Friday, August 23, 2019

Airspy HF+ Discovery: Sensitivity Measurements

Time to find out how sensitive the HF+ Discovery is! Since it is basically the same receiver as the HF+, with preselectors, I expected sensitivity on MW to be roughly the same. Which turned out to be true.
On 500 kHz, I measured -110 dBm, on 1000 kHz -111, and on 1500 kHz -110 dBm. Using SDR#, v.1708, 6 kHz bandwidth with AM mode, and a 30 % modulated, 400 Hz signal from the signal generator.

The "Receiver Sensitivity Measurements" table has been updated accordingly. Excellent numbers.

Tuesday, August 20, 2019

Airspy HF+ Discovery Has Landed

Well admittedly, the Norway transport was on road, taking twice as long as from Shanghai to Oslo. But it arrived! Just fired it up at my home in Tana, no antennas available, so only to get a feel of it (feels warm to touch) and do the latest firmware update. Sensitivity measurements will be done on Friday.

My kitchen weight says 32 grams. By a good margin the lightest SDR I've had so far.

Sunday, July 28, 2019

Antenna Test: The NTi MegaDipol MD300DX

Not much is happening DX-wise during the light Arctic summer, but I had the opportunity to check out a dipole antenna sold by bonito.de, the NTi MegaDipol MD300DX.
For the time being, you can check it out yourself on my KiwiSDR, see link on the right hand side.

Beverage antennas are the norm at my KONG (Kongsfjord, Arctic Norway) location, because I and my co-users are exclusively MW DX-ers. For general listening, especially on SW, other antenna designs may be better, and for some time I have had a 70-metre longwire up as an all-purpose antenna for use with my KiwiSDR. Many years ago I tested a Mini-Whip antenna, and also the venerable Clifton Labs Z1501 active whip. Two years ago I bought a Wellbrook ALA1530LF for noise detection, and made a comparison with the longwire.
There is no doubt that a properly installed longwire antenna is very efficient on a broad frequency spectrum and may be the preferred alternative if space is not a limiting factor. But often space is restricted, necessitating more compact antenna designs.

Enter the NTi MegaDipol MD300DX. The MegaDipol, priced at EUR 400, comprises of an external antenna unit with two detachable 2.5-metre PVC-coated steel wire elements, and an internal power inserter which powers the external unit via the coaxial cable. The inserter can be powered from a 10-15 VDC supply, or from a 5 VDC supply such as a USB port with slightly less IP values. It is worth noting that the MegaDipol is an E-field antenna, so it should be placed in an electrically quiet environment. For omnidirectional reception, the elements should be placed vertically.


My first test of the MegaDipol was done well away from any potential noise sources, 170 meters away in fact. It was fed from a DX-Engineering coaxial cable. I later added a ground connection to the external unit. At my location, the added grounding did not change the noise floor or signal levels, but the general recommendation is to ground the antenna.
Later, I moved the antenna to a pole much closer to the house. The move from 170 meters away to 30 meters away did not change the noise floor or signal levels.


During the comparison, both antennas were connected to DX-Engineering 75-ohm coaxial cables. The longwire in addition had a matching transformer from DX-Engineering and was grounded on both ends. The MegaDipol was also grounded. The antennas were connected to two KiwiSDRs to facilitate accurate comparisons with identical hardware. Both feedlines had RF isolators inserted; The NTi GI 1000 galvanic isolator for the dipole, and the Wellbrook AFI-5030 for the longwire.
So, how does the MegaDipol compare to the longwire?

Longwave:

I was surprised to see the exceptional performance of the MegaDipol on Longwave. The lower down, the better. On my semi-local NRK 153 kHz, gain was typically 20 dB or more higher than the longwire, and the noise floor was a bit lower. So, all in all up to 25 dB better SNR. The difference decreased with higher frequency as my semi-local NDB “BV” on 399 kHz noted “only” a 10-12 dB difference in SNR.

