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DTV reception in high RF environment

post #1 of 35
Thread Starter 
I am trying to receive Denver TV stations in the SW part of Colorado Springs, CO about 70 miles away. Those of you local know the Ivywild area. The house is at 6,000 ft elevation and the antennas are mounted about 20 feet off the ground. I am using two antennacraft antennas mounted on a 6 ft pole over a rotor connected to a 4 ft pole roof mounted. The MXU59 is a 59 element UHF antenna mounted 5ft over a 10 element Y10713 ch7 and above VHF antenna. I am using a Radioshack 15-321 premap that is mounted on the pole about a foot above the VHF antenna. It's rated at 35 db with a 3.5 db noise figure and 15db FM trap that is turned on. There are separate 4 ft RG6 cables connected from the ant baluns to a Pico macom UVSJ combiner. My home is only about 5 miles from Cheyenne Mountain where all of the high power TV and FM transmitters are located. There have always been problems with intermod and signal overload especially on FM. I am about a mile from the Rocky Mountain front range so there are multipath issues. I have used Rabbit Ears to locate the Denver channels I want to receive and they are channels 7, 9, 19, 34 and 35. The maps do not show much signal from these stations in my area.
I am able to get very strong signals from channels 29 and 43 which are located over 100 miles away but the transmitters are on a heading of 357 degrees which puts the towers in the plains and not the mountains. These channels also show no signal in my area on Rabbit Ears. I can pick up with good signals ch 13 and ch 15 which sometimes degrade when it's very hot; that transmit from the mountains west of Denver about 70 miles away. Ch 13 is at a heading of 327 degrees and ch 15 is at 341 degrees from Lookout Mountain near Golden; also the location of the channels I want to receive which are network stations that have very good news programs. Of the signals I can get are 4 in Spanish, 3 PBS that I also get locally on a translator here, ION, Qubo, shopping, GetTV and Bounce. I am trying to get some of the other subchannels that provide programming that will allow me to "cut the cable."
OK, that's a lot of information. Looking at the signal strength meter on the TV for the channels I want to get I see a bouncing signal strength ranging from 0 to 40 very quickly and no amount of rotor movement can make the signal solid. I am getting two stations with signal strengths in the 30s and 40s but they are solid signals. That stations that are 100 miles away have signal strengths in the 80s. Indeed, ch 15 came in after I put the preamp on and without it the signal strength never got above 35. The radioshack amp has a switchable box next to the TV; it provides DC to mast preamp mounted at the combined output of the UVSJ. Whenever I turn it on and increase the amp gain signals got to zero so I keep it off and the only amplification is the preamp at the antennas.
I think I need help in detuning some of the local signals. I also recognize there may be multipath issues. I would appreciate any advice to help improve the signals and I am very patient in trying a number of options. If I need to put the V ant over the U I will try. I have tried both antennas separately without the UVSJ and have not had any improvement. As a matter of fact the UVSJ doesn't seem to have any signal loss. I have moved the antennas from one part of the roof to another and there are no close in obstructions between me and the horizon but there may be an 8 to 9 thousand foot mountain in the way. I am picking up ch13 with the antennas aimed at the mountains north of me.
Thank you for your patience in reading this tome. I would rather give more info than less. I know must be there a solution to my problem.
post #2 of 35
Perhaps a lower gain preamp that is not subject to overload from your strong local channels will provide better results. Plus those RadioShack preamps have a higher noise figure. Surprisingly the reasonably priced RCA preamp has gotten good reviews from tech pros and is not easily subject to overload. And it has dual UHF/VHF inputs, and an FM trap. Plus a low noise figure of about 2.7. About $24 on Amazon. And Winegard now has a good low noise preamp with a low noise figure. And perhaps consider a variable attenuator or filter to reduce interference from the strong nearby channels. Your antennas seem good for distant reception, and that MXU-59 is actually a good performing UHF antenna that is often overlooked. Good luck.
post #3 of 35
Trying to receive the very weak RF7 and RF9 from Denver is very difficult considering you have a very strong nearby RF8 which will overpower RF7 and RF9. You need to reduce the received strength of RF8, and one way to do that is to take advantage of the two antenna nulls that exist at 90 and 270 degs. You need to turn your Y10713 until it is broadside to the RF8 transmitter. (See TvFool for the direction.) This will give you the best chance of receiving RF7 and RF9 but there is no guaranty. Good luck.
post #4 of 35
Channel 8 is likely 70-90 dB stronger than channels 7 & 9. It's unlikely you'll ever be able to get those two with this great of a signal differential by any adjustment of the antenna. You *might* be able to use a two antenna array such that a deep null is in the direction of Cheyenne Mtn, but that's likely to be a real long odds experiment.

