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On/in a 'closed' system , it really doesn't matter unless the TV's involved won't reconize ATSC using a QAM channel map. I would have to 'assume' that switching channel maps, also switches modulation reception.
 

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Discussion Starter · #22 ·
I suspect that's generally true. But I actually had a bit of a surprise using one of those cheap mStar tuners. (I think it was an iView but they're all pretty similar.) In an effort to clear out the channel map I set it to Cable mode and did a full channel scan, thinking it would look for QAM signals and ignore the ATSC ones. But surprisingly it still found the VHF ATSC channels in my area! (RF 2-13 are the same frequencies for cable and OTA.)

So apparently those cheap mStar boxes will pick up ATSC channels even in cable mode. So if you want to broadcast ATSC on cable frequencies (either using a closed-circuit system in your home, or if you're a ham radio operator and this is legal on amateur TV channels), you could probably receive the broadcast with one of those cheap tuners, even if your TV won't receive it directly.
 

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Hi! Yesterday, I received the CM-1050 I had ordered during the Memorial Day VIP sale. My initial impression is that it was quite easy to set up and generally appears to perform the function for which it was designed. However, I have some concerns that may result in my returning it:

1. The latency is about 1 second, which is just tolerable, but the lag is pretty annoying when navigating on the Apple TV that I'm using as my HDMI video source, especially if I try to use the touchpad remote that came with the Apple TV. I realize this comes with the territory, and if I keep the box connected to the Apple TV, I'll just have to get used to it.

2. Certain sounds and voices seem to be rendered as something that I can only call "gravelly", some sort of low frequency amplitude modulation that is being imposed on them. The gravelly effect cannot be discerned all the time, just occasionally. It is particularly noticeable when listening to the Apple TV navigation sounds, which sound quite different from when the Apple TV is connected directly via HDMI.

3. Certain video scenes appear a bit jerky when compared with the original material rendered directly through an HDMI input or the original material rendered on my Windows PC. The jerkiness occurs occasionally, not continuously.

The gravelly sound effect is independent of the receiver and independent of any audio settings I may select on the Apple TV, CM-1050, or receiver. Likewise, the video jerkiness is independent of video settings on the Apple TV, CM-1050, or receivers. Both the sound issue and the video issue are totally repeatable when the same source material is replayed over and over. FYI, the Apple TV says it is outputting video in 1080p and the receiver says Channel 7.1 is 1080p; the Audio Codec on the CM-1050 is set to AC-3 (the default) because the other two settings do not work consistently on both receivers. There don't appear to be any firmware updates yet for this box on the CM web site.

To see what I am seeing/hearing, you can download >>> THIS ZIP FILE <<< which contains 5 short video clips:

1. NoGravellyAudio.mp4
2. NoJerkyVideo.mp4
3. GravellyAudio.mp4
4. JerkyVideo.mp4
5. GravellyAppleTVNavigationAudio.mp4

Clips 1 and 2 show what the original material looks and sounds like when I play it on my Windows PC and capture it with Microsoft's XBOX Game Bar (sorry for the excessive bass, it's just something that XBOX Game Bar does on my PC; I don't know how to fix it). This closely approximates what the material and sounds like when the Apple TV is simply connected to the HDMI input of my TV receiver. There is no gravelly sounding audio and no jerky video (thus the file names.)

Clips 3, 4, and 5 show what the same source material looks and sounds like when I play it from my Apple TV to my TV Receivers through the CM-1050 to Channel 7 and capture it with a CM DVR+.

In clip 3, you'll hear the gravelly audio best when the woman washing dishes at the sink speaks.

In clip 4, you'll see the jerky video as the boy enters the scene and pokes his head through the weeds.

In clip 5, I am simply playing with the Apple TV navigational sounds, and if you have an Apple TV, you'll know that these sounds are not what you would normally hear (which I can't easily capture); they have that gravelly undertone.

If you have a CM-1050 and subscribe to Amazon prime, you may be able to reproduce this by watching the first few minutes of The Durrells in Corfu Season 2 Episode 6 through the CM-1050. I'm hoping, in fact, that either someone can reproduce one or both of these two symptoms, or tell me that they don't occur on their system, in which case it's just something weird about my setup.
 

