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-   -   Can three antennas be combined using splitters (http://www.avsforum.com/forum/25-hdtv-technical/185697-can-three-antennas-combined-using-splitters.html)

dsiegel 11-01-2002 07:32 AM

I have one uhf antenna pointing West for CBS. One uhf/vhf pointing south for ABC. NBC is North and I would like to put up another uhf for that. I already have combined two antennas with no problem. Can a third be added?

Thanks

greywolf 11-01-2002 10:14 AM

This has got to be the third time today I've posted this link:

http://www.tvantenna.com/support/tut...combining.html

AntAltMike 11-01-2002 07:28 PM

That page contains a lot of useful information but some poor advice as well.

In particular, one paragraph says:

"There must also be the exact same length of coaxial cable between the two antennas and the combiner, which is basically a backwards two-way signal splitter. The same exact length of coax cable between each of the two antennas and the combiner is needed also to help prevent ghosting from occurring on the TV's connected to the antenna system."

That is nonsense for the application shown. The coax cables must be exactly the same length when two antennas are pointed in the same direction AND their dipole elements are in the exact same plane. It is irrelevant otherwise. If the only TV stations you desire are exactly 180 degrees apart, or, say 160 to 200 degrees apart, then maybe you can just couple them through a splitter and get away with it, because the front to back ratio of these broadband antennas might be 15dB to 20dB, but that is a really poor way to combine two antenna signals.

As far as spacing is concerned, most commercial installers in multifamily dwellings keep them 1/4 wavelength apart, and we don't usually calculate that too closely. If you have two VHF antennas receiving low band channels, keep them at least 5 feet apart; highband VHF, maybe 3 feet; and with UHF, the corner reflectors will keep you from stacking them too closely. No one has 17 feet of extra mast and 15 feet of mast above the roofline (32 feet total mast height) to receive channel 2 from one direction and, say, channel 4 from another. If you want to use two VHF antennas pointed in two different directions, put up a second mast.

The jointennas, described further down that page are the way to go when they meet your needs, which is to say, no adjacent VHF and three channel spacing on UHF, but you can use them as bandpass filters and improve the combining of adjacent VHF and alternate UHF channels by coupling the filtered signals with hybrid splitter/combiners. It is difficult to predict how well such combined antennas will work for you. Give me a zip code and the numbers of the channels you desire to receive (analog AND digital) and I'll run it through the NIA evaluator and see what your chances are of developing a low-budget combiner network.

greywolf 11-01-2002 09:33 PM

Thanks. I'm saving this thread for future reference instead of the web site alone. Your participation in this forum makes the cost of being a member well worth it.;)

Dave McWilliams 11-01-2002 10:28 PM

Mike,

While I'm not the original poster, I'd like to take advantage of your expertise nonetheless. My ZIP is 15010, and my fondest wish is to come up with a way to get channels 25, 38, 43, and 48 in Pittsburgh and channel 36 in Youngstown, which is almost exactly 180 degrees from PIT. My conundrum is finding a single position in my attic (I know, I know) that will allow me to receive 38 and 43 in PIT. My 190" RS combo with preamp will get 43 (and all the rest) in PIT just fine when it's raised as far as possible, but it's no good on 38. I can get 38 perfectly if I lower it about two feet, but then I lose 43. Channels 25 and 48 are fine in either position. It looks like I need two antennas to point toward PIT and another at Youngstown. I've successfully received 36 in Youngstown by pointing a spare 80" RS VHF/UHF (with preamp) in its direction.

I currently own the 190" and 80" combos that I mentioned earlier, and a CM 4221 4-bay that I've had no luck with whatsoever. The attic has plenty of room, and I'd like to keep them there if at all possible. I'm just not sure what combination of antenna/splitters/jointenna would be best. I think this diagram looks very close to what I want to do. Do you agree, and what hardware would you recommend?

Thanks very much for your help.

