SDR Sharp

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k1agh

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Anyone use this program? I'm having an issue with the freq. being off. If I type in 129.900 which has activity on it I cant hear anything unless it tune it to 128.600. Any idea why and what I can do to fix it? What filter settings should I have?
 

rbm

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Here's how you can calibrate SDRSharp for your specific dongle.

The easiest way is to use the 'pilot' of an ATSC TV broadcast.
That is supposed to be 'exactly' 310 kHz within the TV signal. (ie. Channel 14 is at 470.310 MHz)
Using the highest frequency local channels works the best.

Rich

You can see a list of them here. Just check against a few local TV signals because they DO vary slightly.
North American television frequencies - Wikipedia, the free encyclopedia

This shows the view while calibrating to an ATSC TV pilot frequency.
Notice for best accuracy you need to zoom in.
 

rbm

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Since you're in the air band, here are some sample settings for you.

Keep clicking on the magnifying glass in the bottom right corner for the high resolution image.

Rich

 

k1agh

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The NOAA station comes in off freq. too I have to tune it to something else then the actual freq. what ppm should i go for/ how will i know its the right ppm?
 

br0adband

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That's the point of adjusting the ppm setting - it's like a super-duper fine tuner which needs to be adjusted based on the particular SDR device(s) you have and are using. Once you set the ppm for a given SDR device, it should remain the same given the situation (as some devices fluctuate based on thermal conditions and changing temps require you to reset the ppm accordingly). It may vary by a single ppm from time to time, however.

Here's the short-short way to adjust the ppm quick and easy:

- pick a known frequency like a NOAA weather forecast in your area, or the ATSC TV signal mentioned above

- tune it using SDR# or whatever program you're using, just punch in the exact known frequency however it's done for the app you've got

- increase the zoom on the spectrum if possible to enlarge the "peak" so you can visually spot the absolute point or as close to that as you can get clearly

- if the actual indicator that shows which frequency you're tuning to is not lining up directly along that point or very very close to it, your ppm is off

- while that signal peak is still visual, open the radio configuration option and adjust the ppm one way and watch the line which shows the frequency you're tuned to - if it's moving in the wrong direction, then adjust the ppm accordingly (negative or positive) until you get it lined up as closely as possible with the idea being you want to divide the peak equally down the middle aka centered

- once that's done, you've pretty much tuned your SDR device as closely as possible to the actual frequency being received

Once you known the ppm for your given SDR device (as in the case of the popular RTL sticks you'll find they're all going to be different in varying amounts, I own two sticks and they're 50 and 57 so it can get fairly high off the 0 mark) make sure to remember it as required. Also, don't even bother wasting effort to get it perfect 'cause that rarely if ever happens. These devices are only going to be so precise, and some transmissions aren't even on frequency to begin with - your SDR hardware isn't necessarily "off" in some situations. I routinely monitor aircraft communications and when I tune to a known frequency like 135.100 which is Nellis AFB here in my area (one of their approach/departure frequencies) while the tower is actually "on" frequency, some of the aircraft calling in are either a few kilohertz positive or negative more often than not, and you can spot such things easily on the waterfall.

It'll never be perfect, but it can certainly be more than acceptable to tune stuff and monitor it.
 
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k1agh

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that did it thanxs, now for listening to public safety,fd, what should the best filter bandwidth and filter order should it be? what step sizes should i use for air, pd/fire?
 
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rbm

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that did it thanxs, now for listening to public safety,fd, what should the best filter bandwidth and filter order should it be? what step sizes should i use for air, pd/fire?
You can start out at NFM and 7500 Filter bandwidth and go wider or narrower from there to your liking.
Air is as shown in the screen capture above. AM and around 6000 bandwidth. Again, set it to your liking.

Until you start doing digital, it's not that critical.

Rich
 

mancow

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Since you're in the air band, here are some sample settings for you.

Keep clicking on the magnifying glass in the bottom right corner for the high resolution image.

Rich

I use 25 kHz instead of 2.5 kHz so each step lands on a channel.
 

br0adband

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2.5 kHz is my default so I don't have to keep constantly changing it from band to band. ;)
I'm getting to that point nowadays - just using 2.5 kHz stepping across all bands - and only find myself needing to change it if I'm trying to grab some NXDN traffic which all happens to be on offset frequencies here in my area (+/- 3.125 kHz from licensed frequencies). As noted by someone else it's probably indicative of the same supplier being used for the hardware I suppose, all I know is it was incredibly frustrating trying to figure it out at first as to why I wasn't getting decent signals and decodes - it's because I was always "off" by just enough to break decoding. :)
 

rbm

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If you haven't already done so, you can add or modify the line below in your config file as shown below.
(even though the line may 'break' here, it should be a single line in your configuration file.)

That will add 3.125 kHz as one of the 'selectable' step sizes.

"<add key="stepSizes" value="1 Hz,10 Hz,100 Hz,500 Hz,1 kHz,2.5 kHz,3 kHz,3.125 kHz,5 kHz,6.25 kHz,7.5 kHz,8.33 kHz,9 kHz,10 kHz,12.5 kHz,15 kHz,20 kHz,25 kHz,30 kHz,50 kHz,100 kHz,150 kHz,200 kHz,250 kHz,300 kHz,350 kHz,400 kHz,40 kHz,500 kHz,1 MHz" />"

For bandwidths of various transmissions, you can glean a lot of info between the FCC license emission type and the descriptions on this page:
Emission Designators

FCC Emission Designators, what do the codes mean?
Fcc Licensing: FCC Emission Designators, what do the codes mean?

Rich
 
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br0adband

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Yah, I'm aware of the stepping size configuration, I'm the person that asked Youssef to add it to SDR# and he did it less than 24 hours later and the reason was specifically because of NXDN reception (at least for me, that is). ;)
 

PACNWDude

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SDR# has been a great program. I have used it on Windows XP, Windows 7 as well as Mac OSX 10.7.5. Mostly VHF and UHF commercial bands. Thank you for the tuning and adjustments posts on here, very informative.
 
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