The amp you're using is pretty well despised by those who have given it a knowledgeable test. As noted, the inexpensive RCA preamp, a virtual clone of the old CM 7778, has recently shown up on the radar after the tech guy from Antennas Direct released some lab results on it on another forum and another guy from Los Angeles (user name Pete Higgins) posted some pretty fascinating results using it..
post #5 of 35
Thread Starter 
Thanks, where can I get a variable attenuator? I will try the RCA amp.
post #6 of 35
Thread Starter 
Thanks, I will try it. Rainy day today, wonder if that affects signals.
post #7 of 35
A variable attenuator will not make a difference since it will attenuate all frequencies.
post #8 of 35
Thread Starter 
Thanks to everyone for your advice. I have ordered the RCA preamp and the next thing I need is a ch 8 notch filter 180 - 186 Mhz. The problem is locating one. A friend suggested calling the cable company.
post #9 of 35
There is no way you're going to notch out channel 8 deep enough without the filter's skirts also taking out channels 7 & 9.

Based on a generic area TVFool plot at 100', the NM of channels 7 and 9 are lower than -18 dB.

I hate to say it, but you're beating your head against a wall.
post #10 of 35
would a 1/4 wave stub for ch8 be enough notch?
milt9
post #11 of 35
Quote:
Originally Posted by Milt Frankel9 View Post

would a 1/4 wave stub for ch8 be enough notch?
milt9

It doesn't matter how deep you can make the notch.The RF8 transmit signal inherently has noise that spreads into the two adjacent channels. The FCC specifies what level that noise has to be. So the problem for the OP is that the noise level is so strong that it interferes with RF7 and RF9. So it is virtually impossible to receive them unless you can reduce the received RF8 signal level along with the adjacent channels noise levels.
Edited by retiredengineer - 9/12/13 at 3:44pm
post #12 of 35
Does anyone still manufacture a device that merges together two antennas, with phase and gain adjustments on one input, so you could 'null out' an offending signal? It was useful in subtracting an undesired signal, and might be perfect in this application.
post #13 of 35
Thread Starter 
Quote:
Originally Posted by retiredengineer View Post

Trying to receive the very weak RF7 and RF9 from Denver is very difficult considering you have a very strong nearby RF8 which will overpower RF7 and RF9. You need to reduce the received strength of RF8, and one way to do that is to take advantage of the two antenna nulls that exist at 90 and 270 degs. You need to turn your Y10713 until it is broadside to the RF8 transmitter. (See TvFool for the direction.) This will give you the best chance of receiving RF7 and RF9 but there is no guaranty. Good luck.

I rotated the antenna watching RF8 and the signal is so strong there seems to no null at all. I'm beginning to think I'm out of luck with chs 7 & 9 and should concentrate on Chs 34 & 35. I wonder if there are RF overload issues for these channels?
post #14 of 35
Quote:
Originally Posted by retiredengineer View Post

It doesn't matter how deep you can make the notch.The RF8 transmit signal inherently has noise that spreads into the two adjacent channels. The FCC specifies what level that noise has to be. So the problem for the OP is that the noise level is so strong that it interferes with RF7 and RF9. So it is virtually impossible to receive them unless you can reduce the received RF8 signal level along with the adjacent channels noise levels.

