[UK-CONTEST] CC Data

[David G3YYD]

There is a very practical reason to use 45 baud FSK and that is its 
resistance to multipath. Multipath has a lower impact on a 22 
millisecond element length (45.45 baud) than a 13.33 millisecond element 
at 75 baud.  80m is particular bad for multipath within the UK 
especially in the evening. Even with 22msec element length multipath can 
be so bad at times as to destroy even good signal to noise ratio FSK. 
This is why PSK31 is often a hopeless mode to use - multi path and 
doppler shift destroys it.

Incidentally RTTY format with its start and stop elements is very poor 
at handling bit errors. An error in a critical part can cause subsequent 
decoding of characters to get out of step so a one element error results 
in many more characters in error. The same data could be sent in the 
same time using a synchronous coding/decoding format to reduce errors 
(with out any correction coding) by about 34 times. This huge 
improvement comes about because a single element error only results one 
error character and extra "gain" is also obtained as element 0 or 1 
determination is always at the optimum element middle point, which is 
not so with start, data, stop method of standard RTTY. It also requires 
less bandwidth to send the data at the same rate as only 5 elements are 
required rather than 7.5 of RTTY. Therefore element lengths can be made 
longer further improving its resistance to multipath.

If we are looking to add other data modes use Digital SSTV nice wide 
bandwidth occupancy, destroyed by multipath, takes ages to sync but does 
send the data very fast when it works...

David G3YYD

On 12/02/2010 09:49, Roger Cooke wrote:
> Hi Neil.
>
>     Yes, precisely!  I have been using 75 on 20 metres for some time and have had quite a number of
> contacts, hence my vigorous support for it on the RTTY reflector. To that end, BARTG will be organising
> a 75 Baud Sprint in June, only four hours, in the evening on 20/15/10 to see how 75 Bauds will be
> accepted. Make a note of it in your diary, details on the BARTG web site.
>
>
> Regards from Roger, G3LDI
> Swardeston, Norfolk.
>
>
>
>
> ----- Original Message ----
> From: G3RIR<g3rir at yahoo.com>
> To: uk-contest at contesting.com
> Sent: Fri, 12 February, 2010 9:45:56
> Subject: Re: [UK-CONTEST] CC Data
>
> Why do we stick to 45.5 anyway? Surely 99.9% of RTTY is now computer
> generated so a switch to 75 baud would be easy.
>
> Neil, G3RIR
>
> -----Original Message-----
> From: uk-contest-bounces at contesting.com
> [mailto:uk-contest-bounces at contesting.com] On Behalf Of Roger Cooke
> Sent: 12 February 2010 09:42
> To: Steve GW4BLE; G Wood; uk-contest at contesting.com
> Subject: Re: [UK-CONTEST] CC Data
>
> There is paint drying and then PAINT DRYING!!!
>
> PSK is bad enough in contests.  I am proposing RTTY move to 75 Bauds. Now
> that WOULD liven things up a bit!
>
>
> Regards from Roger, G3LDI
> Swardeston, Norfolk.
>
>
>
>
> ----- Original Message ----
> From: Steve GW4BLE<steve.gw4ble at btconnect.com>
> To: G Wood<woody at gray3vip.plus.com>; uk-contest at contesting.com
> Sent: Thu, 11 February, 2010 17:37:02
> Subject: Re: [UK-CONTEST] CC Data
>
>
>
> Already been suggested Graham; QSP from my Cabrillo file -
>
> SOAPBOX: Another fun session on PSK. How about adding SSTV as a mode too?
>
> ;-)
>
>
> Steve
> GW4BLE
>
>
>
>
> -----Original Message-----
> From: uk-contest-bounces at contesting.com
> [mailto:uk-contest-bounces at contesting.com] On Behalf Of G Wood
> Sent: 11 February 2010 11:47
> To: uk-contest at contesting.com
> Subject: [UK-CONTEST] CC Data
>
> Hi All
>
> Usual struggle with PSK last night. Just got a station tuned in then they
> disappeared. Quite a few times the station reappeared but on a slightly
> different frequency so had retune then they went again before got call, VERY
> frustrating. I think a course on the use of NET and AFC is needed by some
> stations. Ratio RTTY to PSK was 4:1. 28 RTTY 7 PSK. After the finish, while
> my brain was cooling down, I had a ghastly thought, what if the Contest
> Committee had another flash of madness and next year decided to combine SSB
> with SSTV!!!! now there's a thought, oops maybe I've lit the blue touch
> paper.
>
> 73's - Graham G3VIP
>
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