AntAltMike 11-01-2002 11:41 PM

Dave:

Why are you messing around with a monstrous combo antenna? About 80% of its size is for VHF. Either hacksaw off the VHF portion, or buy a big UHF-only Yagi, like a Wineguard PR-9032 for maybe $40. You'll be amazed how much difference there is in antenna performance in an attic just by moving the antenna slightly laterally, just because of the variation in the roofing materials that will be on the transmission path. You can experiment a lot better with a UHF only antenna. You should be able to get 38 and 43 with one antenna.

What are you using for a tuner? All of the DirecTV HDTV tuners have two antenna inputs. Even the ones that look like they have one also have an internal diplexer on the satellite input line, so if you have a DirecTV tuner, then you won't need to combine two antenna lines.

You probably should be using a lower gain preamp for your Youngstown channel 36 antenna than for your Pittsburgh one.. You can't combine 36 and 38 with jointennas, but if you absolutely, positively have to try to combine them, then get a tuned Pico or Tru-Spec UHF-BPF bandpass filter tuned to channel 36, and couple it with the other downlead with an ordinary two-way splitter/combiner.

If you have to go with three separate antennas, two pointed at Pittsburgh for channels 38 and 43, plus a 36 antenna, but want to combine them into two input lines, then you can use a channel 36 jointenna to couple that into the Pittsburgh all-but-38 antenna downlead, and put the 38 on the other coax by itself. That will be "cleaner" than mixing a separate channel 38 antenna signal into the main (43++) Pittsburgh antenna because the 36 leaking in from that Pittsburgh antenna will be at a weaker level than would the inadvertent 38 signal, since the 43++ antenna would be pointed away from channel 36, whereas it would be pointed at channel 38.

trich 11-02-2002 06:58 AM

Combining antennas is not rocket science.
I have two with different lengths of cable and they are only 18 inches apart.
The big one picks ups analog and digital stations up to 45 miles.
The small one is pickiing up digital and analog up to 20 miles.
I have not had any problems with this setup.
Mybe I am just lucky.

http://im1.shutterfly.com/procserv/4...c9430000001410

trich 11-02-2002 07:23 AM

This is why I have two antennas. I'm useing a RS [$3.98] combiner.
http://arcimsmaps.decisionmark.com/C...9213761165.png

Dave McWilliams 11-02-2002 08:30 AM

Quote:
Originally posted by AntAltMike

Why are you messing around with a monstrous combo antenna?
Well, because it was on sale for $20 at Radio Shack. :) But, since the boom comes in two pieces anyway, it wouldn't be hard at all to just use the UHF portion. Hopefully I can find a spot to get 38 and 43 in PIT.
Quote:

What are you using for a tuner? All of the DirecTV HDTV tuners have two antenna inputs. Even the ones that look like they have one also have an internal diplexer on the satellite input line, so if you have a DirecTV tuner, then you won't need to combine two antenna lines.
I've got a Sony HD200, and it does indeed have two inputs. Can they really be used for two separate antennas simultaneously? I'll be darned. Not quite sure why I thought that wasn't possible. Unfortunately, the HD200 makes the task of antenna tweaking very difficult. It's the one thing LG really dropped the ball on. So I guess I know what I'll be doing this afternoon.

Thanks again for your assistance.

AntAltMike 11-02-2002 09:12 AM

Quote:
Originally posted by trich
Combining antennas is not rocket science.

Maybe I am just lucky.
Combining antennas IS rocket science. My company specializes in combining antenna signals in metropolitan areas in which several towers, though just a few blocks apart, are on significantly different azimuth headings and so separate antennas must be used for the systems in which we use passive combining into a high powered trunkline. If you search this subject in this forum, you will find at least dozens, and probably hundreds, of posts from members who unsuccessfully attempted to combine antennas using splitter/combiners, but who only succeeded in making things worse.

trich 11-02-2002 10:07 AM

Combining antennas IS rocket science. My company specializes in combining antenna signals in metropolitan areas in which several towers, though just a few blocks apart, are on significantly different azimuth headings and so separate antennas must be used for the systems in which we use passive combining into a high powered trunkline. If you search this subject in this forum, you will find at least dozens, and probably hundreds, of posts from members who unsuccessfully attempted to combine antennas using splitter/combiners, but who only succeeded in making things worse.
_________________________________________________
The towers are north west and north east about 45 degrees apart.
A friend of mine lives south of me and we did his the same way.
So it looks like I was lucky twice.

