Modulator Question

nightwalker

Active Member
I have a whole host of channel modulators. Some broadcast security cameras, some the VCR and DVD outputs and still others do Hauppauge MVP outputs. That being said all the channels are clear and crisp on any TV, be it standard CRT, Plasma or LCD.

In my home office and my wife's I've installed TV cards in the computers trying to get hem to do double duty as a TV. The TV channels are just great, what you'd expect. The channels that are modulated on the other hand are terrible, dark, fuzzy, almost to the point that you have no idea what you're looking at.

I brought in a standard CRT set and put it right next to the computer, using the same video jack, was able to look at the systems side by side. Viewing standard cable channels the picture was equally good on both systems, in fact the computer showed what i thought was a little better picture. Viewing the modulated channels was a different story. Beautiful picture on the TV viewing the modulated channels, on the computer through the TV card, the same fuzzy picture.

There must be something that the computer TV cards don't like about modulated channels that a stand alone TV has no problem with. For the life of me i can't figure out what i could be though.

Has anyone out there also experienced this, and were you able to fix it?
 
Are you filtering out any cable channels (usually by using a low pass filter) on the channels that you're modulating on?
 
Another posibility is the RF signal level from the modulator(s) is outside the range that the computer TV card can handle. The input range of AGC circuits in will vary from device to device (so the picture will look good on some devices). A signal level of 0dBm is ideal with +10dBm being the max. Without a signal level meter it is hard to say whether your signal is too high or low. A Sencore model 573 is a good device for looking at these levels. Another option would be to simply vary the output level of a modulator and see what it does to the picture quality.
 
Guy Lavoie said:
Are you filtering out any cable channels (usually by using a low pass filter) on the channels that you're modulating on?
Yes i am using a low pass filter. I filter out everything over channel 80 and use those empty channels for the modulators. I'm also leaving a blank channel between so there is no interference. Works beautifully on TV's, just he TV computer cards.
 
electriclight said:
Another posibility is the RF signal level from the modulator(s) is outside the range that the computer TV card can handle. The input range of AGC circuits in will vary from device to device (so the picture will look good on some devices). A signal level of 0dBm is ideal with +10dBm being the max. Without a signal level meter it is hard to say whether your signal is too high or low. A Sencore model 573 is a good device for looking at these levels. Another option would be to simply vary the output level of a modulator and see what it does to the picture quality.
this might be a thought. I didn't think about maybe the signal being too strong to those ports on my system. I use an ONQ panel with amplifier to get the signal to some places that are more than 75ft or so away. I'll measure the signal strength at the port and if it's too much I'll cut it down a bit and see what happens.

Thanks for the tip, even if it doesn't work, it gives me something to try ;)
 
jay said:
If the signal IS too strong, you can get inline attenuators.
believe it or not i have an assortment of those just waiting till i can measure the signal strengh. I've never had occasion to use them before and had almost forgotten i had them.
 
What TV tuners are you using? I have had similar problems with certain TV tuner cards... I've been through more than a few. Some would not even recognize a modulated channel. Sorry, I can't recall the names right now, but one was an older Hauppauge PCI card. Now I use only Hauppauge USB2 and they are pretty good with my modulators, but not great.
 
Mark S. said:
What TV tuners are you using? I have had similar problems with certain TV tuner cards... I've been through more than a few. Some would not even recognize a modulated channel. Sorry, I can't recall the names right now, but one was an older Hauppauge PCI card. Now I use only Hauppauge USB2 and they are pretty good with my modulators, but not great.
I'm using a Hauppauge pvr usb2 and a kworld mce 200 deluxe. The Hauppauge seems the better of the two but neither of them does well with any modulated channel.
 
electriclight said:
A signal level of 0dBm is ideal with +10dBm being the max. Without a signal level meter it is hard to say whether your signal is too high or low. A Sencore model 573 is a good device for looking at these levels. Another option would be to simply vary the output level of a modulator and see what it does to the picture quality.
Great info Elecriclight! I had a post a week or two ago asking what to use to check the signal levels on incoming cable. Do you have a link to the model you mentioned? I've searched around and all I can seem to find is 1453 (~$2000) or the 755 (~$400).
 
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