A
rule of thumb with dB:
3 dB = a doubling or -3 dB = a halving of
power (watts)
10 dB = X 10 or divide by 10
power.
20 dB = X 100 or divide by 100 power
Generally, without
instruments to measure, in
communications systems, either VHF FM, or
SSB, empirically speaking, it takes a change of 3 dB to notice any difference.
So, except in very expensive high-performance systems, (many TV and FM broadcast stations use coaxial cable that cost $30 per foot and more, as well as $50K and more for antennas) ...
Don't sweat the small stuff. And 0.6 dB is small stuff.
Now, here's why handhelds have poor range.
1. They're
low power, like about 3 watts.
This is -9 dB compared to 25 watts which standard radios transmit.
2. They have inefficient antennas. (if interested ask)
Estimates vary for the "rubber duck" antennas, but are generally considered to be -6 to -9 dB reduced from a typical mobile antenna.
3. When held 5 feet over the
cockpit floor, let's say 7 feet over the
water, the distance to horizon is 1.4 x sqrt (7) = 3.7 miles.
For a
mast top antenna at 35 feet: 1.4 x sqrt (35) = 8.3 miles.
So, transmit power and antenna efficiency is about -17 dB lower than a standard VHF FM radio and antenna. AND due to height reduction, the line-of-sight distance is much less.
When a handheld is connected to a mast-top antenna, line of sight distance is the same, and antenna efficiency is improved significantly.
Now we're only left with the transmit wattage penalty, about 9 dB.
There will be a considerable improvement.
Chris