I recently encountered a problem when using my Yaesu FT-950. Sometime during the CQ WW WPX Contest, I noticed an annoying tone (“a birdie”) in my receiver. I’ve had this radio for many years, used it quite a bit and this was the first time I encountered this problem. It struck me as very odd because it did not go away when I disconnected the antenna and it did not change frequency when I tuned around.
I immediately had visions of needing to tear the radio apart or send it back to Yaesu for repair. Instead, this happened…
When it comes to troubleshooting problems, it usually pays to fiddle around with it and see what happens.
PSs are notorious for causing RF interference, especially the switching type (but usually cheaper models). I’d try a different regulated type. In my experience most of the better more expensive name brands are fine.
Unless a receiver is completely unshielded, disconnecting the antenna will exclude switching power supply RFI.
I’ve generally found the Samlex and Astron switching power supplies to be pretty clean with regard to radiated emissions. This is one reason I was surprised that the Samlex was interfering with the FT-950.
As I mentioned in the video, the antenna port was disconnected on the FT-950, so the interference was not coming in via that path. Also, note that the problem disappeared with just a little separation between the radio and power supply. This indicates that the emissions are radiated, not conducted.
Now, is this the fault of the power supply or the transceiver? One can argue that the transceiver needs better shielding or that the power supply needs lower emissions. Or both. This is why this technical area is called Electromagnetic Compatibility (EMC)…the goal is having devices work together correctly.
I’m curious what the IF frequencies might be on that radio? Do they correspond to the fundamental or harmonic of the SMPS? It’s interesting the tone is 1100 Hz. Might be a slight offset from the IF.
Ken,
From the Yaesu web site:
“The triple-conversion design features a 1st IF of 69.45 MHz, a 2nd IF of 450 kHz, and a 3rd IF of 30 kHz (FM: 24 kHz), with each stage’s advanced filtering protecting the stages to follow from unwanted signal voltage, leading to a quiet, ultra-robust receiver with impeccable total system performance.”
The Samlex web page says the power supply switches at 25 kHz. That’s probably not a tightly controlled frequency.
I am going to guess that the PS switching freq gets into the 3rd IF. I suppose it could be a harmonic of 25 kHz getting into the 2nd IF.