Here in the NYC market, most of the major stations all transmit from the top of the Empire State Building. So I was wondering this:

What causes major variances in reception between stations transmitting from the same location? Is this something that only happens with indoor antennas due to their unpredictability or does it happen with good rooftop antennas too?

Thanks!

Regardless of the location, DTV stations broadcast at different frequencies and for technical reasons different power levels, both of which can cause differences in reception.

Having said that, an indoor antenna is much less reliable for DTV reception than an indoor antenna.

Also, interference effects between the direct signal and reflected signals (multipath interference) depend on wavelength, which in turn depends on frequency, i.e. channel number.

I see no reason why an outdoor antenna, subject to significant multipath, would not perform similar to an indoor one. I know I receive signals from a single transmitter location using various different antenna aims/angles. One setting only gets all stations some of the time. One has to explore each individual channel over a period of different weather conditions to learn what the best aim is for each one. Outdoor is better and stronger signal, but with significant multipath, I'd always want a rotor to have a chance to solve reception difficulties as they occur.

I see no reason why an outdoor antenna, subject to significant multipath, would not perform similar to an indoor one.And what is your background with RF, to make such a statement?

I just have personal experience Ken. I'm addressing the aim of an outdoor antenna versus an indoor one, not the technical response of the two. Simply put, I'm saying, even with an outdoor antenna, it may need to be adjusted due to wind, temperature and multipath. I've read here where a gentleman in a home next to a ridge was finding his best signal aiming 180 degrees from the actual tower location. I use that aim with indoor antennas here at times. 90 degrees is often best as well. During wind events, I find 45 degrees is more stable for some channels. Outdoor antennas get reflections too. Reflections aren't constants. Perhaps I'm in error.

Almost universally and all things being equal, an outdoor antenna will perform better than an indoor antenna due to not having the physical structure interfere with the ideal line of sight that TV signals are best received with.

and remember the signals have to travel through walls and metal to hit an indoor antenna.

Currently I am receiving OTA from a single tower farm, Walnut Grove. TVFool says that these stations are "green" and able to be received via an indoor antenna. This is true. However, the aim of the antennas, I use several, is not a constant.

I propose, were I to put an antenna on the roof and try to receive channels that TVFool says are not green, and 1 or 2 edge but receivable, that these channels would be candidates where a single aim of an outdoor antenna would not necessarily be as good as having a rotor to be able to adjust to varying conditions. I'd need to aim it, and re-aim it for best results during all conditions just like the indoor antennas I have looking for green line-of-sight (LOS) ones.

As for Bix's original question about outdoor antennas, yes, I believe outdoor antennas are subject to multipath issues which will make it necessary to aim differently for channels originating from the same location. Water may also be an issue at that New York location.

an indoor antenna may have its signal reduced 30 to 50 percent traveling through your buildings. that loss of signal can cause problem of no reception or drop outs as signal varies due to all reasons (season, day/night, weather, in addition to what Ken said in message 2).

also once indoors the weaker signal can be reflected off walls (multipath) and that cause problems for an indoor antenna.

so an indoor antenna weakens your signal and creates more multipath compared to an outdoor antenna. in many cases that doesn't matter which is very good, it some cases it does (even close to a transmitter within line of sight as well as the more frequent at a distance).

in some locations you could be within line of sight of a transmitter and on the far side of a structure and get a strong reflection of a signal from some other angle due to buildings or cliffs. you may have to aim based on that to get the reflection which might be your strongest signal or to null the reflection while still getting the main signal.

The Bob Hess blog is interesting here: www.cbs13.com/blogs

Walnut Grove is east of my location. My best aim for a Silver Sensor looking to receive channel 13...due west.