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@JHBrandt , I just noticed your earlier comment about "Latency" being adjustable on the modulator. I tried 100 and 0; these made the latency much more acceptable, but also increased the incidence of video jerkiness and, to some extent, caused some audio dropouts. I also tried 1000 hoping it would eliminate the jerkiness in the clip I posted, but it did not (seemed about the same as 500). So back to 500 for now until I know more about what I am actually doing.

Standby, I have a very promising update on this. See the next post.
 

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I've found solutions for both the (1) latency, and (3) jerky video problems:

EXECUTIVE SUMMARY
Change the Apple TV video output from 1080p to 720p, and change the Latency Video Profile setting on the modulator from 500 to 75.


THE NITTY-GRITTY
I now recall that when I got my Apple TV several years ago (as a present from my son) and plugged it into my HDMI switch, it set itself to output HDMI at 720p. It would not work if I tried to manually change it to 1080p, and the Apple TV didn't offer 1080i. This is likely due to a limitation of the HDMI switch, and 720p was just fine because my TV was old enough that any higher resolution was down-converted to 720p by the TV; that is its native resolution.

When I put the CM-1050 into the loop, the Apple TV automagically switched itself to 1080p, and the modulator's ATSC output was 1080p. Since this was not going through the HDMI switch, but rather coming into the set via RF, it was accepted and displayed just fine (internally converted to 720p, but showing 1080p on the display). This all initially appeared to work well, BUT...

Either the CM-1050 is not quite 1080p capable, or (much more likely) my HDMI cable was not quite 1080p capable, thus the occasional jerkiness when the bit rate cranked up (perhaps all those weeds along with the panning camera in that clip did it).

But manually setting the Apple TV back to 720p, I was able to eliminate all the video jerkiness, and even able to crank the CM-1050 Latency setting down to 75 without it coming back (which reduced the perceived lag during menu navigation to somewhere between 0.1 an 0.2 seconds, entirely tolerable even with the touchpad.)

Now on to trying to figure out the gravelly audio issue (which overall is not that annoying, but hopefully I can still find a fix).
 

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Hey, this thing goes both ways!

To clarify, I had assumed that its RF output contained every signal that was present on the RF input PLUS the new channel added by the modulator. What I didn't realize is that the added channel is also reflected back up through the RF input cable. So the new channel is sort of merged into my entire antenna distribution system (at least downstream of the distribution amp). What this means is the modulator need not be inserted before the first splitter to be a "whole house" solution; I can watch the new channel on the two sets in the house that are NOT on the RF output side of the modulator. This is certainly a very unexpected advantage.
 

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Discussion Starter · #27 ·
That's an interesting discovery. It sounds dangerous though: if someone connected its RF input directly to their TV antenna they would inadvertently broadcast their "in-home" channel to their neighbors! That can't be intended behavior - it could interfere with cell-phone signals, depending on the RF channel selected. I'm surprised it even got FCC certification doing that!

At least you have a distribution amp blocking its signal from being inadvertently broadcast, so you're safe. I'm safe too - my "upstream" is just another RF modulator; no chance for any stray signals to get back to my antenna. But unless this is a rare anomaly that only affects yours, it's something its users need to be very careful about.
 

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That's an interesting discovery. It sounds dangerous though: if someone connected its RF input directly to their TV antenna they would inadvertently broadcast their "in-home" channel to their neighbors! That can't be intended behavior - it could interfere with cell-phone signals, depending on the RF channel selected. I'm surprised it even got FCC certification doing that!
OMG, you are absolutely correct!
I disconnected both RF-in and RF-out cables and tried my 7.1 on the kitchen TV - no signal as expected. Then I connected a little rabbit-ear dipole to the RF-in connector. Went back in the kitchen and there was a perfect picture on 7.1. Then I fired up my 2nd DVR+ (also connected only to the antenna) on 7.1; signal strength and signal quality were 100! My VHF folded dipole is in the attic 1.5 stories up, 25 feet away, and oriented at nearly a right angle to this little dipole; it is not amplified (other than by the distribution amp further downline). I don't know if this signal would reach my neighbor's house (nor am I going to ask him to scan for it), but it is certainly much stronger than I expected. I don't have a field-strength meter to explore further.
IMG_8599.JPG
N.B.: Because RF 7 is VHF-HI, this could have been picked up by my DB-8 UHF antenna, which is amplified, but it's even further away and in a different attic 2 stories up, and again literally at right angles to this little dipole.