Dave McWilliams 11-02-2002 03:03 PM

Well, my antenna tweaking did not go particularly well. I tried moving the UHF portion around by hand in the attic, but was not successful in getting both 38 and 43 in one location. It's difficult because I need to use a preamp, so I suppose I'll just have to tack the brackets that hold the mast to the framing lumber to check different locations. Doing it by hand without the preamp just didn't work. I also tested it up on the roof, and of course it worked like a champ just holding it by hand about six feet above the ridge line. Curiously, the signal strength dropped to nothing on 38 once it got any lower than that.
Quote:
Originally posted by AntAltMike
[b]What are you using for a tuner? All of the DirecTV HDTV tuners have two antenna inputs...
The HD200 evidently does not. Or, more precisely, two antenna inputs that will work simultaneously. So it looks like I'll be combining and joining. Actually, my old DST-3000 would not let you use two inputs for antenna simultaneously either. From the DST-3000 manual: Note: Signals from a terrestrial antenna and cable TV can be connected to the IN FROM ANT connector and diplexed into the SATELLITE IN connection simultaneously. However, the receiver does not support the simultaneous connection of two terrestrial antenna signals or two cable signals. The Sony manual doesn't mention anything about diplexing at all.

UncD2000 11-02-2002 03:08 PM

Trich, polar response graphs for your two antennas would probably show a virtual null at 45 degrees off axis. Most Yagi-types are typically least responsive 90 degrees off axis, so transmitters at right angles would be ideal for combining signals. You were "lucky" in your choice of highly directional antennas.

Dave, I think Mike was suggesting that you keep the 2nd antenna separate and run a cable from it to the B input of the HD200. This would be a last resort if combining the two fails. I have a similar problem, but my A antenna gets the problem channel fine most of the time. When bad atmospheric conditions cause problems on that channel, I switch to the B antenna which receives that channel only. Before I moved I had four masts on the house and garage with antennas from 25' to 63' AGL. Now I am restricted to indoor stuff in the attic and garage, and finding the "sweet spots" is a new type of challenge.

magic123 11-02-2002 03:26 PM

Best way to get the best reception is to keep it simple. Unless you need a VHF antenna at this point in time, only have a UHF antenna. With a good antenna, you will need no pre-amp up to 40 miles. A rotator, in nearly all cases, is good to have..for now and in future. If you possibly are able, antenna outdoors at least 25 feet above ground level with not many objects close to it higher than antenna is. An antenna should have a decent 'look' at the transmitting tower. The cleaner the look, the better the reception and the resulting picture on your tv. Again, keep it simple. Do not 'cut' antenna line into house any more than you have to. Every time you do, you lose ..maybe..20 percent of signal. Use RG6 Quad wire, at least. Happy Viewing.

Dave McWilliams 11-02-2002 03:47 PM

Quote:
Originally posted by UncD2000

Dave, I think Mike was suggesting that you keep the 2nd antenna separate and run a cable from it to the B input of the HD200...
The HD200 documentation is incredibly poor on this subject. The specifications state that the input labeled CABLE IN can be used for 8VSB cable or terrestrial. Unfortunately, I wasn't able to get that input to work for antenna at all.

AntAltMike 11-02-2002 04:36 PM

Quote:
Originally posted by UncD2000
... I think Mike was suggesting that you keep the 2nd antenna separate and run a cable from it to the B input of the HD200.
Actually, I expected the SONY HD-200 to support them simultaneously. I expect to be setting one up for a customer next week and will experiment with it at that time.

The RCA DTC-100 channel guide recognizes the same DTV channels from antenna A and antenna B independently. I assumed that the other two-terrestrial input products did also, but I never actually tested them, as the only instances when I had to use a two-coax solution had DTC-100s

I'd like you to again try connecting the two antennas to the two inputs: one directly and the other diplexed, but then run the automatic add channel program so that the receiver will at least have a chance to find and map them.

