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Discussion Starter · #1 ·
I'm trying to setup two RadioShack VU-90XR antenna's in basking Ridge, NJ 07920. one pointing at NYC the other at Philly, they are stacked Vertically in my attic with 5 feet between them and facing 120 degrees from each other, with a Channelmaster 7777 amp.

When not combined I get a good signal from NYC 56 and 44 even without the amp, and a great signal with it. I don't get anything on the Philly antenna without the amp but with it I get a great signal from 64 and 26, a good signal from 32, and occasional access to 43


When I combine the antennas the signal strength from the Philly antenna drops a little, but everything still comes in good, on the other hand the NYC stations signal is cut in half, 44 is too weak and 56 is marginal ( viewable most of the time )


I'm guessing that the NYC stations are bouncing of the mountains and coming in the Philly antenna, not strong enough that I could use 1 antenna, but enough to mess up the good NYC antenna. Or channel 43 is bleeding over to 44 and washing it out. I think I need to put a signal blocker on the Philly antenna blocking 44 and 56, or blocking all and just passing 26,32,43,and 64. As more stations come on line or increase their power I'll need to add more blocks.


Will this work? What product/products should I be looking at?
 

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Combining antennas like this is generally doomed to failure. I say generally because a couple of people on this board have managed, through judicious use of some voodoo, to make it work. Your simplest solution is a rotor or run two separate lines and use an a/b switch.
 

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 Here is a great thread on using multiple antennas.
 

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What you need if you *really* want to do it this way are notch filters to completely remove the signal at the frequencies of each channel you get via one antenna from the other antenna.


You'd examine the channels you receive from each and identify the ranges you need to notch out of each, then find a notch filter that was either adjustable or specific enough to eliminate most of those frequencies. This will probably entail multiple notch filters.


The problem with multiple notch filters is that there's a certain insertion loss for each one of these, so you want to minimize the number you place inline or you're effectively reducing the rest of the signal more than is desirable.


In your real world experiment, you're really having problems with the NYC stations being overridden by noise coming on the same frequencies, so you might be able to just eliminate the NYC station frequencies from the one antenna.


However, notice how you need channel 43 from Philadelphia and channel 44 from NYC? Those are adjacent frequencies. It's almost impossible to get a notch filter that has a sharp cutoff such that you could cut out one channel while maintaining the adjacent channel completely intact. These narrowband notch filters are expensive. Of course, so are the wide band notch filters. :)


Tunable notch filters that aren't fine enough for adjacent channel retention:

Data sheet: http://www.eagle-1st.com/prod/pr4/Filt200/T200ds.htm

Prices: http://www.eagle-1st.com/plist/pl4/pl42a.htm


Tunable notch filters that are probably good enough to retain adjacent channel information if you're lucky:

Data sheet: http://www.eagle-1st.com/prod/pr4/Filt400/T400ds.htm

Prices: http://www.eagle-1st.com/plist/pl4/pl42b.htm


Each filter costs from $135 to $279 depending on the frequencies involved and the size of the notch.



Here's a table of broadcast TV frequencies:

http://www.arrl.org/tis/info/catv-ch.html


You could manage by notching the entire range from channel 44 through channel 56 out of the Philadelphia antenna since there's no Philadelphia channels within that range. One notch filter required with a 72MHz-120MHz notch (72MHz just reaching up to the last NYC station; 120MHz being the largest notch going up to the first Phialdelphia station after the NYC ones).


Finally, the problem becomes that the good notch filters from this manufacturer that give you that clean a notch don't operate up at the frequencies you need. The TNF220xx filter would be usable if it was clean enough at the edge to get rid of the channel frequency from UHF 44 enough so as it wouldn't interfere with UHF 43 and enough to no longer interfere with the real signal on the NYC antenna.


Perhaps there's other manufacturers... in fact, I'm sure there are, but these I found first. But that should give you an idea of what's involved. Ideally you'd do the reverse on the other antenna so that you notched out the Philadelphia frequencies from the NYC antenna. Of course, that adds more expense and potentially reduces the usable signal because of insertion loss.


Of course, all this is "in theory." Often with over-the-air reception "in theory" is not related to "in practice." So if you try this, be prepared for disappointment and loss of all the money you spend trying this.
 

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Cheapest way is for each antenna to have its own downlead and then select between the two with an A/B switch at the DTV receiver. (Two DTV receivers would require a couple of 2-way dividers and a 2nd A/B switch.)


This would be way cheaper than the rotor (requires a 2nd cable anyways, works only for one receiver) and also cheaper than the multiple filter/combiners (plus whatever add'l amplification necessary to overcome insertion losses).
 

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Discussion Starter · #6 ·
wow thanks for all the info, I cant use a rotor do to space problems. I've read articales on setting up two antennas, but haven't seen that much info on filters, other then that they exist.

