Jack Pearson at 3rd and Lindsley

From Wednesday, July 12, 2017. Great song from a great set.

 

Shot w/Sony A9. Handheld, ambient audio.

Time Jumpers — I Hear You Talkin’

From July 10, 2017 at 3rd and Lindsley. Vince Gill is normally in the lineup, but this night he was practicing with the Eagles.

 

Shot with Sony A9. Was right next to the stage, so the angle wasn’t great, but the audio was very nice.

Snippet of Randy Moore at Margaritaville, Nashville

Ambient audio. A9 recording at 4k. Recorded until people were seated in front of me.

 

Beltre Homer in Slow Motion

Caught the first homer of the night Friday night in Slow Motion.

Shot using Sony A9 in 120fps mode, then rendered at 25% speed using Vegas Pro.

 

Sushi from Yoshi’s

Had dinner at Yoshi’s in Jack London Square while I was in the SF area. Yummy. Wouldn’t fit on the expense report, though. Also wanted to sample the jazz in Yoshi’s theater, but they had a comedian that night, so I passed.

Golden Gate Time Lapse

The new camera (Sony A9) has a time lapse feature in it. I tried it out while at the Golden Gate Bridge. Captured 10 minutes at 2 frames per second. You’ll need to click to view.

Golden Gate Pre-Dawn

Got up way early yesterday so that I could stop by the Golden Gate Bridge on the way to the airport.

Sundown over San Franscisco

Looking across the bay from San Leandro at sundown.

Measuring Relative Antenna Receive Performance

I have been working on a project aimed at answering the question “Which antenna is better at receiving?” While I was able to find ways to test antennas for resonance (SWR) and impedance matching, and while those tests should correlate to antenna performance, I wanted to be able to directly compare two antennas across a broad range of frequencies (like 20 MHz – 1.2 GHz) and know which antenna worked better and at what frequencies.

A few caveats:

  • This test will not show the absolute performance of an antenna. It will only show relative performance between two (or more) antennas.
  • While the signals transmitted during this test are both low power and of short duration, you should take measures to ensure that the signals will not interfere with any life-and-safety devices (for example, I would not recommend doing this anywhere near a medical facility).
  • I am not an RF engineer. The results could be invalid for some reason that I am not aware of (but I am open to any and all feedback).

Setup:

For each antenna:

  • Transmit low-level signal using HackRF into antenna 1
  • Receive signal using RTL-SDR from UUT (Unit Under Test)
  • Step frequency from 20 MHz – 1200 MHz in 5 MHz steps, approximately .5 seconds per step
  • Capture received frequency and signal strength (dBFS) for approx. 2 minutes (results in many measurements per frequency)
  • Average signal strength at each frequency
  • Performance plots are all relative to the BCD436HP stock antenna

To actually achieve the above, I drove both SDR devices with the following GnuRadio Companion setup:

 

In the above, there are a few parameters that are typically modified:

  • center_freq_min: Sets the lowest RX/TX frequency
  • center_freq_max: Sets the highest RX/TX frequency
  • freq_step: Sets the stepping increment
  • Poll Rate (inside the Function Probe block): Determines how long the setup dwells at each frequency step (1/poll rate seconds). Shown value of 50 (i/e dwell for 1/50 seconds at each frequency) is actually faster than the flow will actually run (which seems to be around 1/4 second per step). I just used that value to have a minimum dwell time. Some applications may be useful to dwell for a longer time.
  • File (inside the File Sink block): Sets the file name for the output data.

Assuming the hardware is plugged in, for each antenna all you need to do is change the name of the output file, then run the flow for long enough to capture samples at each step. For the above, setup, I ran each antenna for 2 minutes. This resulted in hundreds of samples at each frequency step.

One problem I quickly found was that the file sink only writes one value to the output file per reading. So, the block “Add Const” just before the file sink adds the frequency setting to the received signal strength. Since all of the RSS values are between -99.99 dBFS and 0 dBFS, I used the formula -(func_center_freq[0]/10000) in that block. This results in values like “-63519.726562” being written to the file (which translates as 19.726562 dBFM at 635 MHz).

The next problem to overcome is that I wanted to manipulate/graph the data in Excel, but the actual output file is just a series of binary float32 values. For each datafile, I used the python code below to convert the binary output file into a csv file that Excel could read:

import numpy

import scipy

f = scipy.fromfile(open(“input_file”), dtype=scipy.float32)

numpy.savetxt(“output_file.csv”,f)

f.tofile(“output_file.csv”,sep=”\n”, format=”%lf”)

Now, I have an Excel file that looks like:

-2060.098389
-2060.660645
-2060.694092
-2061.014893
-2061.200928
-2061.266113
-2061.273682
-2061.317383
-2061.320068
-2061.333496
-2061.379395
-2061.424072
-2061.433105
-2061.478271
-2061.493164
-2061.721924

I parsed out the frequency with the formula =MID(A3,2,FIND(“.”,A3)-4) (A3 has the raw value to parse), then parsed out the dBFS value with =VALUE(MID(A3,FIND(“.”,A3)-2,5)).

