[GreenKeys] Diversity

[John Vendely]

Hi Jeff,

Diversity reception is still common on HF, but its implementation has 
changed a lot since the R-390 era.  Space diversity is much less common 
now, with frequency or time diversity (or both combined) being more 
common.  In many cases, such diversity features are built into the modem 
waveforms themselves, and do not require separate receivers.

A good example of this is the older BR-6029 time/frequency diversity 
modems made by Barry Research, in which a binary bit stream was 
distributed over 8 FSK tone pairs, each shifted one second in time.  The 
BR system has been virtually abandoned, but there is some occasional 
amateur use of these modems.

More sophisticated implementations of the time/frequency diversity 
concept exist in most of the new DSP-based modems used by the military.  
Some systems achieve frequency diversity through use of independent 
sideband, in which the modem signal is transmitted on both sidebands, 
which tend to fade  independently of each other. Military Link-11 
systems on HF commonly use ISB for frequency diversity.  Some ISB 
systems also introduce a time delay into one sideband, to achieve time 
and frequency diversity.

Of course, there's relatively little use of binary FSK on HF compared to 
just10 years ago, but I have recently heard some frequency diversity FSK 
systems still in use.  The FSK channels were spaced by some 10s of kc, 
but they were definitely carrying the same (encrypted) data.  And of 
course, wide shift FSK (850 or 1000 Hz shift) inherently has some 
diversity of tone fading which the better modems make use of.  The 
Russian navy still has a few 1kc or 1.2 kc shift FSK systems in use.

73,

John K9WT


On 3/24/2013 1:49 PM, Jeffrey D Angus wrote:
> Looking at that converter Larry posted, does anyone actually RUN
> diversity on reception these days?
>
> Diversity to me brings up images of a pair of large antenna arrays,
> and two Collins R-390As with a complex "voting" system to decide
> who's got the best bits to decode.
>
> Which leads to my next question. Is there any "modern" diversity
> software out there. Something that can, for example, talk to a pair
> of CAT enabled transceivers and a pair of sound cards like the USB
> SignaLink series?
>
> Jeff-1.0
> wa6fwi
>
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