Per Tower Guy, the current CM-7777 is recommended if all of the follownig are true:
- There are no TV signals with a TV fool NM greater than 40 db.
- There are no FM signals with a signal strength 10 db higher than the strongest TV signal. (or you use a 7-69 antenna)
- The antenna is split to more than 2 TV sets.
- The cable length is longer than 50 feet.
- The weakest signal of interest has a NM plus antenna gain of less than 6 db.
You may find this site useful, click CALCULATING SYSTEM NOISE TEMPERATURE
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