I was very surprised on the costs of filters, I was really just looking for a temperary solution untill more stations come online or boosted their signals to full power. I was expecting filters to be around $10 each, it is just a frequancy spacific Ohm resister isn't it? Is there a cheaper solution if I don't care about missing channel 43?


Hopefully channel 8 will come online soon and I wont need 43 both PBS NJN. and If philly's FOX 42 and WB 54 ever boost their signals to full power, I'll probalbly just dump the NYC antenna, or use it for VHF only.


I couldn't follow how you matched a 72MHz-120MHz notch to channels 44-56 from that broadcast frequancies chart I got 650-725


Anouther option is a A/B switch I could place in the attic but control from my livingroom, rather then running anouther line.
 

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Discussion Starter · #7 ·
I thought of anouther solution, I have anouther wire running from my Tivo in the living room through the attic and to my bedroom. The Tivo transmites on channel 3, so could I have the antenna signal going down the line and the Tivo signal going up the line. ie the Tivo and A/B switch on one end and a TV and antenna on the other. I guess the only way to be sure is try it.
 

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Quote:
Originally posted by dswallow
It's almost impossible to get a notch filter that has a sharp cutoff such that you could cut out one channel while maintaining the adjacent channel completely intact. These narrowband notch filters are expensive.
.....and most (all?) are designed with NTSC in mind. Other members have found in many cases they do not work for DTV applications, because of an inability to filter out enough of the adjacent signal.
 

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Quote:
Originally posted by rphooper
I couldn't follow how you matched a 72MHz-120MHz notch to channels 44-56 from that broadcast frequancies chart I got 650-725
72MHz is the size of the band between UHF 44 and UHF 56 (the size of the notch). You could also use one with a larger notch size, up to 120MHz because of the lack of any signals you care about in that range.
 

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Quote:
Originally posted by rphooper
I thought of anouther solution, I have anouther wire running from my Tivo in the living room through the attic and to my bedroom. The Tivo transmites on channel 3, so could I have the antenna signal going down the line and the Tivo signal going up the line. ie the Tivo and A/B switch on one end and a TV and antenna on the other. I guess the only way to be sure is try it.
You'd be broadcasting channel 3 via your antenna if you connected the TiVo to the same cable connected to your antenna. The FCC might not care for that, and neither would your neighbors.


Actually, you'd need to notch out channel 3 from your antenna, and ensure you used something that blocked channel 3 from making it to your antenna. With that, it'd probably work. But, too, you really wouldn't be notching out just channel 3, but a bit of the adjacent channels too. So if you were needing to get something on channel 2 or 4 via the antenna, you'd have problems.


And then Ken's comment about digital TV signals not surviving well using these narrowband notch filters probably makes it moot, though if you don't care about channel 43, it's still probably workable.


There are much cheaper filters than these tunable notch filters, but they're usually for rather wide ranges of frequencies. Channel Master has 3 UHF filters they call "jointennas" that are divided into 3 sections of the UHF band. I don't think any of them would give you the stations you really want.


You could always give up on antennas, and go "gray market" subscribing to Bell ExpressVu in Canada, which delivers all the networks in HD (and east and west coast versions at that), though you'd be looking at laying out around $600 for equipment, at least $15 a month for service and mounting a 20" satellite dish.


If you had a rotator perhaps you'd find that there actually is a position you can place both antennas in where everything works for your needs without further need of adjustment/rotation. I wouldn't dismiss that possiblity. You could substitute a friend with a cell phone for a rotator while checking this out, but you really need the person's body out of the way of the antennas to know for sure if you've got it good. If its a borderline issue with signal multipath caused by using two antennas, I might give this possibility a try. You may also need to experiment with changing the length of one of the antenna downleads. Slightly tilting one or both of the antennas up or down may also have an effect depending on where the interference causing the problem is coming from.


If all of this sounds like everything you want to try is/will be a pain, you're right. It is. :)
 

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Has anybody used the Channel Master jointennas? I was in touch with CM yesterday and CM told me to order them through a local dealer. One has to specify which particular channel to filter out. Takes about 3 weeks to get them once an order is placed. They are about $31 each.

http://www.channelmaster.com/pages/cjs1.htm


UHF:


Models 0585-1 Channels 14-29

Models 0585-2 Channels 30-49

Models 0585-3 Channels 50-69


VHF: models 572-583 (channels 2-13)
 

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As a practical matter, you can't "notch" out an adjacent digital UHF signal. In fact, as a practical matter, you can't even delete an adjacent analog UHF signal cleanly enough to permit reinsertion at that frequency.


