[majortom]

Mythtv channel scanner doesn't know or care where you are located.
If I remember right the exact UI is a little different if using an hdhomerun (an IP based tuner interface) vs say a more traditional USB or PCI based ATSC tuner.
Overall jist being the same though.

FULL scan, Scan based on a previous scan (import previous), what they call existing transports, couple other options..

I can take some screenshots and u'll get the jist, But I don't have a USB based ATSC tuner hooked up at the moment to compare and verify the differences still exist.

In his first post on Oct 5th, he said his issue had started "a couple days ago..."

 

[mailtodevnull]

Hello, back again. CFTO-DT has been hit and miss. Some days it comes in strong and my recordings work well. Other days I cannot achieve a lock at all.

I did end up installing the VHF retrofit kit, now that it's semi-warm outside again, but this has not resolved the issue. I still am unable to lock on to 9.1 CFTO-DT.

The S/N is 2.3dB, which is similar to neighbouring channel CBC 5.1, 2.5dB

----

majortom -- I did also try hooking the antenna up to my TV tuner, and it also cannot lock onto CFTO-DT.

 

[Jorgek]

When CFTO 9.1 moved to RF channel 8, I also encountered drop outs. I'm using a 4221Hd pointed at Grand Island NY. CFTO is received on the back side of the antenna. I made a folded dipole for RF channel 8. Fed both antennas into a UVSJ and all is well. LOS I'm 13 miles from the CN tower. You would think that being so close to the transmitter that CFTO would not be an issue.

 

[majortom]

The Snr indication in Mythtv is broke... I don't know why they don't fix that... but has been broke that way for over 10 years,
as long as I can remember...
They are taking the log base 10 of a number that is already in decibels...
You would have to download the source code, edit one file, 'tv_play.cpp' compile it and install in order to fix that....

 

[mailtodevnull]

majortom -- sorry, I keep forgetting the MythTV SNR is broke. I'll give dvb-fe-tool another try next time I am able to receive 9.1

Today I deleted all the channels and re-scanned, and CFTO didn't make the cut. Duh, should've seen that one coming. So now I am actually unable to do any further testing until the channel shows up again. Tried manually adding the channel but MythTV won't even try tuning to it for whatever reason.

Back to the original issue, though... some contextual clues that may be relevant:

* I am located ~50km as the crow flies from the CN tower
* The cable run from antenna to tuner is likely over 50 feet long, and contains a single splitter.
* Here's a report from rabbitears.info: https://www.rabbitears.info/searchmap.php?request=result&study_id=31321 -- CFTO is listed as "fair", maybe due to lower power VHF signal?

Choose your own adventure:

1. An email to CTV Engineering returned an auto-reply suggesting that FM interference could cause issues, and suggested an FM trap. Does the VHF Retrofit kit come with an FM trap already?
2. Likewise, the same email suggested a preamplifier may be recommended. (Is the db4e already amplified?)
3. Get up on the ladder and disconnect the splitter.

Re: option 3 -- is there still signal loss if I disconnect the coax going to the 2nd TV and keep the splitter in place, or do I have to remove it altogether and join the two cables...

 

[majortom]

CTV engineering is providing you sage advice...

But being that close to TO, what I would do in order...
1.) install the Antennas Direct VHF adapter kit that you bought on to the DB4e. I am betting that will work.
2.) buy a preamp, such as the RCA tvpreamp1z
https://www.google.com/search?q=RCA...WQct8KHVwRCnwQ_AUoAXoECA0QAw&biw=1366&bih=591
The preamp will make up for the losses in your 50' coax run + splitter, which I'd expect to be around 3 dB coax + 3.5 dB 2way splitter, and then some. Allowing for more TVs / tuners to be connected to the system without any further degradation. Here i have an 8 way splitter in my basement, and since my preamp is up top near the antenna, every TV in the house receives ~ the same SNR.
It comes with a switchable FM trap (you can switch it in or out). I'd do this 2nd cause it will likely improve your Buffalo reception as well.
You might have to re-orient your antenna for best reception when the preamp is introduced.
3.) If any of that is still unreliable, get a VHF Hi yagi and aim it for the CN Tower.
https://www.newark.com/stellar-labs...559827|&CMP=KNC-GUSA-GEN-SHOPPING-AllProducts

You might even be able to aim the yagi to Springville, NY and get WBBZ from Springville on RF 7, and CFTO on RF 9 from the rear.
That is what I do here, but in reverse.. For me since I'm south of Buffalo I aim the Yagi to the CN tower for CFTO (70 mi from me), and there is still
enough signal on RF 7 for WBBZ from Springville on the rear.

 

[mailtodevnull]

Prompt reply The VHF kit was installed and did not resolve the issue unfortunately. A rescan picked up no new channels, but that was expected since CFTO-DT is the only station broadcasting within VHF range. Still am unable to lock, but would definitely be interested in seeing what the SNR is, should I be able to pick up the station again.

