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nkirkley 28-Jun-2015 10:30 PM

Charlotte North Carolina questions
 
4 Attachment(s)
I was wondering if anyone might be able to help me with my OTA reception. I currently have the older DB8 (without the ability to aim in two directions). I will attach pictures of my setup.
My question(s) arenít necessarily about having issues receiving, but, maximizing reception. I want as much as I can pull in, especially WXII, WSPA, WIS, and possibly a few others from far away. Currently, I receive all the channels in Charlotte and a good portion of those in Winston-Salem-Greensboro-High Point area. I would like very much to pull in WXII from that market. I have at times, but it is VERY inconsistent.
Lastly, I would like to tap into the Spartanburg area and possibly grab channel 7 (WSPA) and channel 10 in Columbia. Oddly enough, as a kid, we used to be able to pick them up at Lake Norman. They would always show different NFL games as the CBS or NBC affiliates in Charlotte. So, in light of that, it would be nice to get that again. Now, I do realize that the DB8 is not the type of antenna to receive these channels as they are VHF, but, would it be worth mounting a VHF antenna above the DB8 and pointing it in between the two markets? I do have a rotor, so, if need be I could always rotate for a tighter signal. Also, I could raise the antenna a few feet if necessary, as long as it stays below 12 feet above the roof line. I believe that's my FCC limit, after that the HOA might start complaining.
My set up is as follows, DB8 antenna, amp (pictured), RCA rotor. Also posted is my signal report link. If anyone has any suggestions, it would be greatly appreciated.
http://www.tvfool.com/?option=com_wr...82303479b5b3c3

rabbit73 30-Jun-2015 12:08 AM

1 Attachment(s)
Welcome to the forum, nkirkley:

It looks like a lot of people have viewed your thread, but no replies. You are lucky to have so many good signals, but I understand your desire to have a few more. What you want is not going to be easy, but I'll give you my analysis for what it's worth over a few posts as I think it through.

I will try to identify the problems that you will face, some of which you are already aware of.

It's good that you have the older DB8. The older bowtie antennas used a ferrite core balun which is good for VHF and UHF, so you shouldn't have any trouble receiving WTVI on real channel 11. The newer bowtie antennas use a printed circuit board balun that doesn't pass VHF very well.

Quote:

I want as much as I can pull in, especially WXII, WSPA, WIS, and possibly a few others from far away.
The way you have listed them is by increasing difficulty.

WXII, NBC, real channel 31, NM 11.6 dB, 2Edge path, 79.3 mi, 19 degrees magnetic; this is your best one of the three. You might be able to get it with what you have, but the curvature of the earth starts to interfere with signals at about 70 miles. You can see the transmitter terrain profile by clicking on a callsign in your tvfool report. The transmitter is at the left end, your location at the right.

WSPA, CBS, real channel 7, NM -3.3 dB, 2Edge path, 93.4 mi, 275 degrees magnetic; this will be more difficult not only because of the curvature of the earth, but because of the pine trees that are taller than your antenna, unless you can aim between them.

You need a VHF-High antenna for WSPA, but they are now in short supply. You would have to settle for a VHF/UHF combo like the Winegard HD7697/7698P, a DIY antenna, or something like the Ability Fracarro BLV6F VHF-HI (CH7-13) High Gain Wideband YAGI Antenna.
http://www.abilityhdtv.com/product-i...nna-pid65.html

WIS, NBC, real channel 10, NM -12.1 dB, Tropo path, 77.5 mi, 192 degrees magnetic; not much hope for this one. Tropo signals are unreliable, and WIS has adjacent channel interference from WTVI on real channel 11 that is 72.1 dB stronger.

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010

RECEIVER PERFORMANCE GUIDELINES

5.4.2 Adjacent Channel Rejection

Quote:

The receiver should meet or exceed the thresholds given in Table 5.2 for rejection of first adjacent-channel interference at the desired signal levels shown above the columns therein.
http://forum.tvfool.com/attachment.p...1&d=1435623055

ADTech 30-Jun-2015 12:18 AM

The ferrite core balun DB8 was last manufactured in 2008. It was no better on VHF than was its replacement with the PCB balun and combiner. They're UHF antenna designs, never actually intended for VHF reception.

nkirkley 30-Jun-2015 12:54 AM

I have been reading different threads on this board and was really hoping you guys (Rabbit and Adtech) would jump in on mine. Thanks for your replies. Yes, I get WTVI very well, and in most respects, I get plenty of channels. Last count, 51. However, I guess I am being greedy and hope to squeeze just a few more in. I think Charlotte can be in an optimal spot to get stations from other cities. I know growing up, on old analog, we could pull in stations from Asheville, Spartenburg, Greensoboro, and Columbia on occasion. With digital, I was hoping to do it all over again, except this time, without all the snow.

