RTL-SDR panadpter issue.

[K7XRL]

I have been using an RTL-SDR USB dongle as a panadapter with HDSDR.

I have tapped the IF in my radio (Yaesu FT-450D) and installed a buffer amplifier along with a little SMA connector on the back panel of the radio. I connect the RTL-SDR here and it has been functioning properly except for one issue.

There is a persistent spike or birdie that is about 24 KHz above the center frequency on the waterfall with both the LO and Tune frequencies the same.

I have the DC correction selected in the software, and that does eliminate the spike at the center. But this other spike at 1500hz is persistent.

I have tried two different tap points in the radio to tap the IF and both exhibit this spike. Other hams who own this radio have used both tap points and do not see the spike.

This same RTL-SDR does not show the spike when connected directly to a VHF antenna, nor does it show the spike when connected to an upconverter instead of the IF in my FT-450D.

I have also tried tapping the IF without a buffer amplifier and going directly into the RTL-SDR but the spike is still there.

I have also turned off the transciver but left the power supply and the SDR on and the spike goes away so I don't think it is noise from the radio's power supply, which wouldn't follow the tuner around anyway.

What can I do to eliminate this spike? Is there some configuration setting in HDSDR besides the DC offset setting that I am missing?

 

[donf99]

I see the same spike at +24KHz on my FT-450D. As the offset does not change from the tuning center point, it must be generated in the receiver chain in the radio and getting through the low-pass filter on the G4HUP TAP board. The FT-450D uses a second IF of 24KHz, so this is undoubtedly where it is coming from, probably being picked up by the wire connecting the 1st mixer tap point to the buffer board.

Best,

Don
WD9DMP

 

[K7XRL]

I see the same spike at +24KHz on my FT-450D. As the offset does not change from the tuning center point, it must be generated in the receiver chain in the radio and getting through the low-pass filter on the G4HUP TAP board. The FT-450D uses a second IF of 24KHz, so this is undoubtedly where it is coming from, probably being picked up by the wire connecting the 1st mixer tap point to the buffer board.

Best,

Don
WD9DMP

Don,

Thank you for this insight! I wish the software I use (HDSDR) had an RF notch filter option but the developer has stated it is a lot more processor intensive than an audio notch.

73

Ron
K7XRL