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Old 20-Oct-2016, 11:39 AM   #1
richardrosa
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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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Old 20-Oct-2016, 12:51 PM   #2
rabbit73
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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:
A dual-4bay UHF, and a High-Band Yagi. Both of which are mounted on a 5' mast on my roof.
What make and models?
Quote:
I have an old, analogue Field Strength Meter that I have been using to adjust the direction of the antennas.
What make and model? I am interested in FSMs and signal level meters (SLMs), and enjoy making measurements as you might notice in my signature.

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.



The antenna was moved to another location, and the signal was picked up during a scan and could be decoded:

Attached Images
File Type: jpg CH42missing_1.jpg (99.6 KB, 963 views)
File Type: jpg CH42Pilot_1.jpg (86.4 KB, 796 views)
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Last edited by rabbit73; 11-Sep-2017 at 2:45 PM.
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Old 20-Oct-2016, 2:40 PM   #3
richardrosa
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Quote:
Originally Posted by rabbit73 View Post

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.
Here you go -> http://www.tvfool.com/?option=com_wr...d6dbf19cecb97a

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:
What make and models?
What make and model? I am interested in FSMs and signal level meters (SLMs), and enjoy making measurements as you might notice in my signature.
UHF antenna ->http://www.solidsignal.com/pview.asp?p=hdb8x
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:
The antenna was moved to another location, and the signal was picked up during a scan and could be decoded:
I don't have a lot of property, or a large house. I did some measurements before selecting the mast location. Where the mast is right now is probably the best overall signals for the 4 reliable channels. There WAS another location on the roof that was slightly better, but WAY too close to the AC service entrance for my comfort.

Thanx for the reply.


Richard Rosa
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Old 20-Oct-2016, 3:14 PM   #4
rabbit73
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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:
I also thought about adding a rotor, but it looks like most of the decent rotor manufacturers have gone away...
Not too many left; the CM9521A is popular, but it doesn't have long-term reliability. You would have to step up to a ham rotator like the Hy-Gain AR40 or Yaesu 450.
http://www.eham.net/reviews/products/24
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Old 20-Oct-2016, 4:11 PM   #5
richardrosa
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Quote:
Originally Posted by rabbit73 View Post
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.
Yeah I though about that. If I could wipe out ch 27 completely that would be great. However, like with most other TV equipment, I cannot seem to find a REASONABLY priced single channel filter. I also don't think that this is the issue with Channel 10.

Quote:
It sounds like you have picked the best location possible for your antenna.
Not too many left; the CM9521A is popular, but it doesn't have long-term reliability. You would have to step up to a ham rotator like the Hy-Gain AR40 or Yaesu 450.
The CM seems to have WAY to many issues. I DON'T want to have to climb back up onto the roof in the dead of winter to fix a bad rotor. The Yaesu looks good, but hard to justify the $$$ to my other half.. This adventure was justified on the basis of cost. If I start spending too much on equipment, she will demand the cable back

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?


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Old 20-Oct-2016, 4:59 PM   #6
rabbit73
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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.





DM5000 in use; Sony KDL22L5000. Disabled 1/10 dB for photo.



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:



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:



Old chart that might be of interest to you:

Attached Images
File Type: jpg Sadelco-DisplayMax_5000-2.jpg (67.6 KB, 1449 views)
File Type: jpg SadelcoDM5000inUse_1.jpg (104.1 KB, 1451 views)
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Old 20-Oct-2016, 7:53 PM   #7
richardrosa
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Signal Meter

Quote:
My Sadelco 719E was about $600 when I retired in 1988.

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
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Old 20-Oct-2016, 8:03 PM   #8
rabbit73
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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.
Quote:
0 dbmv was the holy grail of signal levels.
It pretty much still is for a drop outlet to a TV, but tuners can handle a wide range of signal strength.
Quote:
I used to understand Radio/TV when analogue ruled. Digital seems to have changed the laws of physics :-)
The laws of physics and antennas haven't changed; what has changed is the "Digital Cliff" for digital signals which creates the sudden signal dropout, which is a lot different than increasing snow with weaker analog signals.



Quote:
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.
That is correct; only 0.001 kW (1 watt) out of 1.000 kW (1,000 watts) is sent your way because of the transmitter antenna array.
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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Old 21-Oct-2016, 12:48 AM   #9
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Quote:
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.
How did you bypass the preamp? Did you completely remove it from the circuit?

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.



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.



