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Old 3-Jul-2015, 7:18 PM   #1
MarcCharette
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Join Date: Jul 2015
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Do you think it's possible to get this channel?

Here's my report: http://www.tvfool.com/?option=com_wr...8e039f6fd92a37

I'm trying desperately to get CHCJ-DT because it has a lot of programming I want to be able to get. I can get every channel up to that easily. I have the antenna pointed as close as I can to 116 degrees.

Here is a street view of generally the way the antenna is pointed.
https://www.google.com/maps/@43.4637...7i13312!8i6656
Note that the apartment building is not in the way because obviously the antenna is mounted on my roof and not the road

My setup:
Antenna: Clearstream 2 (is actually a 2V but I removed the VHF antenna because the one nearby VHF station was too strong)
Pre-amp: Channelmaster 7777
Distribution amp: Some generic amp that adds +10db (I lose CITY-DT if I don't have this because I have it split 5 ways)
About 90' cable between preamp and distribution amp

I added the channelmaster 7777 last night and was able to get a CHCJ but it drops frequently/goes pixelated. Any suggestions for anything I can do to get it clear? I am not opposed to getting a different antenna or adding a second one if it will help

Last edited by MarcCharette; 3-Jul-2015 at 7:23 PM.
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Old 4-Jul-2015, 2:03 AM   #2
rabbit73
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Welcome to the forum, Marc:

It sounds like without the preamp you don't have enough gain, and with it you have too much. The 7777 probably wasn't the best choice; the 7778 would have been better. To quote Channel Master:
Quote:
The Titan 2 High Gain Preamplifier is recommended for professional installers only. Due to the high gain output of this product, it can result in over amplification if not used in the appropriate scenario. Over amplification can cause issues with the television tuner’s ability to receive and display some or all channels.
You are probably having problems with preamp or tuner overload.

Your strongest UHF signal CIII has a Noise Margin of 51.7 dB. If you add the gain of the C2 of 10 dB, that brings you up to 61.7 dB, which the 7777 doesn't like.
https://www.antennasdirect.com/cmss_...uctions%20.pdf



Interpreting Noise Margin in the TV Fool Report

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

If you then add the 7777 gain of 30 dB, that brings you up to NM 91.7 dB, which is way too much for the tuner.

In terms of signal Pwr dBm as listed on your tvfooj report, CIII is -39.1 dBm. Add the antenna gain of 10 dB brings you up to -29.1 dBm. Add the preamp gain of 30 dB brings you up to +0.9 dBm. Tuners are not expected to handle signals stronger than -5 dBm for a single signal or stronger than -8 dBm for more than one.

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 DTVsignal 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.
As an inexpensive test I suggest you add an attenuator between the antenna and the preamp input. It might be possible to find a happy medium.

https://www.antennasdirect.com/store...ttenuator.html
http://mjsales.net/collections/atten...ant=1083705673
•Attenuation values 1, 3, 6, 8, 10, 12, 16, 20dB (FAM)
click on 1 dB to see other values, up and down arrows are faint

http://www.3starinc.com/drop_in-line_attenuator.html
http://home-automation.smarthome.com...=&w=attenuator

Try a combination of the variable attenuator and fixed attenuators; you might need more than 20 dB. Replace that combo with equivalent fixed values.

If that doesn't work, try a more directional UHF antenna; the C2 beamwidth is very wide. Consider the DB4E.

If that doesn't work, try a separate DB4E with its own preamp and a Tin Lee custom single channel bandpass filter for real channel 35.
http://www.tinlee.com/index.php
http://www.tinlee.com/catv_filters.php?active=1
http://www.tinlee.com/bandpass_filters.php?active=1
Talk to one of their engineers, and email your tvfool report to him.

Quote:
I have the antenna pointed as close as I can to 116 degrees.
116 degrees true, 126 magnetic.

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 in the US), 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.

The data is probably not up to date, but I see some strong FM signals that might interfere with TV reception. An FM filter is needed; see attachment 2.
Attached Images
File Type: jpg NMChartC.jpg (71.3 KB, 445 views)
File Type: jpg MarcCharetteTVF FM est.JPG (108.1 KB, 90 views)
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Last edited by rabbit73; 11-Jul-2015 at 8:18 PM.
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Old 4-Jul-2015, 2:47 AM   #3
MarcCharette
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Wow I couldn't have got a more detailed response if I had paid for it! I had thought about overload but figured since I have the antenna pointed a fair bit away from CIII then it wouldn't have been an issue. I'm new to OTA tv so forgive my limited understanding of signal strength, but wouldn't putting an attenuator on it then also lower the signal for CHCJ, making it harder to get?

