This note is for users of the TS-2000 who could use the ability to reduce Rx bandwidth to as narrow as 50 hz.
Andy K3UK asks about mitigating the problem of a strong signal near your weaker target signal. Phil points out IF DSP is better than AF DSP, but a technique described by Hans N0AN will help quite a lot. The following is all by N0AN from notes on another reflector. The DSP filtering in the TS-2K is quite good. One trick that a lot of people don't seem to use or know about is for superb reception of psk31/rtty etc. Run the radio in split mode. Here is how to do it. 0. Select your favorite psk31 freq on the "A" vfo (left side, receive, USB) 1. Select SPLIT vfo's. 2. Make "A" your left VFO (arrow points to left by the "A") 3. Make "B" your right VFO (arrow points to the right by the "B") 4. Hit the A=B button to put both vfos on the same freq and mode. 5. Select CW for your receive mode (hit cw button) 6. Set your bandwidth control to 2000 hz for now 7. Set your shift control to 900 hz for now 7a. Turn XIT on and set it to -800 hz (this puts your transmit and rx on the same freq, even though you have different modes selected (cw on rx, usb on tx) 8. Press and hold the TF-set button, and while holding it, hit the SSB button..this sets the transmit vfo in the SSB mode. This may sound like a lot, but it is actually quite simple, and you only have to do it once! You are now set to receive on VFO A (left side) in CW and to transmit on VFO B(right side) in SSB. Due to setting XIT to -800 Hz, they are on EXACTLY the same frequency. Now...as long as you use the receive window of your software (like MixW) to change frequency by selecting different signals on the waterfall/spectrum by clicking with the mouse, you don't have to do any retuning! You have approximately 1500 hertz of bandwidth to play with, without touching any knobs. So...what does this get you? You can now use the filter width and shift controls (lower left side of front panel) to allow you to receive in any bandwidth from 2000 hz down to 50 hz!!! You have virtual privacy when you narrow the receive filter down to 50hz, believe me. I set my shift control to about 900 hz, because I want to be able to copy psk31 signals down to about 350 hz and up to about 1500 hz. If you choose 900 hz for your shift, you can still copy most of the band. You can click anywhere in the waterfall/spectrum on a signal and instantly begin copying, no knobs, no messing around, but perfect reception. Then it is a simple matter to start closing down the rx bandwidth with the left knob. Reduce it one click and you drop from 2000 hz wide to 1000 hz....all the way down to 50 hz if you want. Now...as you start reducing the bandwidth significantly with the left knob, you will need to adjust your shift to correspond to what the station you are listening to tone freq's actually are...in other words, if you reduce things from 2000 to 600 hz, and you were listening at 1100 hz, you will lose the rx signal until you adjust the shift knob to a bit closer to 600 hz (assuming the station you are listening to is on 600 hz in the waterfall/spectrum display.) While all this might sound overwhelming, it is really quite simple and one gets good at it. --------- Addendum ---- from followup notes by N0AN Simply put, two things control how you receive a signal with this setup: a. The receive bandwidth (left knob) b. The receive shift (right knob) The ideal is to set the receive shift to the center freq of the signal you are listening to, BUT, the wider you have you bandwidth set, the more tolerant things are to having your shift off. When things are "wide open" at 2000 hz, you can set the shift to 900 hz and forget it. When you start to tighten down the bandwidth, you need to move the shift center freq (right knob) to more closely agree with where you are actually listening. ============================= If you find it necessary to change the radio receiver VFO frequency, just do this after tuning the radio to a new frequency: Hit A=B button Press and hold TF-Set Hit the SSB button (while holding the TF-Set button...let up on the TF-Set after you have tapped the SSB button. You have now done the following: Set the A and B VFOs to the same freq and mode Reset the B vfo to USB (it got changed to CW when you hit the A=B button) I find I don't have to do this very often as 99% of the psk31 activity is on a specific band of frequencies centered at about 14.070 or 14.071 (cw receive). At 50 hz wide, that couple of kilohertz is a LOT of bandwidth, so you don't have to retune very often...you just use the waterfall/spectrum display and your mouse click for tuning. I've used this trick successfully with both a TS-870 and the new TS-2000, and it works beautifully. QRM on psk31 is a thing of the past with the outstanding dsp filtering in this radio. Once one learns the method for setting things up that I described above, it is psk31 heaven! At 50 hz bandwidth (and your shift set right on the money), there is no qrm. 73, .hasan, N0AN.. p.s., notice when you close down the rx bandwidth your waterfall/spectrum display changes dramatically, showing the actual shape factor of your received bandwidth....a nice idication of how well the dsp filtering is working in the TS-2000 ----- Original Message ----- From: Andy obrien To: digitalradio Sent: Thursday, May 28, 2009 5:08 PM Subject: [digitalradio] Really beating the AGC issue with PSK ? From time to time we have had discussions here about the problem with PSK (and other modes) when a strong stations appears to grab the waterfall and wipe out all the other stations within a 2-3 Khz range. Because of this phenomenon, when I purchased a new rig, I looked for one that could have AGC totally off (when needed) and one that can employ narrow DSP filtering. I must say that I have not really solved this issue . I can see a marginal difference with AGC turned off but strong signals still essentially desensitize other stations in the waterfall. The DSP features do better and I can get rid of the phenomena by turning to a narrow filter. However this does not help if the offending station is with 300 - 500 Hz ( a lot when dealing with narrow digital modes). Does anyone have any advice on how to once and for all solve this issue? My rig is a TS2000 Andy K3UK .