Quote:
Originally Posted by George Molnar View Post

Does anyone still manufacture a device that merges together two antennas, with phase and gain adjustments on one input, so you could 'null out' an offending signal? It was useful in subtracting an undesired signal, and might be perfect in this application.

Quote:
Originally Posted by kgcj View Post

I rotated the antenna watching RF8 and the signal is so strong there seems to no null at all. I'm beginning to think I'm out of luck with chs 7 & 9 and should concentrate on Chs 34 & 35. I wonder if there are RF overload issues for these channels?

A Google search for the Microwave Filter model 2903 returns http://theoldcatvequipmentmuseum.org/220/221/CATJ/17_Sept-1975.PDF
which contains a good explanation about eliminating co-channel or adjacent channel problems, but it doesn't show as a current product on Microwave Filter's website.
post #15 of 35
You may consider contacting Tinlee Co. and see what they can offer in terms of filters.
post #16 of 35
Quote:
Originally Posted by tylerSC View Post

You may consider contacting Tinlee Co. and see what they can offer in terms of filters.

See posts # 9 and 11.
post #17 of 35
Thread Starter 
Thanks to everyone's input. I tried the RCA amp and there was no improvement over the RS amp which has a double output so I can have more than one TV connected in different rooms. I have given up on trying to receive RF7 and RF9 because of local channel 8. I have taken down the VHF antenna and tried the UHF at different spots on the roof and on a higher mast. Turns out that having the antenna higher was detrimental and the original location of the antenna was the best. Seems that there are too many obstructions between Lookout Mtn and my location since I can get many stations even farther away but with antennas situated more to the East. Several of these signals are nearly 100 miles away. I'll keep playing with it to get more UHF signals here. Thanks again.
post #18 of 35
Quote:
Originally Posted by kgcj View Post

Thanks to everyone's input. I tried the RCA amp and there was no improvement over the RS amp which has a double output so I can have more than one TV connected in different rooms. I have given up on trying to receive RF7 and RF9 because of local channel 8. I have taken down the VHF antenna and tried the UHF at different spots on the roof and on a higher mast. Turns out that having the antenna higher was detrimental and the original location of the antenna was the best. Seems that there are too many obstructions between Lookout Mtn and my location since I can get many stations even farther away but with antennas situated more to the East. Several of these signals are nearly 100 miles away. I'll keep playing with it to get more UHF signals here. Thanks again.
If you want a better chance at distant UHF signals, then you will have better results with a lower noise preamp. The RadioShack is not recommended for deep fringe. I think the Kitztech 200 will provide best results, or you could consider the new Winegard LNA-200 Boost XT, or possibly the Channel Master 7778. The newer CM-7777 may be too strong because of your nearby locals.
post #19 of 35
Thread Starter 
I will check into other amps. I have done some research and have determined that none of the stations I can receive are on Lookout Mountain. I think enough of the Rampart Range must be in the way to block signals. I can get RF15 quite well and the transmitter is located near Lookout but a little bit East.
post #20 of 35
No amplifier is going to solve this person's dilemma. You simply cannot pick up extraordinarily faint signals when you're being overwhelmingly drenched by very, very powerful signals. The differentials are simply far to large.
post #21 of 35
Thread Starter 
Two more ideas to try.
1. Might I have better luck with one of the DTV converter boxes. Are the tuners better than the average TV? Since they are not HDTV could they have a better tuner and have a signal strength meter that can be used to tune in the signal with the rotor?
2. Might I have better luck with changing the antenna to a vertical orientation? I expect the transmit antennas are circular and maybe there is more power in the vertical phase.
Thanks
post #22 of 35
Quote:
Originally Posted by George Molnar View Post

Does anyone still manufacture a device that merges together two antennas, with phase and gain adjustments on one input, so you could 'null out' an offending signal? It was useful in subtracting an undesired signal, and might be perfect in this application.

