3rd harmonics of FM stations in the 327 receiver

04jun13: measure the 104.1,102.9 fundamental with a dipole
30may13:measuring 104.1, 102.9 harmonics, intermod products from route 10.
30apr12: measuring 104.1,102.9 harmonics from route 10.
2005-2006:measurements of FM station harmonics through the telescope, az dependence,.

04jun13: measuring fm stations fundamental with a dipole

    The log periodic that we had used to measure the fundamental and 3rd harmonic of the fm stations only went down to 190 MHz. Since the fm stations are  at 102.9 and 104.1, we did not get an accurate measurement of the  fundamentals. We made two dipole antennas covering 310.5 and 103.5 to try and improve the measurement.
     The dipoles were made by:

     On 4jun13 we drove out to the same site as 30may13 and tried to measure the signal strengths using the dipoles and the log periodic antenna.
    The first plot shows the 3rd harmonic measured with the dipole and the anritsu spectrum analyzer (.ps) (.pdf):
The second set of plots shows the fundamental measured with the dipole while the 3rd harmonic was measured by the log periodic (.ps) (.pdf):


processing: x101/130604/rfivan327.pro

 30may13:Measuring 104.1,102.9 harmonics,intermods from route 10.  

We (dana and phil)  measured the fundamental and 3rd harmonics of the fm stations 104.1 and 102.9 from route 10. The setup was:
The plots show the fundamental and 3rd harmonics of the fm stations (.ps) (.pdf)


processing: x101/130530/rfivan.pro

30apr12: 104.1,102.9 harmonics from route 10. (top)

    On 30apr12 we (angel and i) took the rfi van up route 10 to look at the 3rd harmonics of the FM stations:

The 327 MHz receiver has seen:

The setup for the measurements:

The plots show the spectrum analyzer measurements (.ps) (.pdf):


processing: x101/120430/rfitowers.pro

2005-2006: measurements made on the telescope:

Links to plots/images:
strength and azimuth dependence of the harmonics (.ps) (.pdf)
 dynamic spectra of first azimuth spin(.gif)

2005/2006 Summary (top)

  • Third harmonics of FM radio stations are showing up in the 327 MHz receiver.
  • They are not being created in the receiver since they remain when rf filters are placed in front of the first amp.
  • Some show a constant  azimuth dependence, some are more variable in time.
  • Some of the harmonics are weaker because they fell at the edge of the 25 MHz filter that we were using.
  • there is a comb 1.2 MHz apart around the 308.7 and 312.3 3rd harmonics of 102.9 and 104.1.

  • The FM stations:

        The whip antenna and the spectrum analyzer was used to measure the strength of the FM stations at the observatory (the whip is not on the platform so there may be a difference). The spectrum analyzer was set to a span of 10 MHz (about 300Khz rbw).
    freq strength on
    spec Analyzer
    3rd Harmonic
    107.3 -33 321.9
    102.9 -39.3 308.7
    104.1 -42.8 312.3
    100.3 -57 300.9 *
    106.5 -65 319.5
    101.9 -68 305.7 *
    100.7 -68 302.1 *
    105.7 -79 317.1
    * these frequencies are outside the 327 band we measured.

    2005-2006 data

         The azimuth swing data from 28oct05 was used to check out the strength of the harmonics (see 327 az swings). There were 5 complete azimuth spins between -90 and +270 deg azimuth. The dome was at 19 deg. A 25 MHz band was centered at 320 MHz with 2048 channels. The azimuth moved at .3 deg/sec.

        The plots show the strength and azimuth dependence of the harmonics (.ps) (.pdf):

        The strongest harmonic is 312.3 from FM 104.1 followed by 321.9 (107.3), 308.7 (102.9), and then 319.5 (106.5). The dynamic spectra of the first az spin also shows that 312.3 is the strongest/most spread out signal

    2005/2006: Some observations:


    processing: Y05/051028/FM_harmonics.pro