There should only be around 0.5 db loss for the F-F barrels.
You should have higher loss from the cable itself.
What is it for?
F couplers like the one below (commonly found at Home Depot), can be used to join to coax cables together. Signal loss is minimal; however, main factor for signal degradation would be the total length of coax used. To our best understanding, 25+ feet and above will see signal drop. I personally use these in my home; however, total length was under 15ft. If you notice any issues with services using couplers, let us know so that we can take a closer look at the account.
Difficult to say specific dB drops unless you have an RF analyzer connected, as my comment is a general guideline; if signal from the tap is already strong enough, then you may not notice any signal loss when running your specific length. You can try running this line, and if you do notice any quirks (such as pixelation on TV or intermittent connectivity on the modem), please let us know so that we can request for your account information for a closer analysis.
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