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Old 10-Jun-2019, 3:19 AM   #20
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,738
It Works for Me

Using the equipment that I have available, I was able to add analog channel 65 to my OTA channels:

Obviously, the TV must be able to receive analog channels as well as digital channels.

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
-92 dBmV (-141 dBm) with the TV port terminated.
Attached Images
File Type: jpg Adding a Channel with a Modulator.jpg (69.8 KB, 1510 views)
File Type: jpg Blonder Tongue HAVM-1UA_1.jpg (79.1 KB, 1378 views)
File Type: jpg How to Use a CM3201 Filter.JPG (62.0 KB, 1423 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 14-Jun-2019 at 12:02 AM. Reason: Added measurements
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