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TOPIC: SunSDR2 DX Output-Power oscillating when driving SPE Expert

SunSDR2 DX Output-Power oscillating when driving SPE Expert 15 Jul 2021 06:42 #1

  • DG3EK
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Hi folks,

me again. So far I’ve followed the tips setting up the SunSDR2 DX with my new SPE 1.3k-fa.
I’ve setup all the power levels to drive the amp. Band switching and so on works fine.
I’ve noticed when operating on 10m, that the output power to drive the amp measured by the sun itself, starts to oscillate. When the amp is bypassed, all is fine.
Looks for me like rf getting back in.
Anyone had similar problems and a suggesting for fixing it? Some ferrite in the cables?

73 de Phil
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SunSDR2 DX Output-Power oscillating when driving SPE Expert 15 Jul 2021 22:09 #2

  • SM0JCA
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Hello,
Yes, typically rfi. When running power by an amp, all sorts of RFI or COMMON MODE feedback will occur. Ferrite #31 material and coax cable RF chokes are needed för me as will as line filter for 230 V AC. I have toroid ferrite on 12V power cable to the radio as well as ferrite on mic cable, phones cable, CAT cable and PTT cable as well as the power cord to the amp. Also a thick copper braid to a good grounding pole. My antennas are close to the house and I am sure all electrical wires are picking up RF and is acting like antennas and getting common mode currents. Now I have no RFI/Common mode problems. If you reduce power from the amp, try to find out at what level the oscillation on 10 m diminishes, that is a good sign for RFI. You also might have to include the PC för the radio in the system with ferrite on data cable, USB cable etc etc depending on the severity of the problem. A friend had to use 3x3 ferrite toroids 240 #31 on the 12v power cord to get rid of common mode current into the radio.
Welcome to POWER!
73 de Erik SM0JCA
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SunSDR2 DX Output-Power oscillating when driving SPE Expert 16 Jul 2021 08:07 #3

  • DG3EK
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Hello Erik,

thanks for your advice. It’s my first amp so :pardon:
I’ve ordered some ferrite cores beads from Würth Elektronik. I also test the behaviour with “lower” power (around 500W) and see whether it still oscillates.
What I’ve also noticed is while setting up the power correction table my power supply for the Sun has started humming like it’s delivering full current but it just supplied around 5A so.
Maybe that’s also RFI coming via the power supply line that’s around 2m long.
I’ll check and report.

Have a great day :yes:
73 de Phil
dG3ek
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SunSDR2 DX Output-Power oscillating when driving SPE Expert 16 Jul 2021 10:09 #4

  • SM0JCA
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Hello Phil,
One of the first things to do is to install a good RF isolation choke to block common mode currents in the antenna coaxial cable capable of >1+ kW power.
I am using a Balun Design choke installed close to the amp and the coax cable is good quality RG213.
73 de Erik SM0JCA
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SunSDR2 DX Output-Power oscillating when driving SPE Expert 16 Jul 2021 12:02 #5

  • SM0JCA
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Hello Phil,
I made myself a small Common Mode current meter to measure current on all cables in the shack.
This instrument is not difficult to DIY or can be found at MFJ.
Here you have a link to a lot of knowledge about Common Mode and a DIY meter design/construction.
owenduffy.net/module/icm/
Another link:
www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

Good luck and happy DX-ing.
73 de Erik SM0JCA
Last Edit: 16 Jul 2021 12:12 by SM0JCA. Reason: Added link
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