DTV Antennae ?

[pallophotophone]

Hi,

Has anyone ever tried to use 2 powered indoor DTV antannae with their outputs combined ?
I had a thought, but it might have a problem w/ phase cancellation.
If I installed 2 antennae aprox. 5 feet apart, and combined their outputs w/ a tap or a splitter - using it in reverse- would the signals cancel out if one antenna received a signal that was out of phase, if that is a consideration in the digital realm ? What I wanted to do was position each antenna in the best possible location for a particular group of stations, but use only one piece of coax (CAC-6) to distribute it.
A rooftop installation for me isn't a reality. But 2 antennae on the enclosed back sun porch is!
Presently the signal just is too erratic on the S meter.

I'll bet someone know the real answer to this.
MANY THANKS !!!

Pallophotophone

[ChrisW6ATV]

I have never heard of anyone having luck with combining two TV antennas into one splitter/tuner input. Generally, you get the worst of both antennas, not the best. Your best bet might be to put a small-sized outdoor antenna like a StealthTenna into your sun porch.

[pallophotophone]

Thank You, Chris

I never heard of that one. But it will get tried!

Best,

Bob H.

[sanford12]

This could actually make it worse. Receiving from 2 different points can confuse the tuner. trying to assemble the same digital signal from 2 different points at slightly different times and maybe reflected from different surfaces could fugger things up. A bow tie antenna is one of the best for digital and don't take up much room.

[old_tv_nut]

combining antennas generally works if one or especially both of the following conditions are met:
1) the antennas are strongly directional and aimed in different directions for the different stations (won't happen using small indoor-style antennas)
2) each antenna/amp is followed by bandpass filters for the desired channels

Otherwise, you will get a strange and unknown combined pattern of reception with a possibility of cancellation as well as reinforcement in any given direction.

Some cities with stations concentrated in two areas instead of one have resulted in well known solutions that even have been named after the city, for example , the "Indianapolis rig." Of course, with stations changing frequencies and sometimes even locations for digital broadcast, these rigs have had to be modified.

[DavGoodlin]

Can you separate the bands? A VHF channel in one direction and UHF's in another would allow you to use a bowtie for UHF and a VHF antenna. The cancellation would be a factor if the undesired signal were of sufficient strength. Directional antennas would mitigate this. A 4-bay bowtie is a good compact UHF antenna. Try an Antennacraft U-4000, then a Blonder Tongue ZUVSJ VU combiner. For VHF-UHF, the Winegard CC7870 splitter from Solid Signal.com seems to work well for me.

Dave "antenna rabbit"

[IsthmusTV]

In support of what Dave just wrote, the current issue of Popular Communications has an article about doing just that: Combining a UHF antenna pointed at one cluster of stations and a VHF pointed at another. The installation is in an attic and the author does mention the need for an amplifier to overcome the loss of the combiner.
http://www.popular-communications.co...ent_issue.html

Good luck,

Clark

[old_tv_nut]

I am using separate V and U antennas in my attic, with just a passive combiner. Works fine for driving one set (about 38 miles from the transmitters), but I do have an amplified splitter so I can drive multiple sets.

[Username1]

There are a few good answers here. You should begin by determining what bands the channels you want to get are on. See how strong they are using the meter, or by the online signal websites out there. Assuming you have a few on Vhf, and some on Uhf get the biggest antenna you can have for each application. Amplify them separately as needed. You may need to use 2 preamps, possibly an attenuator, and then a combiner and then feed that to a distribution amp, and then a single coax to all yer stuff. I did this with 2 Uhf preamps and a attenuator, and a combiner with one vhf preamp because the UHF channels are the real trouble where I am. But combining 2 antennas trying to get the same channel you may get multipath distortion which will possibly cancel, or degrade the desired signal, But it will also and most importantly add noise! That is the biggest bad for this digital stuff. I have a spectrum analyzer and I did the two antenna thing, and the amount of noise outranks everything good. If'n yer in a real fringe area use good low noise preamps, and distribution amps. Use good cable, ground it to keep the noise down. http://www.tvfool.com/modeling/ This site is pretty good to see your estimated signal strength and noise margin. And the noise is important, design a good system and you will be happy. SolidSignal.com has some good combiners, low noise preamps of all kinds, and dist. amps, and a attenuator. Using a separate path for each signal V vs Uhf also keeps the noise down cause the amps have band width limits. Also if you use a directional antenna you may have to point it and tune for one of the poorest channels, and let the amps make up for the channels that can afford to suffer when pointing the antenna.

[Penthode]

Amplified indoor antennas are a nuisance. They are ineffectual and create more trouble than they are worth. Amplification is only really useful in fringe reception areas so long as there are no high power transmitters of any kind in the vicinity. I would only use a preamp on an outdoor antenna to overcome loss due a splitter or loss from the coaxial feeder in a fringe reception area and only after precautions were taken (such as filter or trap insertion) to prevent intermodulation with strong local stations.

To give an example of the cheap antennas which have been available, here is a link to the FCC for a citation issued to a resident in Los Angeles. She had a Philips amplified indoor antenna which was self oscillating and interfered with a Verizon cell tower. The resident was issued the citation...

http://www.fcc.gov/eb/FieldNotices/2...-292933A1.html

Remember, poor reception may be due to other factors rather than just low signal level, such as local interference raising the noise floor, and receiver front end intermodulation due to poor receiver agc or selectivity issues.

Cheers,

Terry

[zenith2134]

Hi--my results are totally location-specific but here it goes:
In my garage where I work on things I set up a DTT990 box with two antennae. I have a 300 ohm dipole in the attic of the structure with a 300-ohm loop in parallel...the UHF loop sits on the ground, literally, in soil with a long line of twin-lead going to the combiner box(Heath brand)...between the two I can pick up the entire NYC digital televison spectra; both UHF and VHF, and after much testing, I've found that the signal drops off sharply If I run only one antenna at once.

Whacky? yes. But it does work!

[ChrisW6ATV]

That is what counts. Using one of the best digital tuners (that is a Zenith DTT900, right?) is part of your success story as well.

[zenith2134]

Sure is! I got two of 'em, one is integrated into a 1985 13" color JVC with blackstripe tube....as a 'portable' mains powered set...works like a charm.

[Electronic M]

Is the Zenith DTT901 I'm using the same as or comperable to the 900?

Mine don't get much use and has been limited to a pair of newer UHF/VHF rabbit ears, but does seem to out do my even less frequently used Magnovox boxes.

Tom C.

[old_tv_nut]

Originally Posted by Electronic M

Is the Zenith DTT901 I'm using the same as or comperable to the 900?

The 901 is the same as the 900 for digital reception. The 901 also includes analog signal pass-through when turned off, in case there are any analog stations in your area (getting less important as low-power and translator stations go digital).