Nearly a decade ago, I posted here that I had a couple of Microwave Filter phase shifters - one for VHF lowband and one for VHF high band - that I was willing to sell cheap. I paid $700 each for them but the senior living community in Charlottesville, Virginia that I had bought them for went to cable, so I would have let them go for half that, but I eventually discarded them. If you are willing to spend that kind of money, you can call Microwave Filter and they might have some lying around even if they are no longer in the catalog, but if you have time on your hands, and a signal meter, you can simply point a second antenna at the channel 8 transmitter, attenuate it to match the signal level coming off your main antenna, and then - here's the tricky part - you need to phase cancel the two coupled signals, which you can do either by making up a couple dozen jumpers that vary in length by one inch increments, or better yet, you can slide the antenna along its axis line to the position where channel 8 is weakest.
Edited by AntAltMike - 9/25/13 at 10:26am
post #23 of 35
I just ran zip code 80906 through TV fool at default height, 100 feet, and 500 feet above ground level. You don't really have a prayer. At 500 feet above ground level, your situation becomes 10 dB or so worse, because your reception of channel 8 improves. What are the best tuners getting by with for signal level and S/N? Isn't it around -83 to -85 dBm with an S/N of about 16? You'd need about 30dB of VHF highband antenna gain to approach that threshold even in the absence of a strong interfering signal,
post #24 of 35
Thread Starter 
Update: I haven't made any hardware changes recently but yesterday I was able to pickup RF18 and RF32 from Lookout Mountain with good signals for several hours. There was a cold front coming through and perhaps there was some favorable atmospheric condition. I tried this morning and I could see some signal strength but not enough to lock. This is the first time I got any signal from Lookout Mountain.
Kurt
post #25 of 35
Probably a tropo duct. Enhanced signal path conditions that allow signals from 1-3 (typically) time normal coverage area to be received as long as as the atmospheric condition is present.

If you don't know what that is, but if you happen to be a Deep Space Nine fan, think of a tropospheric duct as an "unstable" wormhole.
post #26 of 35
You might also want to make the antenna for the "offending" station, a channel-cut yagi...that would offer a bit of "pre-filtering" of the signal you want to cancel.
post #27 of 35
Thread Starter 
Quote:
Originally Posted by kenglish View Post

You might also want to make the antenna for the "offending" station, a channel-cut yagi...that would offer a bit of "pre-filtering" of the signal you want to cancel.

I'm not sure I understand the "pre-filtering" concept. Do I have a ch 8 antenna made and find some way to create an out of phase situation with the local RF8 interfering with Rf9 and RF7 from Denver? If so, how can I do it? Don't know if it's tropo-ducting but RF32, Fox 31 from Lookout Mtn has been coming in quite well from time to time. Would be nice if it could be a regular occurrence.
post #28 of 35

I also think the Kitztech 200 will provide best results, or you could consider the new Winegard LNA-200 Boost XT.EoRNcT It doesn't matter how deep you can make the notch.The RF8 transmit signal inherently has noise that spreads into the two adjacent channels. The FCC specifies what level that noise has to be. So the problem for the OP is that the noise level is so strong that it interferes with RF7 and RF9.

post #29 of 35
Your situation is a lost cause. There is no point in you looking into this any further.
post #30 of 35
Thread Starter 
Update: I moved the antenna and have a shorter cable run to a TV that gives me a signal strength. On a regular basis I see a signal strength of 30 for Denver RF18 and RF32 that is quite consistent and steady. Unfortunately, the SS must get to 34 just to display a pixalated image. I think I am using RF amps with the highest gain and am so close to getting the signal to a usable threshold. There have been times I can get the above stations and RF38 in Greely when there is tropo ducting when a weather front comes through. Is there a rule of thumb regarding the distance between the two yagis (UHF and VHF)? The UHF is above the VHF and about 4 feet in between? Should I position the combiner/amp in a certain place in relation to the yagis? It's now under the VHF yagi. Should the feed lines to the yagis be the same length? The line from the UHF is about 2 feet longer than the line from the VHF. How close should other antennas be near the yagis? I am a Ham and there are a lot of antennas on the roof; one only about 3 feet away, a vertical.
Should the bottom yagi be a minimum distance off the roof? It's about 5 ft now. Thanks for any help.
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