How to connect to VHS devices

[byetocable]

Title should have read... two VHF devices... sorry

This question is not directly related to antennas but the principle is the same.

I have a TV capture card in my computer. It has two tuners and can take a single RF feed (cable or antenna) and record two shows at the same time.

My need is to feed in two RF signals from two cable boxes. One set to Ch4 and the other to Ch3. My question is, what can I use to combine the two RF coax feeds into one to send to the capture card's coax connection?

Thanks for the help on this.

[Tim]

I would try using a two-way TV splitter connected in reverse. You would have about 3.5 dB of signal loss.

[byetocable]

I saw that they actually make a two way splitter/combiner so I ordered one of these. The signal out of the cable box is amplified so the slight loss should not be much of an issue I don't think.

[ADTech]

You cannot operate adjacent channel 3 and channel 4 NTSC, they will interfere with each other.

[Tim]

I just tried an experiment here with a couple of old RCA digital converter boxes I had from back in the analog to digital transition. I used a splitter to connect my antenna to both boxes. I set one box to output on channel 3 and the other on channel 4. I then used another splitter in reverse to combine the two outputs and ran it to an old 9" analog B&W TV. It worked fine. Of course this is not exactly what the OP wants to do, but it is similar. From that experiment I would surmise that sometimes it might work and sometimes it might not.

[byetocable]

Originally Posted by Tim

It worked fine. Of course this is not exactly what the OP wants to do, but it is similar. From that experiment I would surmise that sometimes it might work and sometimes it might not.

You're actually doing exactly what I need to do. Combining two analog cable boxes into a single tuner. I'm hoping your experiment works for me.

Thanks for taking the time to test it.

[Tim]

I would imagine that it depends a lot on the strength of the signals. If they are too strong I would guess it would cause issues.

[byetocable]

Originally Posted by Tim

I would imagine that it depends a lot on the strength of the signals. If they are too strong I would guess it would cause issues.

It may also be that today's digital tuners are so accurate they are not as affected by close proximity channels as the TV tuners of years past.

I hope so, anyways. I need for this to work.

[Tower Guy]

The limitation is the lower sideband filtering in the higher channel modulator. In olden days the LC filtering was usually poor. In today's modulators the LC filters have been replaced with SAW filters. This makes passive combiners of analog signals possible. If you find interference on channel 3, try reversing the channels of the two modulators. One of them may have better lower sideband rejection.

[Tower Guy]

Another trick would be to use an attenuators on the channel 4 modulator. That would reduce the amount of lower sideband into channel 3.