In one client's system I'm using a PVI single channel ATSC modulator. Its output is fed via a backwards splitter into an antenna distribution system. Everything looks normal for such a system although I haven't measured actual signal levels yet, as my meter is in need of repair.

So...

The output of a DirecTV RF client goes into a PVI MiniMod2 that's set to channel 17.1. This is ATSC, so the frequency is 491 MHz, that is, UHF 17, not Cable 17. The signal is mixed into the client's OTA antenna system. A Tvfool report shows no station on 17.1, but a strong station on 18.1. (For thoroughness I will check performance on 16.1, since there's no co-channel or adjacent channel situation there.)

I saw several things happening yesterday with little time to get all the details.

One 2015 Sony TV has severe lip sync problems.
One 2008 Sony TV has some kind of digital "stuttering" similar to sounds I've heard with occasional poor cell phone connections just before a call is dropped.
My cheap Best Buy $100 utility TV goes blank from time to time but has no lip sync or other problems.
An LG TV has no problem with the signal.

All I can figure at the moment is that the RF signal level at the TVs might be too high for them to handle properly. That seems like quite a stretch but I guess it's possible.

The client is set to output only 1080i so it won't change output resolution as program resolution changes. (This was recommended by PVI.)

Any ideas?

1. What does the mod manufacturer say?
2. What is the dB output of the modulator?
3. Does the mod have a spectrum analyzer to determine frequencies? Some brands do
4. have you gotten an idea as to gain off the antenna?
5. How far apart are the two gain figures?
6. What happens when you have no antenna hooked up in combination and simply drive the mod to the sets?

I haven't called them yet. As another member posted here the other day, PVI seemed at first to be very attentive; then once the item was sold to me it's been hard to get hold of anyone. The Trouble Ticket that I created, labeled as High Priority, got no response for several days. I lucked into the proper settings, it seems, just by messing with the cursor pad.

My meter is in need of repair. Early on I was told it was somewhere between +20 dBm and +30 dBm.

No, but what do you mean, "to determine frequencies"? Frequencies of what? FWIW, its documentation has a list of channel frequencies (491 MHz is what the modulator calls channel 17)

I'd say the gain is 1... at 100 MHz.
I have to apologize for the stupidity of this one: the system uses an FM turnstile antenna. I grabbed the wrong box one day and that was all I had. I put it up because the client's main interest was the modulated signal, not the OTA signal. The lowest frequency of interest is channel 7 at 175 MHz, almost an octave above the FM antenna's peak response frequency; the highest is 800 MHz, three octaves up. That said, the site has direct line of sight to the LA market's antenna cluster some twenty miles away. Despite this horrible conglomeration of wrong things, after about 14 dB of splitter attenuation we get ALL the local channels!

What two gain figures?

Damn good question!

The client only recently moved in. A lot of the time out there has been dedicated to working out wiring challenges in a home with a slab floor, daisy-chained CAT3-looking phone wiring, and a second story attic that's so small in height, and filled with insulation, that it looks like it could only be wired by a trained rat.

Ernie,
Those modulators put out +45dB of signal. If you are not going thru at least -30dB of attenuation thru the system, then you are WAY over driving everything. That would be similar to going thru two 16 way splitters or 1000 ft. of RG-6 coax.

There is a setting in the menu to adjust the output of the modulator to what you need.

And yes, you HAVE to leave channel spacing between channels (no adjacent channels). And you need to find out what frequency channel the incoming ATSC broadcasts are using. Local station on 18.1 might not actually be broadcasting on the channel 18 UHF frequency. Example: Our local channel 11.1 actually broadcasts UHF channel 15.

I thought I remember you said you had designed RF systems in the past? Old age getting to your memory? :)

Last answer. ZeeVee, which is a more expensive product, offers a spectrum analyzer to determine what frequencies are in use, and what frequencies are open for modulation. ZeeVee outputs 45 dB of signal, but can be adjusted down in 5 dB increments. As you might guess, having signal strength about the same for all signals, modulated or not, is a good idea. Those are the two gain figures I was alluding to.



Good luck with your project. Sounds like it will be an interesting experience for you.

Thanks for this!

Perfect. Thanks. I used to have a collection of attenuators. I'll just buy some more.
Being picky, you don't mean -30dB of attenuation. The minus sign implies lowering of level and "attenuation" means lowering of level. You mean 30dB of attenuation. And you probably mean +45dBm.

Hmm. Will look for it.

I've been aware of this since the first digital channels popped up all over the UHF part of the spectrum. Sorry I didn't say so, but I always refer to the "Real" channel numbers, not the "Virtual" channel numbers, when I'm talking about antennas. Or, like you, I call them UHF 17, etc.

What did I forget?

Wanna buy an RF amplifier that's good from 5 MHz to a whopping 300 MHz? I've got one for sale....

This, combined with what you said earlier, makes me unsure whether the spectrum analyzer is part of the modulator, or a separate item. Which is it?

And, incidentally, we're able to pick up a low-power analog TV station, channel 6, in Big Bear, CA, in the general direction of the LA market antenna cluster. Who'd a thunk?

The spectrum analyzer is part of the interface on the ZeeVee. No separate box.


By the way, you also have a web interface on the PVI which makes it a little easier to navigate everything - as there is a lot in the menu system. Some things might not even be on the built in display menu, I've never configured one like that; I've always used the web interface. It also allows you to save a copy of the profile you made as backup.

Which makes me think. If you are using ATSC signals from an antenna, you need to make sure you are using 8VSB modulation on the modulator. And not QAM256 for a cable system. This would certainly confuse a TV tuner having mixed signals on same feed.
But 1st!!! You need to get into the menu and lower than RF output from +45dBm - calculate your losses and figure out what output you do need to use.

Edit: Added the next line:

Brad, I'm discussing the Minimod2. Is that the unit you're discussing?




When I saw this --

Since it mentioned connecting directly to a TV, I then thought it was not necessary to attenuate the signal. Also, there's no instructions in the manual regarding adjusting the output level, nor even defining it. The manual is not very good.


But I had seen this:

I didn't think to look for output attenuation built into the unit. PVI just said they all have the same output. If they can be internally attenuated, they won't necessarily all be at the same level. If this had a caution to first be sure they are all programmed to the same level, then, yeah. But no.

Hmmm.... Missed you were using a MiniMod2. I have never used that piece.

I can not find a manual or detailed data sheet for that unit anywhere on the internet. Crazy!!!
It appears to be programmed by the buttons and built-in screen only. I have no idea what the dBm output is and if it can be adjusted.
You will have to keep bugging PVI until someone there answers the phone or calls back.

Well, no... and I was sure to include the model number of the product. It's on about the fifth line of the first post:

I wish you had seen that. A lot of time was wasted looking for features that this piece doesn't have.


I've already told PVI that this is crazy, but they say it works for them. But it is truly crazy.

To get the manual, you have to go to their website and enter the serial number of the unit you have bought, or scan a QR code. This information is on the carton, NOT ON THE DEVICE, so good luck if you happen to lose it.

Beyond that, I always like to look at manuals before I buy them, or, as you did, look at a manual in order to help out someone who's asking questions.


It's about +30 dBm. I got my meter fixed.

...and yesterday, after hearing a recording I made of the "stuttering" audio, they concluded the modulator must be bad. That's a good thing! Now we'll see how they handle this.