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Old 4-Nov-2014, 8:05 AM   #41
rabbit73
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I want to now address your original concern about damage from overload:

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 IM distortion to interfere with the reception of weak desired signals, but the spurious signals are at or below the noise floor. 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 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.

You will find the preamp chart by holl_ands here:
http://imageevent.com/holl_ands/files/ota

Scroll down to Modified solid signal Chart Comparing Preamps - RevB
It doesn't list all amps, but it gives you the general idea.

He also has a DTV Preamp Signal Overload Calculator - Rev M that calculates Max Input Signal to Maximize SFDR (Spurious Free Dynamic Range).

There is also a system noise figure chart.

Last edited by rabbit73; 4-Nov-2014 at 8:44 PM.
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Old 5-Nov-2014, 2:17 AM   #42
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And now to put some of your numbers into an estimate, I will use the guidelines from ATSC A/74:

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010
http://www.atsc.org/cms/standards/a_74-2010.pdf

5 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.
and from ADTech:
http://forum.tvfool.com/showpost.php...3&postcount=31
Quote:
I think he's fine as long as he doesn't amplify the C2V's output. If we accept the simulator's estimate of about -25 dBm at the antenna, add in 8 dB for antenna gain, subtract 1-2 dB for the insertion loss of both the AC7 and integrated U/V combiner, subtract 3 dB of coax loss (about 50'), and subtract the Roamio's tuner noise figure (??), we're still well under -20 dBm signal power at the inputs to the individual tuners which would be expected to tolerate maximum signals up to nearly 0 dBm.
As you can see, ATSC says that a tuner should be able to handle a signal as strong as -5 dBm and provide satisfactory reception. ADTech has calculated that the signal into your Roamio is under -20 dBm, which is 15 dB weaker.

for more than one signal ATSC says:

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.
Your signal is also weaker than that.

In my previous post about THREE TYPES OF OVERLOAD, a -5 dBm signal would fall between type 1 and type 2 overload, but closer to type 2.

When I was experimenting with my Apex DT502 digital to analog converter box just after it came out, I connected two preamps in series between the antenna and the Apex. When I looked at the monitor, there was no signal on the screen. At that time I didn't know as much about overload as I do now, so I didn't understand what was wrong. It was type 2 overload causing complete loss of reception.

The signal from the antenna was +20 dBmV, which is the way my SLM (signal level meter) measures signals, or equal to -28.8 dBm. The gain of the first preamp was 25 dB, which brings us up to -3.8 dBm. The second preamp gain was 15 dB, which is +11.2 dBm into the tuner. The tuner was not damaged. I haven't tried type 3 overload because I don't want a toasted tuner.

My newest TV is a SONY KDL32R400A. Using a splitter to send a signal to the TV and my SLM, I measured the signal level at 100 on the Diagnostics Screen signal strength scale and it was +40 dBmV, which is equal to -8.8 dBm. The engineer who designed the circuit must have been reading ASTC A/74.

In this country engineers use the symbol dBm for signal power; antenna installers and cable guys use dBmV. Other countries use dBμV (note the little tail on the u which means "micro"), which is dB microvolts. It's also signal power but its reference level is defined in microvolts. The conversion factor between dBmV and dBμV is 60, so 40 dBmV is equal to 100 dBμV, which is what the Sony engineer was thinking. 100 on the signal strength scale equals 100 dBμV.....nice!

I then inserted a variable attenuator (using the method described in the link in my signature) and brought the signal level down to dropout, which was about -85 dBm and noticed that the units on the signal strength scale were equal to about 1 dB. So, I was getting a TV and a signal level meter for the price of a TV.

My older SONY KDL22L5000 signal strength reading never gets up to 100 no matter how strong the signal. The reading is derived from the AGC (Automatic Gain Control that controls the sensitivity of the tuner) voltage. The newer SONY must have a different type of circuit, perhaps an RSSI chip like in cell phones which gives you strength in bars.

