I’ve been licensed since 1999 and upgraded to General and Extra in 2008 but I hadn’t been on the amateur HF bands very much. When I graduated from Grad School, I bought myself and setup a new HF station.
This post is going to be about my experiences, things I’ve learned along the way, and maybe some things that may not be obvious to someone starting out. I will add to this post.
This is not meant to be “all-inclusive” by any means and not meant to be a substitute for elmering and experience. It’s meant to be for someone who has operated VHF/UHF for a long while but just venturing out into HF.
I’m bitter in alot of this post because many points draw on real interactions I’ve encountered. It’s not to discourage you to operate HF but to be better than the other guy acting like a jerk. Common sense helps tremendously. Folks out there who are all about the points, number of exchanges, getting that last contact, and awards common sense almost always goes out the window. Just remember you have a choice to not work those stations.
A quick note… ac6v.com has a TON of good information on everything from “antennas to zones.” I think it could be organized a little better and layout is a little 1996ish, regardless 700 amateur radio topics are covered. The Google search at the top really helps finding things.
I saw a news story on the ARRL website that talked about the Russian International Space Station cosmonauts plan to send Slow Scan TV images around the holidays. December 18 and December 20, 2014. Those are two of my interests, SSTV (or digital modes in general) and spaceflight. From the news story:
The Russian Amateur Radio on the International Space Station (ARISS) team members plan to activate slow-scan television (SSTV) from the ISS on December 18 and December 20. The expected SSTV mode will be PD180 on a frequency of 145.800 MHz with 3-minute off periods between transmissions.
I setup my station to monitor 145.800 MHz on both days to see if I could receive any images, I did!
Station setup: MP Antennas Classic Mobile NMO Antenna – This is a local company in Cleveland and were reviewed in QST. Been using their antennas for a long time with great success. Since the antenna is multi-polarized (the MP in the company name), it is supposed to be a good substitution for receiving satellite transmissions without a directional antenna and not worrying about Doppler Shift (which needs to be accounted for in some cases). The height is about 15 feet.
The antenna was connected to my ICOM IC-7000 with DSP settings turned off on 145.800 MHz FM. Used this radio only because my SignaLink USB is connected to it and the one I use for digital operation on all bands. MMSSTV is the Slow-Scan TV program I use.
Last time on Dongle Bits, I talked about the $20 European TV tuner dongle that was hacked allowing direct access to the signal data. The result is a cheap wideband receiver for your computer. We’re going to take a look at key settings you should know about when using these devices. Then look at some software and projects that transform these into systems that would have cost hundreds or thousands of dollars!
PPM and Settings
An important thing to know about these dongles: they are cheaply made and not tested for accuracy. They are designed to receive DVB-T signals at a bandwidth of 6 – 8 MHz where a few KHz error doesn’t matter. This is obviously not true when you’re dealing with FM signals that are 16 KHz wide or digital at 12.5 where a few KHz will put you on a completely different frequency or channel.
PPM stands for parts per million and is the difference in received frequency vs. frequency shown. To visualize this, use SDRSharp to receive a known FM signal. The center frequency shown will be different from the signal on the scope. Typical PPM offset is anywhere from 45 – 65 and will be in the programs settings. The dongle will drift another 2 – 5 PPM over the next 20 – 45 minutes as it warms up. Gain is obviously another setting that will help you receive signals. The RTL AGC setting works but will err on the side of too much gain. Manually, using more than 32.8 dB will overload and produce duplicate signal spikes. The Correct IQ setting will get rid of phantom spikes at lower gain settings.
The crystals on the RTL-SDR dongle can be replaced with higher accuracy temperature controlled crystals (TCXO) that have a variance of 1 ppm! These crystals are $10 but you have to wait for them to ship from China. Pre-modified dongles are available but you will pay three times the price for the dongle.
PCs aren’t the only place these SDRs can be used. They can be plugged into an Android device too. You will need a USB OTG cable (on-the-go) and Android 3.1 or later. Search Amazon or EBay for “USB OTG.” OTG is a standard for plugging in USB keyboards, mice, and thumb drives into mobile devices. Running external USB devices off the internal battery will drain it much faster. A powered USB hub would off-load the dongle power consumption. Apps include SDR Touch (wideband receiver program), ADSB Receiver, and SDRWeather for monitoring NOAA weather alerts on your device.
What can I do with this thing?
The definitive source on all things RTL-SDR is at the appropriately named www.rtl-sdr.com website. This site has it all. They regularly post software, updates, projects, and new developments. There is something new just about every week.
Some features of RTL-STR.com are The Big List Of RTL-SDR Supported Software. This is the list of software packages that support RTL-SDR on all platforms. Software ranges from wideband receivers to single purpose programs. This will give you some ideas of things to try with RTL-SDR. SDRSharp was written to have plugins extend the functionality of the program. These include plugins that make SDRSharp scan frequencies, add an audio FFT, scope, level meter, or CTCSS (PL) detector.
With the onset of many digital standards and narrowbanding, there are more digital signals out there you may not be able to identify by hearing them or seeing them on the waterfall. This Signal Identification Guide has known types, frequencies they may be heard on, mode, bandwidth, sample audio, and waterfall image. I find myself using the Radio Reference database search utilities to help identify signals and their owners (a premium account maybe needed for some features).
My first SDR project was to use the Raspberry Pi as a SDR remote network server. The Raspberry Pi could be placed in an attic or basement connected to an antenna and controlled by another computer.
Audio can be piped from one program into another using Virtual Audio Cable (VAC). Some time ago, during one of the digital nets on the .76 repeater in Cleveland, I used SDRSharp and VAC to receive the FLDIGI messages being passed on the net. The signal path looked like this: received RF signal (146.760) -> RTL-SDR (signal data) -> SDRSharp (audio out) -> Virtual Audio Cable -> FLDIGI (audio in) -> message decoded on screen. If I had a HackRF, I probably would have been able to transmit messages without using any “ham” gear.
The next and probably final article, I will demonstrate tracking airplanes equipped with ADS-B transmitters and listening to trunked P25 public service radio systems for under $100.