You can also buy a cheap infrared A/B switch for under $40 that works with any of your other remote controls. One of mine responds to any long (like over two second) infrad command. I think I saw another that could "learn" an input command from any remote.

Dave McWilliams 11-02-2002 05:14 PM

Mike,

The HD200 definitely only supports one terrestrial input at a time, so it looks like I might be stuck with the three antennas and one coax line into the receiver. Does something like this strike you as a possible solution?

I did think about the A/B switch solution earlier, but I'd rather expend some time and effort now with the hopes of having a more seamless operation later. (Of course if I really wanted it seamless I should just put it on the roof and forget it, but that's another story...)

Thanks again for your help!

Scooper 11-02-2002 05:53 PM

magic123 - I'm afraid I have to disagree with your comment about "UHF under 40 miles with no pre-amp" comment. That may very well work IF you don't have any vegitation / trees in the way. I'm only 23 miles from most of my UHF stations, but my house sits in a clearing in a forest. Even using a CM3221, UHF reception is simply not possible without a preamp AT MY LOCATION. Oh yes - my antennas are out above the roof, and I still have the Winegard AP4700 UHF pre-amp to make it work. When I get a DTV tuner, I'll see how that responds.

magic123 11-02-2002 07:18 PM

Scoop....I am sorry I did not say..all reception situations are different. I just speak for myself and my situation and experiences. In fact, at 50 miles, for me, I am finding out a pre-amp does not improve the actual signal strength much..just helps to maintain it when you cut line several times. I am spending this week end learning much about reception of digital signals. Most important, for me, is a highly directional antenna to lock on the sweet spot. This does not vary by many degrees, certainly not more than 10, probably more like 5 degrees. Happy viewing.

AntAltMike 11-02-2002 08:09 PM

But you need 3 UHF antennas and that drawing doesn't have them.

Point a combo at Pittsburgh and peak it on 43. Point a UHF only at Pitts and peak it on 38. Combine these two antennas with a Channel 38 Jointenna and then go into a preamplifier with VHF gain of 15-17dB and UHF gain of 25-28dB.

Aim a UHF antenna at Yorkstown, go to a mid-gain UHF preamp, then through a channel 36 bandpass filter: either a tuned UHF-BPF (preferred), or use a channel 36 Jointenna as a bandpass filter by terminating the unused port. Then combine with a two way combiner (reverse splitter).

If this coupling degrades channel 38, put a weak attenuator pad (they come in 3dB increments) on the 36 input into the two way combiner. Conversely, if it degrades channel 36, pad down the broadband input into the combiner

Dave McWilliams 11-02-2002 09:00 PM

Thanks for all your help, Mike. I'll let you know how it turns out.

AntAltMike 11-03-2002 06:40 PM

FWIW, I just connected an off-air antenna to a Sony HD-100 this afternoon, and it had three antenna inputs. One for satellite, one for analog broadcast TV and one for digital broadcast TV. It would not tune digital broadcast TV channels from any input other than the dedicated digital broadcast TV antenna input.

Over the next few weeks, I'll experiment with any DirecTV/HDTV receiver that I come across in my travels and post my observations regarding their ability to tune broadcast TV signals from either of their broadcast antenna inputs. I know that I will be servicing an account with a Hughes E-86 this week. It could be that I just have been lucky in that each time I have had to settle for a two antenna coax configuration, those customers always had RCA DTC-100s.

Mike__P 11-04-2002 10:03 AM

Who here knows where to get a jointenna to reject 24-1 in tampa? Currently I am using a two way 3.5db splitter, but I think a jointenna would work better. My local antenna guy says they can't get them anymore as channel master has decided not to continue manufacturing them.

AntAltMike 11-05-2002 03:41 PM

They are special order. I just ordered four yesterday. Expect to have to pay for them in advance.

If you reject channel 24 with a tuned Jointenna, then you will also reject 22-26. Can you afford to do that? If you need to reject channel 24 to avoid a preamp overload, but if you need 22, 23, 25 or 26, then you will need to get those channels through an alternate signal path (second coax).

