Internal signal generator

[nl...@nlsa.com]

I need help interpreting Linrad’s display of its internal generator (F11).  My display looks nothing like the example on Leif’s website.

The signal does not appear to be swept in frequency and I don’t see the low-level signal at all.

My receiver is an IQ+ which has a zero-if bump in the center of its passband.  I think that the test signal is superimposed on this bump; perhaps this explains my weird S-graph display.

Any suggestions would be welcome.

W9IP

[MRO]

Perhaps someone could just tell me whether the signal generator in Linrad 5.02 actually behaves as described in the online notes.  

1. Does it sweep in frequency when Linrad is playing back a recorded file?  

2. Does the low-level signal key on/off ?

3. Is the high-level signal always at the center of the passband?

Thanks,

Michael, W9IP

[Earl Shaffer]

HI Mike.

I wasn't aware of a signal generator in Linrad so I can't help with that but I DO know that Linrad is deaf at the Zero frequency null (DC) so your signal must be offset from that. 

WB9UWA.

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[Leif]

The internal signal generator replaces the data read from a file
with data generated by linrad itself. The purpose is to test the
selected processing parameters with ideal signals.

There are two cases. If the recording is 16 bit data the synthetic
signals are 16 bit, and if data is 18 bit or float the synthetic
data has high precision (do not remember the format)

I downloaded frh1135.bz2 from here: https://sm5bsz.com/arrl2001/index.htm
It is 18 bit data and i played it in linrad after specifying the unpacked
file in adfile.

When I press F11 I get a single strong carrier exactly at the centerfrequency.
There is no hardware involved so there is no notch at the center frequency.
The zero at the center frequency is associated with hardware that use
soudcardsbecause soundcards are AD-coupled. Digital hardware like the Perseus
or SDR-IP do not have any notch at the centar frequency.

I find that the instructions for using the internal generator is missing.

F7 adds random noise (at least under Linux)
F8 reduces the signal level in steps of 10 dB starting 0.14 dB from the point
of saturation.
The other functions seem to be missing.

The version used here: https://www.sm5bsz.com/lir/map65/map65-netlevels.htm
is linrad-03-33 and it is available on the development page https://sm5bsz.com/linuxdsp/linroot.htm

The help file, help.lir contains this information:
F8 = Reduce the strong signal when F11 is in use.
F9 = Truncate input (for test only)
F10 = Add noise when F11 is in use (Linux only.)
F11 = Enable internal signal generator.

This was all long ago and I do not remember, presumably the 03.33 version will
work as demonstrated at map65-netlevels.htm

73

Leif

[nl...@nlsa.com]

Leif,

Thank you for the assistance.  I downloaded Linrad 03-33 as you suggested.  Trying to play back one of the 2001 recorded files didn't work because the newly-installed instance of Linrad lacked calibration files:

 

Nevertheless, I was able to invoke the internal generator more successfully than with Linrad 5.02.  When receiving live data, pressing F11 zeroes the noise floor and places the low-level signal in the center of the passband.  The high-level signal sweeps upward in frequency.

I configured Linrad 03.33 as per Fig 1 in  https://www.sm5bsz.com/lir/map65/map65-fft1levels.htm

 

First FFT bandwidth (Hz) = 100 (bw is 117Hz)
First FFT window (power of sin) = 8 (Gaussian)
First FFT amplitude = 100
First backward FFT version = 0 (float format)
First backward FFT att. N = 2 (min attenuation)
Second FFT bandwidth factor in powers of 2 = 0
Second FFT window (power of sin) = 4
Second forward FFT version = 0 (float arithmetics)

 

Questions: Why is the SNR of the low-level signal so high?  It should be about 16 dB

 

 

W9IP

--

There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:

http://w3sz.com/Linrad%20Installation%20&%20Configuration%20User%20Guide%20-%20V1-0.pdf

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