Local Oscillator "rejection" on Transmit

General discussion and support for the Peaberry SDR V2.

Local Oscillator "rejection" on Transmit

Postby oh2gaq » Mon Sep 16, 2013 5:39 pm

Hi, thanks for the well-put-together kit and instructions, it all went together like clockwork. After building the kit it was easy to adjust the RX and TX Image Rejection, basically to give 70 db or more rejection of the image. On receive, the automatic LO spike suppression in HDSDR does a good job also. Performance is just what I need except for perhaps 1 item.

On the transmit side, I wonder what the typical performance is with respect to the LO rejection ? There is of course no adjustment (as far as I can see) for that. I have measured the LO rejection when generating a SSB signal, and the LO is between 35 db (when measured at 28 MHz) and about 45 db when measured at 14 MHz. In both cases the wanted USB signal was at the level before significant extra distortions were apparent. You can get better LO rejection figures, if you increase the level a bit, not more than another 5 db though. Measurements were made using a Tek. 492 SA, low distortion audio source to drive the microphone interface (Sound Blaster USB interface) and at the output of the driver stage without the PA being enabled.

I am using the Peaberry to drive a 144 MHz transverter, and the whole thing is used as a tuneable IF for microwave transverters on many microwave bands.

73's,

Hamish, OH2GAQ
oh2gaq
 
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