I had a chance to measure another R400A, and it gave me the same reading at 100 on the signal strength scale.
Attached Images
File Type: jpg SONYSSVSdBmVchart.jpg (59.6 KB, 500 views)
File Type: jpg SONYgoodSIG.jpg (72.9 KB, 363 views)
File Type: jpg SONYbadSIG.jpg (105.4 KB, 409 views)
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Last edited by rabbit73; 6-Nov-2014 at 6:07 AM.
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Old 5-Nov-2014, 5:34 PM   #43
mulliganman
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Quote:
Originally Posted by ADTech View Post

As for the intermittent errors on 10.1 and 33.1 from Fordland, I don't know. Might have been from something as mundane as a burst of noise from a switched device, might have been some wind-induced multipath that the decoder couldn't correct.

It's understandable about not wanting to move the 91XG up to the second floor peak should that be needed, it looks like it would be a very big job.

Swapping the C2V to a more directional 7-51 antenna would likely improve those SNRs, but the replacement antenna would be far larger. TANSTAAFL, you know.

Quad Shield won't make a difference.
I think I'm going to "sit" on this for a little while and observe seeing if I notice any patterns, etc.

While I do that, I would like to know if I decide to try to put the 91XG on the second floor peak what mounting equipment would I need to do that? It seems like when I had run a TV Fool report at different heights that somewhere in the 50 foot range made KRBK line of sight. I'm not sure if the 2nd floor peak meets that requirement or not, but it is still worth a consideration.

I was also wondering what are some of the better 7-51 antennas? I"m not sure I will be going that route but would like to know just in case.

I would also like to say thanks to both of you for your assistance and input to this point. It is greatly appreciated!
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Old 5-Nov-2014, 5:49 PM   #44
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The simulator calculates that the KRBK signal path switches from 1-edge to LOS between 105 and 110'.

However, given that the resolution of the digital elevation model used for the simulator may easily have 5 or meters of vertical error and the cell in which it places each elevation for the complete signal path evaluation is either a 30 or 100 meter square, it's far from a precision calculation.

An LOS signal path is not a requirement for solid reception (but it sure helps) and most people who use antennas rely on paths that calculated to 1-edge or 2-edge paths. The important thing is to get the right antenna into a spot that happens to coincide with a signal that's "good enough". Goldilocks, if you will.
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Last edited by ADTech; 5-Nov-2014 at 5:51 PM.
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Old 6-Nov-2014, 1:37 AM   #45
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Quote:
Originally Posted by ADTech View Post
The simulator calculates that the KRBK signal path switches from 1-edge to LOS between 105 and 110'.

However, given that the resolution of the digital elevation model used for the simulator may easily have 5 or meters of vertical error and the cell in which it places each elevation for the complete signal path evaluation is either a 30 or 100 meter square, it's far from a precision calculation.

An LOS signal path is not a requirement for solid reception (but it sure helps) and most people who use antennas rely on paths that calculated to 1-edge or 2-edge paths. The important thing is to get the right antenna into a spot that happens to coincide with a signal that's "good enough". Goldilocks, if you will.
I think I may have been getting that calculation mixed up with where KRBK is at 1 edge conditions according to the simulator. Are you not thinking that the peak of the 2nd story would be better for KRBK?
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Old 6-Nov-2014, 2:55 AM   #46
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Quote:
I would also like to say thanks to both of you for your assistance and input to this point. It is greatly appreciated!
You are welcome! Glad we were able to make a big improvement in your reception without causing harm to you or your equipment. And, you are getting your money's worth from your AC7 because it is now doing what it is supposed to do.

The computer simulation is not that precise. The results that you are getting in signal strength, errors, and picture quality is what counts.

What does your tvfool report look like with the new coordinates? I think I only have the one you gave in post #2, or did I miss it?

