Canadian TV, Computing and Home Theatre Forums banner

301 - 320 of 329 Posts

·
Premium Member
Joined
·
1,117 Posts
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:
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.
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.
http://www.digitalhome.ca/forum/showpost.php?p=1597002&postcount=3490
 

·
Premium Member
Joined
·
1,117 Posts
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.
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.
 

·
Registered
Joined
·
556 Posts
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).
 

·
Registered
Joined
·
435 Posts
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

 

·
Registered
Joined
·
4,861 Posts

·
Premium Member
Joined
·
1,117 Posts
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?
 

·
Registered
Joined
·
4,861 Posts
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.
 

·
Premium Member
Joined
·
1,117 Posts
Thanks for the details; very useful when aiming an antenna for best signal quality.

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





 

·
Registered
Joined
·
4,861 Posts
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.
 

·
Registered
Joined
·
4,861 Posts
Hauppage 950Q Signal Strength dBm

After reading some old abandoned patches from 2 years ago that had never made it in to the mainline kernel that modify the driver to indicate the signal strength in dBm. Played around with the linux driver for the Hauppauge 950Q yesterday AM, to get it to work with today's 950Q drivers' code.

Works pretty good, certainly not a signal meter or spectrum analyser, but good enough to help investigate whether a degraded SNR issue may be caused by too many strong signals, interference, or just plain too weak of a signal. Should also aid in dialing in your antenna.


 

·
Registered
Joined
·
4,861 Posts

·
Registered
Joined
·
4,861 Posts
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.
A few more USB devices that would work OK with UDL's linux-media modifications.
Signal Strength in dBm, SNR in dB, spectrum_scan, but no iqplot.
Hauppage 950Q.
Geniatek (mygica) a681 (aka Mohu USB TV Tuner for Windows 10).
Which can be had on ebay for ~ $25 US.
I bought 4 of them for $10 a piece about a month or two ago in order to work on getting it working in Linux.
originally it did not, but it does now with UDL's kernel.
In addition I have since confirmed the Hauppauge Wintv DualHD works as well, along with iqplot.

Edit: Full disclosure, I did have 1 of 4 of the a681 devices fail on me.
I suspect it failed while taking windows10 updates, when I had the windows drive in,
was hoping to gather more logs to help in getting the linux driver functioning, when it went brain dead.
They did send me a new one to replace it at no charge however.
 

·
Registered
Joined
·
595 Posts
Not to denigrate your excellent work in signal analysis, I found the Hauppauge 950q quite lacking in tuner sensitivity in comparison to my Panasonic Plasma's tuner, neither WGRZ or WUTV were viewable during the winter months and WKBW was pixellated most of the time, none of my Erie regular stations showed an image, WFXP (which is now less strong than WSEE) came through with my tv's tuner but not even a hint on the Hauppage 950Q.


These USB dongles and external tuners do have a LOT of nice features but I have yet to find one that matches my tv's tuner (now using a Samsung 55nu8000 with even better tuner than the Pansonic Plasma).

I'm in a unique spot, 170' AGL and am blessed to receive WGRZ at 106.8 miles and WKBW at a similar distance year round. None of the external tuners I've bought have come close to matching what my tv's have given, the worst being the Homeworx/Mediasonic HW 150PVR, second worst Hauppaugge 950Q,and the HDhomerun Hdhr4-2us which was close but still not equal to my tv's tuner. None of these were able to show a solid picture during winter on the above mentioned channels but my tv does.

Anyone wanting to do some testing is welcome to my 950Q and Homeworx HW150 FREE, just post honest result and pay postage, the Hauppauge will probably cost $3-4, the homeworx maybe $20. PM for details.
 

·
Registered
Joined
·
4,861 Posts
Not to denigrate your hunting... but I think there's a lack of spunk for wanting to understand... the old inquiring minds wanna know..
Apparently your not interested enough to ever wanna, that's all good, understand.
I find the HW-150 is able to receive anything the other tuners in the house are able to.
My 950q is actually broken, so that would be convenient. I think I broke it while trying to replace it's USB Connector.
Would rather see someone else who doesn't already have one take it.
Give it a week or two, if no one else wants your 950q, then I'll send ya a PM re the 950q.
 

·
Registered
Joined
·
4,861 Posts
Lately was working on this cheap USB tuner dongle, sold by mohu, which is a rebadged usb device from Geniatek, model A681.

When I rcv'd it, there was no driver available for Linux. There still isn't in the mainline kernel, but we added support for it in Updatelee's media tree and in darksky's raspberrypi tree. It uses a MaxLinear mxl603 tuner, and Panasonic mn88436 demod.
Makes for a cheap alternative, as they can be found on amazon for ~$30.
I was lucky and found mine for $10...

https://gitlab.com/Dark-Sky/rpi-udl-linux/commits/master
https://gitlab.com/updatelee/v4l-updatelee

It works pretty well so far and to my knowledge is the only atsc device I have come across which supports all 4 key metrics, strength dBm, cnr in dB, post viterbi bit error rate and packet error rate in dvb v5 api format. Supports spectrum scan now also.

So, dvbv5 applications such as this one can report the metrics the way the v5 api is designed.



 

·
Registered
Joined
·
4,861 Posts
I wouldn't mind trying, but not being a developer, would probably not meet their standards.
Maybe some day I will send an email to one of the developers, see if they would help to get it in there.
I can hook you up with an image for say the raspberry pi, would take all the thinking out of it, plug and play.

Darsky has this all tidied up in Manjaro Arm for the pi nowadays too. Manjaro Arm is hosting his image for the pi3b, pi3b+ (aarch64 though).
basically download image, send to an sd card with 'etcher' via linux or windows, plug sd card in to pi and boot it. Follow the on screen steps to intialise host, username, etc, and when it reboots it resizes the root partition to max allowable given the size of the sd card automatically.

Else if ya wanna install Arch Linux on an X86_64 machine, I have some PKGBUILDs We can point ya to, in order to do all the compile and install legwork for you... For the kernel piece at least.

Edit: Cheap tuner I was mentioning. Works OK in windows too once you install the Win 10 driver
https://www.amazon.com/Mohu-USB-TV-Tuner/dp/B07PYLGWSN
 
301 - 320 of 329 Posts
Top