OTA Signal Analyzers, Meters, Aimers, Bench Gear, Diagnostic Software - Page 21 - Canadian TV, Computing and Home Theatre Forums

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post #301 of 311 (permalink) Old 2015-04-04, 06:50 PM
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Unless you're within a stone's throw of a TV Tower...and maybe not even then....I don't think you can PHYSICALLY DAMAGE a Preamp (or TV Tuner) input with "TOO" strong a signal.
I agree; that's what I call type three overload:
Quote:
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.
Quote:
Highest TVFool I've ever seen is about -10 dBm....plus Antenna Gain....yields about 0 dBm signal, which is only ONE MILLIWATT. It would take somewhat MORE THAN 1 Volt on the input of the RF Transistor to actually DAMAGE it (MOSFET/HEMT typ. 5-10 VDC, perhaps 1-3 VDC with low-voltage Integrated Silicon Tuners). If Max Input was 1 VDC, this would be MORE than 13 mW (V^2/R), which is MORE THAN +10 dBm....NOT gonna happen.....
The closest I ever got to that was +9 dBm (+58 dBmV) out of a CM3410, when I fed its input -6 dBm (+43 dBmV), which means it hadn't gone into compression yet.
Signal Amplifiers (Amps, Preamps, Distro Amps)

If you can not measure it, you can not improve it.
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post #302 of 311 (permalink) Old 2015-04-05, 06:45 PM
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Originally Posted by Pete Higgins View Post
For what it's worth... You would think that having a signal strength meter and tuning for best signal strength would be the way to go. That's counter to what I've been finding at my location although on the majority of my channels they do coincide. I have several channels where I get pixelation with my antennas oriented for best signal strength and they break clear when I reorient the antennas for best SNR. Usually 1-2 bars lower.
I have had the same experience with some of my channels.
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My Samsung TV only displays signal strength so when I'm rotating my antenna array I use my computer and the Hauppauge HVR-1800/SNR meter to optimize the final antenna parking. Works better for me. Using my Software Defined Radio (SDR) spectrum analyzer I can narrow the span to a portion of a single channel and see that the signal strength lowers but can't see any reason I should be receiving the channel better.
The reason is that a signal that is weaker but higher in quality has fewer errors to correct by the FEC than a signal that is stronger but lower in quality.

I have used the signal quality scale (inverse of errors.....BER) on my Apex DT502 and the SNR and Errors readings on my Sony Diagnostics Screen to optimize antenna aim.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #303 of 311 (permalink) Old 2015-12-08, 10:01 AM
 
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Ottawa RTLSDR Info

I ordered the NooElec dongle today. I am overwhelmed by the available SDR software. Which signal strength software do u use?
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post #304 of 311 (permalink) Old 2015-12-08, 12:06 PM
 
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I use RTLSDR for the spectrum analyser (with the SDR stick), but the Hauppauge Signal Monitor (with an Aero-M tuner, which is not an SDR stick) for signal / noise ratio (which is more important than signal strength in DTV reception).
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post #305 of 311 (permalink) Old 2015-12-10, 08:39 AM
 
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My Hauppauge 2250 has two tuners. The monitor(s) won't tell me which tuner/channel they are monitoring. Guess I have to go into WinMedia setup and disable 1. Tiresome!
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post #306 of 311 (permalink) Old 2016-01-12, 11:42 PM
 
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Just finished using the RTLSDR rtl_power script to scan the full UHF band.

I'm using the keenerd repo from github. To generate the heatmap, I'm using the rtl-gopow utility.

I then used an ImageMagick script called grid to create gridlines every 48 pixels ( 125KHz * 48 = 6MHz )

Command:

Code:
rtl_power -f 470M:698M:125k -g 20 -p 60 -i 1
The results:

UHF 14 through 51


DB4e | CPA19 | 2 x HDTC-2US | Mac Mini | EyeTV 3
My scanning and reporting scripts here

Last edited by 905shmick; 2016-01-13 at 10:52 AM.
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post #307 of 311 (permalink) Old 2017-05-30, 01:29 AM
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I modified the linux driver for this usb atsc tuner to allow plotting the received constellation, using updateDVB.
Working pretty good here...

a weak distant cblt
https://www.dropbox.com/s/p59zq8f1dh...qplot-cblt.png
strong local wned
https://www.dropbox.com/s/w9ue0jg7fg...qplot-wned.png
256 qam from cable
https://www.dropbox.com/s/mlte1gq973...-iq-256qam.png
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DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #308 of 311 (permalink) Old 2017-05-30, 09:01 PM
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Thanks for the links to your constellation diagrams. I am always interested in signal measurements.

The way I interpret them is cblt poor, wned good, and cable QAM excellent; is that correct?

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #309 of 311 (permalink) Old 2017-05-30, 09:27 PM
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Well, its all relative...based on the SNR, I wouldn't call 20 dB for a station 70 miles away poor, especially if it is reliable and stable over time. The fuzzier the constellation is, the more error correction is helping to recover any bits received in error in it's travels over the air interface...
It is very cool to be able to rotate my antenna and see the impact on the received constellation graphically in real time...
For 8VSB, there isn't much need for every signal to be in the 30 dB SNR range where the user is... The way I understand it, if the SNR was measured right there at the transmitter, it would likely be in the mid 30s dB tops. If not, it could be a sign of something unhealthy going on, possibly even resulting in some near out of spec skirts in it's output spectrum.

While reviewing the driver source code, I was also able to find clues in the source code as to when the demodulator sees multipath, so I have altered code a bit further to indicate that in a kernel debug message that ya can see in kernel logs (not passed to user land for anything).. Kinda cool too, but without access to real chipset documentation or test equipment, I have no way to confirm. Just reading the original driver author's comments in the code, and taking a guess as to what he/they meant at the time they wrote it.

The cable signal probably wasn't the best signal available. I see many other QAM channels in the 38 to 39 dB range. I don't normally look at CATV signals,
but I did want to test it to make sure it was able to display the 256 QAM constellation too.
IMO for a wired cable signal that you are paying for, there shouldn't be much variation from one channel to the next. I haven't found a cable signal that was 'marginal' reception wise and probably won't.

At any rate it's not to be confused for real test equipment which none of us will ever have at our disposal, but is not bad for a $70 USB tuner.
All in all, I am really liking this tuner...

BTW, updateDVB is the same application that I use for looking at satellite signals (as mentioned earlier in this thread), and none of the constellation plot capability required any modification to the application side. I only modified the kernel module for the device, and the application worked straight away.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #310 of 311 (permalink) Old 2017-05-30, 10:50 PM
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Thanks for the details; very useful when aiming an antenna for best signal quality.

I played with your images; hope you don't mind.






If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #311 of 311 (permalink) Old 2017-06-04, 07:34 PM
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list of devices using the lgdt3306a demodulator, with linux support
hauppauge quadhd (pcie, sans analog)
hauppauge hvr2255 (pcie)
hauppauge WINTV_DUALHD_01595 (usb, sans analog)
hauppauge 955q (usb)
plus the xbox branded version of 955q

The only one of these that I have tested is the 955q.
But in theory the others should work for this also.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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