Re: Whats new in VARA 4 ? #VARA #qrp


Rick Muething
 

Andy,

Comparing FT8 and FT4 with VARA and P3, P4 is like comparing a golf cart to a Porche!

FT8, FT4 are great for exchanging minimal information (call sign, signal report, Grid square) and they do that well BECAUSE they are so SLOW  and narrow bandwidth  (Higher Eb/No  ....just as Claude Shannon describes in his 1948 landmark paper on channel capacity. They satisfy a niche especially if one is trying to make the maximum number of contacts at low power  each exchanging a very short message.

VARA, P3, P4  Transmit much larger data (text + attachments up to say 30 K bytes)  at ~1000 x (or more) than the FT8 or FT4 rate .  They require stronger signals than FT-4 of FT-8 and a wider bandwidth.   These modes again operate in exact accordance with Shannon's thesis (now proven).  They are what you want to use if you are transmitting a sizeable message/attachment or have to send a large amount of traffic.  These modes are also automatically adaptive (changing their Eb/No and FEC level automatically)  so they can follow a changing path over 20 dB or more and with varying amounts of multipath. 

As hams we should all try to understand the basics of what Shannon proved.  It would make better use of our limited spectrum an different bjectives.  But comparing VARA and FT8 is like comparing an High Definition commercial TV transmission with a deep space photo taken from NASA Voyager using a 10 watt transmitter at 10 bits/second.   Both have their uses but are not in competition.

Rick Muething, KN6KB,  Winlink Development Team

On 7/6/2020 2:46 PM, Andrew OBrien wrote:
I think FT8 and FT4 have shown that wide adoption of a digital mode is achieved when popular awards , like DXCC , are associated with use of the mode . If , for some odd reason, ARRL developed an award for receiving email from 100 or more DXCC entities via VARA ... VARA  would have many more users . Despite VARA , Ardop, Winmor and Pactor having some utilization in emcomm . these modes seem destined to be niche products in the ham world . 

Andy
K3uk 

Digital modes via SDR = Multipsk or SDR-Radio.com

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