Calculate proper length of antenna for better signal

To increase signal quality, make sure the antenna length matches the frequency you are receiving at. I've had a 20-40 db increase in signal just by extending or retracting my antenna a couple of inches. A simple process is this:

1. Have on hand a ruler with centimeter markings (I use a retractable tailor tape measure)
2. Open your calculator and do 300 / your_frequency (in mhz) = wavelength
3. wavelength / 2 = how many meters long a half wave dipole would be. If this is too long, divide by 2 again to get the length of a quaterwave dipole in meters.
4. Extend the length of your antenna (I use ANT500s from my SDRs) to one of those lengths using your ruler. You should prefer half wave, but quarter wave is fine too.

For example, I'm listening on the national calling frequency for APRS (144.390) i'd do the following:

1. 300 / 144 = 2.08
2. 2.08 / 2 = 1.04 (half wave dipole length, way too long for my ANT500)
3. 1.04 / 2 = 0.52 (quarter wave dipole, 52 centimeters can be done easily)
4. Measure out 52 centimeters on the tape measure, use it as a guide to extend the antenna to the proper height.

How to loopback audio from one app to another for SDR

Piping the decoded audio from one application to another can be super annoying in linux. Fortunately there is a utility in apt that makes it dead easy (at least on Ubuntu). Simple steps:

• apt install pavucontrol
• start your applications (gqrx/fldigi/direwolf/whatever)
• execute pavucontrol
• In the "Playback" tab, make sure your "output" app is showing up and bouncing the sound meter
• In the "Recording" tab, make sure your "receiving" app is showing up. Click the sound card button and select the "monitor" entry
• Should start working immediately.

For FLDIGI to show up it needs to start recording from the sound card, I had to go to Configure > Sound Card > Audio > Devices > select "PortAudio" > leave capture and playback at "default"

Decoding APRS via SDR

APRS uses packet radio and FLDIGI doesnt support it for some ungodly reason. You can chain a few tools together to get the decoded output.

1. Plug in and attach your RTLSDR, or whatever, to your VM
2. start up GQRX, start receiving
3. Tune to 144.390 to get an APRS signal (North American calling freq for APRS)
4. Set the following: 
• Filter Width: Wide
• Filter Shape: Sharp
• Mode: Narrow FM
• AGC: Fast
• set the squelch to silence the noise
5. In the audio section, hit the "UDP" button which should start streaming the audio over UDP port 7355.
6. In another tab: apt install direwolf
7. direwolf -r 48000 udp:7355

You should get output like below:

A Review of Outernet's Satellite Reciever

I recently came across mention of the Outernet project. They market themselves as a simple, low cost, receive only packet radio receiver. It seemed like an interesting enough project and at $99 for a preprogrammed board/all the hardware I'd need I figured why not.

Setup

Setting it up was relatively simple, just hook up the CHIP, battery, LNA, and panel antenna as we were good to go. After about a couple minutes of the board starting up you'll see an open Wifi network called "Outernet". Connect in, visit "10.0.0.1" and enter "outernet:outernet" for the login (case matters on the username).

The Interface

You'll then be presented with the main interface. Click the circle in the upper left corner to get a listing of the "apps" installed. It's pretty spartan, but then again that's what the project is. Click on the "Tuner" app, it should look like this:

In the drop down box on the Satellite tab, make sure the proper satellite/location is chosen, otherwise you simply won't ever get a lock. Once you chose the proper satellite, and double checked to make sure everything is hooked up properly, you can start pointing the panel at the satellite. I used the n2yo.com satellite tracking site to help me roughly aim the panel. It doesn't have to be exact. I used the "SNR" value on the Status tab to help me aim. Once I got a consistent reading above 3.0dB I knew it would be sufficient. Cloudy days give me about 5-7 and clear ones give me 7-10dB. If you are around 1-2dB or less, something is wrong.
I ended up mounting my panel to an old tripod so I wouldn't have to hold it. Not pretty or rugged, but works for the time being:

I also configured the board settings to connect to my home network as a client versus setting up its own hotspot. You can do this using the "Network" app from the interface.

So everything is set up, now I have data downloading. That was fun. Probably not $99 fun, but I got some new hardware out of it and I got to say I did something with satellites. Personally, it was just barely worth the $99.

While the kit is received only, Outernet does allow people to submit files to be included (up to 10KB, and moderated) in the transmission.