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:
A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm to –5 dBm for both the VHF and UHF bands.
5.2 Multi-Signal Overload

Quote:
The DTV receiver should accommodate more than one undesired, high-level, NSTC or DTV signal at its input, received from transmission facilities that are in close proximity to one another. For purposes of this guideline, it should be assumed that multiple signals, each approaching –8 dBm, will exist at the input of the receiver.
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Old 21-Oct-2016, 2:02 AM   #10
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Quote:
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.....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.
That is the ch 10 pilot. What are you using as a tunable receiver? Have any trees grown into the signal path. You do have one strong FM signal coming from the south, based on my estimate of your location. The FM filter in the preamp might not be enough.
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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Old 21-Oct-2016, 11:39 AM   #11
richardrosa
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That is the ch 10 pilot. What are you using as a tunable receiver? Have any trees grown into the signal path. You do have one strong FM signal coming from the south, based on my estimate of your location. The FM filter in the preamp might not be enough.
Using a couple of radios. An Icom R7000 and Kenwood TH-F6 (Handy Talky).
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:
How did you bypass the preamp? Did you completely remove it from the circuit?
Yup. With the loss on the wire, I figure it would knock the signal down enough.

Quote:
You don't have just one very strong channel, you have two;
I think you nailed it. Didn't think about that. I would LOVE to remove ch 27 (full time religious station), but I cannot find any reasonably priced, single channel filters. If this was HF, I could probably 'roll-my-own', but I've never been very good at winding coils with any accuracy. I've got a number of pads that WILL knock down everything. The problem is that the CT UHF stations are not strong enough to overcome this. As I indicated, without the preamp, they don't survive the coax losses. If you know of any place that sells inexpensive channel traps, let me know.


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
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Old 21-Oct-2016, 2:57 PM   #12
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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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Old 21-Oct-2016, 3:36 PM   #13
richardrosa
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Originally Posted by rabbit73 View Post

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.

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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Old 21-Oct-2016, 4:17 PM   #14
richardrosa
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Originally Posted by RF Steve View Post
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.
It SOUNDS a bit like 'enhancement' although why only this station is puzzling. The transmitter is about a mile away from two other stations that are 'rock-solid' signals all day & night. Add to this, the terrain that the signal is travelling over is quite mountainous. Nevertheless, this is probably the best explanation.

Thanx!

Richard Rosa
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Old 22-Oct-2016, 12:00 AM   #15
rabbit73
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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:



The path for the WVIT signal is a lot easier. Note that the WVIT transmitting antenna is much higher than the WFSB transmitting antenna.



Here is a coverage map for WFSB; you are on the extreme fringe:



And a closeup:



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.
Attached Images
File Type: jpg richardrosaTVFp2WFSB.jpg (133.8 KB, 1288 views)
File Type: jpg richardrosaTVFp2WVIT.JPG (116.2 KB, 1319 views)
File Type: jpg richardrosaTVFcovWFSB.JPG (92.4 KB, 1344 views)
File Type: jpg richardrosaTVFcovWFSBcu.JPG (118.3 KB, 1401 views)
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Last edited by rabbit73; 22-Oct-2016 at 12:58 AM.
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Old 22-Oct-2016, 1:07 AM   #16
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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.

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Old 22-Oct-2016, 1:25 AM   #17
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Originally Posted by richardrosa View Post
I would LOVE to remove ch 27 (full time religious station), but I cannot find any reasonably priced, single channel filters.
Jan Jenca, in Slovakia, sells custom notch, bandstop and other filters on ebay that are a lot less expensive than custom filters sold by Tin Lee Electronics.



http://www.antenne-komponenty.eu/eng...zlucovace.html
Attached Images
File Type: jpg Jan Jenca Notch Filter_1.jpg (31.4 KB, 2336 views)
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Old 22-Oct-2016, 1:38 AM   #18
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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.



Attached Images
File Type: jpg HDB91XtiltadjRev.jpg (64.6 KB, 1439 views)
File Type: jpg HDB91Xtiltbracket2.jpg (59.1 KB, 1272 views)
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Old 22-Oct-2016, 2:22 PM   #19
richardrosa
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Originally Posted by rabbit73 View Post
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.

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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Old 22-Oct-2016, 2:37 PM   #20
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Quote:
Originally Posted by richardrosa View Post
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.
Yes, the sudden loss of the digital signal at the Digital Cliff makes it difficult to solve reception problems. With analog, we had a rough idea of the strength of the signal by how snowy it was. With digital, we don't know if it is even there, much less how strong it is, when the tuner can't pick it up during a scan.

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.



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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Last edited by rabbit73; 22-Oct-2016 at 3:43 PM.
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