Wow, the video is amazing. I had no idea this was available. I can't
wait to try it out myself.
If I knew the DX was using "skimmer like" techniques, I would be much
less apt to jump around, looking for where he worked the last guy.
73 de Terry KK6T
PS - I was not able to work ST0R on RTTY :-(
On 8/11/2011 9:53 AM, Joe Subich, W4TV wrote:
> The "skimmer like" techniques are there already .... see the video
> from CE0Y/I2DMI - http://www.mdxc.org/ce0yi2dmi/ using microKEYER II
> with N1MM Logger/MMVARI in "DXpedition mode" for Windows or the 9X0TL
> videos you reference using Digikeyer II. cocoaModem and RUMped for
> OS-X. The point here is that both I2DIM and DL2RUM put a priority on
> RTTY.
>
> Using multi-channel decoding techniques would reduce the issues with
> "length of transmission" (the brag tape effect) on RTTY such that it
> should be as efficient as the multiple callers in a phone pile-up and
> the need for the DX to constantly be saying "I want only the W7A
> station", "EU only", etc.
>
> With multi-channel receive techniques, the DX station should be able
> to maintain a queue two or three stations deep and "knock them off"
> at rates of two to three a minute for extended periods of time just
> like phone or CW.
>
> It's a matter of devoting as many complete high quality stations
> (transceivers, amplifiers, antennas, and operators) and "band slots"
> to RTTY as the DXpeditions devote to phone or CW. Unfortunately, most
> operations tend to put RTTY on the band with poorest propagation, don't
> start RTTY operations until the third or fourth day, terminate RTTY
> operations early, and fail to use ops who specialize in RTTY (e.g.,
> those as skilled at RTTY as an N5KO, etc. is on CW). One of the
> 10-10-10 PJ operations was so poor on RTTY compared to phone/CW that
> for most of the time their RTTY station was an FT-840 and a trapped
> vertical while all of the other stations (multiple per mode) were K3,
> FT-1000MP, IC-7600 with amplifiers and yagis, full size verticals,
> etc.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 8/11/2011 12:09 PM, Kok Chen wrote:
>> On Aug 11, 2011, at 8:02 AM, Joe Subich, W4TV wrote:
>>
>>> With nearly three times as many CW QSOs as RTTY (Digital) QSOs and
>>> five phone QSOs for every two RTTY QSOs, there is still a long way
>>> to go before major DXpeditions are giving RTTY more than "lip
>>> service."
>> I suspect this will improve as DXpeditions adopt better tuning
>> techniques for RTTY. IMHO.
>>
>> With CW, you can listen for signals and decode a signal that are a
>> full kHz away (guys like N5KO use the filters in their own brains for
>> CW; Trey's advice to me was to call away from a CW pile if I know
>> that he is the op at the DX end).
>>
>> With voice, you make use of the "cocktail party effect" (the term is
>> actually used in technical papers, see also here
>> http://en.wikipedia.org/wiki/Cocktail_party_effect).
>>
>> You cannot do either in RTTY if you are tuning with a VFO knob.
>>
>> If the pile is heavy on the previous RTTY QSX, it could take a bit of
>> waiting for a call to appear cleanly on the DX's screen, or for a
>> really large signal to override everyones power combined (like the FM
>> "capture effect," but with one station against the power of many
>> stations combined, versus one station against one other station), or
>> having to retune slowly using the VFO knob. None of this is
>> especially fast.
>>
>> If the DX uses an RTTY skimmer, or a waterfall with memory, they
>> could find a station far away from the pile to work. Just find the
>> first station that is in the clear within a 20 kHz (or however wide
>> the receiver can tune) passband to work next.
>>
>> You can imagine that for CW, you are instantaneously working with a 2
>> dimensional field (time and frequency). With a traditional way of
>> tuning RTTY, it is one dimensional (time only). But you gain back
>> the advantage compared to CW when you use a skimmer or
>> memory-buffered waterfall tuning (standard waterfalls won't give you
>> that of course).
>>
>> All digital modes are machine decoded today anyway, so you might as
>> well take advantage of that fact to pull out one signal from among
>> many signals. (Whether you prefer to call it RTTY or something else
>> -- the technology today that people use for keyboard modes is far
>> different from the "RTTY" that was used with mechanical teletypes;
>> the only similarity to real steam powered RTTY is the use of two FSK
>> carriers, a shift of 170 Hz and a baud rate of 45.45 Hz. And if you
>> don't write your own software to do the demodulation, that
>> distinction between the different digital modulation modes is blurred
>> even further.)
>>
>> Bear in mind that dynamic range is not so big a problem if you are
>> the DX. They can polish off all the large signals first before
>> working their way to the weaker ones. The limitation of being able
>> to concurrently decode RTTY signals whose signal strengths are
>> separated by "only" 10 or 15 S units is not a problem. At some
>> point, that weak signal that is barely above the noise floor is going
>> to be within 10 S units of the loudest signal present at the time.
>>
>> Once a DXpedition adopts wideband, agile tuning for RTTY, we too
>> would have to change our pileup busting behavior. The key is to look
>> for an empty hole, no matter how far away from the previous QSX it
>> is. That has already been shown to be true with 9X0TL. In Tom's
>> Quicktime video, you can also watch 9X0TL clear out the strongest
>> signals first but eventually get to the weak ones.
>>
>> I don't myself really look forward to that progress (where the DX can
>> pick you off quickly as long as you are above the FSK decoding
>> threshold with respect to their noise floor). Working DX becomes
>> "shooting fish in the barrel" and the challenge goes away. How hard
>> anyway is it to find an empty bandpass to transmit. He eventually
>> finds you.
>>
>> BTW, the above scheme also applies to working a DX that is "begging"
>> in an almost empty subband where you have no idea what his QSX is.
>> Today, you have to wait for him to slowly tune across you while you
>> are calling. If you are weak, he will usually miss you completely if
>> he is not a seasoned RTTY operator (this happens to me so often that
>> I prefer to let the DX find a strong station first and then call next
>> at that frequency; the strong station acts as a beacon for the
>> inexperienced RTTY op to hone in on). With a skimmer or waterfall at
>> his end, he will notice you the instant you transmit.
>>
>> The skimmer allows inexperienced ops to be pretty much as effective
>> as the experienced ops -- is that what we want eventually? (Even a
>> child can use a cell phone.)
>>
>> 73
> > Chen, W7AY
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