Next, I averaged the dBFS at each frequency:

=ROUND(SUMIF(B1:B112640,F1,C1:C112640)/COUNTIF(B1:B112640,F1),2)

In the above, “F1” is a cell that has the frequency to be averaged, and the large ranges contain the parsed data. Doing this for every frequency, I ended with the following table of dBFS values:

20 63.85
25 63.88
30 63.84
35 60.06
40 42.92
45 41.88
50 34.49
55 38.36
60 47.31
65 41.36
70 30.43
75 37.89
80 38.33
85 38.54
90 37.69
95 33.37
100 27.64
105 36
110 42.46
115 49.02
120 45.52
125 47.92
130 51.07
135 44.23
140 43.69
145 38.11
150 37.92
155 38.68
160 22.94
165 22.4
170 20.84
175 24.41
180 29.73
185 34.83
190 42.46
195 50.95
200 52.05
205 48.9
210 45.08
215 41.32
220 40.9
225 39.87
230 41.14
235 38.49
240 36.73
245 35.75
250 37.71
255 35.61
260 31.88
265 26.57
270 32.17
275 31.01
280 31.87
285 34.06
290 32.43
295 32.8
300 33.97
305 30.27
310 32.21
315 29.19
320 33.99
325 33.87
330 29.05
335 27.73
340 29.15
345 24.6
350 27.17
355 24.34
360 24.89
365 24.45
370 23.26
375 25.45
380 24.02
385 24.09
390 21.45
395 20.92
400 24.78
405 25.11
410 20.82
415 24.58
420 23
425 24.28
430 31.27
435 27.74
440 30.79
445 37.04
450 41.75
455 38.53
460 35.06
465 30.46
470 28.73
475 22.38
480 24.97
485 23.65
490 24.59
495 25.2
500 20.36
505 20.57
510 20.93
515 21.68
520 20.33
525 22.34
530 23.78
535 25.06
540 24.97
545 28.33
550 29.23
555 31.93
560 39.83
565 31.4
570 28.5
575 29.33
580 25.17
585 25.87
590 30.54
595 28.42
600 25.19
605 25.29
610 24.94
615 25.57
620 22.81
625 24.09
630 22.95
635 19.45
640 22.57
645 22.1
650 17.86
655 22.23
660 23.72
665 23.86
670 28.09
675 28.93
680 32.36
685 33.46
690 34.59
695 35.78
700 37.55
705 38.28
710 38.15
715 34.67
720 33.53
725 33.7
730 29.98
735 31.68
740 29.02
745 28.88
750 27.41
755 28.34
760 28.27
765 27.13
770 29.82
775 27.61
780 25.07
785 28.69
790 27.33
795 25.28
800 28.06
805 28.23
810 28.72
815 27.27
820 28.38
825 30.02
830 30.61
835 31.47
840 33.03
845 28.5
850 33.26
855 35.71
860 36.72
865 41.11
870 37.37
875 34
880 35.53
885 32.75
890 34.36
895 31.75
900 31.49
905 31.21
910 31.13
915 32.49
920 35.46
925 29.31
930 31.33
935 27.55
940 25.62
945 29.99
950 29.71
955 31.42
960 31.67
965 35.61
970 32.62
975 31.69
980 32.47
985 35.24
990 34.57
995 38.57
1000 40.03
1005 40.08
1010 50.21
1015 50.33
1020 42.01
1025 42.55
1030 44.34
1035 43.54
1040 42.59
1045 39.21
1050 46.41
1055 38.18
1060 38.17
1065 49.99
1070 40.05
1075 39.09
1080 41.01
1085 39.61
1090 40.16
1095 37.67
1100 40.67
1105 44
1110 43.2
1115 42.1
1120 41.36
1125 44.48
1130 48.7
1135 46.2
1140 44.56
1145 47.01
1150 44.56
1155 52.04
1160 49.63
1165 46.8
1170 50.03
1175 44.87
1180 50.45
1185 53.15
1190 45.48
1195 53.77
1200 49.65

Doing this for each antenna, I next subtracted the BCD436HP Stock Antenna measurements from each of the other antennas’ measurements, resulting in a table that showed only how much better or worse the UUT antenna is than the stock antenna. Graphing those values for each antenna looks like the below graphs.

Antennas tested:

  • RS 800 MHz antenna
  • Comet SMA503
  • Pryme Dual Band Whip (no longer available)

Graphed Results

Because Its Been A While Since I Posted a Picture of a Cat