The following is one of my personal experience of installing a TV Antenna. I believe you will also benefit from my experience.
The antenna is now installed on my roof and connected to my radio through my roof via a Coaxial Cable.
Now, before letting everyone get excited about what this means, let's compare my previous outdoor settings with the current settings.
Today, I am using a 30-meter long LMR400 Coaxial Cable. I used RG58 Cable before, but it was only 20 meters.
From the point of view of the Coaxial Cable, even if I increased the length by 30%, my loss actually dropped, and the loss at 70cm dropped by more than 4 dB. If you remember, a loss of 3 dB is equivalent to losing half of the signal, so before my 5 watts of power reach the Antenna, using RG-58 has already lost more than half.
In addition, the two antennas are different. Not many, but enough to make a difference. Because of the icing on the cake, the new antenna is a third longer, so my new antenna has a better line of sight, even if it is installed at a similar height, it is higher from the ground.
As you may remember, loss and gain depend on frequency, so calculations need to be made for each frequency band to be used. In my case, I have to do it twice, once for the 2m band and once for the 70cm band.
Get the power output from your radio, subtract the Coaxial Cable loss and increase the antenna gain. The final result is a number that represents the gain or loss of the entire system. If the loss of the Coaxial Cable is the same as the gain of the antenna, you won't lose anything, but you won't get any gains.