Mediumwave:

While I had groundwave signals on LW for the comparison, summer daylight limited my comparisons to late evening skywave signals from the south – in the longwire’s lobe. Generally, the longwire does seem to have stronger signals, but the noise floor on the MegaDipol was lower. So, in effect, the difference was only slightly in favour of the longwire.

Shortwave, up to 7 MHz:

A bit like MW performance. The noise floor on the MegaDipol is lower, but so are signal levels. The net result isn’t very different, and one should note that the longwire’s length of 70 meters is very well matched with this part of the spectrum. A shorter longwire would likely not perform as well.

Shortwave, above 7 MHz:

The MegaDipol’s performance compared to the longwire increases with frequency. On a 31-metre band signal, the MegaDipol and the longwire were practically identical in SNR values. From there and up to 30 MHz, the MegaDipol performed increasingly better than the longwire. Skip on 27 MHz was mostly undetected on the longwire. A shorter longwire would probably fare a bit better than the long one, though.

VHF:

The MegaDipol claims to hear up to 300 MHz. I compared the MegaDipol with a 3-element FM antenna on the FM and DAB frequency ranges. On FM, I only had one rather weak Finnish station to compare. It was fair on the FM antenna, not heard on the MegaDipol. On a 225 MHz DAB channel, both antennas heard the signal, although the FM antenna had a 10-dB better signal level. Noise levels were identical.

Directionality:

By mounting the two elements horizontally instead of vertically, it is possible to add directionality to enhance or reduce signals from chosen directions. Late in the test, NTi supplied me of 5-metre elements, one of which was placed semi-horizontally (sloping from 2.5 to 1.6 meters) off the direction of a wind park a few km away. The signature RFI of the Siemens wind turbines, increased noise levels from around 750 to 500 kHz, was reduced into general noise level when I pointed the horizontal element in its direction. The signals from 153 kHz and 399 kHz were also reduced a few dB, although a deeper null might have been possible if I had placed the direction of the horizontal element more precisely.

Overall:

It’s a shame that I don’t have the Z1501 active whip anymore. It would have made a very interesting comparison. Since the Z1501 is out of the equation and considering previous comparisons I did with the ALA1530LF, the longwire and the Mini-Whip, I can safely say that the MegaDipol is an excellent overall performer, and the number one compact antenna I have tested so far.  The price tag may be discouraging for some. However, the Wellbrook loop checks in at GBP 225, and even the cheap longwire’s matching transformer is USD 60. So, small, active antennas usually come at a price. Longwires are cheap – if you have the property to fit one.

Tuesday, July 09, 2019

QSL: PJZ86 R. Curom, Willemstad, Curaçao, 860

"Z86" was heard with quite a good signal on my Perseus SDR at the Smøla island location in mid-February. My first-time logging of a station from Curaçao. I sent off a Facebook report at the time, and received a confirmation today.

Saturday, July 06, 2019

Rare Arctic E-skip on FM


A 30-minute, but strong Es opening yesterday brought 70 loggings from Denmark and Sweden. The opening was extremely narrow, comprising all heard stations within an 11 degrees bearing. Distances varied between 1065 and 1872 km.

I used a very modest 3-element FM antenna placed in the attic, connected to an SDRPlay RSP1A running at 8 MHz (6 MHz or so effective). I used SDR Console to decode and record IQ files to an external SSD for later playback.
Very narrow signal path. Log program: FMList.org.

If you want to look at the log, click this link.

Monday, June 24, 2019

Aerial View of my Radio Location

While enroute to Tromsø on a Wideroe DHC-8 200, we passed Kongsfjord at a perfect angle for taking a photo of my radio location. The arrowhead-like peninsula is named Veines, popular with birdwatchers and hikers. During WWII, the occupants set up a coast defence battery there as a part of Festung Norwegen.

