhead and behind the bulk of a mountain. It probably won't get KGUN's VHF signal, but you never know. Bore-sight the boom of the 91XG at the visual horizon as a starting point.

Also, keep in mind that a number of your local stations operate translators from the other side of Tuscon due to the difficult terrain on the north of the city. You might try re-aiming the U/V combo WSW and re-scanning to see if you can pick them up.

[John Candle]

Aim the antenna at the repeater/translators.

[youngclarkh]

Good suggestions. I think I will try hitting the repeaters. It looks like it may be possible to get all the channels I am interested in, except for FOX.

An omnidirectional antenna should get the following from there:

04 NBC
13 CBS
16 ABC
28 PBS
44 CW

[John Candle]

The thing about omnidirectional antennas is that they Do Not reject multipath / reflected signals , and you are in a Very High multipath situation. Do not use a nondirectional preamp/amplified antenna it will amplify the multipath and make the reception even worse. At receive situations where the transmitters are on top of a mountain , and the receiving antenna is close to the mountain , and the reception is blocked by that same mountain , repeater/translators are often put a distance away so that antennas can receive the main transmitters via~ the repeater/translator. Highly Directional antennas are the best to use in high multipath situations.

[GroundUrMast]

The thing about omnidirectional antennas is that they Do Not reject multipath / reflected signals , and you are in a Very High multipath situation. Do not use a nondirectional preamp/amplified antenna it will amplify the multipath and make the reception even worse. At receive situations where the transmitters are on top of a mountain , and the receiving antenna is close to the mountain , and the reception is blocked by that same mountain , repeter/translators are often put a distance away so that antennas can receive the main transmitters via~ the repeater/translator. Highly Directional antennas are the best to use in high multipath situations.


Well said.

[John Candle]

I suggest a Winegard HD7210P Ghost/multipath killer antenna with No preamp , the forward beam width of this antenna is wide and the antenna rejects signals at the sides and back of the antenna. Point the antenna at about 214 magnetic compass about half way inbetween 40 and 44. And turn the antenna to the left and right for the strongest signals of all the channels in those directions. If you are lucky you will get them all , if not then you will need to use 2 antennas.

[John Candle]

Also Ground the coax that goes from the antenna to the inside of the house with a coax grounding block , the electric service ground wire is the best , if not that then use a cold water pipe as the ground , the cold water pipe needs to be real metal that goes into the ground , not plastic. The reason I am making a big point of this is not because of lightning , the point is that your receiving situtation has a lot of multipath and the grounded shield of the coax will direct undesirable signals to ground. Make sure to have good metal to metal electrical contact , and no , paint is not a good conductor.

[John Candle]

The receive location is in the Catalina Foothills or Tanque Verde.

[ADTech]

The receive location is in the Catalina Foothills or Tanque Verde.

You should be able to do better than that. Try the vicinity of 32.284566,-110.734184

Feel free to use the forum's EDIT feature instead of multiple posts one after the other as new thoughts enter your head. Paragraphs and punctuation are also helpful when communicating through the medium of the written (or typed) word.

[youngclarkh]

Thanks you John Candle for all the feedback. You saved me from running off and buying an omnidirectional antenna.

The exact location of my receiver is 32.284721 -110.734161

I have now attempted a full 360 degree rotation of the receiver, rescanning the channels every 5 degrees. In doing so I have verified that pointing the antenna directly at the Repeaters (253 degrees True North) gives me the best results, using my current antenna.

I now get the following Real channels: 13, 16, 28, 40, 44

I knew I had no shot at picking up 25 (FOX) because they don't have a presence at the repeater location. The real mystery though is why I can't pickup 4 (NBC). That is very disappointing.

This is the info on the channel 4 transmitter:
K04QP-D 4 (4.1)
NBC
Max ERP: 0.300 kW
Eff. pwr: 0.300 kW
Rx: -49.7 dBm NM: 41.3 dB
Az: 253.1 degree (true)

Perhaps my antenna won't go that low in the VHF range? If this is the case is there something I can add to my antenna to pull in NBC?

[Tower Guy]

Perhaps my antenna won't go that low in the VHF range? If this is the case is there something I can add to my antenna to pull in NBC?

You need a very good antenna to reject multipath, even for the translators. Your antenna is capable of low band reception. I'd guess that the difference is a better F/B ratio on UHF than VHF. Those mountains to the east of you are very close and very tall.


In order to get FOX, I'd still try a 91XG, and then you should get NBC too.

[youngclarkh]

You need a very good antenna to reject multipath, even for the translators. Your antenna is capable of low band reception. I'd guess that the difference is a better F/B ratio on UHF than VHF. Those mountains to the east of you are very close and very tall.


In order to get FOX, I'd still try a 91XG, and then you should get NBC too.

First) Are you suggesting a 91XG directed at the translators? If so, how would that get me 25 (FOX) since it doesn't transmit from there?

