SKD2018 HD Modulator (Thor Petit clone) - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 18 Old 12-15-2019, 01:35 PM - Thread Starter
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Cool SKD2018 HD Modulator (Thor Petit clone)

Decided this modulator needs (or these need) a thread of its own. (Note: click the > next to my handle in this quote to see the earlier discussion in the SL thread)
Quote:
Originally Posted by JHBrandt View Post
Just grabbed one of those from eBay. It appears to be this: https://www.soukacatv.com/household-...lator_p46.html

Yes it's one of those cheap Chinese modulators. I haven't hooked it up to a computer yet - I just configured it from the front panel - but at first glance it seems to stack up well against the SL mod:

  • Defaults to 1080i. With the SL mod, 720p30 is the only option.
  • Virtual channel/subchannel defaults to 2.1. There is a 2.1 in my area, but I don't watch it, so the default is OK for me. I assume if I hook it to a PC, I can reconfigure it to a different VC a la the Thor Petit.

    The SL mod defaults to VC 0.0, which is invalid and causes tuners to employ random "correction" strategies (the mStar boxes like iView fall back to the RF channel number + program ID, which is 4, so if you set it to RF 69, the iView will give it VC 69.4; OTOH, my DTVPal made it channel 70.0 )
  • Supports ATSC or something called J.83B. Google says J.83B is the QAM standard for North American cable. Don't really need QAM but it may come in handy for testing tuners someday.
  • The signal seems a bit cleaner. The SL mod's signal adds a bit of interference to the channel immediately below the one you're using, so you probably wouldn't want to set the SL mod to RF 37 if you have an RF 36 in your area. But with this mod, it looks like you could get away with it.
  • As noted above, it's almost $90 cheaper.

Downsides? A couple, but nothing major: first, it's harder to set up from the front panel. Instead of entering the channel number, you must enter a frequency. When I plugged mine in, it displayed 473.0, which I happened to recognize as RF 14. I changed that to 743.0, which is RF 59 (a nice vacant channel). 773.0, which is RF 64, would've been simpler (only need to change the first digit) but I happen to use RF 64 for an analog signal (my old satellite receiver).

Second, I saw the signal drop out a couple of times. The first time was expected: I started Vudu on my DVR+, which uses HDCP. So the signal probably dropped out momentarily until the HDMI handshake could complete with HDCP enabled. But the second time I was just watching whatever TV channel my DVR+ happened to be tuned to; there shouldn't have been any HDMI handshake. (I haven't yet seen it happen a third time, though.)

At any rate, the SL mod displays a bouncing "No Signal" instead of just "going dark" for a few seconds. I tested the new mod by turning off my DVR+. Edit: Slight amendment to what I had previously posted: when turning the DVR+ off, the new mod goes dark for a few seconds, then comes back on with a static screen reading "DTV." When the DVR+ is turned back on, it goes dark for a few seconds, then comes back on with the picture from the DVR+.

So that was kind of weird. Edit: And I found one more downside: I can't get WMC to recognize the new mod's signal. The HDHR's own software plays it, so it's specifically a WMC issue. WMC won't tune the SL mod's signal either, but that's understandable because of its invalid 0.0 virtual channel number. Don't know why it won't work with the new mod.

Hardly a show-stopper, though. At this point I'd say I got my $237 worth.

Edit: After thinking about things, I made a couple of changes to my configuration. I hooked the DVR+ back up to the SL mod, and hooked my Roku to the new mod. The Roku is "always on" so I won't have to worry about the modulator going dark momentarily when I turn the Roku off or on.

I also reset the new mod to 665 MHz (RF 46), a channel that happens to be very clean and free of noise in my neighborhood. (RF 46 is part of the uplink segment of LTE band 71, but apparently my neighbors have no T-Mobile phones that use it yet.) RF 46 is actually cleaner than obvious choices like RF 37 or RF 45, and by choosing an RF channel below 52, my DVR+ can actually tune to the Roku now!
So this weekend I finally hooked it up to my network. The only problem I had was that OOTB, it wants to be at IP address 196.168.1.10. I checked my router and found I already had a device at that address. so first I had to disconnect that device, assign it a different fixed IP address, and reconnect it. Then I connected the modulator to my network and was able to browse to its internal Web server. That brought up this System Status page:

As you can see there are several additional pages you can choose from the menu on the left.

"Basic Parameters" looks like this:

The "System Time Service" switch defaults to OFF but if you switch it on as I did above, a prompt for an NTP server appears. This defaults to a NTP server in China as you can see in the above screen shot. The Chinese server works fine but you can change it to us.pool.ntp.org or any other NTP server of your choice.

If you do this, the modulator will send the correct time to your TVs. This helps avoid confusion and is especially useful with DVRs, as it lets you schedule a recording from the modulator.
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post #2 of 18 Old 12-15-2019, 02:39 PM - Thread Starter
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Above I posted that Windows Media Center wouldn't tune the SKD2018. I found a workaround, using the "Modulation Parameters" page:

"Transport Stream Way" can be set to Air (8VSB) or Cable (QAM). If you select Cable you can choose QAM64 or QAM256 under "Constellation;" if you select Air, 8VSB is the only Constellation option. 6 MHz is the only bandwidth option for the SKD2018 modulator (that option exists because they have a DVB modulator that allows a choice of 6, 7, or 8 MHz). Audio encoder can be either AC3 (this is what virtually all OTA TV stations use) or MPEG2 (which is what the SL modulator uses).