My house is in the black circle. This summer I have an NTi MegaDipol set up in the red circle. The antenna is currently available on the ArcticSDR.


Friday, May 31, 2019

SDRs - Does the Enclosure Matter?

Traditional receivers, and most SDRs, have been encased in aluminium. Conventional wisdom says this is because they need to be protected from RFI. In later years though, some of the SDRPlay SDRs have had plastic enclosures, and the new Airspy HF+ Discovery is also said to be encased in plastic. It's been said that the RSP1A enclosure has an inner metal paint. That could be, but it looks like plastic, and it feels like plastic.

Anyway - aluminium enclosures are offered as a third-party solution to those who prefer metal, and I ordered one. When it arrived, I naturally had to remove the plastic enclosure, so I thought why not test the device with real signals, and without signals, in its original enclosure, the new metal enclosure, and bare? Just to find out how efficient they would be.

So I ran tests on FM and SW with 8 MHz bandwidths and compared spectra and waterfalls in SDR Console.

The results were...interesting. As a matter of fact, there was no difference whatsoever, even when the RSP1A board lay bare on the floor.

So, is conventional wisdom wrong? Not necessarily, my test is circumstantial evidence only. That said, my radio room has four PCs running, 5-6 SDRs and even a couple of rather dirty switching PSUs. So, lots of potential RFI. But the RSP1A was as immune bare as it was enclosed.

I'll keep the metal enclosure though, it's a bit smaller than the original plastic one, and looks much better. And there are other hazards to electrical equipment than RFI. Especially when they're on the floor!


Saturday, May 11, 2019

Some Candidates for the MW SDR DX-er


I’ve been a MW DX-er since my teens. Any other part of the radio spectrum is mostly tuned casually. Hence, I tend to evaluate my SDRs only by their MW performance.

A dedicated MW DX-er has some prerequisites for his or her receivers:
  • Sensitive enough to pull in signals in a low signal level environment.
  •  Robust enough to not overload easily when signal levels are high.
  • Access to software which can record and play back the entire MW band as efficiently as possible.


With the SDR being a “software defined radio”, it is true that software does define the radio experience. Software for the MW DX-er is worth a study of its own. However, at this stage, I thought it might be interesting to have a look at hardware that I have either tested myself, or that I think I know enough about to evaluate for MW DX-ing.


I even thought out a rather complex system for ranking the SDRs since they come in a large variety of price and performance levels. But the system relied on too many subjective factors, so for the time I settled for making an “Editor’s Choice” at the end of this article.

Software supplied with the hardware are listed in bold. Only Windows software versions are listed. Links to the SDR's home page and eHam.net review pages where available.

Name
Description
RFSpace CloudIQ

9 kHz-56 MHz. Ethernet. External 5V, 0.5A. Max sampling rate: 1807 kHz (1500 kHz tuning range), good for MW. Sensitivity -111 dBm. Good front end. Two antenna ports, software switchable. USD 630. Out of stock – discontinued? Available as used but scarce. Software: Spectravue, SDR Console. Receiver link. Eham review.
RFSpace NetSDR

0-32 MHz. Ethernet. External 5V, 1.3A. Max sampling rate: 2 MHz (1600 kHz tuning range), good for MW. Sensitivity -102 dBm. VHF/UHF add-on board optional. USD 1450 in 2011. Discontinued, available as used but scarce.  Quite large footprint. Software: Spectravue, SDR Console. Receiver link.
Expert Electronics ColibriNANO

0-55 MHz. USB. USB power (USB 2.0 is ok). Max sampling rate: 3 MHz, 1536 kHz (1230 kHz tuning range) is good for MW. Sensitivity -90 dBm, noise floor is on the high side. EUR 300. Available. Smallest SDR. Software: ExpertSDR2 (no IQ file playback!), HDSDR. Receiver link.
Microtelecom Perseus