Mike__P 11-05-2002 06:09 PM

Here in Tampa, I don't think anything is scheduled for 22,23,25, or 26. From whom did you order one and how much do they cost. I think I would like to get a couple.

Dave McWilliams 11-10-2002 05:26 PM

I priced the Jointenna at Warren Electronics, and they were around $25 plus shipping.

I spent a good portion of the day looking for spot in the attic that will get the Pittsburgh stations, and finally found a place that gets everything but the low power stations. That gets me down to two antennas. I then tried pointing a UHF 180 degrees toward Youngstown (for channel 36) and combining the two with a combiner, but then I lost 38 in Pittsburgh. I'm leaning toward using a $25 remote controlled A/B switch from Rat Shack to deal with my situation. That will give me more flexibility if another channel pops up that I want to pull in later on.

Thanks again for your help, Mike.

tvantennaman 12-05-2002 10:14 PM

Quote:
Originally posted by AntAltMike
That page contains a lot of useful information but some poor advice as well.

In particular, one paragraph says:
"There must also be the exact same length of coaxial cable between the two antennas and the combiner, which is basically a backwards two-way signal splitter. The same exact length of coax cable between each of the two antennas and the combiner is needed also to help prevent ghosting from occurring on the TV's connected to the antenna system."

Quote:
That is nonsense for the application shown. The coax cables must be exactly the same length when two antennas are pointed in the same direction AND their dipole elements are in the exact same plane. It is irrelevant otherwise.
In order for the signals from the two TV antennas in the picture to arrive at the combiner at the same exact time, equal lengths of coax cable must be used between the antennas and the combiner. Without equal lengths of cable between both antennas ghosting will occur unless bandpass filters and channel traps are used. And for the application shown in the picture (I wrote the tutorial and installed this antenna system in Greenwood, Indiana) this antenna system is receiving channels 4, 42, and 63 from the south and channels 6, 8, 9 (DTV), 13, 20, 23, 25 (DTV), 40, 45 (DTV), 46 (DTV), and 59 from the north. There are equal lengths of coax cable between the two antennas and the UHF/VHF band separators that separate the signals so I can attenuate channel 4 by 20dB.

Then everything gets combined back together using another UHF/VHF combiner and a backwards 2-way splitter before the 19dB UHF preamplifier. Measurements were taken with a Tektronix spectrum analyzer and each of the channels were as flat as a pancake. I like to use a simple backwards 2-way splitter to combine broadband signals together so that as many stations (analog and digital) can be received from both directions. And if everything is carefully measured out this setup works great.

Quote:
If the only TV stations you desire are exactly 180 degrees apart, or, say 160 to 200 degrees apart, then maybe you can just couple them through a splitter and get away with it, because the front to back ratio of these broadband antennas might be 15dB to 20dB, but that is a really poor way to combine two antenna signals.
So what do you do if you live in Frederick, MD between two major cities, like Washington and Baltimore and you have many channels from each direction that you would like to receive without using a rotator? Use JOIN-TENNA combiners? I don't think so. You'd have to use a ton of them and the ghosting would be horrible with all of those, which would affect the digital channels. Your only solution would be to combine two broadband antennas together using a simple combiner...such as a backwards 2-way splitter. Good yagi antennas do a great job of nulling out back and sidelobes, unlike most consumer antennas. That's why it's so important to look at the antenna specs and understand them before buying an antenna.

Quote:
As far as spacing is concerned, most commercial installers in multifamily dwellings keep them 1/4 wavelength apart, and we don't usually calculate that too closely. If you have two VHF antennas receiving low band channels, keep them at least 5 feet apart; highband VHF, maybe 3 feet; and with UHF, the corner reflectors will keep you from stacking them too closely. No one has 17 feet of extra mast and 15 feet of mast above the roofline (32 feet total mast height) to receive channel 2 from one direction and, say, channel 4 from another. If you want to use two VHF antennas pointed in two different directions, put up a second mast.
Most antenna installers today, including some commercial antenna installers, either don't understand the basics of how radio waves work and the proper techniques of installing antennas or they simply don't care. According to the 2002 Blonder Tongue Broadband Reference Guide in chapter 11, "D) The minimum spacing between antennas of different channels and is the figure given for the antenna with the lowest frequency".

