Topband: FT8 - the end of 160m old school DXing?

[JC]

Hi Top Band lovers

The emotion should be aside , lets dig into the technology and ask why things are that way nowadays.

Computer is not only part of the radio  but the radio itself is a computer today.

The reason FT8, or JT9 and others digital modes dig signals we can't hear can be understood in 3 different levels.

1- The signal do noise ratio, as the name explain itself, is the ratio between power noise for a nominal bandwidth  and the signal level. There are two ways to increase the signal to noise ratio . First and most common is to reduce bandwidth, and that's why CW is a better weak signal mode than SSB, CW can be used down to 100 Hz and SSB 2 KHz.  Let's check some number's, assuming the Noise figure is 5 db the MDS for different bandwidth are.

BW =      1 Hz  >  MDS = -169 dBm
BW =      2 Hz  >  MDS = - 165 dBm
BW =    10 Hz >   MDS = - 159 dBm
BW =  100 Hz >   MDS = - 149 dBm
BW =  500 Hz >   MDS = - 142 dBm
BW = 2000 Hz>  MDS  = - 135 dBm

To copy a signal at noise level or near the MDS the BW has a huge impact. Narrowing the BW  from 500 Hz to 2 Hz the increase in signal to noise ratio, it would be  -142 to -165, it means 23 db improvement. 

The JT modes uses the DSP digital data and calculations to get a practical BW less than 2 Hz!. In order to accomplished that the clock on both PC must be in sync by few milliseconds. That is not new at all, in the 70's we learned the coherent CW can provide few hertz of BW but it was very difficult to synchronize the clock between both transceivers that time without internet.

When you compare 2 KHz to 2 Hz BW the improvement is 30 db!. The JT modes are designed to narrow bandwidth. Joe could use a "JTCW" mode and decode CW and play it back on the speaker and let our brain to decode it. Instead JT modes uses Salomon and other modern algorithms that decode better than the human brain using multiple tones.

2- The call sigh decode guessing against a list is not much different from a  DX Cluster spot.

3 - JT modes is a weak signal but not a solution for manmade noise, The second way to improve signal to noise ratio and can be used with the first one is to narrow the beam width of the receiver antenna. Increasing RDF the signal to noise ration also increase a 1:2 ratio, based on my 10 years or more measuring signal to noise ration con different RDF. 

Comparing signals using two instance of WSJT n the same computer, one on each receiver of my IC7800, one signal decode from my TX antenna was -19 dBm, the same signal decode on my HWF was +1 dBm. The RDF and rejection from manmade noise can increase another 20 db on the JT modes using a TX vertical.

If a JT node can copy -20 db using a vertical, the same JT mode can copy -40 db using a high RDF receiver antenna. 

The new technology can evolve to synchronize new SDR transceivers using an internet connection resulting a 2 Hz BW for a CW signal!  This  can become reality, think about that!


What concerns me is the fact that the technical level of the new ham is declining too fast. There is the feeling that "GOOGLE" can explain  everything and we don't need to know things any more, just ask ALESIA,,,   

The people going  to FT8 are enjoying the contacts but does not understand why? And if they don’t mind why should us care about it?

Ham radio is beautiful, enjoy all you can the way you can!

The best antenna is the one you have and not the big gun that you don’t have, and can’t use.


73's
JC
N4IS