Your HD spectrum at 25 feet.The first "hump"
is the fundamental frequency band (centered at 750 MHz). The second
is the third harmonic (the energy band that creates sharp
transistions). After your HD signal has traveled a couple of hundred
feet down a coax...
Do you know how much high frequency energy is left?
Why should you care?
At 125 feet you can see that overall levels have dropped and that the upper end of the harmonic band is flattening out.
At 300 feet it is all over. No upper
harmonic band at all, so no square waves, and what is left of your
signal is even a decent sinewave.
You need a way to know exactly how close to the error cliff your HD
signals are
The HRM-1500, besides giving an easy to read "gas gauge" display also give you quantitative readings that fundamental verses harmonic energy values
As the display to the left demonstrates your HD signal can plunge towards the error cliff in short order.