FM antenna & TV cable interfere - Leadtek TV2000 XP Expe

[beamguy]

My Leadtek TV2000 XP Expert card has two inputs for antenna or cable, one for the FM tuner and one for the TV tuner. After solving some ground hum issues I was starting to be happy with the reception from my Comcast Cable TV input - though it is clear that this tuner is extremely sensitive to ground loop noise.

Then I plugged in my FM antenna. For awhile afterwards I was quite baffled as to why my signal on channel 2 was now completely black & white diagonal lines, and the other low channels were extremely degraded. Then I thought to unplug the FM antenna and presto, the picture came back on my lower channels.

My FM antenna is a large directional dipole antenna in the attic. It is an older design that picks up the lower channels 2-6 much better than the upper ones, for channel 2 it picks up a pretty strong signal. Also - the signal frequencies of broadcast channel 2-13 are very close to the HRC cable assignments. It seems pretty clear to me that my problem is that the signal from the FM input is being added to the TV input.

So here is my question. Is this by design - or is my card defective? If I send it back which should I choose? Would a card with a philips tuner have a more logical separation of the two input sources?

[DTSL06]

I have the same TV card. But I use a the cable to get the FM. If you have FM on cable support, connect the FM lead to a cable and see if it fixes the prob. If not then it could be a bad card. I have no prob with cable TV and FM thru the card via a cable spitter. I use my card almost like a TIVO and record TV programs to HD to watch later or listen to FM while working. I also tested just the supplied antenna and I get no interference.

[beamguy]

There are no FM radio signals on my cable.

I am suspicious that the two inputs are simply run into a combining circuit on input, then sent to either the FM or TV tuner. In your case splitting then adding the same signals back together would not cause any harm. In my case having two strong but different signals on nearly the same frequency will cause interference.

I'm curious to know what would happen if you don't use a splitter but simply run the cable into one or the other of your inputs. Will both the FM & TV work? If so that would confirm my suspicion about the design of the RF circuitry on the card. That would also be a better configuration for you, since the splitting/combining of the signals can cause distortion.

[DTSL06]

They work fine seperately when connect one at a time also, no interferenec at all. I use to have only the TV connected and not the FM. Maybe u can try using the T antenna that was supplied with card. Like u said maybe you reception from the FM is too strong. I was using the T for a while b4 I split the cable. I dont notice any interference when both are connected via the spitter or seperate inputs.

[FOO]

I'm confused as to what you are trying to do
Do you want to listen to the radio on your computer or
watch/capture video ?

[beamguy]

They work fine seperately when connect one at a time also, no interferenec at all. I use to have only the TV connected and not the FM. Maybe u can try using the T antenna that was supplied with card. Like u said maybe you reception from the FM is too strong. I was using the T for a while b4 I split the cable. I dont notice any interference when both are connected via the spitter or seperate inputs.

I'm still curious if before you had the splitter you would have picked up the FM signals just fine with nothing attached to the FM antenna input. That would confirm if my card is defective or just doing what it was designed to do.

It is true that using a big directional antenna I get a strong signal on channel 2 from both sources and the T antenna would would give me a wimpy little signal less likely to interfere with the TV - but that does not sound like progress to me. I'm not willing to pay the cable company for FM when I can pick it up quite fine from the air for free. I should add that the Leadtek tuner does give a very good FM sound.

[beamguy]

I'm confused as to what you are trying to do
Do you want to listen to the radio on your computer or
watch/capture video ?

I have a capture card that claims to be capable of both.

My problem is it will do one or the other, but cannot be plugged into both signal sources at the same time despite having inputs for two separate sources.

[DTSL06]

I'm still curious if before you had the splitter you would have picked up the FM signals just fine with nothing attached to the FM antenna input. That would confirm if my card is defective or just doing what it was designed to do.

.

Srry, I shld have mentioned that I have to have the T connected to get FM, when I 1st only had the cable connected I was only watching TV and not listening to FM. Funny u have to pay for the cable FM since mine is included if I want it or not as part of my cable package.

Just so to clear things up.

Cable TV connected alone works fine for TV
T antenna connect alone works fine for FM
Cable and T connected both works fine for both TV or FM
Cable split for TV and FM works fine for both TV or FM.

srry for any confusion.

[beamguy]

Here are the results of the test that I suggested on my card...


In this image there is NO INPUT to the TV. I have plugged the large FM antenna into the FM input connector. The TV input has nothing on it. The channel needed to be fine tuned to pick up the broadcast channel 2 on a slightly different frequency.


Here is the image when the cable is plugged into the TV input with nothing on the FM input...



And finally, here is the image on channel 2 when both FM & TV inputs are connected to their proper inputs.


This interference occurs to some extent on all the lower frequency channels. These do not come in order on Cable HRC. Channels 1-6 are followed by 95-99, and then 14-22. The cable signal is lost above this frequency when fed into the FM input, suggesting that there is some sort of a mild band pass filter on the input, but not selective enough to keep out the lower TV channels.