Wow. I think this may have been more than I wanted to know about RTTY and
160m! :)
Randy, K5ZD
> -----Original Message-----
> From: cq-contest-admin@contesting.com
> [mailto:cq-contest-admin@contesting.com]On Behalf Of Bill Coleman
> Sent: Thursday, August 08, 2002 01:59 AM
> To: Don Hill AA5AU; CQ-Contest; RTTY Reflector
> Subject: Re: [CQ-Contest] NAQP RTTY 160M Survey
>
>
> On 8/5/02 20:44, Don Hill AA5AU at aa5au@bellsouth.net wrote:
>
> >Working with Wayne, K7WM, the contest manager for NAQP
> >RTTY, I've come up with a survey on my website asking RTTY
> >contesters to express their opinion on whether or not 160M should
> >be added to the RTTY part of NAQP (like it is for CW and SSB).
>
> Very interesting.
>
> This topic has come up before -- why not include RTTY on 160m?
>
> Traditionally, hams have found that 45 baud RTTY doesn't work so hot on
> 160m. The reason for this is the same reason that 300 baud packet doesn't
> work so hot on 40m, and virtually not at all on 80m.
>
> The specific problem has to do with the nature of the communications
> channel on HF, well below the MUF. At these frequencies, there will often
> be several propagation paths between two points. This multipath
> propagation produces some interesting effects, including the observed
> fading of the mark or space frequency.
>
> There is one other effect -- multipath distortion of symbols. Since each
> path has a slightly different distance, each change in the digital signal
> arrives at slightly different times at the receiver. As you move further
> below the MUF, the effect is much more pronounced. At some point, digital
> symbols are smeared together, and cannot be easily separated.
>
> Higher symbol rates (300 baud) show this effect at higher frequencies. 45
> baud RTTY has been used effectively for many years on 80m -- but not on
> 160m.
>
> The solution is simply to increase the symbol length. For single-bit
> modes like Baudot RTTY, this would also decrease the information rate.
> But, better to get the information across slowly than not at all.
>
> PSK31, with it's lower symbol rate, may be more effective on 160m than
> conventional Baudot RTTY. Slowing RTTY to 30 or 22 baud ought to be more
> than sufficient to make reliable communications possible on 160m.
>
>
>
> Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
> Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
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