[Elecraft] K3 Reduced BW FSK

Wed Feb 13 20:42:25 EST 2013

Guess I should have added...TIC

:-(

On 14 February 2013 12:12, Joe Subich, W4TV <lists at subich.com> wrote:

>
>  As anyone who was in the WPX RTTY contest this past weekend knows,
>> anything that can help reduce the unnecessary interference from
>> overly wide transmissions is more than welcome.
>>
>
> Although Andy's work showed clearly that shaped AFSK could be very
> spectrally efficient, most of his testing was done with a K3 in AFSK
> mode *with the AFSK filter engaged*.  Elecraft are already head and
> shoulders above the other manufacturers by including and AFSK filter
> and an automatic audio gain control (ALC) which makes it nearly
> impossible to generate "wide" AFSK even if the user engages "all
> knobs to the right".
>
> This is not the case with AFSK on other transceivers - *particularly*
> when operated with audio connected to the microphone input of a rig
> designed for a dynamic mic.  Most dynamic mic rigs expect *only*
> 5 mV of audio drive to the mic jack and will distort significantly
> when drive with more than 50 mV - something that no adjustment of
> the mic gain can resolve since the mic preamp is a fixed gain stage
> *before* the mic gain control.  In spite of this, many manufacturers
> of low cost audio interfaces continue to sell noting but mic cables
> and their documentation continues to instruct users to turn the sound
> card level *all the way up*!
>
> When one overdrives a mic stage - here's what the spectrum looks like:
> http://www.subich.com/BAD_**AFSK.jpg <http://www.subich.com/BAD_AFSK.jpg>.
>  In this case audio was being fed
> to the "mod in" pin on an Icom ACC jack but at more than 700 mV on an
> input rated for 100 mV RMS it was still much too hot.  One can see the
> AFSK signal, the second harmonic, the third harmonic, "suppressed"
> carrier and the incompletely suppressed lower sideband.  As bad as it
> is, this capture does not show the horrendous effects of hum evident
> on many AFSK signals either.
>
> While it is great that Elecraft give us the tools to make sure we are
> stinking up the band but until all rigs include AFSK filtering ahead
> of the modulator, I would much rather deal with the modest "key clicks"
> from some of the traditional transceivers than the 3 - 5 KHz wide
> mass of hum and harmonics from an improperly operated AFSK transmitter
> - and I suspect anyone who has had to deal with the interference from
> an improperly set-up AFSK rig will agree.
>
> 73,
>
>    ... Joe, W4TV
>
>
>
> On 2/13/2013 7:06 PM, Mark n2qt wrote:
>
>> I had missed that this wasn’t discussed on  this reflector, so first a
>> little history
>>
>> At the end of December, on the RTTY reflector, Andy K0SM/2 produced
>> measurements showing that the
>> use of FSK, which had been the ‘gold standard’ for generating RTTY was
>> actually not as spectrally efficient
>> as correctly adjusted, shaped AFSK generated RTTY.   This was shown in
>> his write-up posted at
>>
>> http://www.frontiernet.net/~**aflowers/k3rtty/k3rtty.html<http://www.frontiernet.net/~aflowers/k3rtty/k3rtty.html>
>>
>> Note that this does NOT indicate that there was any sort of problem with
>> the K3, just that there was a chance
>> to be better.  Other manufacturers also have this same chance to improve.
>>
>> A little later, Ed, W0YK, also known as P49X in many contests, announced
>> that he had successfully used
>> experimental DSP firmware from Elecraft in the BARTG rtty contest.
>>
>> “The K3 DSP firmware engineer coded a  wave-shaping filter that narrows
>> the transmit bandwidth similar to
>> what their AFSK filter provides. The resulting spectrum image looks  like
>> the better, i.e., narrowest, of the
>> images in K0SM's  recent work.”
>>
>> Elecraft then allowed Ed to share this firmware with others who were
>> interested in trying it, which is how I got it.
>>
>> As anyone who was in the WPX RTTY contest this past weekend knows,
>> anything that can help reduce the
>> unnecessary interference from overly wide transmissions is more than
>> welcome.  It is great that Elecraft has
>> reacted so quickly to this opportunity.  (Would we expect anything less
>> from these guys??)
>>
>> Mark N2QT/WE4M
>>
>> From: Stephen Prior
>> Sent: Wednesday, February 13, 2013 3:22 AM
>> To: Mark
>> Cc: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] K3 Reduced BW FSK
>>
>> Mark,
>>
>> You will have to enlighten us (well, me anyway) - just what pre-beta
>> software are you referring to?
>>
>> 73 Stephen G4SJP
>>
>>
>>
>> On 13 February 2013 04:10, Mark <n2qt at verizon.net> wrote:
>>
>>    Just a report that I used the pre beta low bandwidth fsk software on
>> both k3s during the
>>    WPX RTTY contest.  Made over 1900 low power contacts, with no apparent
>> problems
>>    (As expected).  As close as some stations felt comfortable operating
>> next to me, it looks
>>    like it helps.
>>
>>    With the ever increasing popularity of rtty contesting, improvements
>> like this helps
>>    us all.
>>
>>
>>    Mark. N2QT/WE4M
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-- 
*Gary - VK1ZZ
Skype: Gary.VK1ZZ
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