Reception Mysteries
Greetings All,
I have a few questions regarding reception to ask the technical folks on this forum. About 4 months ago I decided I had had it with Cable, and figured that I should go back to Over-The-Air TV. I purchased two antennas: A dual-4bay UHF, and a High-Band Yagi. Both of which are mounted on a 5' mast on my roof. The antennas are coupled with an RCA pre-amp that has separate VHF/UHF inputs. The pre-amp feeds about 75' of RG-6 to the back of the set. Everything (except the TV) is new within the past 4 months. I live on the West Side of the Hudson River about 60 miles north of NYC. Although my house is about 300' in elevation, there are NO signals to be had from New York, as I am in the shadow of Storm King Mountain and my neighbours. However, I pull in 4 stations reliably from Connecticut: WVIT (Channel 35), WCCT (Channel 20) WEDH (Channel 45) & WTIC (Channel 31). In addition, WNYW in NYC appears to have built a satellite station on Mt. Beacon on channel 32. Even though I have Line-of-sight to the transmitter, the signal is marginal, and not always reliable. I suspect that the transmitter antenna is highly directional and is being 'beamed' in a direction outside of my area. There is also another local station, WRNN (Channel 48) that broadcasts on the same tower, with a MUCH stronger signal level. For some reason, my TV seems to have an even tougher time keeping a lock on this channel than the weaker channel 32. Thinking MAYBE the pre-amp was adding some noise or overloading the set, I have tried bypassing it, with no change to the ability to decode. Without the pre-amp, most of the other UHF signals don't make it to the TV. Although the lack of this station is not a big deal, I would like to understand what is happening. In addition the UHF stations, I WAS receiving WTHN (Channel 10) with the VHF antenna. However, about two weeks ago, my TV set stopped decoding what was being pulled in. I have an old, analogue Field Strength Meter that I have been using to adjust the direction of the antennas. According to this meter, the signal level has NOT changed, but my set can not locate anything to display. A tunable receiver also shows a strong pilot signal (192.31mhz). Using a USB TV tuner gives the same results (no decode), so I don't think this is a problem with the TV. Has something about this station changed within the past month? Any advise or information is welcome. The other weirdness relates to another Connecticut channel, WFSB (Channel 33). From about 9pm at night to about 7 to 8am in the morning, the signal is good, and reception is clear. Around 8 in the morning the signal starts fading dramatically. By 10am there is NO signal at all (as per the F.S. Meter) According to the maps, the transmitter site is fairly close to the WVIT transmitter, so I would expect similar propagation characteristics. Although there is probably not much I can do about the signal. I AM curious as to why this phenomena is happening. I did NOT think that UHF frequencies were affect by daily changes in the upper ionosphere. Yet this channel (and this channel alone) seems to be behaving like an AM radio signal. Other than a change of address, I don't think there is much I can do to solve these issues. However, being a technically oriented individual, I am dying of curiosity as to WHY these things may be occurring. Any light that could be shed on this mysteries would be greatly appreciated. Thanx in advance Rich |
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Welcome, Rich:
You have asked some interesting questions. Without knowing more about your location, we can only give general answers, because every reception location is unique. Please do a tvfool report, using exact address or coordinates of the location of your antenna. Your exact address will not show in the report and any coordinates will be shortened. With an active link to your signal report, we can click on a callsign to see the terrain profile between the transmitter and your location. http://www.tvfool.com/index.php?opti...pper&Itemid=29 Quote:
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If my tuner is not able to pick up a channel durng a scan, I use the same technique that you use. I try to make a measurement of the signal strength to see if is even there. http://www.avsforum.com/forum/25-hdt...l#post22105317 This signal is strong enough, but the signal quality (SNR and uncorrected errors) is poor, so it can't be decoded. https://forum.tvfool.com/attachment....1&d=1505140865 The antenna was moved to another location, and the signal was picked up during a scan and could be decoded: https://forum.tvfool.com/attachment....1&d=1505140865 |
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Note that a good number of the stations that the report says SHOULD be receivable are NOT (especially those from NYC and Albany). As I indicated, East is the only direction that I get decent signals from. Too many mountains to the south and north. I've even tuned in some Boston stations a couple of times this summer. I always though ducting was a VHF only phenomena! If I point the UHF antenna to the North, I can just barely receive Ch 22 out of Woodstock. But then I loose everything else. I also thought about adding a rotor, but it looks like most of the decent rotor manufacturers have gone away... Quote:
VHF Hi Antenna ->http://www.mcmelectronics.com/produc...-2475-/30-2475 PreAmp -> http://www.solidsignal.com/pview.asp?p=tvpramp1r The F.S.M. is a Channel Master Model 7275 leftover from my younger days (40+ years ago) as an MATV/CATV tech. Quote:
Thanx for the reply. Richard Rosa |
Thank you for the report. I will study it, get back to you, and try to make some intelligent answers.