But no matter what I tried, neither WMC's "Add Missing Channels" nor its "Scan for More Channels" options would add the modulator. The trick that finally worked was to "hijack" an existing but unused channel that had already been added to WMC earlier. And obviously, it had to be a channel no longer on the air, at least on the frequency it used when initially added.

Luckily, I found a few channels in WMC from stations that had moved in the repack and have not yet gotten back on the air. I ended up picking 51.6, which used to broadcast on RF 51 and is currently off the air completely. So I changed the RF channel to RF 51, the channel number to 51, the subchannel to 6, and re-enabled 51.6 in WMC. (Also changed the "short name" to Roku for benefit of other tuners, such as my iView.) It worked!

Even if 51 returns to the air someday, I probably won't add the "new" 51.6 to WMC. It was all religious and/or infomercials so I can live without one of its subchannels.

(BTW, the reason I picked 51.6 was a quirk of my iView firmware: if I key in "6" the iView will search for either a channel or a subchannel number of 6. DFW doesn't have a channel 6, and none of the TV stations with channel numbers below 51 has a .6 subchannel. So on my iView, I can tune to my "Roku" channel by just entering a 6.
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post #3 of 18 Old 12-30-2019, 02:29 PM
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Initial observations;

Power consumption; 4 watts no input, full (20db) attenuation, 6 watts w/ HDMI input & 0db attenuation,
The unit does get warm, but not hot. There are vents along both sides,
Boot time; 32 sec,
4.7db loss thru RF 'loop' using channel 30 as the test channel,
Output runs between 27.4 dbmV and 7.2 dbmV,
MER hovers around 32db (per spec),
No 'spurs' (harmonics) noted, clean output (which I wasen't expecting)

The three front panel controls are not user friendly, basically forcing one to use the web interface. Why not a simple channel up/down as opposed to changing each frequency (not channel) digit one at a time in one direction,
The power supply (that I received) is not power strip or outlet friendly. It's 'L' shape that lays flat with the blades at one end. It may block an adjoining outlet on a power strip assuming you place it at the end of the strip,
Disconnecting or connecting the HDMI input drops the RF signal for around 3 sec.
There is a 'splash screen' when no HDMI input is available,
If you change the signal source (Input) resolution (720p to 1080p for example) on the 'Basic Parameters' page, the 'Input Resolution' does not change. On the 'System Status' page it does without refreshing the page,
Depending on what channel you decide to use, if it is one that has a weak channel directly above it, it may cause a problem with that channel. More so, if you have it set for the full output. (27dbmV is fairly strong)
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Last edited by videobruce; 12-30-2019 at 02:54 PM.
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post #4 of 18 Old 12-30-2019, 02:29 PM
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RF tests

Equipment;
Siglent SSA3032X SA
Applied Instruments XR-3 SLM

I was surprised at how 'clean' this is, even at full output. I have a older HDTV video signal generator (Sencore VP-403C) with a RF output, it is anything but 'clean' as far as spurs' above the frequency (ch 30 in this case).

Note the Constellation diagram, in the lower left and the upper right, the shift or 'tilt' to the pattern which I don't recall seeing before (OTA). Any engineers out there can chime in on that aspect. The opposite corners are ok.
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post #5 of 18 Old 12-30-2019, 02:29 PM
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Interior pics

Admittedly, I wimped out regarding the two main SOC's U1 & U40 under the heat sinks. I didn't want to take a chance not knowing just how 'secure they are.
Note in the 1st pic in the upper left corner, the unused serial port and the battery backup. Also note a test port jack. On the other side. note the entire 'RF' section that apparently was designed for a 'shield', has none.
The 2nd pic, the board out of the chassis was rotated 180 degrees.

The board was basically well built except for some residue under the header for the display (see the 3rd pic) and a few other items. There was one 'mod' in the upper left corner which caught my eye just right of that SOC.
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post #6 of 18 Old 12-30-2019, 06:35 PM
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Quote:
Originally Posted by videobruce View Post
Note the Constellation diagram, in the lower left and the upper right, the shift or 'tilt' to the pattern which I don't recall seeing before (OTA). Any engineers out there can chime in on that aspect. The opposite corners are ok.
Looks like IQ imbalance. The gain of the I channel is a little different than the gain of the Q channel.

Here's what it looks like with 64QAM (along with phase noise).


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post #7 of 18 Old 01-04-2020, 05:38 AM
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What equipment (w/ that SI chip) was used for that display?

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post #8 of 18 Old 01-04-2020, 07:03 AM
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Quote:
The signal seems a bit cleaner. The SL mod's signal adds a bit of interference to the channel immediately below the one you're using, so you probably wouldn't want to set the SL mod to RF 37 if you have an RF 36 in your area.
I didn't see that in my scan. Thou I did not look for sub-harmonics (below) the test frequency, the 'haystack' seemed clean, mirrored on both sides.

