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There have been a lot of recent buzz in the DXing community about software-defined radios, otherwise known as SDRs. These radios, typically housed in a small USB thumbdrive-like units or small external hard drive-like enclosures without screens, can connect to your computer and can be used to DX multiple radio bands.
Recently Jim H., a DXer who lives in Stanardsville, VA, introduced me to the RTL-SDR USB dongle, which costs a whopping $9.95 on Amazon.com. I’ll admit, I was highly skeptical of this device’s capabilities due to its price and relatively unknown manufacturer. Coming from powerhouse DXing radios such as the Sony XDR-F1HD and Denon TU-1500RD, I was expected to be let down.
Unfortunately, I was kind of let down, although the novelty of having a computer-based tuner did amaze me.
SET UP
There was a slight learning curve with using the RTL-SDR dongle. The device came with no software or instructions. It also came with a remote, indoor antenna and a rubber band–the latter of which I am not sure of its purpose.
Jim H. recommended that I use the HDSDR program with the radio. After a bit of tinkering around (I’ll explain more below), I got the radio working.
A word of caution: The RTL-SDR comes with an MCX antenna connection. You will not be able to connect a regular roof antenna to this radio without an MCX to coax adapter. One end of the wire is spliced to the MCX wire supplied with the RTL-SDR’s indoor antenna. The other end, with a 1.18″ headphone plug, is connected to a female-to-female 1.18″ plug, which in turn is connected to a 1.18″ to coax adapter. This convoluted setup likely has severely impacted the performance of this unit, as noted below.
RADIO RECEPTION
This is the sore spot of my review. With my current radio setup that has brought in FM signals over 1500 miles away, all I can get on my SDR is local signals <50 miles away (stereo reception only with signals up to 30 miles away). Baltimore’s 92.3 WERQ, which comes in full stereo most of the day at 56 miles away, was undetectable on the RTL-SDR.
When the radio can actually pick up a signal, depending on which program is used, it’ll pick up RDS complete with PI code displayed. I really liked this feature.
I, unfortunately, receive heavy overload with the dongle, especially in the upper FM band. I do use an amplifier to help boost reception, however, I barely can get local signals without its assistance. None of my powerhouse DX radios can get stereo reception from signals even 20 miles away without an amplifier, so I’m not even going to attempt to use the dongle without the boosted signal.
VIDEO COMPARISON OF RECEPTION VS. REGULAR RADIOS
The above video shows the marked difference in selectivity and sensitivity in the lower FM band. The first portion of my video shows me tuning in all frequencies between 90.9 and 96.3 on the SDR dongle radio (using SDR Sharp), while the latter half of the video shows me tuning in the same with the Denon TU-1500RD radio. Note how many more signals (including some with legal IDs or liners!) were heard with the Denon tuner vs. the dongle.
SDR RADIO PROGRAMS (HDSDR) TO USE WITH THE RTL-SDR DONGLE
Assuming the SDR radio can tune in more than local frequencies, purchasing the dongle is only half of what’s needed to succeed. A SDR radio program is required to get the unit to function as desired. I’d recommend against using any software that possibly comes with an SDR radio, especially if purchased from Amazon.com or eBay. Two programs that seem to have a good following among SDR hobbyists is SDR# and HDSDR. I chose the latter upon recommendation from Jim H.
Installation of HDSDR program itself was easy.
One thing to note with the HDSDR is that you have to hit ‘START’ in the lower left-hand corner to listen to the radio (as noted in the picture to the left). This threw me for a loop for a while before I discovered the button. You also need to make sure ‘FM’ is selected within the program, above the tuned frequency. You also have to set the sampling rate to get the best quality sound. You can see an example of how my sampling rate is set. To get to the pictured menu, hit the F6 key or click ‘Bandwidth’ on the left menu.
You may also need to adjust the slider to the right side of the screen (under the “FM-BW:192000” text) as I’ve found the sampling rate may not automatically adjust as desired before sliding the bar.
The YouTube video above shows me tuning several frequencies via the HDSDR program. In the program you will see two frequencies, a ‘LO’ at the top (which is the radio’s oscillating frequency, apparently), and the true tuned frequency, below. You can ‘detune’ a radio station (for example, instead of 97.100.000 for 97.1 MHz, you could tune in 96.955.395). This comes in handy for bypassing the pesky IBOC sideband interference on frequencies adjacent to local FMs.
According to the program, the RTL-SDR tuner can apparently receive signals between 0 KHz and above 1.3 GHz (I gave up tuning upward in HDSDR). I haven’t picked up anything other than NOAA weather radio stations outside of FM, however, I’m sure my settings were off.
As with many SDR radio tuning programs, HDSDR includes a waterfall function that basically shows both a horizontal and vertical waveform of the station being heard. Below the waterfall portion of the program is what I’d describe as a live waveform.