Edit: I figured out how to tune to things using VLC.

Here is CBC:

$ dvb-fe-tool -mg -a0
FREQUENCY = 509000000
MODULATION = VSB/8
DELIVERY_SYSTEM = ATSC
Lock   (0x1f) Signal= -60.00dBm C/N= 30.41dB
Lock   (0x1f) Signal= -60.00dBm C/N= 30.41dB
Lock   (0x1f) Signal= -60.00dBm C/N= 31.14dB
Lock   (0x1f) Signal= -60.00dBm C/N= 31.14dB

Here is CFTO-DT:

$ dvb-fe-tool -mg -a0
FREQUENCY = 186000000
MODULATION = VSB/8
DELIVERY_SYSTEM = ATSC
       (0x00) Signal= -95.00dBm
       (0x00) Signal= -95.00dBm
       (0x00) Signal= -96.00dBm

 

[majortom]

yeap, that is like neg nuthin...
Proceed to the next step...
Correction to my earlier estimation of your losses...
based on this... https://hauppauge.com/pages/products/data_quadhd.html
Since that is a quad tuner, with one coax input, internally is like having a 4 way splitter connected to 4 separate tuners,
for a net loss of say 7 dB from the coax connector to one of the tuners/demods... (we don't get something for nothing)
So, 50' of coax ~ 3dB
Two way splitter at the end of your downlead 3.5 dB
Net loss of one of the four tuners - 7 dB

So, net losses from your antenna to one of those 4 tuners is 3 + 3.5 + 7 = 13.5 dB.
That is more than 20 times less signal at one of them tuners, than what was at the antenna terminals.
I would say you need a preamp and a better vhf antenna, bigtime.

From here I was able to pickup CFTO for 3 months straight fairly reliably with that VHF retro kit installed for VHF.
But I have always had a Preamp on my mast.

 

[rabbit73]

AntennasDirect DB4e and a Hauppauge WinTV-QuadHD installed on a machine running MythTV.

Do you get an SNR reading if you use the WinTV Digital Signal Monitor?
https://www.hauppauge.com/pages/support/support_digital_signal_monitor.html

I think my 955Q reads a little high for marginal signals.

This is what your FM report looks like, but the database might not be up to date:
http://www.fmfool.com/modeling/tmp/617c83b5c0/Radar-FM.png

Some of the FM signals are quite strong, but maybe not strong enough to cause interference to VHF-High. The ones from 45 degrees are weaker.

Another way to check your VHF-High signals is with a $20 SDR dongle and free open-source spectrum analyzer software. My channel 9 is marginal:

The main advantage of the spectrum analyzer is that you can see the signal if it is there, even if your tuner can't pick it up. You can also estimate the SNR and check the noise level from electrical interference which is higher on VHF than on UHF. Here is a severe case of electrical noise interference:

https://www.digitalhome.ca/forum/186-antenna-research-development/287147-converting-uhf-yagi-vhf-antenna-7.html#post3090963

 

[majortom]

Edit: I figured out how to tune to things using VLC.

might wanna try this sometime... https://bitbucket.org/majortom/tune-s2/src/master/
I haven't tested on a stock kernel since probably kernel version 4.02, but give it a whirl.
Nuther handy little tool.

install dependencies:
apt install libgps-dev libgps22
clone repo:
git clone https://bitbucket.org/majortom/tune-s2.git
checkout 'stock' branch if using stock linux kernel:
git checkout origin/stock 
compile:
make
install it:
sudo make install

I think my 955Q reads a little high for marginal signals.

yes it is, for SNR at least. And he is using the same lgdt3306a demod, so will be the same.
It is good to know that in windows it also reports on the high side SNR wise under marginal conditions.
Don't think I have ever played with the lgdt3306a based devices I have in Windows before.

 

[rabbit73]

yes it is, for SNR at least. And he is using the same lgdt3306a demod, so will be the same.
It is good to know that in windows it also reports on the high side SNR wise under marginal conditions.
Don't think I have ever played with the lgdt3306a based devices I have in Windows before.

When I brought a strong signal down to the "Digital Cliff" with a variable attenuator, the 955Q SNR didn't read too high. Since the channel is occupied, the SNR is probably derived from the MER, which can be affected by more than one factor.

Here is an SNR comparison between the HDHR4-2US and the Hauppauge 955Q at the "Digial Cliff". The 50% Signal Quality for the HDHR, ~>15 dB SNR, is the lowest it can go and still have reception:

The Hauppauge 955Q tuner dropped out first.

This is below the "Digital Cliff". Signal Quality of 42 % is 13.86 dB SNR. It doesn't go below 41% which is 13.53 dB SNR.
0.41 x 33 (MAX SNR) = 13.53 dB

Starting a couple days ago, no longer able to get a lock onto CFTO-DT (9.1).

Have cut the cord a couple years back, but am new to consuming OTA broadcasts through MythTV. A couple days ago, my recordings for late night TV shows on CFTO-DT started failing.

