Can three antennas be combined using splitters - Page 2 - AVS Forum
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post #31 of 40 Old 12-06-2002, 07:12 AM
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Originally posted by AntAltMike
I know that I will be servicing an account with a Hughes E-86 this week
Mike, any luck with the Hughes E-86 or DST-3000? How about the Panny? Thanks!
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post #32 of 40 Old 12-06-2002, 07:25 AM
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It's probably been six months since I last installed a DTC-100, but as I recall, the guide had separate, successive entries for, say, digital broadcast channel 4 sourced by input A and digital broadcast channel 4 sourced by input B: similar to the way that a Sony HD-200 program guide lists DirecTV 4, then Analog 4, then digital 4.1 or 4.48 in succession in its guide before listing channel 5.

As I recall, it was easy to make the receiver run a signal quality test so you could compare the "signal strength" number for each input and then select the guide entry for the desired channel that came from the better quality signal source. Not being much of a home theater guy, early on in an installation I generally stick the remote in the customers hands so that he will understand how to operate his equipment after I leave, so I don't remember the exact order of entering the DTV stations into the RCA guide, but I believe that scanning for channels was a single command that scanned both antenna inputs A and B. I don't think that I scanned one and then scanned the other, but I might have: I really don't remember. I just remember it being easy enough that how I did it didn't leave the kind of impresion in my memory that struggling with it probably would have.
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post #33 of 40 Old 12-06-2002, 11:40 AM
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Excellent comments Mike. Combining broadband antennas onto a single feedline for non-stacking purposes certianly requires knowledge and some good luck, stacking antennas for increased directivity requires paying careful attention to details which are not a factor for non-stacking purposes. I do think when possible, combining antennas correctly, with the use of join-tennas/channel traps/etc. when possible and necessary can be very benifical.

Anyhow, If a signal coming in from an "undesired" direction is quite strong, as you mentioned, the best of directional antennas won't be able to reject enough of the signal coming in off the side or back. One way or another, I think it's quite likely in most circumstances one antenna will interfere with the other's pattern to a degree that may affect reception. It's also tricky I think because one can't expect the RF in any given area to stay the same, for one reason: because stations do move around on the dial occasionally, something we will likely see more of in the next few years.

Many, many years ago, I used to use a set of Yagis that were designed and Cut specifically for the frequencies stations were broadcasting on in Dayton/Cincinnati. You aimed one towards Dayton, and one towards Cincinnati, combining them together on the Same feed. This worked quite well, until several new, desired stations began to pop up on different frequencies.

I currently use the DTC-100 and 2 antennas pointed in different directions, with seperate feedlines and it works beautifully. One antenna is on a mast atop a tower, the other one is side mounted to tower a little less than 1/2 wavelength below it for Channel 2, a local desired analog station. Since they are on seperate feedlines, I don't think the distances between the 2 antennas are as critical, but, for other reasons, I really wouldn't want to put them any closer together.

"Full search" on DTC-100 will auto scan on both A+B, "Quick Search" will search for channels only on the input you're currently using. "Antenna Info" screen/Channel profiles are seperate for each antenna input.

Jeff
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post #34 of 40 Old 12-06-2002, 12:38 PM
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Quote:
Originally posted by magic123
..is to buy 1 highly directional antenna for UHF and 1 directional antenna for VHF..get them both oriented on mast..then, use a rotator.
It's also likely that in many cirumstances, a single, broadband VHF/UHF Combo antenna will work very well, currently, perhaps UHF only if VHF reception is not needed or desired. If an antenna is properly orientated towards the signals coming from the towers however, if the towers of desired stations for reception lie in generally the same direction, in most cases a antenna statically aimed in the correct direction should do the trick. Oftentimes however, the towers don't lie in the same general direction from a given receiving location.

Anyhow, I think you're bringing up a good point here. For maximum Flexibility, a Rotator is certianly the way to go. In my circumstance, currently all the local TV broadcast towers lie in 3 directions. Only 2 stations lie in the 3rd direction, So most of the time, having two antennas aimed in the main 2 directions required works wonderfully, and it isn't necessary to reaim the antennas. However, there is often alternate, and occasionally desired programming coming from one of the stations in the third direction, for which I use a rotor to aim one antenna towards in order to achieve good reception. I also use the rotor for reception of signals via DX from more distant markets when conditions allow.