The picture to the right shows local Washington-area FMs 103.5 WTOP (left) and 104.1 WPRS (right). Both stations run HD Radio/IBOC. To the left and right of each frequency you can easily see a ‘quieter’ signal popping up. This is the stations’ HD Radio sidebands, which for these stations, are broadcasted on 103.3/103.7 and 103.9/104.3, respectively. Quite interestingly, the HD sidebands appear as purple in the waterfall view–understandably given it is an analog representation of a digital signal. This is helpful especially during DX openings because you could easily determine which is an analog signal (as evidenced by the changing waveform) or an IBOC sideband.
Using the HDSDR program allows you to visually see if a station is coming in with IBOC or not. In the screenshot to the left, I have seven stations coming in between roughly 97.5 FM and 100.5 FM. Please refer to the letter at the top of the screenshot noting each station below:
A. 97.9 WIYY Baltimore, MD, 56 miles away.
B. 98.3 WSMD Mechanicsville, MD, 31 miles away.
C. 98.7 WMZQ Washington, DC, 25 miles away.
D. 99.1 WNEW Bowie, MD, 39 miles away.
E. 99.5 WIHT Washington, DC, 26 miles away.
F. 99.9 WFRE Frederick, MD, 59 miles away.
G. 100.3 WBIG Washington, DC, 24 miles away.
As seen with the more ‘intense’ waveforms in the waterfall portion of the screen, 98.7 WMZQ, 99.1 WNEW and 99.5 WIHT were coming in the strongest. The other stations had much weaker signals. You can also see from the size of the waveform that 98.7 WMZQ and 99.5 WIHT were playing loud music, while 99.1 WNEW was airing spoken news reports. The weaker signals, i.e. 98.3 WSMD and 99.9 WFRE, show up in the SDR but are inaudible upon tuning them in.
RECORDING
A huge benefit of these radios is the ability to record multiple FM frequencies at once. My USB dongle can record about 2.8 MHz of radio bandwidth, roughly 15 FM frequencies, all at once. But it doesn’t stop there–you could easily, while playing back the audio file, manually tune any frequency within that 2.8 MHz within the recording. This is a HUGE benefit to DXers because you could ‘park’ your radio on an empty frequency during a DX opening, and, at a later time, tune 15 frequencies around the ‘parked’ frequency in real time to DX. It is like setting 15 unattended radios to record. This all, of course, assumes the dongle can actually pick up signals that aren’t local.
The YouTube video above demonstrates the HDSDR and RTL-SDR radio’s recording capabilities. As noted in the video, the ‘waterfall’ function of the HDSDR program allows you to quickly see any incoming signals–something valuable for DXers especially during Es openings.
The only real downside of recording using the dongle is that it does seem to use roughly 6-10 MB of data a second. An hour of recorded RF would likely be close to 3 GB. So, to really get the best use out of this device, I recommend a large-capacity hard drive. For DXing purposes, I suggest deleting the original recorded files after pulling out positive radio IDs, rendering excessive storage spaces for the resultant large recorded files to be an unnecessary long-term need. You also cannot tune outside of the selected 2.4 MHz swath of RF while recording. To record another set of frequencies, you would need to stop the recording.
Since the HDSDR/RTL-SDR combo requires the use of your computer’s sound card, this may pose an issue for DXers who already record their traditional, non-software-based computers via computer. A workaround would be to use multiple sound cards on one computer or to use a separate computer for traditional radios and a second one for the USB dongle.
CONCLUSION
I’m sure most of my disappointment while using the RTL-SDR radio is due to living in an ‘RF hole’ and having to use amplifiers to boost signal levels to something acceptable for DXing. Even so, it surprises me that such an otherwise interesting radio dongle can’t get distant signals that always boom in on my regular DXing radios. The signals are there, but the SDR dongle isn’t getting them. I actually waited a little bit before writing this review because I wasn’t sure if I should write a bad review on a product that seemingly every other DXer has had good results with. But, as one DXer told me prior to publishing: The best journalism comes from honesty. Perhaps my exact SDR is a lower-quality model without the capabilities that other DXers have. Maybe one day I’ll be able to test it in an ideal RF environment.
With that said, I still recommend the RTL-SDR to others. For me, the radio is more of a novelty than an actual DXing radio. I predict in the future that SDRs that rival the performance of my Sony XDR-F1HD and Denon tuners (such as the much-revered Perseus radio) will be priced well within the reach of the average DXer and I’ll give SDRs another try. When that happens, I’d consider going all-SDR for DXing. But until then, I’m sticking to my traditional DXing radios.
Perhaps I’m doing something wrong and my computer settings are off — if so, please feel free to contact me with advice. I’ll update this review if there’s a mis-matched setting and reception improves.
FM Radio DX 