I wonder if CFTO is using their DTX Digital Auxiliary Facility?
https://www.rabbitears.info/tvq.php?request=items&facid=9155500

 

[majortom]

what I have seen in linux on the 955q, and any other devices based on lgdt3306a demod is, it will cut out at around the same point as any other device. eg other devices will indicate near 15 dB at that point, while the lgdt3306a based devices like the 955q will indicate ~ 17.5 dB. At higher SNR conditions it seems to jive pretty well with other devices. The linux source code is using the below formula to calculate the snr.
It is reading so called Mean Square Error, and Power registers to populate the formula below.

static u32 lgdt3306a_calculate_snr_x100(struct lgdt3306a_state *state)
{
    u32 mse; /* Mean-Square Error */
    u32 pwr; /* Constelation power */
    u32 snr_x100;

    mse = (read_reg(state, 0x00ec) << 8) |
          (read_reg(state, 0x00ed));
    pwr = (read_reg(state, 0x00e8) << 8) |
          (read_reg(state, 0x00e9));

    if (pwr == 0) /* no signal */
        return 0;

    [B]snr_x100 = log10_x1000((pwr * 10000) / mse) - 3000;[/B]
    dbg_info("mse=%u, pwr=%u, snr_x100=%d\n", mse, pwr, snr_x100);
    return snr_x100;
}

Most but not all of the other atsc demods I have come across, will incorporate a lookup table of snr values.
Like someone developing the driver had test equipment to document the snr value for given register readings,
rather than calculate it directly.

 

[dsspredator]

I wonder if CFTO is using their DTX Digital Auxiliary Facility?

I am 31 miles south of the CN tower. I have an Antennas Direct DB4E and a winegard UHF preamp.

CFTO RF 8 is rock solid at 30 dB with the antenna pointed south towards WGRZ.

Very solid signal on the back side.

 

[rabbit73]

I am 31 miles south of the CN tower. I have an Antennas Direct DB4E and a winegard UHF preamp.

CFTO RF 8 is rock solid at 30 dB with the antenna pointed south towards WGRZ.

mailtodevnull is 26 miles SW of CFTO and is getting a signal strength reading of -96 dBm, which is only 10 dB above the thermal noise floor; something is very wrong.
https://www.rabbitears.info/searchmap.php?request=result&study_id=31321

Edit: I figured out how to tune to things using VLC.

Here is CFTO-DT:

$ dvb-fe-tool -mg -a0
FREQUENCY = 186000000
MODULATION = VSB/8
DELIVERY_SYSTEM = ATSC
       (0x00) Signal= -95.00dBm
       (0x00) Signal= -95.00dBm
       (0x00) Signal= -96.00dBm

 

[majortom]

Here is CFTO-DT:

$ dvb-fe-tool -mg -a0
FREQUENCY = 186000000
MODULATION = VSB/8
DELIVERY_SYSTEM = ATSC
       (0x00) Signal= -95.00dBm
       (0x00) Signal= -95.00dBm
       (0x00) Signal= -96.00dBm

Double check that frequency you had used in VLC to tune CFTO earlier.

The correct frequency for CFTO (RF Ch 8) is 183 MHz, not 186 MHz.

This is what mine looks like while tuned to CFTO, not coming in at the moment from here, but note the tuner
I am using (not one of the lgdt3306a based demods) still yields a CNR reading.

 

[rabbit73]

Check your mythtv-setup configuration.

The correct frequency for CFTO (RF Ch 8) is 183 MHz, not 186 MHz.
Double check that frequency you had used in VLC to tune CFTO earlier.

Good catch; I missed that.

RF 8 is 180 to 186 MHz. Mid-channel, 183 MHz, would usually be used.

 

[majortom]

yeah, disappointed I didn't see that earlier:frown
In any event, the tuner I was using above that provides all 4 metrics (in linux), even when below lock like that was the mohu a681, which is supported in windows 10, but not normally in the stock linux kernel.


https://www.amazon.com/Mohu-USB-TV-Tuner/dp/B07PYLGWSN
which is almost identical to this one from mygica (ebay link).
https://www.*********/itm/GENIATECH...925541?hash=item239c95e8e5:g:zNUAAOSwkaZZcsMy

 

[majortom]

In case ya ever wanna try it, patch to fix the SNR in the OSD, from years ago has not changed, other than maybe the specific line numbers to edit.

https://pastebin.com/edF3J4Zm

I believe really only impacts one .so in /usr/lib. /usr/lib/libmyth-30.so.30.0.0
And this is what it will look like after compiling, install.

 

[rob50312]

mailtodevnull the VHF kit needs to attached such as to have span aimed toward CN Tower and not attached as per instructions which would aim it at Buffalo.Attach the VHF rod turned 90.

 

[rabbit73]

the VHF kit needs to attached such as to have span aimed toward CN Tower

Good suggestion. I assumed he knew that already, but better to be certain.