I can't read the legends on the graph of the Eagle premium product, but I believe I can interpret it anyway. The graph shows the attenuation of the filter at 0.7% of center frequency. As broadcast channel 44 has been allocated the 6Mz wide band from 650Mz to 656Mz, then its center frequency is 653 Mz. 0.7% of 653 Mz is 4.57Mz, so roughly speaking, the -3dB attenuation points for this filter, if center-tuned to channel 44, are about 650.72 and 655.29Mz. In other words, when center-tuned, it would be doing virtually nothing to attenuate the channel 44 signal at the bottom end of its band where its powerful signal pilot is, nor at the top end.


Now, let's eyeball this graph a little further. The -3dB roll off points appear to be about 2.8 divisions apart At 653Mz center frequency, each horizontal division therefore represents about 4.57Mz/2.8, or 1.63Mz per division. You can see that where the plot crosses these 1.63Mz division lines, about 651.37Mz and 654.63Mz, the attenuation is only 4dB, yet nearly one half of the channel 44 digital signal energy is outside of these frequency boundaries and is attenuated by 4dB or less.


Now, if you eyeball the chart a little further down, to where the plot crosses the 10dB attenuation level, which might be enough attenuation to begin to make a difference in so far as mitigating interference from the undesired signal is concerned, the bandwidth of that degree of attenuation is about 0.8 divisions, which means that only the portion of the signal from about 652.19Mz to about 653.82Mz gets attenuated by 10dB or more.


The likelihood that this narrow, irregular attenuation of the undesired signal will significantly or even noticeably improve the quality the desired signal when the two antenna signals have been mixed into the same downlead is slim, at best, and you'd need a spectrum analyzer to even attempt to tune such a filter to your maximum benefit.


If I were desperate, I might center-tune one such narrow notch to the pilot frequency of channel 44 and tune another to about 654.5 or so, looking at my spectrum analyzer sweep to see where it pulls the high end of the channel 44 plateau down some 10-15dB, and then I'd tune a cheaper notch filter to the middle of the band. The total parts cost to attempt to blot out this one channel would be nearly $600. Take a look at the digital and analog channel assignments for New York and Philadelphia on 100,000 Watts, and you'll see that there are about a dozen such conflicts that you would have to address to use this methodology to mix these two leads using filters.


It may not suprise you to learn that I do things like this for a living. I design and install master antennas systems in large buildings and sometimes I have to squeeze signals from different antennas into a single downlead when it is difficult to do so. I service one large unit condominium in which I have attempted to mix adjacent digital channel signals into one downlead and cannot reliably do so even though I have a lot more equipment than you do and a more favorable reception situation as well. And if I could get them into balance, I would lose that balance as soon as either channel changed its transmission power.


If I am ever forced to deliver adjacent channels from different antennas on one coax, I'd buy some demodulator/modulator equipment from Drake for under $2,000 to shift the weaker signal to a vacant frequency, but there is no reason for a residential viewer to even consider this. You should use two antennas with two separate downleads and an electronic A/B switch, which you can buy from Radio Shack for $30, or you could use an RCA DTC-100, which has antenna inputs "A" and "B" that can be integrated into a single channelguide.
 

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Quote:
Originally posted by bwam
Has anybody used the Channel Master jointennas?
The channel 2-13 Jointennas have been discontinued, and they were only for alternate channel use. If you used one to pass channel 12, for example, its channel 12 bandpass filter would not perceptibly attenuate any undesired signals present on channels 11 or 13, but its "all other channels" input would not pass desired channel 11 or 13 signals, either.


The UHF Jointennas will wipe out two adjacent UHF channels on each side of the tuned channel on low UHF channels, and three adjacent UHF channels on each side on high UHF channels, so a Jointenna tuned to channel 44 would not filter channel 43 off the channel 44 antenna's downlead, but also, it would not pass the desired channel 43 signal on its through lead.
 

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Quote:
Originally posted by AntAltMike
If I am ever forced to deliver adjacent channels from different antennas on one coax, I'd buy some demodulator/modulator equipment from Drake for under $2,000 to shift the weaker signal to a vacant frequency, but there is no reason for a residential viewer to even consider this.
First, all that other stuff is good to know. Thanks for that!


Second, this quoted part reminded me that someplace I'd seen a device that shifts an entire broadband block of signal around. Are you familiar with any of that sort of equipment or know if it might be possible to accurately shift a digital television signal to a different frequency such that a tuner would pick it up?
 

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Quote:
Originally posted by
someplace I('ve) seen a device that shifts an entire broadband block of signal around. Are you familiar with any of that sort of equipment or know if it might be possible to accurately shift a digital television signal to a different frequency such that a tuner would pick it up?
Back in the late 1970s and early 1980s. some cable companies would put a few premium channels unscrambled on midband and furnish a mid-band to UHF frequency block shifter to subscribers. At the time, I owned an Advent model 1000A Videobeam projection television that had vernier channel tuners that let me tune midband channels directly using the potentiometer intended for channel 6 or 7, so I got my HBO for free. Channelmaster had those frequency shifter boxes in their catalog as recently as a decade ago for something like $40, but they are in the wrong band for our application.


