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RF Issues

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  • Jack
    I have a second story shack with a 500 watt amp and the antennas are fairly close. Obviously not ideal but I do like it better than the basement dungeon. I
    Message 1 of 12 , Apr 8, 2013
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      I have a second story shack with a 500 watt amp and the antennas are fairly close. Obviously not ideal but I do like it better than the basement dungeon. I have a common star ground to all the metal boxes in my station. I am able to connect my microphone directly to my K2 transceiver and get great reports with no mention of RF feedback problems. However, trying to use StationProII causes serious audio problem. So far, I've tried reworkng the pod wiring. and trying various combinations of toroids. Rewiring the pods with better cables helped a bit but not fixed. I am now thinking about trying a pi network (.001 uFs and 470 uH) on mic leads going to the transceiver. Any thought on this or other approaches? Thanks.

      73,
      Jack (W0FNQ)
    • Paul Christensen
      Jack, A Pi network or any other type of differential-mode RFI filter may help, but you almost certainly have a common-mode issue. There are two potential
      Message 2 of 12 , Apr 8, 2013
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        Jack,
         
        A Pi network or any other type of differential-mode RFI filter may help, but you almost certainly have a common-mode issue.  There are two potential issues when using differential-mode filters: (1) the filter affects the integrity of the audio waveform.  Run a 1 kHz square wave through a differential-mode filter and see what comes out when its terminated into varying loads; and (2) the filter can become self resonant, making the filter perform well on some bands while performing poorly on others. 
         
        When two inductors are wound on a single core, the result is that total common-mode inductance approaches 2*L (with high mutual coupling) while differential-mode inductance cancels and equals zero.  This is why a common-mode choke with high inductance can still preserve the integrity of an audio waveform that would otherwise result in extreme overshoot and ringing through a differential-mode filter like the Pi.  For our purposes, bandwidth is much more limited (and the effects of ringing) than for other wideband audio applications, but the same rule applies.   
         
        You mentioned using toroids with no improvement but maybe you can tell us more about where and how they were used?
         
        I would concentrate my energy at the K2's mic input connector.  In several tough cases, 10 turns of mic cable through a large #31 ferrite core completely eliminated the problem.  Simple snap-on cores where no choking turns almost never work well.  The choking reactance is built up through the number of turns.  If you see partial improvement there, then try a distributed approach with 10 turns wound on a #31 core at the mic connector of the Station Pro. 
         
        K9YC has some good material on the subject:
         
         
        Notice in his material that as the turns are increased or decreased, the peak common-mode reactance is shifted up or down in frequency.  Generally, it's a good idea to try and hit a target on the band where most RFI occurs.
         
        Paul, W9AC
         
         
         
         
         
        ----- Original Message -----
        From: Jack
        Sent: Monday, April 08, 2013 8:19 PM
        Subject: [stationpro] RF Issues

         

        I have a second story shack with a 500 watt amp and the antennas are fairly close. Obviously not ideal but I do like it better than the basement dungeon. I have a common star ground to all the metal boxes in my station. I am able to connect my microphone directly to my K2 transceiver and get great reports with no mention of RF feedback problems. However, trying to use StationProII causes serious audio problem. So far, I've tried reworkng the pod wiring. and trying various combinations of toroids. Rewiring the pods with better cables helped a bit but not fixed. I am now thinking about trying a pi network (.001 uFs and 470 uH) on mic leads going to the transceiver. Any thought on this or other approaches? Thanks.

        73,
        Jack (W0FNQ)

      • Jack
        Paul, Thanks for the in-depth reply. My thoughts about the pi were based on the output design used in the W2IHY Audio Equalizer I use. His design seems to
        Message 3 of 12 , Apr 9, 2013
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          Paul,

          Thanks for the in-depth reply. My thoughts about the pi were based on the output design used in the W2IHY Audio Equalizer I use. His design seems to work quite well based on the reports I receive on the air. His design uses filters on both positive and negative leads of the mic; I didn't explain the topology in my initial post. As I mentioned, connecting the equalizer directly to the K2 results in good audio reports. BTW, I did apply the K2 pin ! modification recommend by Elecraft.

          I have been following Jim Brown's article. I use his recommendations for feedline chokes on my antennas, station grounding, and interconnects. I purchased a bunch of 2.4 inch mix 31 toroids to try and tame the situation. Earlier in the process I had at least 10 turns through a toroid on the mic cable; my current configuration doesn't have one. It makes sense to revisit that arrangement before I try the pi network. In my latest trial, I cut the ends from an S-video cable and used that cable for the mic lead thinking that the twist and shielding would be decent. Unfortunately I made it too short for another 10-turn toroid. I'll cut a new one and try.

