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,.

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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:

• We strung wires on a fiberglass post . we cut the lengths to the approximate lambda/4.
• The network analyzer was used to tune the lengths to get a maximum null in S11. This was down outside.
• A ferrite clamp was placed around the coax that fed the 2 halves of the dipole.

     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):

• analyzer setup: preamp on, rbw 100 Khz, vbw  30 Khz, avg 20 traces.
• Black, red trace: the are avg 10, peak hold when the antenna was held up on the 5 foot dipole pole.
• blue,brown: avg10 and peak hold when the dipole was extended about 12 feet on the van's mast.
• all measurements had a stronger signal at lower frequencies (unlike what we later measured with the log periodic at 310 MHz).
  
• the 12 foot mast measurement is also about 35 db stronger than the 5 foot hand held measurement.
• the 12 foot measurement had about 15 feet of cable while 5 foot extension had a much shorter cable.
• The ferrite clamp we used was probably not doing a very good job of isolating any currents on the feed  coax shield. We probably need to use a balun to have a correctly connected the dipoles to the coax line.

The second set of plots shows the fundamental measured with the dipole while the 3rd harmonic was measured by the log periodic (.ps) (.pdf):

• black is an average of 10 traces while red is a peak hold.
• Top: The fundamental measured with the 103 MHz dipole
• These values are about 30 db higher than those measured with the log periodic back on 30may13.
• The noise floor is also about 30db higher than the 30may13 measurement.
• We did have a 20db external amp, but i'm pretty sure it wasn't connected for this measurement (but maybe i'm wrong?)
• You can also see some other fm  stations below 102.9. These were barely visible using the log periodic.
• 2nd frame: The 3rd harmonics measured using the log periodic.
• These values are close to those measured on 30may13 with the log periodic.
• 3rd frame: I removed 2db from the fundamental measurement to remove the dipole gain
• bottom frame: i removed 6.5 db from the 3rd harmonic measurement. This is the gain of the log periodic antenna
• The table in frame 3 shows that
• 102.9 3rd harmonic is 96 db down from the fundamental
• 104.1 3rd harmonic is 80db  down from the fundamental.

Summary:

• the dipole for the 3rd harmonic had large changes in value when we put it 12 -15 feet in the air on a mast.
  
• The dipole was probably not fed correctly.
• Using the 103 MHz  dipole for the fundamental and the log periodic for the 3rd harmonic we measured:
• 102.9 3rd harmonic down 96 db
• 104.1 3rd harmonic down 80 db
• Since the 103 dipole was fed the same was as the 312 MHz dipole, the dipole fundamental measurement was also probably incorrect.
• We need to put a correct a balun on each dipole, or just buy the calibrated dipole set from AHsystem.

processing: x101/130604/rfivan327.pro

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 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:

• locations:
• The towers are located at 18.2887, -66.6606
• The van was located at 18.3157, -66.6830 (lat,long)
  
•  This is at the turnoff to 6612 from route 10.
• See Google maps image showing van and tower (.pdf)
• The van is at marker A, the towers are at marker B.
  
•  this was a few hundred meters closer to utuado (along route 10) from the 30apr12 measurement.
  
• The distance from van to tower was about 3.9 km.
  
• We used the log periodic antenna for the measurements (same as 30apr12).
  
• anritsu spectrum analyzer was used. Its setup was:
  
• preamp on, rbw=30 Khz for fundamental, 100 Khz for 3rd harmonics, average 10 and peak hold.

The plots show the fundamental and 3rd harmonics of the fm stations (.ps) (.pdf)

• Top: fm station fundamentals:
• Black is an average of 10 traces, red is a peak hold
• The RBW is 30 Khz.
  
• HQ = 102.9 MHz
  
• Radio Redentor= 104.1 MHz
  
• The difference between the two frequencies is 1.2 MHz
  
• Dana pointed out that the log periodic did not have an element long enough for 104 MHz.
  
• The peak amplitude occurred when we pointed a little off of the tower direction.
• Because of this, the amplitudes measured are probably less than the actual values.
• Bottom: 3rd harmonics of the fm stations.
• The rbw is 100 Khz.
• The log periodic had an element that covered this frequency. The maximum amplitude occurred  when we pointed at the towers.
• green trace:308.7: 3rd harmonic of 102.9. Peak value: -103dbm
• blue trace: 312.3: 3rd harmonic of 104.1. Peak value  -96 dbm.
• purple traces: Let Frq1= 102.9, Frq2=104.1
• These are intermod products between the two transmitters:
  
• 309.9 MHz = 2*Frq1 + frq2
• 311.1 MHz =2*Frq2  + frq1
• these intermod products are also seen in the  dynamic spectra recorded at AO (see 2005-2006 dynamic spectra)
  

Summary:

• The 3rd harmonics are clearly seen in the spectrum analyzer 4 km from the towers.
• So the harmonics we see in the 327 receiver are not being created inside our receiver.
• The measured ratios of measured 3rd Harmonic/fundamental are:
• I used the average of 10 traces.
  
• 102.9: -50dbm - (-109dbm) = 59 db down
• 104.1: -79dbm - (-107dbm) = 28 db down
• The log periodic did  not cover the fm band adequately so the absolute difference is probably off.
• The relative difference is probably meaningful:
• 102.9's  3rd harmonic  is  60 db down
• 104.1's 3rd harmonic  is only 28 db down.
• If 102.9 is ok, then 104.1 probably has problems with it's 3rd harmonic filters.
• We should go back out to the site and measure the fundamental and 3rd harmonic with an antenna that covers both frequencies. We could then have a correct ratio of fundamental to 3rd harmonic.
• Looking at the azimuth swings done back in 2005-2006
• see: (strength and azimuth dependence of the harmonics (.ps) (.pdf)
  
• the 104.1 3rd harmonic has a definite azimuth dependence that repeats for the 5 azimuth swings.
• The102.9 3rd harmonic does not have a fixed azimuth dependence.
• This also points to 104.1 as the greater problem of the two stations (and maybe  the source of  the intermod products).
  

processing: x101/130530/rfivan.pro

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