Last edited by rabbit73; 6-Nov-2014 at 7:42 AM. Reason: changed my mind
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Old 7-Nov-2014, 12:20 AM   #47
mulliganman
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Quote:
Originally Posted by rabbit73 View Post
You are welcome! Glad we were able to make a big improvement in your reception without causing harm to you or your equipment. And, you are getting your money's worth from your AC7 because it is now doing what it is supposed to do.

The computer simulation is not that precise. The results that you are getting in signal strength, errors, and picture quality is what counts.

What does your tvfool report look like with the new coordinates? I think I only have the one you gave in post #2, or did I miss it?
The ones I gave ADTech are really about the same. I just wish I could figure out why I am getting the error messages on ABC-KSPR channels. It is my strongest signal. I guess we have concluded the 10-1 is due to VHF being more susceptible to interference...

Last edited by mulliganman; 7-Nov-2014 at 12:29 AM.
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Old 7-Nov-2014, 2:26 AM   #48
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Quote:
I just wish I could figure out why I am getting the error messages on ABC-KSPR channels.
The signal might be too "hot" for the Roamio tuner. A simple test would be to insert a 2-way splitter between the C2V and the input of the AC7, which would attenuate the signals 3.5 dB; two splitters in series or a 4-way splitter would attenuate the signals 7 dB.

If you want some actual fixed attenuators:
http://www.mjsales.net/itemsearch.asp?FamilyID=221

They also have power passing attenuators, but you don't need that kind now.

Quote:
I guess we have concluded the 10-1 is due to VHF being more susceptible to interference...
Yes, electrical interference is greater on VHF. It could also be from multipath reflections coming from other directions because of the simple Vhf antenna. Again from ATSC A/74:



A more directional VHF antenna would reject many of those reflections.

Note from the table that the greater the difference in time between the main signal and the echo (reflection), the weaker the echo must be to not interfere with reception.

How often do you see the uncorrected errors? Once-a-day for a few minutes, or more like almost constantly?

Do you see picture and audio problems on your TV only when you have errors?
Attached Images
File Type: jpg Multipath Echo Table.JPG (33.8 KB, 1043 views)

Last edited by rabbit73; 7-Nov-2014 at 7:59 AM.
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Old 7-Nov-2014, 2:43 AM   #49
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My primary interest is in measuring signal strength and signal quality of DTV signals, so I wanted see what the Roamio Diagnostics Screen looked like.

I downloaded the Roamio user manual, but I didn't seen any screen shots:
http://assets.tivo.com/assets/resour..._19AUG2013.pdf

I then did a Google search:
https://www.google.com/?gws_rd=ssl#q=TiVo+Roamio+SNR

This is for cable, but I think OTA is similar
Troubleshooting Digital Cable Signals (BOLT, Roamio, Premiere, Series3)

Checking signal lock and signal strength

1. Navigate to the Signal Strength-Cable screen:

From TiVo Central > Settings & Messages > Settings > Channels > Signal Strength-Cable

2. Press Select to display the Signal Strength Meter. A warning screen appears, telling you that using the Signal Strength Meter will stop all recordings.

3. Select OK, access this setting. The signals strength meter appears.

Checking the signal quality

1. Tune to a channel that is having a problem.

2. Write down the channel number and then press RECORD to lock the tuner to the channel (Series3 only: If two CableCARDs are installed, this also locks the tuner to the CableCARD).