The MATV industry uses heterodyne channel converters that downconvert a UHF broadcast analog channel to a VHF one that sell for under $200 each. A couple of years ago, I asked a few manufacturers if a digital signal so downconverted could be tuned by a digital tuner and the manufacturer's techs each said no, but the technicians who answer the phone for a living are not necessarily the best and the brightest. I didn't bother to test any because I didn't have any distribution problems that warranted it at the time, but maybe this weekend, I'll try to make time to shift a healthy digital UHF signal down to a VHF channel and see if either of my digital tuners can find and lock onto it. I have a WIN TV-D board in one of my PCs and I have an unopened broadcast TV set top box that I bought from Sears several months ago (STR-151 or something like that) so I'll see if either will process that downconverted signal.
 

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dswallow-


I live in Basking Ridge on a hill. Use two antennas joined with short 300 ohm cable into amp (I use CM 3041). Then use as long and heavy a shieled cable as you need to get to your receiver in one piece. The main objective is to minimize your signal losses. Get compass and required pointing from www.antenna.org. For Phily channels start with 3-1 (CBS) and for NYC start with 2-1 (CBS again). They should be your strongest signals. If you can't get these I wouldn't worry about anything else. I use a baby monitor to hear when the channels lock in from the basement where my TV is at. I arc left to right to get the range of angle and leave the antenna pointed at the middle. Then I would go through the other channels running between basement and attic. Same procedure over and over. Good exercise. My experience is over receiving the following channels: 2-1, 3-1, 5-1-2, 10-1, 12-1, 17-1, 29-1, 39-1-2-3-4, 52-1-2, 57-1, 65-1-2. The two antennas do not need filters given the channel frequencies and the directions they need to be pointed. Filters would introduce extra connections and loss. I also use RS antennas (one Yagi one VHF-UHF) in attic. However, to do it right and get the best possible solution I would move to best long range Channel Master Yagi and/or Bay antennas for UHF. I may still. I still like two separate antennas because once the position is optimized then you never touch it. They have no weather issues. They pick up all the channels in a single receiver scan. With one antenna you have to scan once, rotate, then add the other channels, usually manually or you'll lose those from the initial scan. All the channels are in now (except 39-1-2-3-4, which I think is now 52-1-2, and 11-1 , PIX which is at very low power). It sounds like the amp you have is fine but the 3041 I picked up in Lowes made all the difference from the RS models I was using. Night and Day as all the stations just appeared like magic. It was in this thread that I became aware of it. Before it, not even an occasional pixel. Good luck...It is very possible from Basking Ridge to be in DTV nirvana as long as you don't have major obstructions (like a mountain between you and the signals). Get the best equipment it's really very inexpensive compared to the investment you've already made in the HDTV gear.


tonyo123
 

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Quote:
Originally posted by rphooper
I can't use a rotor due to space problems.
All the DTV assignments in New York and Philadelphia are UHF, so you don't need a long-boomed clunker like the VU-90XR. You would get better performance with a Channelmaster 4228 8-bay bowtie, and since it had a turning radius of about 2 feet, I'm sure you could use a rotor with it.

Quote:
The two antennas do not need filters given the channel frequencies and the directions they need to be pointed.
:(

YMMV
 

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Discussion Starter · #18 ·
Ok my heads spinning right now ( so much information)


mike

There are a few VMF DTV stations in my area channel 8 PBSNew Brunswick should be transmitting soon, and WB in NYC is temporarily using channel 12, but yea I should have got the 4228, I bought the first VU90 over a year ago


tony

from what I read the in the NJ thread the 7775/7777 sounded better then the 3041, without amp I only got 44 and 56 for the last year, Its been great to finally have ABC. I live more in a valley then you I live by the VA hospital, I'm guessing you live near The Hills with a great view to Philly, from the top of the mountain, I've never gotten a trace from half the stations your getting. Also putting my antennas in the attic reduces their effectiveness.


dswallow,

thanks for letting me know my Tivo would be transmitting, I probably wouldn't have noticed until the FCC came knocking on my door.;)


It sounds like the filters are more pain then they are worth, I'll just have to run another wire, I have a DTC-100 so that will work for now., but I see one big problem come next year.

I'm going to buy the "Directv HD Tivo" as soon as Its out and I'll bet it wont have two OTA inputs, or a way to select an A/B switch or turning a rotor. at that point I'll just have to use just one antenna.
 
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