          Thanks again for your thoughts.

          73,
          Jack (W0FNQ)
        • Jim Garland
          Hi Jack, I ve just started reading this thread. You must have a lot of RF in your shack! Second floor stations are often prone to RF feedback. Have you
          Message 4 of 12 , Apr 9, 2013
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            Hi Jack,

            I've just started reading this thread. You must have a lot of RF in your shack! Second floor stations are often prone to RF feedback.  Have you considered using a tuned ground (I believe  MFJ makes one) to anchor your equipmnent more closely to ground potential? Also, are you using a shielded ethernet cable between the RF relay unit and the controller of your StationPro?  Most ethernet cables of the sort one buys at Office Depot or Radio Shack are unshielded. Also, make sure your key and speaker leads are shielded.

             

            There aren't many places where RF can get into the mic line, since the SP controller only directly switches DC, audio, and data. If you've not done so already, you might try systematically disconnecting each line (speaker, key, computer, Amp ALC, etc.) and see if you can pinpoint where the RF is entering.

             

            Also, can you describe the symptom more fully? What power level do you begin to hear it? What does it sound like? Do you hear any sound from your speakers when the problem begins? Does it make any difference whether you are using headphones or a speaker?

            73,

            Jim W8ZR

             

            From: stationpro@yahoogroups.com [mailto:stationpro@yahoogroups.com] On Behalf Of Jack
            Sent: Tuesday, April 09, 2013 7:35 AM
            To: stationpro@yahoogroups.com
            Subject: [stationpro] Re: RF Issues

             

             


            Paul,

            Thanks for the in-depth reply. My thoughts about the pi were based on the output design used in the W2IHY Audio Equalizer I use. His design seems to work quite well based on the reports I receive on the air. His design uses filters on both positive and negative leads of the mic; I didn't explain the topology in my initial post. As I mentioned, connecting the equalizer directly to the K2 results in good audio reports. BTW, I did apply the K2 pin ! modification recommend by Elecraft.

            I have been following Jim Brown's article. I use his recommendations for feedline chokes on my antennas, station grounding, and interconnects. I purchased a bunch of 2.4 inch mix 31 toroids to try and tame the situation. Earlier in the process I had at least 10 turns through a toroid on the mic cable; my current configuration doesn't have one. It makes sense to revisit that arrangement before I try the pi network. In my latest trial, I cut the ends from an S-video cable and used that cable for the mic lead thinking that the twist and shielding would be decent. Unfortunately I made it too short for another 10-turn toroid. I'll cut a new one and try.

            Thanks again for your thoughts.

            73,
            Jack (W0FNQ)

          • Jack
            Thanks Jim, I have considered the artificial ground (counterpoise), but because I seem to have a clean signal with the mic (equalizer) connected directly, I
            Message 5 of 12 , Apr 9, 2013
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              Thanks Jim,

              I have considered the artificial ground (counterpoise), but because I seem to have a clean signal with the mic (equalizer) connected directly, I would rather not go that route. I will look at the ethernet cable more closely; I had not considered that. I have some good cat5 cable if I need to replace.

              Right know I don't have the details of what it sounds like -- only general reports of "bad audio." I have the Android App GLSDR. I don't know if you are familiar with that network? Basically, hams using an SDR setup will connect over the internet so that others can listen to what they receive at their location. It include the ability to select the receiving frequency. I sometimes connect my SDR rig to the network. In that past, I have used this to listen to my station at a distance. I'll give that a go again to see if I can get better info. Otherwise I need to get some more detailed reports under various conditions.

              If I didn't operate both SSB and digital modes, I wouldn't bother with chasing the problem and just directly connect the mic. Thanks for the comments and the great design-- it is overall a great addition to the shack.

              73,
              Jack (W0FNQ)
            • Jim Garland
              Hi Jack, By any chance are you using computer control of your K2, e.g., HR Deluxe or DX Lab Suite? If so, perhaps your problem isn t RF pickup but rather
              Message 6 of 12 , Apr 9, 2013
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                Hi Jack,

                By any chance are you using computer control of your K2, e.g., HR Deluxe or DX Lab Suite? If so, perhaps your problem isn't RF pickup but rather pickup from the RS232 line getting into your microphone audio. That can happen when using the StationPro with a commercial RS232 cable, since the microphone wires and the PC data are routed through the same 25 wire serial cable? (This possibility is discussed in a writeup on my website.) I didn't think the K2 had a remote data input on the back panel, but I might be mistaken.