3. Navigate to the DVR Diagnostics screen:

From TiVo Central > Settings & Messages > Account & System Info > DVR Diagnostics

4. Under Tuner 0, look at the channel number. If the channel listed is not the problem channel, press Chan Down until you see the information for Tuner 1 (if you have a 4- or 6-tuner TiVo DVR, you might need to continue scrolling until you reach the correct tuner for the problem channel).

and found this document from TiVo: (link no longer available, do Google search)
Troubleshooting Digital Cable Signals: Roamio Series, Premiere Series, and Series3 DVRs
http://support.tivo.com/app/answers/detail/a_id/150

It had some images for the Diagnostics Screen. I copied the one for the errors, and edited it to make it a little lighter because the original was too dark:



RS is short for Reed–Solomon:
https://www.google.com/?gws_rd=ssl#q=RS+errors
http://en.wikipedia.org/wiki/Reed%E2...ror_correction
Attached Images
File Type: jpg TiVoHD_Diagnostics_RS_errors (2).jpg (192.8 KB, 1152 views)

Last edited by rabbit73; 18-Mar-2016 at 3:25 PM.
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Old 7-Nov-2014, 2:46 AM   #50
mulliganman
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Quote:
Originally Posted by rabbit73 View Post
The signal might be too "hot" for the Roamio tuner. A simple test would be to insert a 2-way splitter between the C2V and the input of the AC7, which would attenuate the signals 3.5 dB.
Yes, electrical interference is greater on VHF. It could also be from multipath reflections because of the simple V antenna.

How often do you see the uncorrected errors? Once-a-day for a few minutes, or more like almost constantly?

Do you see picture and audio problems on your TV only when you have errors?
If I put the 2 way splitter on the C2V before the AC7 combiner, would I just "cap" the extra out?

I can't say that the errors are there every single time I check. I have been going into the DVR Diagnostics nightly to check. I just noticed tonight the RS Uncorrected is up around 80 or so on 33-1. It isn't a completely unwatchable picture or non-stop picture problem when the errors are there. The best I could describe it is as a lined pixelation cut out that appears on the screen that is quite annoying.

I guess if the splitter doesn't work the only option I would have left would be to replace it with some sort of directional antenna?
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Old 7-Nov-2014, 2:49 AM   #51
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Quote:
Originally Posted by rabbit73 View Post
My primary interest is in measuring signal strength and signal quality of DTV signals, so I wanted see what the Roamio Diagnostics Screen looked like.

I downloaded the Roamio user manual, but I didn't seen any screen shots:
http://assets.tivo.com/assets/resour..._19AUG2013.pdf

I then did a Google search:
https://www.google.com/?gws_rd=ssl#q=TiVo+Roamio+SNR

and found this document from TiVo:
Troubleshooting Digital Cable Signals: Roamio Series, Premiere Series, and Series3 DVRs
http://support.tivo.com/app/answers/detail/a_id/150

It had some images for the Diagnostics Screen. I copied the one for the errors, and edited it to make it a little lighter because the original was too dark:

Yes that is what the diagnostic screen looks like. I received a Wineguard HDA 200 amp in the mail today but I am assuming it wouldn't help anything although the amplification is supposed to be controllable via a nob or something. But, it may be "noiser" than the Winegard LNA 100. What do you guys think?
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Old 7-Nov-2014, 3:16 AM   #52
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The HDA200 quite a bit noisier than an LNA100. You shouldn't have any need for it.
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Old 7-Nov-2014, 3:25 AM   #53
mulliganman
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Quote:
Originally Posted by rabbit73 View Post
The signal might be too "hot" for the Roamio tuner. A simple test would be to insert a 2-way splitter between the C2V and the input of the AC7, which would attenuate the signals 3.5 dB; two splitters in series or a 4-way splitter would attenuate the signals 7 dB.

If you want some actual fixed attenuators:
http://www.mjsales.net/itemsearch.asp?FamilyID=221

Yes, electrical interference is greater on VHF. It could also be from multipath reflections coming from other directions because of the simple V antenna. Again from ATSC A/74:



A more directional VHF antenna would reject many of those reflections.

Note from the table that the greater the difference in time between the main signal and the echo (reflection), the weaker the echo must be to not interfere with reception.

How often do you see the uncorrected errors? Once-a-day for a few minutes, or more like almost constantly?