0-40 MHz, USB. External 5V, 0.75A. Max sampling rate 2 MHz (1600 kHz tuning range) is good for MW. Sensitivity -103dBm. Good front end. EUR 800 in 2019, few available. Discontinued? Available as used but scarce. Software: Perseus, HDSDR, SDR Console, Jaguar Pro/Jaguar Lite. Receiver link. Eham review.
Elad FDM-S2

9 kHz-52 MHz + FM and 135-160 MHz. USB. External 5V, 750 mA. Max sampling rate 6144 kHz, 1536 kHz-option (1230 kHz tuning range) is good for MW. Sensitivity -106dBm. EUR 525, available. Software: FDM-SW2, SDR Console. HDSDR. Receiver link. Eham review.
Winradio G31DDC

9 kHz-50 MHz. USB. External 12V power. Max sampling rate 2000 kHz, 1600 kHz tuning range is good for MW. Sensitivity -106dBm. Robust front end. GBP 700, available. Software: Winradio (IQ recordings will not store/display date and time! No IQ recording scheduler!), HDSDR (current dll only supports bandwidth up to 1000 kHz, 800 kHz tuning range). Receiver link. Eham review.
Winradio G33DDC

9 kHz-50 MHz. USB. External 12V power. Max sampling rate 6000 kHz, 1666.7 kHz sample rate gives a 1250 kHz tuning range which is good for MW, but 32-bit sampling gives double-sized IQ files compared to other SDRs. Sensitivity -110dBm. Very robust front end. GBP 1600, available. Software: Winradio, more options than the G31DDC software, HDSDR (not tested, but known to be restricted to maximum 1000 kHz bandwidth). Receiver link.
SDRPlay RSP1A

1 kHz-2 GHz. USB. USB power, 180 mA. Max sampling rate 10 MHz, 1536 kHz option (1230 kHz tuning range) is good for MW. Sensitivity -101dBm but drops off on LW. 2 MHz lowpass filter gives reasonable front end. DAB notch filter. USD 109, available. Software: SDRUno, HDSDR, SDR Console. Receiver link. Eham review.
SDRPlay RSPDuo

1 kHz-2 GHz. USB. USB power, 180 mA (single tuner). Max sampling rate 10 MHz, 1536 kHz option (1230 kHz tuning range) is good for MW. Sensitivity not measured but likely similar to the RSP1A. Three antenna ports, Hi-Z port for SW/MW. 2 MHz lowpass filter gives reasonable front end. DAB notch filter. USD 280. Available. Software: SDRUno, HDSDR, SDR Console. Receiver link. Eham review.
Afedri SDR-Net

100 kHz-35 MHz. Ethernet (USB possible but too narrow IQ bandwidth). External 5V power, 370 mA. Max 2500 kHz sampling rate, 1333 kHz tuning range option is good for MW. Sensitivity -104dBm (overloads if gain is set too high), reasonable front end when gain is set low, otherwise poor. USD 260. Available. Software: HDSDR, SDR Console, various others. Receiver link.  Eham review.
SDRs not sampling the full MW band
Description
Airspy HF+
9 kHz-31 MHz + 60-260 MHz. USB. USB power, less than 0.5A (USB 2.0 port is ok). Max tuning range is 660 kHz. Sensitivity -112dBm. Very robust front end. USD 200, available. Software: SDR#, HDSDR, SDR Console. Receiver link. Eham review.
Seeed KiwiSDR

10 kHz-30 MHz. Ethernet. External 5V, 1.2A. No IQ sampling. Up to 8 simultaneous channels. Sensitivity -102dBm. Good front end. Can be set up as server. USD 300, less during Massdrop campaigns. Available. Software: None. Runs on any HTML-5 browser, like Chrome, Edge, Firefox, Safari. Receiver link.
SDRs not reviewed
Early Elad and RFSpace SDRs. SDRs with upconverters. SDRPlay SDRs lacking a 2 MHz low pass filter. Any SDR over USD/EUR/GBP 2000. SDRs typically unavailable. SDRs with no, or limited MW coverage.
In the pipeline
Not much, as per May 2019:
Elad FDM-S3 seems to be in its final stage before launch. EUR 950. Two software-selectable antenna ports?
Airspy HF+ Discovery is just around the corner. USD 100. One antenna port. Same sampling bandwidth as today’s HF+
RFSpace CloudSDR – ETA at Q4/18 has been changed to Q4/19. USD 900? Will we see it?

