+++++++++++++++++++ Reply-To: "Don Wilhelm" From: "Don Wilhelm" To: "Samuel Ramac" , Subject: Re: [Elecraft] Data mode filters Date: Tue, 22 Jan 2002 21:24:26 -0500 > Can anyone comment on the proper way of setting the data mode filters? Samuel, The 'proper' way to set the data mode filters depends partly on the data mode that you want to use. If you are using the computer soundcard to do the decoding, most of these programs work FB with the normal SSB filter which has the advantage of less passband ripple than does the variable bandwidth filter when used at wider bandwidths. No matter which filter you chose for data mode, you want to be certain the audio tones for that particular digital mode will fit within the passband (vary the BFO setting to accomplish that). Spectogram will be handy to set things up and if your choice is to use a narrow filter, it may be essential. For RTTY, the audio tones to be decoded are 1445 and 1275 Hz for 170 Hz shift RTTY. So you want the passband to be enough greater than 170 Hz so tuning the receiver onto the signal will be not critical (I would suggest 400 to 500 Hz bandpass width). Then you would set the BFO so that both the 1275 Hz and 1445 Hz audio tones are well within the passband as viewed on Spectogram. For PSK31, the procedure is similar, but most folks simply use the normal SSB filter and let the software and soundcard do the audio filtering. You can use a more narrow filter setting to achieve a better S/N ratio, and if you chose to do that, just decide how narrow a bandpass you wish to work with and at what audio frequencies and follow the same procedure as for RTTY above. If I were to make those choices for PSK, I would create a passband from about 800 Hz to 1200 Hz (400 Hz) - but that is just my personal choice - you can pick anything between about 300 Hz and 2700 Hz and accomplish the same thing. Good luck with it, 73, Don Wilhelm - Wake Forest, NC W3FPR home page: http://www.qsl.net/w3fpr/ QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net +++++++++++++++++ Date: Wed, 23 Jan 2002 06:27:08 -0500 To: "Samuel Ramac" From: Charles Greene Subject: Re: [Elecraft] Data mode filters Cc: elecraft at mailman.qth.net At 02:04 AM 1/23/2002 +0000, Samuel Ramac wrote: >Can anyone comment on the proper way of setting the data mode filters? Samuel, It depends upon whether you have the KAF2 audio filter installed and plan to use it or not. I find it useful. If so, you should align all the crystal filters using the KAF2 frequency as center frequency. Always align FL1 to OP1 for best look at the entire audio band and to eliminate the "TX/RX frequency offset" you get when switching in any filter other than OP1. Also do you plan to use CAT control using the KIO2? A couple of the programs that each have several digital modes are MixW and Zakanaka, and both have an "align" macro that changes the audio frequency to your selected audio frequency usually the center frequency of the K2 filters and at the same time, change your K2 dial setting a corresponding amount so you still transmit the same frequency. Use Tom Hammond's procedure using Spectrogram and a noise source for alignment which is on the K2 website. I have my filters set at as follows: FL1=OP1, FL2=1200hz, FL3=600Hz, FL4=150 Hz with the same center frequency set the same as KAF2. Having said this, there's some merit to having two filters with slightly offset frequencies. Concerning QRM, if it is right on you and is strong, no filter is going to help. But usually it is a little one side or the other of your frequency. So you might want to set FL3 and FL4 both at 150hz wide and set FL3 with a center frequency of 850 hz and 750 for FL4 so you can get rid of QRM either low or high around a center frequency of 800 hz, for example. It's somewhat like Eric's idea of setting the SSB filters to give high pass, low pass and band pass. In this case, the band pass right on your operating frequency can be the KAF2 but the nice thing is you can use KAF2 in conjunction with either FL3 or FL4. I only tried this briefly and have not explored it thoroughly before taking down my K2 for mods. You might try aligning your CW filters the same way. If you don't have KAF2 or don't plan to use it, it is a good idea to align the filters with a center frequency for all in the range of 1200 to 1400 Hz. That way, you stay away from operating at the lower audio frequencies as they are prone to have audio harmonics in your transmit filter bandpass. It isn't possible to use a common frequency for the center frequency for all filters much above 1400 Hz. GL, 73, Chas, W1CG +++++++++++++++++++