Any advice or pointers would be greatly appreciated!!!

rabbit73 30-Jun-2015 1:19 AM

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It was the snow that made it possible to get the analog channels. Analog signals fade out gradually because we can tolerate a little snow, but digital signals suddenly drop out at the "Digital Cliff," when the increasing errors are more than the FEC (Forward Error Correction) can correct.

http://forum.tvfool.com/attachment.p...1&d=1435623949

rabbit73 30-Jun-2015 1:45 AM

3 Attachment(s)
There are two obvious problems that I see. The first one is your very strong signals. WSOC has a Noise Margin of 75.0 dB even before adding your antenna gain and distribution amp gain.

http://forum.tvfool.com/attachment.p...1&d=1435624961

Interpreting Noise Margin in the TV Fool Report

http://www.aa6g.org/DTV/Reception/tvfool_nm.html

Very strong signals can create spurious signals from IMD (Intermodulation Distortion) in a tuner or amp that will wipe out weak signals. More details about overload if you ask me.

The second obvious problem is from your very strong local FM signals that can interfere with TV reception. You need an FM filter or 2 in series.

http://forum.tvfool.com/attachment.p...1&d=1435626070

You can see that the WXII signal barely makes it to your location:

http://forum.tvfool.com/attachment.p...1&d=1435627349

color code here:
http://www.tvfool.com/index.php?opti...id=15&Itemid=1

nkirkley 30-Jun-2015 2:14 AM

Wsoc
 
You are right, WSOC is very close by. Signal is so strong it pixelates at times, Not sure what do do about that. If I disconnect amp, then I will lose the other stations from out of town. Tell me about the FM filter and where I would put one?

nkirkley 30-Jun-2015 2:26 AM

Also, please tell me a little bit about overload and how I can tune down WSOC but keep the other channels. Thanks!

rabbit73 30-Jun-2015 2:31 AM

I added another image to my previous post showing WXII signal coverage.

I have to take my wife to the doctor tomorrow morning. More posts when I have time.

ADTech 30-Jun-2015 2:52 AM

Actual signal powers from the nearby UHF stations will be anywhere from 10-25 dB below the power predicted due to the receiving location being well below the main lobe of the UHF transmitting antennas. VHF channels and FM will be much closer to predicted levels as they use lower gain antennas with more signal directed towards the ground in the near area. Keep in mind that TVFool does not use any data (if it was even available) regarding the vertical transmitting pattern as most of that data is not in the FCC database.

Quote:

You are right, WSOC is very close by. Signal is so strong it pixelates at times
Add a small amount of attenuation at the input to your amp. You'll have to balance the strong signals with the weak, you likely won't be able to balance it perfectly as the power differential between the strong and weak is too great.

rabbit73 30-Jun-2015 11:13 AM

Before I go any further:

How long is the coax from the antenna to the CM3414 distribution amp?

(I really hate the new black labels on the CM34xx series of amps. Before PCT International bought out Channel Master, the labels were white and a little difficult to read. The new black labels are nearly impossible to read.)

Have you grounded the coax with a grounding block?

The coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge, but the system will not survive a direct strike.

I have three concerns about grounding the coax and mast:

1. For your personal electrical safety, grounding the coax will drain any leakage current from your connected AC operated equipment to protect you from shock. All AC operated equipment has leakage current, even when it is operating properly. Just because you can't feel it doesn't mean it isn't there. If your equipment becomes defective, you will be protected from shock.

2. Grounding the mast will drain any buildup of static charge to reduce the chance of a lightning strike.

3. Grounding the coax will provide a continuous shield from antenna to tuner that will reject interference. This will keep strong signals from getting directly into the TV set and make FM filters and attenuators more effective.

rabbit73 30-Jun-2015 11:56 AM

3 Attachment(s)
Quote:

Tell me about the FM filter and where I would put one?
Since you don't have a preamp (I hope) at the antenna, you can put the FM filter, or two in series for extreme cases, just before the CM distribution amp. All FM filters are not equal, so I needed to look at the frequencies of your strongest signals. This filter would be suitable:
http://www.mcmelectronics.com/produc...-FM-88-/33-341

http://forum.tvfool.com/attachment.p...1&d=1435663742

Antennas Direct makes one, but it's not quite as good at the high end for WKQC 104.7.
https://www.antennasdirect.com/store...on_filter.html