This refers to the chart on the page which has the "D" column showing the spacing for 1/2 wavelength on each of the VHF TV channels and is true for the UHF channels as well. And unless you are cantilevering the antennas off of a tower, I would agree that you would definitely want to mount two combined VHF-LO antennas on separate masts.

AntAltMike 12-06-2002 12:34 AM

Quote:
Originally posted by tvantennaman
In order for the signals from the two TV antennas in the picture to arrive at the combiner at the same exact time, equal lengths of coax cable must be used between the antennas and the combiner. Without equal lengths of cable between both antennas ghosting will occur unless bandpass filters and channel traps are used. And for the application shown in the picture (I wrote the tutorial and installed this antenna system in Greenwood, Indiana) this antenna system is receiving channels 4, 42, and 63 from the south and channels 6, 8, 9 (DTV), 13, 20, 23, 25 (DTV), 40, 45 (DTV), 46 (DTV), and 59 from the north. There are equal lengths of coax cable between the two antennas and the UHF/VHF band separators that separate the signals so I can attenuate channel 4 by 20dB.

Then everything gets combined back together using another UHF/VHF combiner and a backwards 2-way splitter before the 19dB UHF preamplifier. Measurements were taken with a Tektronix spectrum analyzer and each of the channels were as flat as a pancake. I like to use a simple backwards 2-way splitter to combine broadband signals together so that as many stations (analog and digital) can be received from both directions. And if everything is carefully measured out this setup works great.

You are again taking theory and advice for combining stacked antennas pointed in the same direction and applying it to unstacked antennas pointed in different directions. With two stacked antennas pointed in the same direction and mounted on the same mast, the signals arrive at the dipoles exactly in phase with each other and that phasing is maintained by keeping the coax cables to the coupler the exact same lengths.

In the situation in your photograph, however, the antennas are pointed in opposite directions. Lets analyze this for channel 2. Lets assume that the antennas are physically identical yagis. You have furnished a half wavelength figure for channel 2 of 8.64 feet. If these two dipoles were fortuitously each exactly 4.32 feet from the mast, then the channel 2 wave would hit the further dipole 180 degrees out-of-phase from the way it hit the nearer one. And since the antennas are facing opposite direction, the phase relationship of the dipoles to the coax is reversed, so if the coax lengths for two antennas were exactly equal, then the waves would be in perfect phase and would be added to each other. This would not be the addition of equal signals, however, since the gain on the antenna pointed the wrong way would be about twenty dB less than the gain of the antenna pointed at the channel 2 signal source.

Now lets suppose that a channel 6 is being broadcast from the same tower as the channel 2. Lets say that its half wavelength in the atmosphere is 5.73 feet (8.64 x55.25/83.25). It isn't going to hit the far dipole at exactly 180 degrees out-of-phase from the way it hits the first one, because it is located about three feet (about 90 degrees) beyond the phase inversion point, which demonstrates that even if you are lucky enough to have these two antennas phase matched at one frequency (in this example, 55.25Mz), they will only be phase matched at harmonics of that frequency (110.5Mz, 221Mz, 442Mz), which means that they will NEVER be phased matched for any other TV broadcast frequency because the three broadcast bands are deliberately staggered to avoid harmonics.

Your combined output was flat for two reasons:
1) because your antennas are pointed in exact opposite directions, you have the maximum front-to-back effect mitigating the undesired signal, and
2) Even if you add a significant-strength out-of-phase digital signal to a desired signal, the additional signal would be flat in this case as long as the dipole receiving it is perpendicular to the transmission path, which, in this case, it is. A flat signal does not reliably indicate a quality, "ghost-free" digital signal,