Do you see picture and audio problems on your TV only when you have errors?
Any adventage or disadvantage to using a splitter vs. an attenuator? I'm assuming the 3db attenuator would be the one to get if going that route...
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Old 7-Nov-2014, 3:28 AM   #54
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Quote:
I guess if the splitter doesn't work the only option I would have left would be to replace it with some sort of directional antenna?
We really don't know what is causing the errors on 33.1. If it is from multipath reflections, then a more directional antenna might help. If the errors are caused by some other reason, like an unknown characteristic of the tuner, it wouldn't help.

When you started, most of the things you tried had a high chance of improving your signals. You are now at the point where they might not, and you must be willing to take that chance of failure. That's why I want you to try the simple things first.

Quote:
If I put the 2 way splitter on the C2V before the AC7 combiner, would I just "cap" the extra out?
The purists say that you should cap the unused port with a 75 ohm termination cap; practical experience says it doesn't seem to make much difference. Try it both ways to satisfy your own curiosity.
Quote:
Any adventage or disadvantage to using a splitter vs. an attenuator?
Not that I'm aware of except price and availability, assuming a good quality splitter.
Quote:
I'm assuming the 3db attenuator would be the one to get if going that route...
This is an experiment. You don't yet know how much attenuation would make a difference, if any. Think of it as an adventure, not a chore.

Last edited by rabbit73; 7-Nov-2014 at 6:44 AM.
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Old 7-Nov-2014, 4:43 AM   #55
mulliganman
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Quote:
Originally Posted by rabbit73 View Post
The signal might be too "hot" for the Roamio tuner. A simple test would be to insert a 2-way splitter between the C2V and the input of the AC7, which would attenuate the signals 3.5 dB; two splitters in series or a 4-way splitter would attenuate the signals 7 dB.

If you want some actual fixed attenuators:
http://www.mjsales.net/itemsearch.asp?FamilyID=221

They also have power passing attenuators, but you don't need that kind now.
When you mentioned attenuators, I realized I had 3 of these lying around: http://www.3starinc.com/fam-3_db_in_...uator_pad.html

So, I went up and connected one to the C2V antenna and then connected that attenuator into the all channel input of the AC7 combiner. I then rescanned for channels on the Roamio. Some 8 dash channels I was getting dropped off (they may have been analog stations i am not sure). I then proceeded to go into the DVR Diagnostic menu of the Roamio and checked all channels I was receiving. First off, 33-1 changed from about 80 on the RS Uncorrected amount to 0. Another interesting change is that 49-1 and 49-2 shot up to 67% signal strength (up from 62%) and the SNR went up to 27 dB on those channels. All other channels reported before remained at the constant on both signal strength and SNR from what i reported in post 21. Channel 10-1 also had 0 for RS Uncorrected but it was that way earlier this evening before adding in the attenuator.

What do you guys think about that? Why the jump on 49-1 and 49-2? The jumps wouldn't have anything to do with losing the 8 dash channels would it?

I am going to check again tomorrow evening when i am home from work and see what the levels are reporting then.

Last edited by mulliganman; 7-Nov-2014 at 4:45 AM. Reason: added information
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Old 7-Nov-2014, 6:33 AM   #56
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Thank you for the report. That sounds like an improvement to me. Time will tell if it is a permanent improvement.

There is a story, that has many versions, about Thomas Edison when he was inventing the light bulb. He told a guest at his lab that he had, so far, done 1,000 experiments but had not yet perfected the light bulb. His guest asked, "How did it feel to fail 1,000 times?" Edison replied, "They weren't failures. I found 1,000 ways that didn't work, so I can now exclude them from consideration."

Quote:
What do you guys think about that?
Take a look at this Google search for roamio signals "too hot":

https://www.google.com/?gws_rd=ssl#q...+%22too+hot%22

Last edited by rabbit73; 8-Nov-2014 at 8:34 PM.
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Old 7-Nov-2014, 1:59 PM   #57
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Quote:
Originally Posted by rabbit73 View Post
Thank you for the report. That sounds like an improvement to me. Time will tell if it is a permanent improvement.