The first thing I notice is that you have two signals strong enough to cause preamp and tuner overload (when the antenna is aimed at them) which would produce spurious signals from IMD that would raise the noise floor and wipe out your weaker signals. It sounds like you have picked the best location possible for your antenna. Quote:
http://www.eham.net/reviews/products/24 |
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I looked at the link to your equipment. Nice meter! I'm sure it is out of my price range, but just for curiosity, what does a device like that run these days? Rich |
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Sadelco is now out of business, but their repair facility still sells refurbished meters. Sadelco made meters for CM.
http://www.sadelco.com/ http://www.rcbcal.com/home.html My Sadelco 719E was about $600 when I retired in 1988. It was designed for analog signals, but I found it very useful for digital signals. The DisplayMax800 and DisplayMax 5000 ran about $1000. My wife gave the last 2 to me as a present. She tolerated my antenna experiments because she wanted a battery operated TV for use during power failures. The 719E on the left, 800 on the right. http://forum.tvfool.com/attachment.p...1&d=1440873529 http://forum.tvfool.com/attachment.p...1&d=1476983108 DM5000 in use; Sony KDL22L5000. Disabled 1/10 dB for photo. http://forum.tvfool.com/attachment.p...1&d=1476983108 My Sony KDL32R400A has a Diagnostics Screen that gives signal strength numbers in one dB steps, so I got a TV and an SLM for the same price as a TV. Here is the calibration chart I made: http://forum.tvfool.com/attachment.p...6&d=1474737062 I have bought used meters on ebay, but only bought ones that I was willing to lose my investment or ones that had a return policy. I was thinking of buying this less expensive meter from Solid Signal: http://www.solidsignal.com/pview.asp?p=digiair-pro-atsc Old FSMs gave a reading in microvolts: http://i.imgur.com/ch7LDqQ.jpg Old chart that might be of interest to you: http://forum.tvfool.com/attachment.p...7&d=1429489375 |
Signal Meter
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Way more money than is in the budget. The meter S.S. has is also a bit beyond my means. If I was still doing this for a living (or I win the lottery), then I could justify it to the boss :-) However, thank you for the info. Something to dream about... That chart you posted brought back some memories. 0 dbmv was the holy grail of signal levels. "Amplify if lower, pad if higher." I used to understand Radio/TV when analogue ruled. Digital seems to have changed the laws of physics :-) If I did this correctly, a photo of my meter is attached. Rich |
Thanks for the photo of your FSM. I am always interested in old meters. If your meter still works, it is entirely adequate for your needs.
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http://forum.tvfool.com/attachment.p...7&d=1465958114 Quote:
http://www.tvfool.com/?option=com_wr...dALLTV%26n%3d4 http://www.rabbitears.info/market.ph...&callsign=wnyw click on technical data http://www.rabbitears.info/tvq.php?r...ms&facid=22206 |
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What is happening is the difference between the strongest channels and the weakest channels is too great. This is called the dynamic range. If you need a preamp for the weakest channels, but a preamp will be overloaded by the strongest channels, then the dynamic range is too great. You don't have just one very strong channel, you have two; that's what it takes to create IMD (Intermodulation Distortion) which produces spurious signals that come up from the noise floor and reduce the SNR of your weakest to below 15 dB making them impossible to decode. You are also creating fundamental overload that produces gain compression and harmonic distortion. http://forum.tvfool.com/attachment.p...1&d=1485121101 The Dynamic Range is measured from the top of the weakest desired signal to the top of strongest signal. The SFDR is the Dynamic Range plus the minimum required 16 dB SNR of the weakest required signal to keep the spurious signals ("spurs") below the noise floor of the weakest desired signal. WRNN has a Noise Margin of 68.5 dB. If you add a conservative antenna gain of 14 dB, that brings you up to 82.5 dB, which is overload territory even before adding preamp gain. http://www.avsforum.com/forum/attach...7&d=1444785797 Interpreting Noise Margin in the TV Fool Report http://www.aa6g.org/DTV/Reception/tvfool_nm.html Looking at it in terms of signal strength (power) WRNN has a signal power of -22.3 dBm. -22.3 dBm + 14 dB ant gain + 22 dB preamp = +13.7 dBm; tuner overload ATSC Recommended Practice: Receiver Performance Guidelines Document A/74:2010, 7 April 2010 RECEIVER PERFORMANCE GUIDELINES 5.1 Sensitivity Quote:
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http://www.fmfool.com/modeling/tmp/2...b/Radar-FM.png You can do your own FM report here: http://www.fmfool.com/index.php?opti...pper&Itemid=29 |
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There ARE some trees to the North & South edge BUT I have a pretty clear shot in the direction of the transmitters. Might be FM, as WPDH is also L.O.S. to Illinois Mt. and puts out a pretty hefty signal. I think I may have an extra FM filter in my junk box. I'll give that a try. Quote:
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Two mysteries solved. I probably will not be able to fix the issues, but at least my curiosity has been satiated. Any ideas on why Ch 33 fades in the daytime? Thanx again Rich |
It sounds like your reception of Ch 33 is dependent upon a temperature inversion bending the signal back to earth. In some areas it is quite common for slight temperature inversions that enhance VHF/UHF signal propagation to form on an almost daily basis right after sunset, and last through mid morning. I think this site explains it better then I can.