Anyhow, I had toyed with the idea of adding a jointenna and single channel antenna for the desired station in the third direction, which does not yet have it's digital station on the air, the digital station being the one I'm most interested in. However, as it turns out, this station is now planning on moving it's digital station to another tower which lies in one of my 2 main directions. So, the moral of the story is, although stations generally seem to try to keep their facilites located in an area near other stations broadcasting in a market, things can and do change, and the only way to have maximum flexibility is to use a rotor --- Something I won't really need at all for reception of local stations, if, in fact, the desired station that now lies in a 3rd direction does move it's digital transmitter as planned -- I'm aware though, that this situation may change again in the future.

If I was in a location such that the towers for the stations in my market were in vastly different directions from my location(which can occur, usually if your quite near the towers), If a less directional antenna wouldn't work, I think I would feel that it was a necessity to find a way to get reception for all those stations without having to reaim antenna(manually or automatically) each time the channel was changed. Either that, or use rabbit ears<g>.

Jeff
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post #35 of 40 Old 12-06-2002, 03:23 PM
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Quote:
Originally posted by bmello
Mike, any luck with the Hughes E-86 or DST-3000? How about the Panny?
The customer with the E-86 didn't have me add the second antenna line (would have had to pull a second coax through 70 feet of 3/4" I.D. conduit), so that one will have to wait. I recently installed a Sony HD-100 with two separate input lines, one labeled for cable and one for antenna, but its "automatic" add channel procedure made me choose between one input and the other. I was hoping that I could use both and that the "capture range" of the cable TV input was wide enough (2Mz) to capture the nearest UHF broadcast channels on that input, but it wouldn't let me.


Funny thing about antennas not connected to one another. I service a fourteen story high-rise in McLean, Virginia, maybe ten miles or so from most of the Washington, DC transmitters, where they keep building taller buildings "behind" it and I have to keep relocating the antennas. They used to have cheap (discontinued) Channelmaster single channel antennas for channels 7 and 9 on the same mast. Then, when another building went up, they developed a little bit of a ghost, so I replaced the 5 element channel 9 antenna with a ten element 7-9 antenna and the improved front to back ratio made the ghost image subside. I also noticed that the channel 7 signal coming off the 7-9 antenna was a little better than off the cut-to-channel 7 antenna, so I made that new antenna the source for both channels.

One day, I decided to clean up the antennas at this headend, and I removed the old, abandoned channel 7 antenna . Before I even left the site, however, one of the residents called the management office to complain that her channel 7 reception had just become terrible. To make a long story short, I determined by measuring from the 7-9 antenna to the rust line formed where the channel 7 U-bolt had been clamped that these two antennas had been exactly one half wavelength apart. Like, within half an inch. And they had been resonating in such a way as to improve the front-to-back ratio of the 7-9 antenna's channel 7 reception, so I had to put the junk antenna back on the mast to restore the picture quality.


In an unrelated fiasco, I once tried to improve the signal quality of channel 8 from Richmond Virginia at a multifamily dwelling in Charlottesville (maybe 60 miles away). I tried stacking a second Blonder-Tongue ten element channel 8 antenna, but the picture did not improve. Because I was working at the top of a 40 foot ladder on a roof that was not flat, I didn't bring a test TV up with me, which makes this kind of work very difficult. Instead, I had a reliable guy watching TV indoors and communicated with him by walkie talkie. When I finally told him I was giving up, he replied that I had just made things better than they had ever been. Well, I hadn't deliberately done anything. Again, to make another long story short, in shuffling different combinations of cabling around, I had inadvertently misconnected one of the stacked antennas to the wrong side of the two-way splitter/combiner, making of one the antenna inputs twenty or so dB weaker than the other and messing up its linearity as well, AND I was standing "inside" the lower of the antennas, meaning I was physically interrupting the signal at the same time, and that combination of errors produced by far the best quality picture.

I later figured out that the most significant contributor to the reception problem was one or more weak FM transmitters that developed harmonics on channel 8 (91.1Mz, 91.9Mz and 92.7Mz are all within a couple of miles) and my ill conceived "stack" was somehow mitigating them.