Quote:
So what do you do if you live in Frederick, MD, between two major cities, like Washington and Baltimore and you have many channels from each direction that you would like to receive without using a rotator? Use JOIN-TENNA combiners? I don't think so. You'd have to use a ton of them and the ghosting would be horrible with all of those, which would affect the digital channels. Your only solution would be to combine two broadband antennas together using a simple combiner...such as a backwards 2-way splitter. Good yagi antennas do a great job of nulling out back and sidelobes, unlike most consumer antennas. That's why it's so important to look at the antenna specs and understand them before buying an antenna.
If you live in Frederick, MD, where the angle between the two antennas is probably a little less than 90 degrees, then you cannot use jointennas because there are too many frequency conflicts between the two markets, including 36Washington/38Baltimore/39Washington and 51Washington/52Baltimore. You can't reliably count on the directionality of your antennas to conveniently null out the off axis signals. There is very little difference between the sidelobe rejection of a residential grade Winegard or Channelmaster antenna and a commercial broadband antenna. Sure, UHF yagis are tighter than VHF, but what if the Washington signals have to be boosted by, say, 15dB to 20dB, whereas the Baltimore ones might not need amplification? That gain on the out-of-phase Baltimore UHF signals will bring them up close to the level of the desired signals from the Baltimore antenna. And unlike the two antennas in your picture, the elements of the Washington and Baltimore antennas will not be perpendicular to the unintended signals, so those waves will hit one end of the dipole before it hits the other and develop unintended signals that will degrade the intended signals.



Quote:

Most antenna installers today, including some commercial antenna installers, either don't understand the basics of how radio waves work and the proper techniques of installing antennas or they simply don't care.
Fortunately, I'm not among them!

Quote:

According to the 2002 Blonder Tongue Broadband Reference Guide in chapter 11, "D) The minimum spacing between antennas of different channels and is the figure given for the antenna with the lowest frequency".

This refers to the chart on the page which has the "D" column showing the spacing for 1/2 wavelength on each of the VHF TV channels and is true for the UHF channels as well. And unless you are cantilevering the antennas off of a tower, I would agree that you would definitely want to mount two combined VHF-LO antennas on separate masts.
Purists recommend one wavelength spacing. Blonder-Tongue, which sells VHF broadband antennas that retail for about $500, recommends a minimum of one-half a wavelength. Most residential customers who cannot afford $500 antennas also cannot afford enough masting to space two VHF lowband antennas even eight feet apart and with the lower antenna six feet about the roof. While I agree with tvantennaman that this problem can best be addressed by putting the VHF lowband antennas on different masts, he didn't in his picture, and I can tell you from extensive experience that spacing them at a quarter wavelength, if you have no practical alternative, will almost assuredly get you acceptable performance.


The only way to successfully combine signals from two antennas pointed in different directions without bandpass filtering is to get lucky. Anyone doing a residential rotor-free antenna installation that includes channels from different directions that are too close together for filtered coupling might as well try the passive coupling, because they might get lucky, and if they don't, the splitter and pads only cost a few dollars. Those who are not lucky enough to be in a situation in which simple passive coupling will work for them will be best served by running two cables to each TV reception area and using an A/B switch to select the correct antenna for each program. The RCA DTC-100 has two off air antenna inputs that "seamlessly" integrate the signals from two off-air antennas into the guide. Otherwise, a remote controlled A/B switch for that purpose can be had for under $40.

magic123 12-06-2002 05:46 AM

Seems to me so much easier (maybe even less expensive in long run) and most likely better results..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. I have found this about the only way you can zero in on UHF/digital signals and, for me, I must do this if I want near-percect reception. It is good to run the lines from UHF and VHF antennas thru a CM 7777..2 inputs..combines inside..1 output. Winegard makes several of these as well.

Budget_HT 12-06-2002 06:57 AM

Quote:
Originally posted by AntAltMike
The RCA DTC-100 has two off air antenna inputs that "seamlessly" integrate the signals from two off-air antennas into the guide.
AntAltMike:

Can you elaborate on this please? I have an RCA DTC-100 but I have not tried this feature.

Are you saying that, using OTA PSIP guide data, that the DTC-100 maintains a single guide for both the A and B antenna inputs and would automatically select between the inputs as needed when selecting a station to view from the guide? If so, do you know how would it handle the same station being available of both Ant. A and Ant. B?

BTW, I appreciate your posts and I have learned plenty from you and others on this forum.


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