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-   -   Calibrating SDR Sharp (http://forums.radioreference.com/software-defined-radio/275611-calibrating-sdr-sharp.html)

moonbounce 10-03-2013 5:46 PM

Calibrating SDR Sharp
 
Anyone know how to calibrate SDR Sharp? For the life of me I can't get it to read the proper frequency that it lands on for example 142125000 will come out as 142125120 the next frequency will be 142365000 and it will show up as 142367988 or it will be 2.5 khz out. Also if I leave a freq. and go back to it later the readout will be different again, not at all consistent. I have tried to align the frequency by using the configure and frequency correction. It will set the correct frequency for one and throw it off for another. I can't seem to get it aligned.

I am using SDR Sharp version 1165 with the frequency manager + scanner. If I don't get a proper alignment of the bandwidth and the frequencies in that band, I can't use the scanner as it will not stop on any of the frequencies in that band as I can get the frequencies aligned.

Moonbounce

rbm 10-03-2013 7:19 PM

While I don't, and won't normally use ver. 1165 here is what works for me with all versions at all frequencies up through 1000 MHz.

My dongles drift about 8ppm from cold start to warm up after around 40 minutes.
And converter will drift also.

Kalibrate, or kal, can scan for GSM base stations in a given frequency band and can use those GSM base stations to calculate the local oscillator frequency offset.

Download it from here:
Kalibrate

See the list of options below.

(I have the 'Kalibrate' files on my D: drive in the folder named 'Kalibrate')
(The commands below are what are in my shortcuts. If you want to run from a DOS window, just enter everything after the 'C:\Windows\System32\cmd.exe /k')

Use this command to find a GSM850 signal in your area.
C:\Windows\System32\cmd.exe /k "D:\Kalibrate\kal.exe" -g 42 -e 22 -s 850

Then, once you have identified a GSM signal in your area, run calibrate using the command below.
C:\Windows\System32\cmd.exe /k "D:\Kalibrate\kal.exe" -e 41 -c 234 -v

For the above command:
GSM Channel 234 (-c 234)
-e is roughly the error rate expected. '41' in this case. (not real critical) (-e 41)

That will give you the:
'Frequency correction (ppm)

Where options are:
-s band to scan (GSM850, GSM900, EGSM, DCS, PCS)
-f frequency of nearby GSM base station
-c channel of nearby GSM base station
-b band indicator (GSM850, GSM900, EGSM, DCS, PCS)
-R side A (0) or B (1), defaults to B
-A antenna TX/RX (0) or RX2 (1), defaults to RX2
-g gain as % of range, defaults to 45%
-F FPGA master clock frequency, defaults to 52MHz
-v verbose
-D enable debug messages
-h help

Then, if you are using a converter, you need to set 'Shift' or 'Offset' for it.
I don't use a converter so I can't help with that part.

If you have 'Snap to grid' selected, SDRSharp will land on an exact multiple of your selected step size.

Rich

Edit: Here is an older run that I did.
The search found channel 136 to be the strongest on that antenna.
http://i129.photobucket.com/albums/p...Kal_Search.jpg

Using channel 136, the 'Frequency correction offset' rounds up to 38ppm. (SDRSharp accepts whole numbers only)
http://i129.photobucket.com/albums/p...Kal_Offset.jpg

moonbounce 10-03-2013 9:00 PM

Thanks rbm, I am making some headway with the Snap to grid, at least it is stopping on either a 0 or a 5, that is a plus ( I am referring to the scanner mode, not manual mode). But I still have a problem with it scanning past active frequencies.

I also have version 1114 and I use it also. Version 1165 is just to pass time and hopefully learn something.

Moonbounce

moonbounce 10-04-2013 7:18 PM

So everything looks good except it won't stop on any frequency. The snap to grid was the trick to getting the correct frequency but no luck getting it to land on an active frequency.

Moonbounce

rbm 10-04-2013 7:26 PM

It sounds like you're making progress.

I haven't used the latest scanner plugin but the earlier version required me to fiddle with the squelch settlings on the plugin.
That would set the threshold of when/where the scanner would stop.

As I recall, when I tried the earlier version, it was sharing a key that was used by another plugin and I didn't like the conflict it caused.

I guess I should give the latest version a try soon. ;)

Rich

rbm 10-04-2013 7:37 PM

Moonbounce, I just did a quick search and found this on the yahoo SDRSharp group ... (Message #11070)
Maybe it will help you.

Rich

Harley & everyone with signal detection issues with my scanner:

In my scanner there are two settings that have the most effect on
whether the scanner will stop on an active frequency.

1. For an FM signal, the Minimum Signal Strength must be set lower than
the lowest strength of a signal. Remember lower means closer to -130,
higher means closer to zero. The peak signal strength of an FM signal
MOVES left and right around its center, so that in any given millisecond
the signal strength may be the highest, or more likely the lowest,
strength of that signal. For example: if an FM signal "bounces" from
between -35 and -30 dB, you have the best chance of stopping with a
minimum of -40dB. This will ensure that the weakest fragment of the
signal will still be higher than the minimum. Make your minimum low
enough that signals are detected, but high enough that the scanner
doesn't get fooled by the noise floor.

2. The Radio Settle Time should be set high enough to ensure reliable
detection of a signal that meets the minimum signal strength. SDR# does
not tell plugin developers when the radio has successfully/reliably
tuned a signal, so I use a small delay to give the radio time to tune to
the desired frequency. A higher number will give you more reliability,
but will slow down scanning. Start high and turn it down once you find
it reliably detecting signals.

More tips:
* calibration is important. Many inexpensive dongles drift in frequency
so you may have to adjust the PPM correction frequently. In addition
(at least in my city) NOAA weather is spot-on but local companies are
often off-center from their assigned frequencies.
* "seconds wait" doesn't take effect until a frequency is tuned in.
* "slow down scanning" isn't used until AFTER a frequency has stopped
transmitting
* squelch is not used to detect a busy frequency
* step size is not used to detect a busy frequency, but IS used after
tuning the radio to watch for the signal strength to drop below the
minimum. In this instance a wider step size is better. The next
version of my scanner lets you disable this feature.
* your computer MUST support an adequate number of threads. SDR# plus
my scanner with all its windows open uses around 9 threads
simultaneously.

If anyone has problems you can always write me directly at
sdrs.freqmgr@... and I am always happy to help. My software is free
but it still comes with support.

I hope this helps; feel free to let me know if you need more.

73s,
Jeff N8GJL

moonbounce 10-05-2013 7:16 PM

Thanks again rbm I won't be able to look at that until Monday, but i will get back to you and let you know how I make out. I also want to try adjusting the ppm like you said and see if I have any luck there, but again it won't be until Monday:(.

Moonbounce

moonbounce 10-07-2013 4:56 PM

So I've been all over the place changing setting and no joy. I have worked on this for hours and can't get it to stop anywhere.

I think I have to leave it alone for awhile, but i will be back.

Moonbounce


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