The reasons for sharing all of this with you are to show that stacked antennas can interact with one another in different ways that are not always predictable, that the fact that something worked well for you does not mean that it will work for anyone else (a lot of people are getting excellent reception from Terk antennas, for example) and none of us ever know so much about developing multiple antenna arrays that we can't benefit from getting lucky now and then.
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post #36 of 40 Old 12-06-2002, 05:02 PM
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Quote:
Originally posted by AntAltMike
Then, when another building went up, they developed a little bit of a ghost, so I replaced the 5 element channel 9 antenna with a ten element 7-9 antenna and the improved front to back ratio made the ghost image go subside.
Mike, do you know whether ghost-cancellation signals from stations and the hardware for reception ever developed? If stations still transmit them, does anyone use the hardware in MATV setups? Thanks. -- John
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post #37 of 40 Old 12-06-2002, 05:28 PM
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There are stand-alone electronic do-dads that can be bought for about $2,000 that are designed to electronically detect and cancel out ghosts. I don't remember the manufacturers, but I get flyers from Nickless Schirmer Company, a commercial MATV distributor, offering them.

Microwave Filter makes a manual frequency shifter that retails for about $700, with models for VHF lowband (2-6), high band (7-13) and UHF (14-69). One points a second antenna at the source of the reflection, and uses the frequency shifter to make it exactly out of phase, and a variable attenuator to make it equal in strength from both sources so that it cancels out perfectly.


A person who posts here occasionally under the screen name "joblo" says he has been doing this on the cheap by cutting a bunch of coax jumpers of progressively different lengths and swapping them one at time and comparing the signal quality on the DTV receiver's signal meter until it maxes out. I think he has been using it primarily to peak the performance of antennas that he has coupled to bring in different desired signals from each when the coupling degrades one of the signals, but the same principle can be applied to a simple, ghost-killing situation. Obviously, this is much easier to accomplish if you have a signal meter to measure the and set the initial levels of the antenna signals.
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post #38 of 40 Old 12-07-2002, 06:11 AM
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Quote:
Originally posted by John Mason
Mike, do you know whether ghost-cancellation signals from stations and the hardware for reception ever developed? If stations still transmit them, does anyone use the hardware in MATV setups? Thanks. -- John
Magnavox made a "television ghost canceling reception system" called the "imageLock". This came out at the 1995 SBCA Satellite Show in Nashville, Tennessee but was discontinued a few years later. It sold to dealers for $120 and retailed for $200. The device took a composite video input (like from a VCR or demodulator) and then used the ghost cancelation reference (GCR) signal on either line 16 or 19 of the vertical blanking interval and compared the incoming signal with what the signal should look like and automatically corrects it...or attempts to anyway. Nearly all TV stations are currently broadcasting this signal, but few people know that the GCR signal is there.

The imageLock does a pretty good job of removing too much color and slight to moderate ghosting on the analog channels, however I don't think that it will work on the DTV channels, since they don't broadcast a ghost cancelation reference signal.

You can find these on eBay for around $50.00. There is also a company on the Internet that still has brand new units. These sell for $100 plus shipping.
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post #39 of 40 Old 02-24-2003, 07:55 AM
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...I'm pretty much out of my element (so to speak) here. :)

Anybody here an antenna expert/installer in the NJ area? I'd like to have my antenna (system) setup so that I can use my new Samsung SIR-T150 receiver to receive as many NYC (and possibly Philly) stations as possible.

At this poing I'm having a hard time getting anything steady. I can get CBS, FOX and UPN and that's it. CBS cuts in and out. Signal seems to be between 50% and 0%, never in between.

I imagine my antenna setup is just screwy. I'd like someone to just make it work. You may contact me via email or phone me at home at 732-560-7353.

Just so you know, my antenna is a RS attic antenna but it's mounted up on the peak of the roof. I have a bi-level so that puts the antenna about 25" above ground. No rotor. RS 10db in-line (pre?)amp is installed.

I imagine multipath is my enemy. I'm about 45-50miles from NYC. Farther from Philly.

If you can't help me physically, please provide me some clues in this forum or via email and I'll be so indebted to you..you wouldn't believe.

I'm mainly interested in getting as many DTV signals as possible. Secondary would be the analog reception but that's really secondary as I have Dish Network Sat for standard def programming.

Thanks in advance for any help you can provide! :D

-- Bob Lindabury
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post #40 of 40 Old 03-10-2003, 04:35 AM
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Great info here, thanks...

-- Cain
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