RTL-SDR great on civ air, not on mil air

[RichM]

Using blog V3 w/sdr# & fast scanner plug-in on an outdoor wide band antenna with an older windows laptop duo core. I‘m running a powered antenna splitter and the signals coming from it are identical when I use 2 hardware scanners. On civilIan air it works flawlessly, I can search the entire band in less than 2 seconds easily beating my Pro197. With detect set at 150 it catches everything every time. Detect at 120 it starts to miss some.

Completely different on mil air, it will skip right over strong active freqs. I can get a 5 bar signal on the Pro197 and the dongle will skip right over showing nothing. With detect set at 200 it will start to catch some of the stronger signals but still miss a lot that the scanner is picking up. Raising the detect level slows it down a lot and kind of defeats its purpose of lightning fast searching.

I can manually enter known active mil air freqs and hear and see them just fine, but when it searches 225-380 it’s seems to lose its sensitivity. Also I’m in a rural area with little interference and close to the action (30 miles from the bombing range, I routinely get 5 bars on my hardware scanners).

I‘m at a loss for a solution since it works perfectly on civ air. The only difference I notice is that the noise floor seems more “active“ in the mil air band. Would a better unit (considering an Airspy mini) possibly have better sensitivity in this band? Perhaps better filtering against the rather active noise floor? It’s definitely not the antenna as my hardware scanners have proven. Not sure what else to try. Ideas/suggestions welcome, thanks.

 

[TDR-94]

If you are interested in trying an Airspy, I have an Airspy R2 I could sell you. PM me for details.

 

[Ubbe]

What program are you using to do the search? It might be some setting to slow down the search rate just a tad.

/Ubbe

 

[RichM]

TDR - thanks for the offer but I think the specs for the R2 exceed my computers capability. In fact this might actually be my problem - not enough processing speed. But as I said it performs great on civ air which seems strange to me.

Ubbe - as stated in my original post I’m using sdr# with fast-scanner plug-in. And the detect rate does slow it down to catch more but at a detect rate of 200 it takes almost 20 seconds to search and is still missing some compared to my hardware scanner. Slowing it down defeats my goal of fast scanning the mil air band.

Incidentally, in the frugal scanner vids showing the super fast scan rate he doesn’t have an antenna hooked up! I can achieve those speeds too with no signals present. The problem is being able to hear and stop on freqs while searching at a fast rate.

 

[RichM]

Also wanted to add my cpu usage is below 50% during searching both civ and mil air bands which seems like acceptable performance. I’m stumped!

 

[Ubbe]

Ubbe - as stated in my original post I’m using sdr# with fast-scanner plug-in. And the detect rate does slow it down to catch more but at a detect rate of 200 it takes almost 20 seconds to search and is still missing some compared to my hardware scanner. Slowing it down defeats my goal of fast scanning the mil air band.

Have tried the updated version? SDR# - SDR# Plug-in: Frequency Scanner updated

/Ubbe

 

[RichM]

Yes I have, it doesn’t work well with my older computer. V1700 I use is very basic no frills version and is very stable and works well for me. Again everything works perfectly on civilian air band.

 

[kb5udf]

What does your spectrum display looks like? Any FM broadcast signals visible in the military aviation band (they are several times wider than an aircraft.)?

 

[RichM]

Spectrum is clean, no large signals, active freqs produce the highest spikes. Noise floor has a lot of small spikes, but they are well below the trigger point setting of about 10.

 

[thewraith2008]

There are a few people around successfully using the SDR# + Frequency Scanner plug-in in the MilAir bands.
While a few of them are using the Airspy R2 and get good results, the RTL-SDR com should work OK but with slower speeds (min Detect 70)

It might help to post:

• Additional PC specs for the Core Duo laptop (hardware and OS related)
• Version of the "Frequency Scanner plug-in" you are using with SDR# v1700
• How you have the plug-in configured.

