combining an RF signal with my OTA antenna
Hello everyone,
My house is a 2 storey home where there is only an RG6 coax cable going to the top level of my home. I use a netmedia triple play modulator (MM73) http://www.netmedia.com/modulators/mm73.html to combine composite signals from three devices to one coax cable outputting on UHF analog channels 60, 62 and 64. I am trying to combine my OTA antenna with the output of the MM73 using a regular splitter/combiner. I am using a good quality splitter, (I've tried a few, that isn't the problem). The splitters I tested are Antronix CMC2002H OR BGI SGHMQK-2, both give the same results. The OTA signal is great as this is just for a 2nd TV set for the guest room. When I connect the MM73 output to the splitter/combiner, the upper UHF channels go to zero signal strength. These channels are 43 (647 MHz) to 49 (683 MHz). There are two local channels in that range that are usually 100% signal strength and 100% quality. They are channels 44 (653 MHz) and 47 (671 MHz). If I leave the splitter connected and just disconnect the MM73 output from the splitter it works great. As soon as the MM73 is connected, the channels mentioned above go to zero signal. There are no amplified splitters, preamps or anything else in the line other than what you see in the picture. The MM73 modulator can transmit on UHF or VHF and is configurable. I tried only using one output and transmitting on channel 30 UHF but the result is the exact same. I even tried a 7db attenuator on the MM73 line going into the combiner, same results unless the MM73 is disconnected. I hope someone can give me some ideas on what to try. I really don't want to have to fish a coax cable up and crawl around in the attic when there must be a simpler solution. Any help is greatly appreciated. https://i.ibb.co/ZHs822Y/diagram.jpg |
The problem isn't the splitters, it's most likely that the modulator isn't very "clean" and is transmitting signals that are below the channels that you've selected. That splatter is interfering with the desired UHF OTA signals. FWIW, those two local stations will be leaving those operating channels sometime in the next year or two as a result of the repack.
Are you sure that your RF modulator can do VHF? The spec sheet indicates UHF only frequencies are offered. If it can do VHF, which channels? Do you have any VHF stations in your area? It would be simple to combine a VHF signal to an existing antenna feed if you don't have any low-VHF using an HLSJ or any VHF channel using a UVSJ. |
Thanks for your response.
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because I have super strong channels on 8 & 10 (10 will be moving to 9 in the near future) I can try this and post my results. EDIT: the modulator does work on VHF but only on channels 70 -94, 100-125. |
I installed a 20 db attenuator on the modulator cable going into the splitter and one of the channels came in, but a bit choppy (I guess it's not really watchable). The modulator output is watchable but not really the best quailty.
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Are your TV channels on 20 and up? If so this will allow the use of channels 14, 16, and 18.
https://www.solidsignal.com/m/product.aspx?p=nf-469 This model would allow use of channels 65, 67, and 69. https://www.solidsignal.com/m/product.aspx?p=lpf-750 You will also need the 20 dB attenuator on the output of the modulator. |
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Between the cable coming from my antenna to the splitter input? or From the modulator output to the splitter input? |
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I don't think that either the LPF or the NF will do the needed job. UHF channels 60-64 are far enough removed from UHF channels 43-49 that the modulated analog signals, if clean, shouldn't interfere with the OTA signals. My recommendation would be to 1) move the analog to 65-69 and then, if necessary, 2) install a HIGH pass filter (~750 MHz) on the modulator's output to suppress the frequencies below that output prior to combining. Unfortunately, that would likely be a custom device. I would still use the suggested attenuation to cool off the whole signal from the modulator. |
The 750 MHz Low Pass Filter goes between the antenna and the combiner(splitter). The attenuator goes between the modulator and the combiner (splitter). The attenuator may need to be a bit more or less than 20 dB. Note that the modulator has a rated output of +30 dbmv. This equates to a NM in the 70 dB range for digital signals or roughly 35 dB for analog signals.
Here’s my thinking: I agree with ADTech that the modulator is putting out signals that interfere with the off air channels. The attenuator will fix that.......BUT the OTA antenna is picking up LTE signals above 700 MHz, so they interfere with the modulator. The LPF-750 will filter out the LTE signals on channels 65-69. |
This LTE filter will do the same thing as the LPF-750 and is cheaper. https://www.channelmaster.com/TV_Ant..._p/cm-3201.htm
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Thanks Tower Guy. I broke down and ordered one.
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See also this thread: combining an RF signal with my OTA antenna https://www.digitalhome.ca/forum/81-...a-antenna.html |
finally got the LTE filter after almost a month. Installed it and the 20db attenuator as per post #8 above.
There is absolutely no difference. |
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Did you try what I suggested on the Canadian forum? https://www.digitalhome.ca/forum/81-...ml#post3079969 Quote:
If that doesn't work, you will need to do what you don't want to do: run another coax line. I'm a little confused by your diagram; it only shows one TV. Is the OTA antenna only for the 2nd TV, or for both TVs? Is the modulator output just for the 2nd TV, or both TVs? |
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Revisit post #7.
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SO this response will be very short because its late. yes i tried this with 37db attenuation. Modulator channels were snowy but this didn't help. I am trying to get CITY TV, channel 44, 653 MHz. Without the modulator it comes in. I even get Fox and ABC but not CITY-TV with the modulator connected. Quote:
The output of the two goes to the bedroom tv and is independent of all other tv's in the house. |
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I revised your diagram to match your description. Is it correct? How do the modulator channels look on the other TVs? You have probably eliminated the overload possibility with the attenuator, but the modulator could be putting out spurious signals in the UHF band, as ADTech has indicated, that would interfere with the reception of your desired UHF channels. Are you still in Newmarket, ON? Is this report correct for your location? https://forum.tvfool.com/attachment....1&d=1559950609 These are suggestions made by ExDilbert: https://www.digitalhome.ca/forum/81-...ml#post3079995 Quote:
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It Works for Me
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Using the equipment that I have available, I was able to add analog channel 65 to my OTA channels:
https://forum.tvfool.com/attachment....2&d=1560133185 Obviously, the TV must be able to receive analog channels as well as digital channels. https://forum.tvfool.com/attachment....3&d=1560133686 http://forum.tvfool.com/attachment.p...1&d=1546799595 https://forum.tvfool.com/attachment....4&d=1560133977 The modulator is leaking through the port to port isolation of the splitter used as a combiner. The attenuator, port to port isolation, and LTE filter reduce the modulator signals reaching the antenna. A preamp below the LTE filter, if needed, will increase the isolation. The attenuator can be increased to bring the modulator signals down to -9 dBmV; the snow begins at about -15 dBmV. Grounding the coax shield will make the attenuator and LTE filter more effective. I have the equipment to measure the modulator signals that arrive at the antenna; most user don't. If they are below the Thermal Noise Floor (for a 6 MHz bandwidth TV signal) at -106 dBm (-57 dBmV) , it is probably safe, as far a causing interference is concerned. Without the CM LTE filter, the modulator would be considered an illegal unlicensed transmitter. These are the measurements for the splitter as combiner that I used: IN Modulator Port: +1 dBmV OUT Antenna Port, TV Port not terminated: -6 dBmV OUT Antenna Port, TV Port terminated w/75 ohms: -23 dBmV The attenuation of the CM 3201 for channel 65 is 69 dB That would make the channel 65 modulator signal at the antenna -75 dBmV (-124 dBm) with the TV port unterminated and -92 dBmV (-141 dBm) with the TV port terminated. |
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