Radio Shack also makes one, but it will not reject the signals at the low end of the FM band effectively (WFAE 90.7).

http://forum.tvfool.com/attachment.p...1&d=1435662622

You can, instead, use a HLSJ to block all signals below channel 7, including the FM band. Use the common and high ports.
http://www.solidsignal.com/pview.asp?p=zhlsj

http://forum.tvfool.com/attachment.p...1&d=1435662850

nkirkley 30-Jun-2015 12:33 PM

Rabbit, I had an antenna guy install the antenna, but, I really don't know what he did as far as grounding. I would have to call him to find out. I am about positive, though, he did not ground anything to the house's electrical box.

I will definitely get the FM filter and give that a shot. That might be just enough to pull in WXII. I viewed your map and you are correct, that signal, if there is one at all, barely gets to my location. I guess that since I have tuned it in from time to time that I thought I might be able to grab it more reliably or frequently if I did a few changes to the antenna, such as raise the antenna.

I will definitely keep you guys posted on what results I do get with the FM filter.

Quick question about radio. When I bought this house, I hooked up an antenna, just something basic, to my stereo to listen to FM. My station was WRFX 99.7. Even though it is only 4.2 miles away, reception was not that great. Is this another example of overloading? Also, for some strange reason, that station would also come in on 95.7, blocking out the actual station WXRC. I thought it was really wierd. Anyhow, I gave up on FM radio. The playlist for that station hasn't changed in over 2 years so it got boring. ;)

rabbit73 30-Jun-2015 12:43 PM

Quote:

You are right, WSOC is very close by. Signal is so strong it pixelates at times, Not sure what do about that. If I disconnect amp, then I will lose the other stations from out of town.
Quote:

Also, please tell me a little bit about overload and how I can tune down WSOC but keep the other channels.
ADTech has it right; it's a balancing act because of the great difference in strength between your strongest signals and your weakest desired signals:
Quote:

Add a small amount of attenuation at the input to your amp. You'll have to balance the strong signals with the weak, you likely won't be able to balance it perfectly as the power differential between the strong and weak is too great.
More details later when I have the time.

nkirkley 30-Jun-2015 12:51 PM

I have one more question for you guys right now and it has nothing at all to do with my original question. When I was a kid, when we would go to my aunt and uncles house, we would cross a particular railroad track on the drive. If you looked down the path you could see a very tall, probably two or three hundred feet off the ground, TV antenna that my dad said Cablevision (now Time Warner) used to pick up some of their stations. Like I said, I was a kid, so, we are talking late '70's. Anyhow, I remember at that time, cable offered WSPA and channel 20 out of Washington DC (don't remember their call letters). Anyhow, would a tower that tall actually pick up signals that far way from Charlotte. I know curvature of the earth is a big issue on signal, but, I also know the higher you go the more you can compensate for it.

ADTech 30-Jun-2015 1:18 PM

Quote:

Is this another example of overloading?
Probably. Either that or the extremely strong signals were getting directly into the receiver's circuitry (ingress) and causing the image frequency reception. This is common on inexpensive receives that lack proper internal shielding.

You can also try an attenuator at the input to the receiver and see if the signal via the normal input can be cooled off, just like for the TV receiver.

rabbit73 30-Jun-2015 1:59 PM

2 Attachment(s)
Quote:

Rabbit, I had an antenna guy install the antenna, but, I really don't know what he did as far as grounding. I would have to call him to find out. I am about positive, though, he did not ground anything to the house's electrical box.
Here are two grounding diagrams:

http://forum.tvfool.com/attachment.p...1&d=1435669013

http://forum.tvfool.com/attachment.p...1&d=1435669787

According to Article 810, the last time I checked, the mast can be grounded with 10 gauge copper or 17 gauge copper-clad steel. However, the coax grounding block must be connected to the house electrical system ground with 10 gauge copper wire.