I'm surprised it even got FCC certification doing that!
I don't see any evidence/documentation/numbers of FCC Certification on the unit, the box, the users guide, or the CM web site.

Apparently, FCC Part 15 allows unlicensed emissions in the VHF-HI band only for biomedical telemetry devices, and then limited to a 200 kHz band, not a full 6 mHz TV channel:

§15.241 Operation in the band 174-216 MHz.
(a) Operation under the provisions of this section is restricted to biomedical telemetry devices.
(b) Emissions from the device shall be confined within a 200 kHz band which shall lie wholly within the frequency range of 174-216 MHz.
(c) The field strength of any emissions radiated within the specified 200 kHz band shall not exceed 1500 microvolts/meter at 3 meters. The field strength of emissions radiated on any frequency outside of the specified 200 kHz band shall not exceed 150 microvolts/meter at 3 meters. The emission limits in this paragraph are based on measurement instrumentation employing an average detector. The provisions in §15.35 for limiting peak emissions apply.
 

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I seem to recall several people who tested the Stellar Labs Modulator back in the day discovered the same issue with it. I can't remember which forum I read it on now, but I remember someone just connecting a decent length of coax cable to the output on one of those and being able to receive it on a nearby TV. Do you have any neighbors with antennas? I'd be curious to know how far your "signal" travels.
 

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I seem to recall several people who tested the Stellar Labs Modulator back in the day discovered the same issue with it. I can't remember which forum I read it on now, but I remember someone just connecting a decent length of coax cable to the output on one of those and being able to receive it on a nearby TV. Do you have any neighbors with antennas? I'd be curious to know how far your "signal" travels.
I can understand broadcasting the signal from the output of a modulator, but I would have thought they'd be required to filter the signal so that it doesn't go back out the input (and thus potentially right to an antenna on the roof.) In my case, it doesn't reach my antenna because I have a KitzTech amp between them that's uni-directional. I've already checked and though the signal (7.1) reaches every set in my house that's connected into the antenna distribution, it doesn't leak out anywhere because I can't scan it in on the one set in the house that simply uses rabbit-ears (which I borrowed temporarily for my OTA test above.)

My neighbor on my immediate right has an outdoor antenna - if I catch him around I might ask him to try scanning in RF 7 after I once again temporarily hook up the rabbit ears to the CM-1050 input. I doubt it will go that far, but you never know. I'll post in this forum if I ever get around to that experiment. In the meantime, I've changed my CM-1050 hookup to only have coax between the input and the nearest splitter, leaving the output disconnected (though I should technically put a terminator resistor on that), and that seems to work every bit as well as the two-cable "series" hookup, and I got rid of a stiff cable I wasn't liking very much anyway.
 

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Web Interface Doesn't Work On iPad:

While the web interface works with all of Firefox, Chrome, and Edge on Windows 10, and with Chrome on an Android phone, it does not work at all with Safari or Firefox on an iPad Air 2 running iOS 13.6. On the iPad, the interface initially appears in the browser and allows entry of the password and subsequent login; But after login, the main (lower right) pane remains white and empty, and none of the four menu items in the lower left pane have any effect when tapped (in fact, they do not even seem to be sensitive as buttons, they just act like ordinary text). Safari content blocker is disabled.

Has anyone been able to use the web interface to this modulator on an iPad or iPhone?
 

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Discussion Starter · #32 ·
Confirmed with Safari + iOS 14.6 on both iPad and iPhone. Might be related to incomplete support of HTML frames, which are rarely used by Web sites anymore, but are used by the CM-1050. I'm surprised Firefox is affected, though, since it works on Windows.
 

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I can understand broadcasting the signal from the output of a modulator, but I would have thought they'd be required to filter the signal so that it doesn't go back out the input (and thus potentially right to an antenna on the roof.)
Some modulators come with a warning, like for the ChannelPlus 5515:
http://pdfstream.manualsonline.com/7/723a266f-5457-4773-8738-47d46407c0ed.pdf

ChannelPlus 5515 Modulator Declaration of Conformity_1.jpg


ChannelPlus 5515 Modulator Isolation_1.jpg


contents
govinfo

https://www.govinfo.gov/content/pkg/CFR-2010-title47-vol1/pdf/CFR-2010-title47-vol1-part15.pdf

