Posted: 10/18/2013 7:40:15 PM EDT
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Sometimes when I try and push above 50w (depends on the band I think), my radio stops transmitting and DM780 locks up. HRD still has the TX button engaged but the radio isn't transmitting. SWR is under 3, usually well under 2. If I reduce power output I can eventually get consistent, uninterrupted transmissions.
My theory is I am getting RFI back to the shack. If so, building and installing a choke balun should solve my problem, right? |
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Sometimes when I try and push above 50w (depends on the band I think), my radio stops transmitting and DM780 locks up. HRD still has the TX button engaged but the radio isn't transmitting. SWR is under 3, usually well under 2. If I reduce power output I can eventually get consistent, uninterrupted transmissions. My theory is I am getting RFI back to the shack. If so, building and installing a choke balun should solve my problem, right? What kind of digital interface are you using? I have found that I needed snap on ferrites on all of my cables connecting from my computer to the interface. The high reflective SWR could be introducing common mode current on the cables causing your issues. 
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Need to know more. What kind of antenna, tuner, feed line? How far is the antenna from the shack? Do you have a station ground? Does the problem occur on all bands or just one? etc. etc. 73, Rob Antenna: HI EARC End Fed Tuner: LDG IT-100 Antenna Distance: 30' but fed through 100' LMR-400 No station ground Occurs on 40m and 20m but seems to worse on 40m Digital Interface: Signalink USB |
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Antenna: HI EARC End Fed Tuner: LDG IT-100 Antenna Distance: 30' but fed through 100' LMR-400 No station ground Occurs on 40m and 20m but seems to worse on 40m Digital Interface: Signalink USB Quoted:
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Need to know more. What kind of antenna, tuner, feed line? How far is the antenna from the shack? Do you have a station ground? Does the problem occur on all bands or just one? etc. etc. 73, Rob Antenna: HI EARC End Fed Tuner: LDG IT-100 Antenna Distance: 30' but fed through 100' LMR-400 No station ground Occurs on 40m and 20m but seems to worse on 40m Digital Interface: Signalink USB You are getting common mode current on your feedline. This RF will finds its way into USB cables, speaker cables, etc. Common Mode Current Link |
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You are getting common mode current on your feedline. This RF will finds its way into USB cables, speaker cables, etc. Common Mode Current Link Quoted:
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Need to know more. What kind of antenna, tuner, feed line? How far is the antenna from the shack? Do you have a station ground? Does the problem occur on all bands or just one? etc. etc. 73, Rob Antenna: HI EARC End Fed Tuner: LDG IT-100 Antenna Distance: 30' but fed through 100' LMR-400 No station ground Occurs on 40m and 20m but seems to worse on 40m Digital Interface: Signalink USB You are getting common mode current on your feedline. This RF will finds its way into USB cables, speaker cables, etc. Common Mode Current Link OK, How do I fix it? Do I use the ferrites you mentioned? Which ones and do you have a good, reliable source? |
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Yep, 10 - 12 Ferrites on the feedline up by the antenna feedpoint should do it.
Another member here had exactly the same problem, but for him when going over 20 watts or so. http://www.ar15.com/forums/t_10_22/668627_Icom_718__Digital_Modes__and_Donner_Interface_Questions.html |
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OK, How do I fix it? Do I use the ferrite you mentioned? Which ones and do you have a good, reliable source? Quoted:
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Need to know more. What kind of antenna, tuner, feed line? How far is the antenna from the shack? Do you have a station ground? Does the problem occur on all bands or just one? etc. etc. 73, Rob Antenna: HI EARC End Fed Tuner: LDG IT-100 Antenna Distance: 30' but fed through 100' LMR-400 No station ground Occurs on 40m and 20m but seems to worse on 40m Digital Interface: Signalink USB You are getting common mode current on your feedline. This RF will finds its way into USB cables, speaker cables, etc. Common Mode Current Link OK, How do I fix it? Do I use the ferrite you mentioned? Which ones and do you have a good, reliable source? All good info here, If the tuner is at the end of the coax, where it is best, a series of counterpoise wires need to be run from the ground side of the tuner in a direction opposite to where the end fed wire goes. Think of it as a dipole with the tuner at the feed point where 1/2 the antenna is missing with out the other wires. If the tuner is near the earth many wires (radials) will raise it's efficiency. A college professor / friend once explained to me that there are really three kinds of wire antenna, dipoles, verticals and loops. If your tuner is near the ground, the antenna really needs radials though the radials need to be at,at least, 90 degrees or the RF fields between the wires begin to couple like ladder line and not radiate. If like a dipole, getting the tuner up in the air and adding the other half of the antenna. A loop is easiest to feed because the impedance doesn't change much from band to band going up in frequency. HTH 73, Rob |