Second) The 91XG is not supposed to get VHF in a range low enough to pickup channel 4 (NBC).

I'm confused

[John Candle]

The HD7210P is a highly directional Ghost/Multipath killer antenna. The HD7210P receives channel 4 and this antenna is designed to reject multipath on the sides and back of the antenna. I know what he is suggesting to do with the 91XG , however I will not say because he is just throwing out information and not being clear what to do with it.

[Tower Guy]

First) Are you suggesting a 91XG directed at the translators? If so, how would that get me 25 (FOX) since it doesn't transmit from there?

Second) The 91XG is not supposed to get VHF in a range low enough to pickup channel 4 (NBC).

I'm confused

My original suggestion of aiming a 91XG at 7° remains untested.

[youngclarkh]

I have been unable to find the 91XG or the 7210P anywhere in Tucson. I am reluctant to buy them over the internet because I can't easily return them if the test fails.

Is there no way to pull in channel 4 using my existing antenna?

[John Candle]

Yes there is , but first if you have not done so already , ground that coax with a coax grounding block , the shield of the coax is one big long antenna , grounding the shield of the coax will help by directing undesirable signals to ground. <-- This might get you channel 4. . . The first one to try is the easyest , lower and raise the antenna a little or a lot , you can even try the antenna at closer to ground level , you can try using buildings as shields but do not block the front of the antenna. . . The next one to try is , Shielding , with a big flat metal shield about 6 feet by 4 feet , you can cover a big sheet of card board with extra thick aluminum baking foil or if you can find thin metal sheating thats used for metal flashing on roofs. What you do is hold the metal up so the long part of metal is horizontal with the ground and the move the shield so that it shields the antenna from all different angles except the front , so you hold the shield up at the back of the antenna and try for channel 4 , then hold the shield at corner back angle and then at the side of the antenna and so forth and so forth. . . . Next you can try this , if the metal receiving elements of your antenna are sticking straight out from the sides of the antenna then sweep them forward , first unlatch the spacer elements that are attached directly to the boom and turn them length ways with the boom to get them out of the way and then unlatch the VHF elements and sweep/move them so they are at about a 45 degree angle toward the front of the antenna. Doing this narrows the forward reception so the antenna is more directive.

[John Candle]

Having the antenna directly connected to one Tv or converter box with no splitters is helpful and if that one Tv or converter box has the ability to select digital channel 4 with out scanning , that will make it easyer. . Another way to eliminate or reduce undesirable multipath is horizontal stacking of 2 identical antennas side by side. One antenna is in a fixed position and the other antenna is moved closer and further away , to find the distance between the 2 antennas that creates a 'null' of the undesirable multipath reflection.

[youngclarkh]

Something exciting just happened.

I went to Best Buy and bought a Clearstream 2. I pointed it at 7 degrees true and rescanned. Now I am getting many of the UHF channels coming off of Mt Bigelow.

09 9.1
19 18.1
25 11.1
23 4.1
32 13.1

In addition I am also picking up channels from other directions.

40 40.1
44 58.1
28 27.1
13 13.1

The signal is not very strong but I have not grounded the coax yet so perhaps once I do that the signal will be stronger.

I am so glad that I don't have to deal with a VHF/UHF combo. Yet I am still getting channel 9 and 13. In addition, this Clearstream 2 is a tiny little thing. Much easier on the eyes.

[John Candle]

You are receiving reflected transmissions. Digital tuners have ability to reject some multipath. I just remembered , FM radio transmissions cause interference in the VHF low band channels 2 thru 6. Pick up a FM Trap at Radio Shack.

[Tower Guy]

Pick up a FM Trap at Radio Shack.

I doubt that will help. The C2 doesn't pick up FM very well.

Most Radio Shacks no longer carry FM traps.

[youngclarkh]

Isn't it true that all U.S. TV transmitters are in the frequency range of VHF channel 7 or higher, which is far above the FM broadcast band?

In addition, all the channels I am getting are in frequency range 9 and above.

[baud]

Isn't it true that all U.S. TV transmitters are in the frequency range of VHF channel 7 or higher, which is far above the FM broadcast band?

take another look at your tvfool report the answer to your question is there.

[Dave Loudin]

The problem is the frequencies for channels 7-13 line up roughly with the frequencies for FM multiplied by 2 (the first harmonic). Very strong FM signals can set up interference at that first harmonic, wreaking havoc with reception of the TV station at that frequency.

BTW, to see the terrain profile used by TVFool's model, click on any station in the list. A separate window will pop up, showing the transmitter at the far left and your location at the far right. You will see how you are shadowed from stations to the north.

[Tower Guy]

Isn't it true that all U.S. TV transmitters are in the frequency range of VHF channel 7 or higher, which is far above the FM broadcast band?

No,there are about 35 stations on channels 2-6.