Accurate Expectations:

If you are interested in getting an Outernet setup, please make sure you have the proper expectations. Here is what you get practically from buying and setting one up yourself:

• Text only daily news from several sources
• 2-day old fancy weather data that looks really pretty
• APRS messages (mostly useless)
• Offline text-only Wikipedia

This is not a replacement for the Internet, no matter what ignorant media people tell you, this is really not a replacement for anything at all. The only possible use case I can really think of is for someone in the middle of nowhere wanting some news/Wikipedia articles to read. The Outernet project is definitely not solving any average person's problems.

It DOES however provide the following:

• CHIP board, Low Noise Amplifier, Panel Antenna, Battery pack, and aluminum cased RTLSDR
• Decent first introduction to microwave satellites
• A distraction
• A cute idea

Would I buy this again? Not likely

Would I recommend this? Meh

"Hacking" Wireless Mics

This isn't really a hack. Wireless Mics are glorified walkie-talkies with a little extra speech smoothing fanciness.

I was playing around with some Sony wireless mics and i noticed a label on the back stating the frequency they operate in. The label said "638.125-661.875". I grabbed my hackrf one and plugged it in. It should be noted that in that frequency range, an RTL-SDR dongle would work as well.

Once I plugged in my HackRF One, I ran hackrf_info to make sure it was recognized and then started gqrx.

I tuned gqrx to the start of the range, 638.125. I was pleased to find that this was the frequency used by "Channel 1" setting on the wireless mic. I flipped the switch on the mic, and bam. A very strong signal appeared on my screen. I centered the cursor over that, adjusted the squelch to tune out the background noise and turned up the volume so i could hear. Lo, and behold thats all that was needed.

Turns out that the wireless mics simply are FM transmitters broadcasting the audio so the receiver unit can pick it up. Well, in this set up my hackrf is the receiver. 

Now, once i learned this i kind of facepalmed a little. 

Someone asked me what the big deal is with this. I told them that lots of times the communications being held over these wireless mics can be confidential. Broadcasting confidential info usually is what people try to avoid.

A great real word example of utilizing this info would be if a reporter is doing an interview with a high profile individual and wants everything to be kept secret until the airing. Well, if someone knew the building the recording was happening, they could record the audio of the wireless mic and break the story first.

Or worse, use the story info to determine if they should carry out hits to keep people quiet.

Physical Pentest App - Scanner Radio

Police scanners can get expensive. Especially since today most police stations are moving over to digital (trunked) communications. I had bought a Yaesu VX8DR so i wouldnt have to worry about missing a frequency. Well it turns out it doesnt do trunking comms so i was fucked... Well, not so much.

A free alternative, although time delayed is using an android app called "Scanner Radio". Most locations in America have a entry for their county or city or whatever for dispatch.

I love having it in my ear while a case a place or do car recon. It's pretty simple, if you hear about a report for a suspicious vehicle in your area, move to another location.

I use the app whenever there is trunked comms for the area my target is in. There is however a delay, and that delay is dependent on what location you are in. I know in Chicago its about a 60 second delay between what happens on the radio and what comes through the app. You have to remember that the audio has to be received by the equipment, transmitted to the servers, relay over the cell network to your phone. That can take a bit.

The best solution is a realtime radio. The second best is the app. It's better than nothing.

VX8DR RX/TX Freqs

Stole this from some forum. just google it and you can find the source.

RX
Frequency Note
0.5 - 1.8 MHz BC Band. AM Radio
1.8 - 30 MHz Shortwave Band.
30 - 78 MHz 6 Meter Ham
76 - 108 MHz FM Radio
108 - 137 MHz Air Band
137 - 174 MHz 144 MHz Ham. 2 Meter
174 - 222 MHz VHF-TV
222 - 225 MHz 222 MHz Ham
225 - 420 MHz General Band 1
420 - 470 MHz 440 MHz Ham. 70 cm.
470 - 800 MHz UHF-TV
800 - 999 MHz General Band 2 Cellular Blocked

TX
50 - 54 MHz
144 - 148 MHz
222 - 225 MHz USA version only
430 - 440 MHz

TX w/ mod
50 - 54 MHz
144 - 148 MHz
148 - 174 MHz MARS/CAP Mod only
222 - 225 MHz USA version only
430 - 440 MHz
440 - 470 MHz MARS/CAP Mod only. FRS/GMRS freq range