Guess I should have added...TIC :-(
On 14 February 2013 12:12, Joe Subich, W4TV <[email protected]> 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: [email protected] >> 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 <[email protected]> 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 >> ______________________________**______________________________**__ >> Elecraft mailing list >> Home: >> http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft> >> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm> >> Post: mailto:[email protected].**net <[email protected]> >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> ______________________________**______________________________**__ >> Elecraft mailing list >> Home: >> http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft> >> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm> >> Post: mailto:[email protected].**net <[email protected]> >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> ______________________________**______________________________**__ > Elecraft mailing list > Home: > http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft> > Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm> > Post: mailto:[email protected].**net <[email protected]> > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > -- *Gary - VK1ZZ Skype: Gary.VK1ZZ Motorhome Portable The Shack* *Elecraft K3 P3 Panadapter KPA500FT KAT500FT** KX3-K * ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