There is a story, that has many versions, about Thomas Edison when he was inventing the light bulb. He told a guest at his lab that he had, so far, done 1,000 experiments but had not yet perfected the light bulb. His guest asked, "How did it feel to fail 1,000 times?" Edison replied, "They weren't failures. I found 1,000 ways that didn't work, so I can now exclude them from consideration."



https://www.google.com/?gws_rd=ssl#q...+%22too+hot%22
Looks like I may have spoken too soon. I couldn't resist checking the levels this morning before I left for work. 49-1 and 49-2 were down to 52% (22 SNR) on the signal strength menu (from the 67% after I first inserted the 3 dB attenuator). I didn't expect to see that all (there were also a small amount of RS Uncorrected errors present on those two channels). Not sure if that was due to the attenuator or something else.

33-1, 33-2, and 33-3 had dropped a little in signal strength too but no signal errors.

I"m not sure what happened...

Last edited by mulliganman; 7-Nov-2014 at 3:58 PM. Reason: clarified
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Old 7-Nov-2014, 9:53 PM   #58
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Quote:
before I left for work. 49-1 and 49-2 were down to 52% (22 SNR) on the signal strength menu (from the 67% after I first inserted the 3 dB attenuator).
Not a surprise. OTA signals constantly vary in strength, especially 1Edge and 2Edge signals.
Quote:
Not sure if that was due to the attenuator or something else.
It couldn't be from the attenuator because it was in the coax line from the other antenna.

Raising the 91XG as ADTech suggested might make 49 stronger.

Quote:
Some 8 dash channels I was getting dropped off (they may have been analog stations i am not sure).
KTKO-LP digital and KTKO-LP analog are both very weak. No surprise there either, because of their very negative NM numbers, based on your old report:
http://www.tvfool.com/?option=com_wr...d24362e8886d03

Quote:
33-1, 33-2, and 33-3 had dropped a little in signal strength too but no signal errors.
Good; that's what the attenuator was supposed to do.

How is 10.1 doing now?

Last edited by rabbit73; 7-Nov-2014 at 11:39 PM.
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Old 9-Nov-2014, 10:17 PM   #59
mulliganman
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Originally Posted by rabbit73 View Post
Not a surprise. OTA signals constantly vary in strength, especially 1Edge and 2Edge signals.
It couldn't be from the attenuator because it was in the coax line from the other antenna.

Raising the 91XG as ADTech suggested might make 49 stronger.

KTKO-LP digital and KTKO-LP analog are both very weak. No surprise there either, because of their very negative NM numbers, based on your old report:
http://www.tvfool.com/?option=com_wr...d24362e8886d03

Good; that's what the attenuator was supposed to do.

How is 10.1 doing now?
10.1 continues to get sporadic RS Uncorrected Errors as well as 33-1 and 49-1. Nothing else seems to do that.

Oddly enough even with the attenuator, 33-1, 33-2, and 33-3 continue to be around 67% signal strength (which is what they are at after inserting the LNA 100 and before putting the 3 dB attenuator in the mix).

I don't mind losing the KRFT channels as there is nothing on there I watch anyway.
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Old 10-Nov-2014, 4:41 PM   #60
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Originally Posted by rabbit73 View Post
Not a surprise. OTA signals constantly vary in strength, especially 1Edge and 2Edge signals.
It couldn't be from the attenuator because it was in the coax line from the other antenna.

Raising the 91XG as ADTech suggested might make 49 stronger.

KTKO-LP digital and KTKO-LP analog are both very weak. No surprise there either, because of their very negative NM numbers, based on your old report:
http://www.tvfool.com/?option=com_wr...d24362e8886d03

Good; that's what the attenuator was supposed to do.

How is 10.1 doing now?
Do you have any other ideas I should try?
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