If you use a separate ground for the mast, it must be bonded to the house electrical system ground with 6 gauge copper wire.

rabbit73 30-Jun-2015 2:24 PM

Quote:

Quick question about radio. When I bought this house, I hooked up an antenna, just something basic, to my stereo to listen to FM. My station was WRFX 99.7. Even though it is only 4.2 miles away, reception was not that great. Is this another example of overloading? Also, for some strange reason, that station would also come in on 95.7, blocking out the actual station WXRC. I thought it was really wierd. Anyhow, I gave up on FM radio. The playlist for that station hasn't changed in over 2 years so it got boring.
Could be multipath reflections, or more likely overload causing image signals that aren't really transmitted, just created in your FM tuner.

rabbit73 30-Jun-2015 2:28 PM

1 Attachment(s)
Quote:

If you looked down the path you could see a very tall, probably two or three hundred feet off the ground, TV antenna that my dad said Cablevision (now Time Warner) used to pick up some of their stations. Like I said, I was a kid, so, we are talking late '70's. Anyhow, I remember at that time, cable offered WSPA and channel 20 out of Washington DC (don't remember their call letters). Anyhow, would a tower that tall actually pick up signals that far way from Charlotte.
Yes, that's the way it was done then.

http://forum.tvfool.com/attachment.p...1&d=1435670914

rabbit73 30-Jun-2015 3:13 PM

1 Attachment(s)
And now, after two detours, back to overload.

Earlier, I showed you that your signals were in overload territory as far as the Noise Margin figures were concerned. I now want you to concentrate on the Pwr (dBm) column of your tvfool report. WSOC has a signal strength (actually signal power because it's dB) of -15.9 dBm. WCCB isn't far behind with -16.5 dBm. If you add the average gain of 12 dBd for the DB8, that brings you up to -3.9 dBm. If you then add the gain of 8 dB for the 3414 and subtract 4 dB for cable loss, you are now at +0.1 dBm. Your tuners will not like that.

ATSC Recommended Practice:
Receiver Performance Guidelines


Document A/74:2010, 7 April 2010

RECEIVER PERFORMANCE GUIDELINES

5.1 Sensitivity


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.

And with two very strong signals it's even worse:

5.2 Multi-Signal Overload

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.

You are now 8 dB stronger than the allowed signal power.

THREE TYPES OF OVERLOAD

There are three types of preamp or tuner overload, in order of increasing signal strength:

1. The strong signals almost cause enough intermodulation distortion (IMD) to interfere with the reception of weak desired signals, but the spurious signals are at or below the noise floor of the weak signals. This is the point that holl_ands uses in his preamp charts to obtain max SFDR (Spurious Free Dynamic Range). No damage will happen.

As the strongest signals continue to increase in strength, more of the weaker signals are damaged until you reach:

2. The strong signals cause overload to the preamp or tuner that makes it impossible to receive any signals. No damage will happen. The strongest signals are still there, but they can't be decoded because the IMD products have damaged them so that they contain more errors (high BER....bit error ratio/rate) than can be corrected by the FEC (forward error correction).

3. The signals are so strong that the input transistor is toast. You are not likely to encounter OTA signals that strong, unless you live next door to a high power transmitter and you have your high gain antenna aimed at the transmitter's antenna.

As a general rule, tuners can tolerate stronger signals than preamps before overload. The difference in strength is approx. equal to the preamp gain.

Forum member holl_ands (who is a communications engineer) has made a preamp chart that shows the maximum input signal for preamps. Many of the preamps are no longer available, but it gives you the general idea.

http://imageevent.com/holl_ands/file...=0&w=1&s=0&z=4

Intermodulation Distortion

The IMD creates new spurious signals within the preamp (or tuner) itself that can interfere with the reception of your weakest desired signals if the spurious signals are stronger than the noise floor of the weakest desired signals. The spurious signals are caused by the interaction between two or more of your strongest signals.

IMD is not the only distortion that can be created within the preamp; you can also have distortion caused by signals so strong that the top of the strong signals are clipped, which causes compression of the signals. This can be seen if you increase the input to the preamp by, for example, 10 dB and the output increases by less than 10 dB.

Spurious Free Dynamic Range

The Spurious Free Dynamic Range needed is the difference in strength between your strongest signal and your weakest desired signal, plus 16 dB for the SNR (Signal to Noise Ratio) of the weakest signal, using the dBm Pwr scale on your tvfool report. This difference is expressed in terms of dB, not dBm, because the original units are the same. The difference between the strongest signal and the weakest signal is the Signal Dynamic Range/Dynamic Range, which is 16 db less than the SFDR, because it doesn't include the SNR of the weakest signal.

http://forum.tvfool.com/attachment.p...1&d=1435674837

Another way to think of SFDR is from the top of the strongest signal down to the bottom (noise floor) of the weakest desired signal. The top of the spurious signals must be at or below the noise floor of the weak signals if they are not to cause interference. The Signal Dynamic Range is from the top of the strongest signal down to the top of the weakest desired signal.

You can also use the NM scale for your calculations, but I prefer to use the Pwr scale because most tuners drop out around -85 dBm.