http://www.dxinfocentre.com/propagation/tr-modes.htm Scroll down to Tropospheric Enhancement (TrE). This quite common in my area, but Tropospheric Ducting (TrD) is very rare in this part of the country. |
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This is one of the many things that drives me CRAZY about digital. Back in analogue days, intermod/crossmod was always observable, and you knew what was going on. Now all you get is "No Signal" (which is a LIE). Without a good spectrum analyser you cannot tell what is happening. Thanx again.. Rich |
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Thanx! Richard Rosa |
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RF Steve is correct about the temperature differential making reception at night possible.
http://www.mike-willis.com/Tutorial/PF6.htm http://www.dxfm.com/content/propagation.htm This is the terrain profile for WFSB shown by tvfool: http://www.tvfool.com/?option=com_wr...ALLTV%26n%3d20 This is the WFSB terrain profile using different software: http://forum.tvfool.com/attachment.p...1&d=1477094309 The path for the WVIT signal is a lot easier. Note that the WVIT transmitting antenna is much higher than the WFSB transmitting antenna. http://forum.tvfool.com/attachment.p...1&d=1477095870 Here is a coverage map for WFSB; you are on the extreme fringe: http://forum.tvfool.com/attachment.p...1&d=1477097217 And a closeup: http://forum.tvfool.com/attachment.p...1&d=1477097217 Another problem with WFSB is that it has co-channel interference from WCBS on the same channel. WFSB needs to be at least 16 dB stronger than WCBS for reception. Since it is in a different direction, the antenna pattern helps to make WCBS weaker. |
WFSB has a Noise Margin of -13 dB, which is only 2 dB above the thermal noise floor at -15 dB NM. It is difficult to receive any channel with a NM less than -10 dB. If you are able to receive a channel with a listed NM of less than -10 dB, you have an excellent antenna system, your tvfool report is wrong, or they have been enhanced by Tropospheric Propagation.
https://forum.tvfool.com/attachment....1&d=1505095023 |
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http://forum.tvfool.com/attachment.p...1&d=1477099490 http://www.antenne-komponenty.eu/eng...zlucovace.html |
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If you want to experiment with another antenna for WFSB, I suggest the Antennas Direct 91XG or the Solid Signal HDB91X. They both have a tilt feature that allows you to tilt the front of the antenna up to capture the signal coming down from the crest of a hill. I have received several reports that it made reception possible, which otherwise was impossible.
http://forum.tvfool.com/attachment.p...1&d=1477100644 http://forum.tvfool.com/attachment.p...1&d=1477100644 |
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Thanx for all the technical info. I gotta be more diligent on web-page link clicking. Didn't realize that terrain maps were available. I DID find the coverage maps, but they didn't always agree with what I was receiving . As per co-channel on WFSB: If I COULD get WCBS out of NYC, that would be great, but I haven't been able to pull ANY signal at all from the south. When I was setting up these antennas, I tried pointing the antennas in the southerly direction, and got NO discernible signal on channel 33, or any other NYC channel. Point it east (at least in the morning), and WFSB came in strong. To my south are hills, mountains and neighbour’s houses, all quite higher than my mast. The VHF antenna I have also has a 'tilt' adjuster. I didn't bother with it, as I figured it might cause polarization issues, but maybe I'll give that a shot (next spring). BTW, I DID try adding an extra FM Trap in-line with the VHF antenna, but didn't seem to make any difference for Ch 10 reception. I've convinced the boss that I need better test equipment, so I have her 'permission' to purchase a more state-of-the art signal meter. The one you recommended from Solid Signal is what I will probably go with. Looks like it has a decent spectrum display, which is what appears to be essential for DTV. Come warmer weather (I don't work on the roof in the cold), I will use it to plot a possible better location for the antennas. Thank you again for all the help and information. Rich |
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The sudden drop off at the digital cliff is caused by the FEC, Forward Error Correction. The tuner is able to correct digital errors up to a certain point. When that limit is exceeded, the remaining errors are uncorrected and we reach the digital cliff with pixelation, picture freeze, and finally dropout. http://forum.tvfool.com/attachment.p...1&d=1477146981 Many people asked me how can we tell if a signal is there when the tuner doesn't pick it up? As you said, a spectrum analyzer is the ideal tool, but they are expensive. I found that even an old analog meter will do the job. I can turn on the audio and listen for the digital signal as I watch the needle on the panel meter. The digital signal is actually an analog AM signal that carries the digital information. It sounds like white noise, and I listen for an increase in noise above the noise floor. I don't have any experience with the Solid Signal meter, and I am not certain that it will help you any more than your present meter, but it is able to measure signal quality in addition to signal strength. In the UK a CAI (Certified Aerial Installer) is required to measure signal strength AND signal quality. The customer reviews on Amazon look OK and this review was done for SS: http://forums.solidsignal.com/conten...ctrum-Analyzer this is the manual from the manufacturer's site <www.emitor.se> http://www.emitor.se/index_htm_files...2013_2_ENG.pdf |
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