Is there really any difference between the upper HF and the lower VHF frequencies in voice communication?

Question

In regards to a wireless system.Range, interference, penetration of structures, weather?

Answer 1

HF is below 30 MHz, where VHF is above 30 MHz. Typical voice operating modes are AM and SSB on HF, and FM and SSB on VHF. AM, FM and SSB are all used near 30 MHz. SSB is by far the best communications, with the greatest range, followed by AM, then FM.

Range depends on antenna height, antenna gain, transmit power and receiver sensitivity. There is not much difference in range bewteen upper HF and lower VHF in this respect. Antenna size decreases as frequency increases. The smallest antenna is typically 1/4 wavelength long. At 20 MHz this is 12.3 feet, and at 50 MHz this is 4.9 feet. This means you can have more antenna in less space as frequency increases. Power output tends to be more difficult above 30 MHz, as many modules are designed to go up to 30 MHz. That's not to say there aren't Low VHF modules too, but they are slightly more expensive, and more complex.

Interference depends on the sunspot cycle (currently we are near the 11 year low). During times of high sunspot activity, the atmosphere is energized, and allows longer communications known as skip. This typically starts at lower frequencies first, and increases. This is known as the MUF (Maximum Useable Frequency). During these openings communications over long distances are open, as if they were next door. The problem with these, is they are very unpredictable. For this reason a higher frequency is desired, but skip can occur in the high VHF range (150 MHz) as well, just less often.

Static interference (Lightning) increases as frequency decreases. FM is not affected by lightning, where AM and SSB are.

Structure penetration increases as frequency increases, but without more specifics here it's hard to say if there would be much difference. At UHF frequencies structure penetration is noticeable better than at high VHF. 50 Mhz tends not to be asbsorbed by foliage as much as 30 MHz.

Weather affects both of these bands. My perception is that weather affects low frequencies more, but that's difficult to quantify. Local propagation is affected by temperature, humidity, cloud cover and such, but I haven't been able to understand exactly why.