Q-MAC Electronics Pty Ltd HF90 Manuale Utente

HF-90 Operation & Installation Guide 

As a rule, the higher the sun is, the smaller the distance 
covered - for a particular frequency.  This means that you can 
use a low frequency to communicate during times when the 
sun is low in the sky (early morning, late afternoon and 
evening), but you will need to use a higher frequency to cover 
the same distance during times when the sun is high in the sky 
(midday).  You will need to observe the above rule carefully if 
your radio has a limited number of frequencies programmed 
into it, as you may only be able to communicate effectively at 
certain times of the day. 
 

There are a number of different factors which will affect the 
success of your communications via HF/SSB radio.  These 
are outlined below:- 

Generally speaking the higher the frequency you select, the 
longer the distance covered.  Frequency selection is perhaps 
the most important factor which will impact on the success of 
your HF/SSB communications. 
 
Correct frequency selection is made easier with the use of a 
Beacon facility (refer to Section 6.3 of this Guide for details 
on the HF-90 Beacon). 

The above rule (the higher the sun is, the smaller the distance 
covered - for a particular frequency) also applies to the 
season, or month of the year.  Generally speaking, you will 
need to use a higher frequency to communicate effectively 
during Summer months, than you would need to in Winter.