Getting a more directional antenna is a good idea. If I can find one locally with a good return policy I might give that a go

Again thanks for your help
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Old 4-Jul-2015, 3:06 AM   #4
rabbit73
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Quote:
I'm new to OTA tv so forgive my limited understanding of signal strength, but wouldn't putting an attenuator on it then also lower the signal for CHCJ, making it harder to get?
Your question is very intelligent. I asked the same question when I was learning about overload. It seems counterintuitive to add an amp for more gain, and then insert an attenuator to reduce gain. The short answer is you gain more in increased SNR for the weak signal than you lose in signal strength. To increase your understanding, I can give you the long answer. You have to try something, because the overload is creating spurious signals that damage the weak signal.
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Old 4-Jul-2015, 3:09 AM   #5
rabbit73
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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 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 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.



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.

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.



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.
Attached Images
File Type: jpg SFDRdiagramJ3.jpg (103.6 KB, 419 views)
__________________
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Last edited by rabbit73; 4-Jul-2015 at 3:37 AM.
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Old 4-Jul-2015, 4:19 AM   #6
MarcCharette
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I think I am going to save reading the longer explanation for the morning when my brain is working

But in any case I will try to track down an attenuator somewhere locally and give it a shot. Not a big investment anyway
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Old 11-Jul-2015, 4:28 PM   #7
MarcCharette
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Still working on trying to get the elusive CHCJ-DT. Ordered a few attenuators of amazon of varying strength. No combination seemed to give any positive results. Just lost other channels the more I added.

So I'm thinking of trying two other options:
Option 1:Get a antennas direct 91XG (very high gain, unidirectional) pointed directly at CHCJ-DT (hopefully maybe pick up some US channels that are in line with it). Then stack it vertically with my existing Clearstream C2 and point that towards CITY-DT (which is the one I often lose if I point the C2 too far towards CHCJ-DT). Only question would be what device to get to combine them on one cable.

Option 2: Ditch the Clearstream C2 (well... hopefully sell it), replace with a Antennas Direct DB8E (the highest gain one I could find) which can be pointed in two directions, so point them in roughly the same orientation as above.

Which option do you think would have the most success? I think #1 might be tough due to trying to combine two antennas on one cable

Last edited by MarcCharette; 11-Jul-2015 at 4:29 PM. Reason: clarification
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Old 11-Jul-2015, 6:04 PM   #8
MarcCharette
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Additionally, I actually measured how high my antenna is (as best as I can since it's mounted on the roof in the center of the house).

This is what I think the height actually is (16 feet)
http://www.tvfool.com/?option=com_wr...8e03736d83703b

This is the old report (20 feet)
http://www.tvfool.com/?option=com_wr...8e039f6fd92a37

That is a dramatic change for CHCJ-DT (a 6 db decrease by going down 4 feet) so I think that is part of the problem. Unfortunately I don't see any way to get higher.... It's already at the end of an 8 ft poll on the roof
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Old 11-Jul-2015, 8:49 PM   #9
rabbit73
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Quote:
Still working on trying to get the elusive CHCJ-DT. Ordered a few attenuators of amazon of varying strength. No combination seemed to give any positive results. Just lost other channels the more I added.
Sorry to hear that it didn't help. With 2 amps and a distribution system, maybe any further tests should be with just one TV, adding amps one at a time.

Quote:
Which option do you think would have the most success? I think #1 might be tough due to trying to combine two antennas on one cable
Actually, both options have the same problem when the DB8E panels are aimed in different directions. When you combine 2 UHF antennas using a splitter in reverse, it often doesn't work because when the same signals arrive at the combining point they interfere with each other if they are not in phase.

When you try another antenna for CHCH, don't try to combine it until it will do what you want for CHCH.

There is a custom (expensive) device that is made by Tin Lee that will combine CHCH on real channel 15 with other UHF channels. It is called the AC7.

Antenna and Installation Advice Needed
http://forum.tvfool.com/showthread.php?t=290

mulliganman used one for Fox on real channel 49:
http://www.tvfool.com/?option=com_wr...d24362e8886d03
question regarding overamplification
http://forum.tvfool.com/showthread.php?t=15025

http://www.tinlee.com/Matv_filters.php?active=3
http://www.tinlee.com/MATV_headend.p...IGNALINJECTORS
http://www.tinlee.com/PDF/AC7-custom...kup%20Info.pdf
http://www.tinlee.com/pricing.php?active=3

Call them and talk to one of their engineers and email your tvfool report to him.
http://www.tinlee.com/contactUs.php

Quote:
That is a dramatic change for CHCJ-DT (a 6 db decrease by going down 4 feet) so I think that is part of the problem. Unfortunately I don't see any way to get higher.... It's already at the end of an 8 ft poll on the roof
There should still be enough signal after you add your antenna gain. The TVFOOL report is just a computer simulation; your testing will tell the truth for your location.
__________________
If you can not measure it, you can not improve it.
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Last edited by rabbit73; 11-Jul-2015 at 9:24 PM.
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