My Picks:

Low price range/entry level: The SDRPlay RSP1A. It is quite sensitive on MW, less so on LW, and may require some attenuation if the signal level is high. 2 MHz low pass filter helps. Several software options. Can double as a sensitive FM and DAB receiver with 6-8 MHz effective bandwidth, depending on PC. All for only USD 109. A steal.

Middle price range: Microtelecom Perseus. It is sensitive on MW and LW, good dynamic range and several third-party options including the bespoke Jaguar Pro/Jaguar Lite software which lifts the Perseus to the top of the sky. EUR 800 but limited stock, occasionally shows up on auction sites. A bit fiddly installation procedure. Others: Elad FDM-S2 (available, EUR 525), RFSpace CloudIQ (out of stock, maybe discontinued, USD 630). The Winradio G31DDC (available, GBP 700) will be a very good alternative if it gets full HDSDR support.

High price range: Winradio G33DDC. Very sensitive, and very good dynamic range. But a hefty price for the performance (GBP 1600), and proprietary software which some may like and some (like me) will not. Others: RFSpace NetSDR, only available on the used market (USD 1450 new). Good sensitivity and dynamic range, several software options.

If IQ recording of the entire MW band is not important, consider the ethernet based KiwiSDR. No IQ recordings, but up to 8 simultaneous channels (USD 300). Audio recordings are possible from all channels. Or the USB based Airspy HF+ with excellent sensitivity and dynamic range. Several software options, 660 kHz alias-free IQ recording (USD 200).

But you will likely discover that IQ recording of the entire MW band is important.


Friday, May 10, 2019

A Second Look at the ColibriNANO SDR

I tested this SDR briefly back in 2017. I never got round to measure its sensitivity back then, and I also hoped that the manufacturer had addressed the many software issues I had. So almost two years after, I did another test. The original write-up (see links to the right) has been updated.

Spoiler: No, it's not worth €300.

Friday, May 03, 2019

A New Look at the Winradio G31DDC

I bought the G31DDC when it was brand new, thinking that this would be an excellent competitor to the Perseus SDR. Actually, it was an excellent receiver, installation goes in a breeze and it uses 12VDC external power, which is a lot easier to find in no-noise versions than 5VDC PSUs. Sensitivity is around -105 dBm, a tad better than the Perseus. But there were "issues"...



First, the Winradio GUI. It is, at least in my opinion, by no means optimised for efficient MW DX. And at the time there were no software alternatives. Second, and by far more important, the IQ files it recorded were not date- and timestamped! Absolutely disastrous, if you record a lot. And to top it all, no scheduler was available. What on earth were they thinking? Later, the G33DDC came along, with the recording issues solved, but still the old inefficient interface. And with the price doubled.

So, after a short while, my Winradio adventure ended.

I did notice later on that dynamic link libraries (dlls) were developed for use with HDSDR, but at that time I had parted with my G31 and G33.

Recently, related to a project I'm working on, I decided to take a new look at the G31DDC. So, I borrowed a unit (thanks TJ!) downloaded the HDSDR dll and tested the unit. Lo and behold, it is a good receiver!  The only downside is that the current dll only supports 1000 kHz sampling (800 kHz alias-free). So, the requirements for a good MW performer are still not met. But I believe that the dll could be revised to allow 1600 kHz alias-free sampling.

Because, with HDSDR, time- and datestamped files and scheduling is no problem at all.