What I wanted to try, but I couldn't really duplicate an OTA reception issue of a strong channel below a very weak channel. I do have an older off air scan of a 30dbmV local (7 miles) below a -7dbmV (55 miles) distance station (both in the same direction) and how the local swamps the distant station masking reception almost impossible. There are 3 other station with similar signal reading I have no issue with, just this one. These 3 do not have a 'local' directly above or below them. (see attachment, a old scan of both, the weaker signal was much stronger than usual when that screen shot was saved)

Something else, with the (what I consider somewhat excessive) loss of the 'combiner' within the modulator, it would make more sense to use a 'tap' (in reverse), something as a 12 or 15db (or more) to reduce the thru 'loss' of your system. Depending on your situation and signal levels of what is on your CATV or MATV setup, the 27dbmV output of the modulator should easily stand a 12-15db loss. This would/should be added after any amps/pre-amps and/or filters/traps. The modulator could even be placed away from the other equipment if needed.
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post #9 of 18 Old 01-04-2020, 08:08 AM
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FWIW's they also have a 'mini' rack mount version (same price) w/ the Ethernet jack on the front;
https://www.ebay.com/itm/ATSC-modula...YAAOSwJBhcfTOs

Note the power supply provided with this.

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post #10 of 18 Old 01-04-2020, 07:20 PM
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Quote:
Originally Posted by videobruce View Post
What equipment (w/ that SI chip) was used for that display?
It's a Silicon Labs evaluation board. The Si2183 does almost every DTV standard except for ATSC. Here it is on my "lab bench" (coffee table).


MCNS stands for Multimedia Cable Network System, which is the fancy name for cable TV QAM.



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post #11 of 18 Old 01-05-2020, 02:41 AM
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Why is there DC present to filter out?

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post #12 of 18 Old 01-05-2020, 10:52 AM
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Quote:
Originally Posted by videobruce View Post
Why is there DC present to filter out?
That bias T is for other projects and just happened to be in the frame. In that case, I was using it as a DC block when connecting my SDR transmitter to a DVB-S2 receiver which outputs a DC voltage to control antenna polarity. You can turn off the voltage on the receiver, but better safe than sorry with a $1200 SDR.


It's also used to power that S-Band downconverter.
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post #13 of 18 Old 01-05-2020, 12:11 PM
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Not to get too far OT, I have done numerous search for explanations of the 8VSB Constellation and the errors it cam show.
There is plenty regarding QAM, but that display is almost self-explanatory on it's own (to a certain extent). Not so for ATSC/8VBS, the example I had here is a good example.
I typed in "Constellation BER" and got a page of beer links.

Do you know any sources that enlighten the subject other than skimming the surface which was all I could really find?

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Quote:
Originally Posted by videobruce View Post
Not to get too far OT, I have done numerous search for explanations of the 8VSB Constellation and the errors it cam show.
There is plenty regarding QAM, but that display is almost self-explanatory on it's own (to a certain extent). Not so for ATSC/8VBS, the example I had here is a good example.
I typed in "Constellation BER" and got a page of beer links.

Do you know any sources that enlighten the subject other than skimming the surface which was all I could really find?
Since MER is derived from the constellation diagram, I suggest your search be done in that direction. MER considers all modulation errors; C/N only considers the affect of noise.









source:
https://www.digitalhome.ca/forum/81-...ml#post2919953
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post #15 of 18 Old 01-06-2020, 02:30 AM
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Noise level is pretty easy to figure out.
On those scans, the 100 to -100 scales what is that relative to, what UOM?

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Quote:
Originally Posted by videobruce View Post
On those scans, the 100 to -100 scales what is that relative to, what UOM?
I have no idea; maybe majortom can answer that.

My guess is modulation %.

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Quote:
Originally Posted by JHBrandt View Post
The signal seems a bit cleaner. The SL mod's signal adds a bit of interference to the channel immediately below the one you're using, so you probably wouldn't want to set the SL mod to RF 37 if you have an RF 36 in your area. But with this mod, it looks like you could get away with it.
Quote:
Originally Posted by videobruce View Post
I didn't see that in my scan. Thou I did not look for sub-harmonics (below) the test frequency, the 'haystack' seemed clean, mirrored on both sides.
Did you scan the Stellar Labs modulator too? That's the one I was talking about in that quote. The Stellar Labs' signal seems to "bleed" a bit into the channel below the one you're using.

But with this Souka modulator, I think it would be fine. The only potential issue might be with the tuner not being selective enough, a situation that can happen even with clean broadcast TV signals. (E.g., pre-repack, I had a very weak RF 18 right below a strong RF 19, which made receiving RF 18 challenging.) But if that's an issue, you could just up the attenuation on the Souka modulator a bit so it didn't overwhelm the tuner's adjacent-channel rejection ability.
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post #18 of 18 Old 01-22-2020, 02:23 PM
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Quote:
Did you scan the Stellar Labs modulator too? That's the one I was talking about in that quote. The Stellar Labs' signal seems to "bleed" a bit into the channel below the one you're using.
I don't have that, I must of mis-read your post.

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