Refraction Question

[Venturatvviewer]

Am in the Ventura Avenue area of Ventura. Zip Code: 93001. Near highway 33. Using a GS-2200 with wing. Getting stations. Not reliably. KNBC4, KTLA5, ION, KXLA, KCET (rarely), KLCS, KOCE (sometimes). Not getting VHF stations. Wondering if anyone knows how refraction works. How low to the ground do the signals get. How to figure out the ideal setup.

[Venturatvviewer]

Here is the link: http://www.tvfool.com/?option=com_wr...da325ef307b8f4

[John Candle]

As the other question askers do , Do this ----> http://forum.tvfool.com/showthread.php?t=4 . Is this a house , apt. , condo , mobile home , motor home , if apt. or condo what floor ? Is this a office or shopping center building ? Is the antenna outside up high ? or inside ? Is the structure wrapped with any type or kind of metal such as metal siding or stucko and stucko Wire ?

[mtownsend]

There are actually multiple phenomenon that are at play.

Refraction is the process of radio waves bending due to the atmosphere acting like a curved lens.

Tropospheric ducting is a phenomenon that mostly happens in evenings/nights when there is a thermal inversion layer (warm air near ground, cold air on top) that help radio waves follow the curvature of the Earth and thus travel further than normal "line-of-sight" distances.

Diffraction is the effect where radio waves "bend" around solid edges like a knife edge or mountain top. Even when there is a solid object in the way (like a mountain), some amount of RF energy is able to bend around those objects to fill in some of the space that would normally be in the "shadow" of that object.



All of these effects can vary over time (e.g., time of day, seasonal changes, etc.) or with changing conditions (e.g., humidity, rain, temperature, etc.).

The signal strength models used by TV Fool already account for these factors, but they only show the "average" situation. Your particular location, current weather conditions, time of day, and surrounding environment may cause you to experience higher or lower signal levels than predicted.

In general, all the "large scale" propagation effects are already factored into the numbers, so there's no need for you to make any adjustments yourself.

The models do not include details like individual buildings or trees, so you do have to take that into account yourself if you have something like that directly in the path of your antenna.



If you want to get an idea of well signals can get around obstructions (mountains and the curvature of the Earth), you can click on any of the rows in the channel list in your TV Fool report. That should bring up a new window showing a "cross section" view of the terrain between the transmitter and your location. The transmitter is always shown on the left and your location is on the right.

You can see how each mountain casts a "shadow" behind it. The signal gets weaker as you get "deeper" into any of the shadows because signals can only diffract (bend around objects) so far.



Given the readings on your report, it doesn't seem likely that you'll be able to get the Mount Wilson signals reliably. The transmitters are about 70 miles away, and you have some local mountains that are in the way. The signals reaching your location are very weak.

What kind of picture(s) are you getting when you tune to these channels?

[Tower Guy]

Originally Posted by Venturatvviewer

Am in the Ventura Avenue area of Ventura. Getting stations. Not reliably.

Consider a Booster at this location

34.295906,-119.325943

A booster is two antennas, one aimed at Mt Wilson, the other aimed at your house. Separate the antennas as much as possible and make sure they don't aim at each other, or use terrain shielding. Use a preamp/distribution amp and channel filters between the antennas. Power the amplifiers with a solar panel. An FCC license is required for a booster.

http://www.taylortransmitters.com/DTVRepeaters.pdf

[John Candle]

Go to the >>Start MAPS<< part of tvfool and raise antenna height , do the signal strengths improve ?

[Tower Guy]

Originally Posted by John Candle

Go to the >>Start MAPS<< part of tvfool and raise antenna height , do the signal strengths improve ?

Yes, at 450'.

[John Candle]

Venturatvviewer if you will like to experiment , might be able to get reflected Mount Wilson transmitters by aiming a directional antenna above the lower part Taylor Ranch Rd. that runs paralell with 33. If you are interested , let me know and I can tell you more.

[Venturatvviewer]

Thanks for all the input! Stucco house. Antenna can be mounted on the roof. Or side of the house. Get better signals for more powerful stations. i.e. 1000KW better than 200 KW. Go to Antennapoint. Highly directional antenna with high gain. Powerful preamp. Gotten most of the stations but at different times and locations. Would be interested in learning more about Taylor Ranch Road and the reflected signal. And would like to learn more about refraction. Is there math about it? Mathematical equations, or software that estimates what the db would be? Anything that can be learned would be interesting and helpful.

[John Candle]

If you will provide the cross streets names that are close to your house it will be a big help. I am thinking that your house is on the valley floor close to the west park playground. Not sure what you said in your last post. The highly directional antenna I suggest is the Winegard HD7698P with NO preamp. Point the antenna at the mountains to the west and a little north at these 34.299238 -119.323883 put these coordinets in at the >Start Maps< part of tvfool. The red balloon pointer ( the tv antenna) will be at that location , put the antenna height at 1 foot so as to get accurate signal readings at places below the mountain ridge. Move the (red balloon pointer antenna) to different places below the mountain ridge. The idea is to find places where the signals are strong. Now at your house you will point the Winegard antenna at different places below the ridge of the mountains. You will be tipping the front of the antenna up so that it points directly at the places below the ridge. What you are doing is finding a good reflective place of the transmitters at Mount Wilson.

[Venturatvviewer]

Corner of Center Street and Ventura Avenue

[Venturatvviewer]

Actually point towards the ridgeline pointed towards Mount Wilson. Get all the stations at different points. On roof. Next to structure. Most interested in where to get VHF. KABC7, KCAL9, FOX11, KCOP13. Would be huge if those stations would be received.