Continued on page 2 of this thread.

rabbit73 30-Jun-2015 3:50 PM

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What can be done:

http://www.tvfool.com/?option=com_wr...82303479b5b3c3

The strength of WSOC is -15.9 dBm, and WXII is -79.3 dBm, for a dynamic range of 63.4 dB, and for a required SFDR of 79.4 dB. That's a big dynamic range to deal with, especially since WXII is a 2Edge signal.

If you don't have enough gain for your weak desired signals without a preamp, and you have too much gain with a preamp, you can insert an attenuator between the antenna and the amp input to try for a happy medium. The cable between the antenna and the amp is providing some attenuation, but it is not enough. The attenuator will not only optimize your SFDR, if possible, but also reduce the strength of your strongest signals. You can use a variable attenuator before your amp for testing and then replace it with fixed attenuators of equivalent value.

https://www.antennasdirect.com/store...ttenuator.html

http://mjsales.net/products/fam-atte...ant=1083705673
•Attenuation values 1, 3, 6, 8, 10, 12, 16, 20dB (FAM)
The up and down arrow for different values is faint; you can click on 1 dB to see other values.

As you increase the attenuation it will tame your strongest signals that are causing overload, but it will also make your weak signals even weaker. You might think it is counterintuitive to add an amp to make the signals stronger, and then insert an attenuator to make them weaker. The advantage is that for every 1 dB of attenuation, the IMD spurious signals are made 3 dB weaker, so there is a net payoff of 2 dB SNR (Signal to Noise Ratio) improvement for every dB of attenuation. If you insert a 6 dB attenuator, you get a 12 dB improvement in SNR.

http://forum.tvfool.com/attachment.p...1&d=1435683995

If you want to read more about my preamp overload tests and the attenuator technique:

Preamp Overload Test 3

http://www.digitalhome.ca/forum/1597002-post3490.html

I have received a lot of positive feedback from people who have tried the attenuator technique and it worked for them; I have received negative feedback from people who thought it wouldn't work but never tried it.:)

If you are unable to tame your strongest signals without damaging your weakest desired signals, it means the required SFDR is too great for the attenuator technique. You are then left with exotic (expensive) solutions like a separate antenna, preamp, and single channel custom bandpass filter for the required real channel number of the weak signal from Tin Lee. If you only have one strong signal causing trouble, you can order a custom single channel bandstop filter to tame that single channel, so you will only need one antenna.
http://www.tinlee.com/index.php
http://www.tinlee.com/bandpass_filters.php?active=1
http://www.tinlee.com/CATV-ChannelEl...e.php?active=1


nkirkley:

Please let us know the results of your tests on this same thread.

Best regards,
rabbit

nkirkley 1-Jul-2015 7:24 PM

Thanks for all your suggestions! I will definitely try the FM filter first!

nkirkley 25-Jul-2015 4:24 PM

Hello Rabbit! I have finally ordered an FM trap and the attenuator. I would have done it sooner, but, went on vacation. Anyhow, once I receive these I assume the plug in would be this. Coax from antenna to FM Trap, then coax to attenuator, then coax from attenuator to amp (splitter). Is this a correct guess? Thanks.

rabbit73 25-Jul-2015 6:35 PM

That is correct. Good luck!

nkirkley 25-Jul-2015 7:58 PM

Thanks
 
Thanks! I will let you know what happens!

nkirkley 6-Aug-2015 9:10 PM

FM Filter
 
Just a follow-up. Neither the FM filter nor the attenuator helped me pull in any more channels. Oh well, it was worth playing around with.

However, with the attenuator, like a splitter, it has two ends to connect coax. Does it matter which connector comes from the antenna and which goes to the amp?

ADTech 6-Aug-2015 9:18 PM

Quote:

Does it matter which connector comes from the antenna and which goes to the amp?
Nope. The attenuator doesn't care.

rabbit73 7-Aug-2015 12:05 AM

Quote:

Just a follow-up. Neither the FM filter nor the attenuator helped me pull in any more channels. Oh well, it was worth playing around with.
Sorry that they didn't help; it was worth a try. You need the attenuator AND the FM filter at the same time.

What attenuator did you use? How much attenuation did you try?

If you keep adding attenuation up to the point that the weak signal is gone, then the dynamic range (the difference between the strongest and weakest signal) is too great for this technique.

Was the coax grounded? If yes, how? If not, the test isn't valid.

nkirkley 10-Aug-2015 4:39 PM

Ging to try again
 
I didn't realize you could fine tune the attenuator. I will give it another shot and get back with you.


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