 

[RichM]

Pentium dual core T4300 @ 2.10GHz, 3 GB ram, 64bit, running Windows 7
Frequency Scanner V-2.2.13.0
Config: dynamic noise floor, use audio mute, detect 120-200 (120 for civ air, 200 for mil air), wait 1, threshold around 13 hysteresis just above noise floor around 5

Thanks for your help, the scanner works awesome on civilian air band with this set up.

 

[thewraith2008]

How have you defined your MilAir scan ranges? (frequencies, detector, bandwidth and step size)

Your target frequencies (the ones with activity) must align to the start frequency and multiples of step size.
e.g. Start freq: 100 Mhz, step size: 25Khz.
100.0000
100.0125 - Will not see activity here
100.0250
100.0375 - Will not see activity here
100.0500
etc...

 

[RichM]

MilAir scan range settings:

Frequency search range: 225.000.000 through 380,000,000 AM
Detector: 200 (it misses more with lower settings and still misses some at this setting)
Bandwidth: 10,000
Step size:25,000
*misses about half of what the hardware scanner hears

CivAir scan range settings:

Frequency search range: 118,000,000 through 136,000,000 AM
Detector: 120-150 (150 is usually more reliable but all day today it has run perfectly at 120)
Bandwidth: 10,000
Step size: 25,000
*catches everything, out performs the hardware scanner like night and day

 

[thewraith2008]

Nothing really stands out from a settings stand point but you have not mentioned all the configuration states of the settings.

While your PC is at the slow end of the scale, if the CivAir is working, then one would expect the same from MilAir.

 

[RichM]

Dynamic noise floor and use audio mute are checked, everything in scanner configure else is not.

 

[RichM]

It seems as if it’s just not as sensitive in this frequency range. I’m aware that strong RF interference could cause deafness but I don’t have any of that at all. I suppose I will just turn up the detect even more until it reliably catches everything. Even In CivAir it will miss almost everything with detect at 100, sometimes it works at 120 but it’s always reliably perfect at 150. Incidentally, lately it seems to be running a bit better, do these things have a ”burn in” period?

My hardware scanner takes about 70 seconds to search the MilAir band so even if it takes 25-30 seconds it’s still a lot faster. And heck for $30 I now have the best Civilian Air scanner I’ve ever used. One thing about this hobby - everything is a compromise, there is no perfect solution for one reason or another.

My main goal with this is to just let it run during the day, searching the MilAir band while I’m at work. In the evening I’ll check the log against my known freqs list and add any new ones to the Pro197 which is what I use for actual scanning listening. Perhaps I’ll record the comms as well down the road. Using ithe SDR# side by side with the hardware scanner was just to get it up and running and evaluate its performance.

Thanks again everyone for your suggestions and interest.

 

[thewraith2008]

I can't really say about how the RTL-SDR com dongle works at 225-380MHz since I don't look at that range.

You mentioned that you did observed transmissions manually in that range that seemed OK so the scanner should be able to trigger on signals in that range.

Sorry I can't offer any other helpful information on this.

 

[Ubbe]

I use RTL-SDR and civ air's 20MHz range are scanned in under 1 sec and mil air's 150MHz range in 5 sec. My computer are 10 years old but a i7-2600 3.2GHz with 8 cores. I have a lot going on in Win7 with 12 surveillance cameras and some other stuff loading the processor between 12-20%. When starting up SDR# and do the search it goes up perhaps 3%-5% so not much added load. It seems just one core of eight are running the program. I have the detector time set to 80mS and the sample rate in SDR# to 2.4MHz and doesn't see anything being missed while I get hits on several scanners. I do see that I can use 50mS detector time in civ air, so there is a difference there.

A 50% cpu load could possible be too much, and the detector time might also indicate that. If you can use the highest sample rate of 2.4MHz it might speed up the detection process and make it more reliable.

/Ubbe

 

[RichM]

Thanks for the detailed reply. I do use 2.4. Not sure why my cpu load is so high as I don’t run anything else while scanning. Something to look into, thanks again.

 

[Ubbe]

I forgot to mention that I use an old version of SDR# 1642 as I haven't seen any improvement for my applications using later versions.

/Ubbe