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Recent content by johnny_b4e

  1. J

    Group delay calculation (phase wrap -180 to 180)

    Hi I'm calculating group delay for branch line coupler port 3 and I get this large peak at center frequency. I'm using ngspice group_delay function. It is clear that its caused by phase transition from -180 to 180 as it is at same frequency as the peak. Is that in fact correct? From my own...
  2. J

    [SOLVED] RF Signal spectrum content explanation

    Here is latest measurement with improved levels: Note that span is 2MHz compared to initial! Datasheet states PN= -105 dBc/Hz at 10kHz offset. So if 1kHz BW then should be -75dBc? And I have -50dBc. I guess its quite bad if I calculated correclty.
  3. J

    [SOLVED] RF Signal spectrum content explanation

    I've patched my clock source to go directly to RF clock input and that removed all visible spurs and reduced noise levels a bit. So in conclusion there was interference on clock signal due to bad design.
  4. J

    [SOLVED] RF Signal spectrum content explanation

    I've done some testing. I changed some settings of internal PLL CP and VCO, this reduced level of spurs. But one interesting change was, when I switched microcontroller internal RC clock source frequency. Changing clock resulted in changes in spur offsets. Here I have to mention that this RF...
  5. J

    [SOLVED] RF Signal spectrum content explanation

    I changed frequency twice (860 and 868), but the offset stays the same both times. Also checked with battery supply, still the same offset. And finally changed data rate and deviation. I know it shouldn't matter in CW mode, but checked anyway. Result was the same. So the fact that peaks stay...
  6. J

    [SOLVED] RF Signal spectrum content explanation

    About system: Power supply is mains AC transformer adapter to 12V, then generic 3.3V regulator. Transmitter is Si4468 as class E amplifier with bias voltage from LDO (TPS73201). Output goes trough two RF switches SKY13323-378LF and SKY13385-460LF TCXO is EPSON TG-5006CG Also, a guesses would be...
  7. J

    [SOLVED] RF Signal spectrum content explanation

    I have transmitter outputting a CW signal at 869.000200 MHz. In spectrogram I see other symmetrical peaks spaced at 165kHz. Clock source is 26MHz TCXO. I was thinking what is the source of them.
  8. J

    problem with getkey function on 8051 in c

    I'm not quite sure if I understand what you mean, but if you need to periodically check for button event try this: unsigned char key_event(void) { static unsigned char LastState; unsigned char pin_state; unsigned char event = 0; pin_state = P1 & 0x01; // Or whatever is your port read...
  9. J

    Radar circuit function

    Is the problem, the fact that it's old (old design) and new radars use different technology, or the circuit itself is flawed? Anyway, this was more of an educational question, I'm sure there are more useful examples.
  10. J

    Radar circuit function

    So, I was searching for typical speed radar circuits and came a cross this: I can't seem to understand how it can detect (measure) level of RF signal. I guess, C1 with traces to chip forms antenna matched for desired radar frequency, but how can general purpose amplifier work with GHz range...
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