Support for diversity reception

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tom1975
Posts: 9
Joined: Thu Dec 26, 2019 8:43 am

Support for diversity reception

Post by tom1975 » Tue Feb 18, 2020 7:49 am

In many situations OTA reception is problematic due to fast fading caused by dynamic multipath. The multipath in suburban areas may be caused by swaying trees in wind, automobiles, aircraft. Increased antenna gain can't fix the problem as numerous studies have shown fades as deep as 30 dB or greater. The only solution is spatial or perhaps polarization diversity. A specific solution is multiple antennas with phase matched pre-detection combining. This method is often awkward to implement in practice. A desired solution is multiple (two or three) tuner channels with post-detection channel selection.

JDazell
Posts: 53
Joined: Fri Sep 09, 2011 4:19 pm

Re: Support for diversity reception

Post by JDazell » Tue Feb 18, 2020 12:43 pm

Tom,

What exactly is your Question or Problem?

tom1975
Posts: 9
Joined: Thu Dec 26, 2019 8:43 am

Re: Support for diversity reception

Post by tom1975 » Tue Feb 18, 2020 2:28 pm

My particular problem is that I'm surrounded by high trees that cause deep signal fade and picture and sound breakup when there is wind-I have a strong signal-fast fading by phase interference is the cause. The problem is particularly bad in the summer when leaves cause greater tree trunk sway. I'm suggesting SiliconDust make a tuner that supports diversity reception-or have a design that supports diversity reception by buying two or more "boxes" that support diversity reception using an adapter. There are a number of studies-although most are for other than TV frequencies-that show the bit error rate reduction achieved with diversity in such environments.

jasonl
Posts: 15174
Joined: Sun Oct 28, 2007 9:23 pm

Re: Support for diversity reception

Post by jasonl » Tue Feb 18, 2020 2:34 pm

Doing it effectively requires support for it in the demodulator, which exists in the DVB-T world but AFAIK not in the ATSC world.

tom1975
Posts: 9
Joined: Thu Dec 26, 2019 8:43 am

Re: Support for diversity reception

Post by tom1975 » Tue Feb 18, 2020 4:41 pm

I don't understand, the demodulator is in the HDHomeRun tuner, but OK it was only a suggestion. ATSC 3.0 will help with OFDM.

jasonl
Posts: 15174
Joined: Sun Oct 28, 2007 9:23 pm

Re: Support for diversity reception

Post by jasonl » Tue Feb 18, 2020 7:28 pm

Diversity mode works by basically daisy chaining demodulators. Tuner A goes into demod A, tuner B goes into demod B, and the output of demod A goes into demod B. Demod B combines what's coming from demod A with what it's getting itself and outputs a hybrid of both, presumably with fewer errors. The demod has to be specifically designed to support it. Some DVB-T demods are designed that way, but I've never heard of an ATSC demod that is. In theory you can also do it with a fully demodulated transport stream, but it's not as helpful, and at that point you might as well just do it in software on the PC pulling off 2 separate devices.

nickk
Silicondust
Posts: 15758
Joined: Tue Jan 13, 2004 9:39 am

Re: Support for diversity reception

Post by nickk » Tue Feb 18, 2020 10:37 pm

Diversity can be done at different levels.

The ideal recovery approach is a diversity aware demodulator being fed by two tuners. That isn't possible, however post-demodulator merging of two transport streams is theoretically possible.

Nick

ahallasjr
Posts: 74
Joined: Wed Jan 18, 2017 10:22 am

Re: Support for diversity reception

Post by ahallasjr » Wed Feb 19, 2020 9:31 am

Use antenna.org to find where your stations are located. Then put up an rotating high gain directional antenna clear of the trees, perhaps with an amplifier to make up for cable loss.

tom1975
Posts: 9
Joined: Thu Dec 26, 2019 8:43 am

Re: Support for diversity reception

Post by tom1975 » Wed Feb 19, 2020 10:13 am

ahallasjr wrote:
Wed Feb 19, 2020 9:31 am
Use antenna.org to find where your stations are located. Then put up an rotating high gain directional antenna clear of the trees, perhaps with an amplifier to make up for cable loss.
The trees are about 100 feet tall-there is no getting higher than them. I know exactly where the transmitters are located and all of interest are within 10 degrees of each other. I have a preamp with low-loss coax. The received signal strength is fine under calm conditions-the problem is fast fading especially at UHF in the summer with wind. Even wind in the winter with no leaves on trees is a problem causing picture breakup with loud audio buzzes. Two UHF antennas, matched cables, and a combiner are arriving today. I'll give spatial diversity a try.

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