                 

                Also, I believe you mentioned you're using a W2IHY audio processor, and if so that might be the source of the problem. Can you temporarily eliminate it and plug your microphone directly into the StationPro controller to see if the problem goes away.

                 

                I'm afraid it's going to be hard to chase down the problem if you can't listen to yourself over the air.

                73,

                Jim W8ZR

                 

                From: stationpro@yahoogroups.com [mailto:stationpro@yahoogroups.com] On Behalf Of Jack
                Sent: Tuesday, April 09, 2013 8:29 AM
                To: stationpro@yahoogroups.com
                Subject: [stationpro] Re: RF Issues

                 

                 

                Thanks Jim,

                I have considered the artificial ground (counterpoise), but because I seem to have a clean signal with the mic (equalizer) connected directly, I would rather not go that route. I will look at the ethernet cable more closely; I had not considered that. I have some good cat5 cable if I need to replace.

                Right know I don't have the details of what it sounds like -- only general reports of "bad audio." I have the Android App GLSDR. I don't know if you are familiar with that network? Basically, hams using an SDR setup will connect over the internet so that others can listen to what they receive at their location. It include the ability to select the receiving frequency. I sometimes connect my SDR rig to the network. In that past, I have used this to listen to my station at a distance. I'll give that a go again to see if I can get better info. Otherwise I need to get some more detailed reports under various conditions.

                If I didn't operate both SSB and digital modes, I wouldn't bother with chasing the problem and just directly connect the mic. Thanks for the comments and the great design-- it is overall a great addition to the shack.

                73,
                Jack (W0FNQ)

              • Jack
                Jim, I am using HRD for station control. I missed the writeup about cables and have now read through it. I will wire up a custom cable and see if that is the
                Message 7 of 12 , Apr 9, 2013
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                  Jim,

                  I am using HRD for station control. I missed the writeup about cables and have now read through it. I will wire up a custom cable and see if that is the issue. I might try unplugging the rs232 from the k2.

                  Thank,
                  Jack
                • Jim Garland
                  Jack, Before you go to the hassle of wiring up a cable, just unplug the RS232 cable from your PC and see if the distortion goes away. Or, even easier, just
                  Message 8 of 12 , Apr 9, 2013
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                    Jack,

                    Before you go to the hassle of wiring up a cable, just unplug the RS232 cable from your PC and see if the distortion goes away. Or, even easier, just shut down HRD and see if the problem disappears.If you're connecting the RS232 cable directly from the PC to the K2, then that won't cause any interference.. That could only happen if you're routing the RS232 line through the StationPro's 25 wire interconnect cable to the K2. If that's what you've got, then it won't do any good just to disconnect the RS232 cable between the K2 and the K2 pod, since the data signals will still be on the interconnect cable.

                    73,

                    Jim W8ZR.

                     

                    From: stationpro@yahoogroups.com [mailto:stationpro@yahoogroups.com] On Behalf Of Jack
                    Sent: Tuesday, April 09, 2013 11:21 AM
                    To: stationpro@yahoogroups.com
                    Subject: [stationpro] Re: RF Issues

                     

                     


                    Jim,

                    I am using HRD for station control. I missed the writeup about cables and have now read through it. I will wire up a custom cable and see if that is the issue. I might try unplugging the rs232 from the k2.

                    Thank,
                    Jack

                  • Dave Trainor
                    Hey guys the Shielded DB25 s are in and shipping again at Mouser! Been a month long wait. Dave, N8ZFM
                    Message 9 of 12 , Apr 9, 2013
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                      Hey guys the Shielded DB25's are in and shipping again at Mouser!  Been a month long wait.


                      Dave, N8ZFM
                    • Jack
                      Update, I replaced the ethernet cable with a 3 foot cat6 cable and that helped quite a bit. I was able to listen to myself on KL7NA server in Walla Walla, WA.
                      Message 10 of 12 , Apr 9, 2013
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                        Update,

                        I replaced the ethernet cable with a 3 foot cat6 cable and that helped quite a bit. I was able to listen to myself on KL7NA server in Walla Walla, WA. At 500 watts on 17 meters (the worst band for me), the signal sounded reasonable -- of course its pretty subjective considering the GLSDR setup. However, I can hear distortion with HRD running. Also the waterfall display goes black when transmitting. I have a length of 7-conductor sheilded cable that I can probably use for a new 25-pin rs232 connection. I don't know if I have the shielded connectors, but noticed the post about them available now. I'll let you know how it goes. Thanks again.