ChannelPlus 5515 Modulator Part 15_1.jpg


ChannelPlus 5515 Part 15.115(c)(4)_1.jpg


ChannelPlus 5515 Modulator Part 15.115(c)(1)(ii)_1.jpg


http://www.cantwellengineering.com/calculator/convert/uV

ChannelPlus 5515 Modulator Part 15 microVolts_1.jpg
 

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Some modulators come with a warning, like for the ChannelPlus 5515:
http://pdfstream.manualsonline.com/7/723a266f-5457-4773-8738-47d46407c0ed.pdf
Ahh, but that modulator only has an output, which implies it's up to the installer to figure out how to mix that output with other RF channels (including antenna) to comply with the FCC regulations. But the CM-1050 has both an output and an input, and the input is clearly shown in the user guide as "Antenna/RF Input", which would imply that CM would be responsible for implementing the isolation requirement within the box. From the photo of the PCB, there must be something going on under that metal shield between the input and output jacks, but "What it is ain't exactly clear🎵". What is clear is that the whole RF section of the PCB has a separate ground plane, connected by a number of strategically placed RF chokes to the main ground plane, so they seem to be serious about isolation. Perhaps the signal on the input jack really does meet all the Part 15 numerical requirements - I don't have the sophisticated test equipment to determine that - all I can see is it provides a solid "100" signal on all my coax back to the amp, which provides the isolation from the antenna.

In any case, I emailed CM to ask if this unit has passed FCC certification. We'll see what they say. It's curiously omitted from the user guide.
 

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Discussion Starter · #35 ·
I checked my modulator too, and discovered it has the same "feature," so it isn't unique to @frank70's unit. In fact, as far as I can tell the "input" and "output" are completely interchangeable!

I would have expected the antenna/RF input to have been combined with the modulator's signal with a circuit equivalent to a reversed signal splitter. That would give ~3.5dB insertion loss (unless they included a low-gain RF amp to compensate) but would have provided good isolation of the modulator's signal from the input in case the input was an antenna.

I should probably check my other ATSC modulators as well, to see if this "feature" is common or unique to the CM.
 

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Ahh, but that modulator only has an output, which implies it's up to the installer to figure out how to mix that output with other RF channels (including antenna) to comply with the FCC regulations. But the CM-1050 has both an output and an input, and the input is clearly shown in the user guide as "Antenna/RF Input", which would imply that CM would be responsible for implementing the isolation requirement within the box. From the photo of the PCB, there must be something going on under that metal shield between the input and output jacks, but "What it is ain't exactly clear🎵". What is clear is that the whole RF section of the PCB has a separate ground plane, connected by a number of strategically placed RF chokes to the main ground plane, so they seem to be serious about isolation. Perhaps the signal on the input jack really does meet all the Part 15 numerical requirements - I don't have the sophisticated test equipment to determine that - all I can see is it provides a solid "100" signal on all my coax back to the amp, which provides the isolation from the antenna.

In any case, I emailed CM to ask if this unit has passed FCC certification. We'll see what they say. It's curiously omitted from the user guide.
That is true. But, if the CM-1050 is considered a Part 15 device, they might not be required to do that. I would at least expect them to provide a note of caution as done by ChannelPlus.

CM-1050 ATSC Modulator Input-Output Jacks_1.jpg


My guess is that there is a hybrid splitter/combiner under the cover with not much isolation between the two ports. Yeah, you would need a signal level meter or a calibrated SDR like the RSP-1A with SDRuno software to measure the signals.

2021-3-8-ch16-measure_1.jpg


2021-3-8-ch16-measure2-jpg.jpg


Justification for correction factor:

bandwidth-and-thermal-noise-chart4-jpg.jpg


SDRplay RSP2 for accurate RF power Measurement_1.jpg



My Thor Petit Modulator measures +19 dBmV on the input jack and +26 dBmV on the output jack for RF channel 24. I don't see a Part 15 label.

Thor Petit HDMI RF MODULATOR3_2.jpg


I used my Sadelco DisplayMax 800 Signal Level Meter:

2SLMs_1.jpg
 

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Wow, that's some serious equipment you've got there! I can see the signal (1MHz at a time) with SDRSharp talking to RTL-TCP and a cheap Chinese dongle on a pi, but it's not really useful for absolute signal level measurements.
 
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