                        73,
                        Jack (W0FNQ)
                      • Jim Garland
                        That s good news, Jack. You re making progress. It sounds like you ve got a combination of RS232 crosstalk and RF pickup. Re changing the RS232 cable, all you
                        Message 11 of 12 , Apr 9, 2013
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                          That’s good news, Jack. You’re making progress. It sounds like you’ve got a combination of RS232 crosstalk and RF pickup. Re changing the RS232 cable, all you need to shield are the mic audio lines and the computer data lines. They have to be independently shielded, of course. You can’t run them through a shared shield.

                           

                          I’m not surprised the waterfall display on HRD blacks out when transmitting. The display monitors the receiver, not the transmitter!

                          73,

                          Jim  

                           


                          From: stationpro@yahoogroups.com [mailto:stationpro@yahoogroups.com] On Behalf Of Jack
                          Sent: Tuesday, April 09, 2013 2:28 PM
                          To: stationpro@yahoogroups.com
                          Subject: [stationpro] Re: RF Issues

                           

                           


                          Update,

                          I replaced the ethernet cable with a 3 foot cat6 cable and that helped quite a bit. I was able to listen to myself on KL7NA server in Walla Walla , WA . At 500 watts on 17 meters (the worst band for me), the signal sounded reasonable -- of course its pretty subjective considering the GLSDR setup. However, I can hear distortion with HRD running. Also the waterfall display goes black when transmitting. I have a length of 7-conductor sheilded cable that I can probably use for a new 25-pin rs232 connection. I don't know if I have the shielded connectors, but noticed the post about them available now. I'll let you know how it goes. Thanks again.

                          73,
                          Jack (W0FNQ)

                        • Jack
                          Jim, et al. Some changes here. I sold the K2 and bought a K3. I found individually-shielded-pair cables (2 pairs per sheath.) Then. I made a new RS232 cable
                          Message 12 of 12 , May 9, 2013
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                            Jim, et al.

                            Some changes here. I sold the K2 and bought a K3. I found individually-shielded-pair cables (2 pairs per sheath.) Then. I made a new RS232 cable following your cable writeup. With the K3, I am able to monitor my audio without transmitting. The direct mic connection with the K3 sounds great, but when routing the mic through the Station Pro, I hear crosstalk with data lines- the rather distinctive data switching sound. I also created a new "Pod" for the K3 following the manual's description. Do you have any other ideas where the crosstalk could be emanating? At this point I am satisfied with running the mic directly to the K3, but I was hoping to use the Station Pro to switch between two mics. Based on on-the-air reports, I seem to have solved the RF issues. 73.

                            Jack

                            --- In stationpro@yahoogroups.com, "Jim Garland" <4cx250b@...> wrote:
                            >
                            > That's good news, Jack. You're making progress. It sounds like you've got a
                            > combination of RS232 crosstalk and RF pickup. Re changing the RS232 cable,
                            > all you need to shield are the mic audio lines and the computer data lines.
                            > They have to be independently shielded, of course. You can't run them
                            > through a shared shield.
                            >
                            >
                            >
                            > I'm not surprised the waterfall display on HRD blacks out when transmitting.
                            > The display monitors the receiver, not the transmitter!
                            >
                            > 73,
                            >
                            > Jim
                            >
                            >
                            >
                            > _____
                            >
                            > From: stationpro@yahoogroups.com [mailto:stationpro@yahoogroups.com] On
                            > Behalf Of Jack
                            > Sent: Tuesday, April 09, 2013 2:28 PM
                            > To: stationpro@yahoogroups.com
                            > Subject: [stationpro] Re: RF Issues
                            >
                            >
                            >
                            >
                            >
                            >
                            > Update,
                            >
                            > I replaced the ethernet cable with a 3 foot cat6 cable and that helped quite
                            > a bit. I was able to listen to myself on KL7NA server in Walla Walla, WA. At
                            > 500 watts on 17 meters (the worst band for me), the signal sounded
                            > reasonable -- of course its pretty subjective considering the GLSDR setup.
                            > However, I can hear distortion with HRD running. Also the waterfall display
                            > goes black when transmitting. I have a length of 7-conductor sheilded cable
                            > that I can probably use for a new 25-pin rs232 connection. I don't know if I
                            > have the shielded connectors, but noticed the post about them available now.
                            > I'll let you know how it goes. Thanks again.
                            >
                            > 73,
                            > Jack (W0FNQ)
                            >
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