Two Net-based SDRs Playing Together

If you have a router or a switch, you can connect several net-based SDRs to one PC. And if you use SDR-Radio, which allows multiple instances of the program to run, you can operate them simultaneously. Since I have one RF Space NetSDR and one Afedri SDR-net I decided to test this. What is needed are different IP addresses for both (or all) SDRs, and different ports. I am no network geek so I had my portion of trial and error, but with the help of SdrNetSetup and disconnecting and reconnecting the Afedri I got both SDRs to play along. On the jpg below the Afedri identifies as "SDR-IP".

Both SDRs are displaying a 1250 kHz span, with little CPU load. Another interesting observation is that when the SDRs are tuned to the same frequency, their audio appear to be perfectly synchronized. There is not the slightest trace of echo or other audio artifacts. Diversity reception, anyone?

The Afedri SDR-net - Second Looks

I had some time this weekend to check into the Afedri SDR-net further. My beverages and the QDFA are all down, so I used one of the QDFA loops (7 m high and 20 m wide) as a temporary ALA-100 loop. It has quite a bit of gain especially on the SW bands.

The Afedri SDR-net sports a 12-bit, 80 MHz ADC, in contrast to the Perseus and SDR-IQ which use 14-bit ADCs, and the QS1R, NetSDR and Excalibur series which use 16-bit ADCs. Apart from a 30 MHz low pass filter, there is no band pass filtering. All the SDRs above except the Excalibur G31DDC have band pass filtering. If you buy an Afedri SDR-net you will accept some compromises, and you will need to do some mitigation measures. The question is of course: Is it worth it.

The Afedri SDR-net is only the second amateur-grade SDR I know which can be connected to the PC via Ethernet, the other being the RF Space NetSDR which sells for USD 1400 (I consider the SDR-IP a commercial-grade SDR). Unlike the NetSDR though, the Afedri SDR-net can also use the more common USB connection. However, the USB connection limits the spectrum to 230 kHz (250 ksamples/s) while the Ethernet connection gives access to 1225 kHz (1333.33 ksamples/s). If you opt for the Ethernet connection (highly recommended), be sure to use a crossover Ethernet cable when you connect the SDR to the PC. A standard Ethernet cable should be used if you go via a router or a switch.

There are two ways to power the SDR. There is a 12.6 VDC input in front (and a DC jack is included), however the DC voltage can be anywhere from 7.5 to 15 V. The problem with the DC input is that another compromise – a switching DC/DC converter working on 930 kHz – will reduce MW performance. My recommendation is to use the micro-USB input for DC power. If so, you can choose to use one of the PC’s USB ports, or you can modify the USB cable to power the SDR from an external, linear 5VDC supply. The USB connection draws 470 mA. This is close to the 500 mA limit of a USB port, so you may want to keep the cable as short as possible. Some laptops are reported to deliver less than 500 mA.

As mentioned by Alex in a comment to this post, a root hub connector will deliver 500 mA, while other hub connectors may be limited in current. Hence, if you're unable to power up the Afedri SDR-net from one USB connector, it may help to try another.

Sensitivity is an important issue for MW DX-ers in quiet areas. I measured around -91 dBm on AM, 6 kHz bandwidth with a 400 Hz tone modulated by 30 %. Internal gain from its Variable Gain Amplifier was set at 14 dB (see below). This is around 10 dB lower sensitivity than the NetSDR. Although sufficient for many purposes, the Afedri SDR-net will not resolve the weakest signals. A Norton push-pull preamplifier, from Kiwa or other manufacturers, will be helpful in many instances if signal levels are low.

Another vital question related to sensitivity is: When does the ADC go into clipping? You can adjust the VGA gain of the Afedri from -10 dB to 35 dB. It is possible to tailor-suit the gain with the use of a small app inside the HDSDR program (which comes with the Afedri). Pushing it all the way up to 35 dB may not be a good idea unless you are certain that there are no strong signals around. In this setting, I got ADC overload by feeding one signal generator signal at -28 dBm signal outside of the received spectrum. Reducing the gain to 26 dB raised the overload threshold to -23 dBm, while at 14 dB the threshold came within a more acceptable -12 dBm. The G31DDC, also without bandpass filters, did not overload within the -8 dBm limit of my signal generator. Of course, one signal does not reflect "real life".

The -91 dBm sensitivity was measured at 14 dB VGA gain. In theory, sensitivity could be higher, but rarely in practical terms (at 35 dB VGA, sensitivity was measured to -106 dBm, at 26 dB it was -104 dBm).

Hence, external filtering will be necessary in most instances. A SW listener near strong MW stations will want a high pass filter to eliminate overload from MW. As for me, in many instances I can probably live with a 26 dB VGA setting, but I will invest in a low pass filter to eliminate the strongest SW station around here, Murmansk-5930. It is sometimes heard with signals above -10 dBm.

It’s a bit too early to make conclusions about the Afedri SDR-net. The Arctic nights are light, and signal levels low, making it difficult to judge how it will perform in real DX situations. My impression however, is that for the price it’s a very capable SDR, able to run with a variety of software. You should however buy or make high pass and/or low pass filters to avoid overloading the ADC. And you may need to use an external preamplifier if sensitivity becomes an issue. So, if you are willing to compromise: Yes, it's worth it.

The Afedri SDR - First Looks

I thought the RF Space SDR-IQ was small, but that was until I saw the Afedri. The latter's footprint is actually smaller than the SDR-IQ's. For comparison, in the picture below it is sitting on top of the Perseus, itself not a mammoth radio.

I haven't had time to much more than getting it up and going, so details will have to wait. It was very much plug and play, actually. I opted for powering it through its 5V USB connection, thus minimizing RFI. And I chose the ethernet connection rather than the bandwidth-restricted USB interface.

Not only is it smaller than the SDR-IQ, it sells for half the price but still offers a 1250 kHz bandwidth compared to the SDR-IQ's 192 kHz. However, the USD 249 price tag suggests that the creator, Alex Trushkin, has had to make some compromises. Like a 12-bit ADC while other SDR makers use 14-bit or 16-bit, no bandpass filters, and somewhat restricted sensitivity.

Still, my first impression is that it's a very cabable SDR, and basically unbeatable at this price level. You can buy a Norton push-pull preamplifier and lowpass and/or highpass filters and still have cash left compared to an SDR-IQ. And the SDR-IQ will not record 1250 kHz, and will not connect to the ethernet.

The Afedri will run with many SDR programs, such as Winrad, Linrad and SDR-Radio.

More as it happens.

Another SDR To Meet The Arctic Challenge

Many hobbyists design SDRs these days. The most promising I've seen so far is the AFEDRI SDR-Net, designed by 4Z5LV Alexander Trushkin. The latest version is not only able to cover the MW spectrum (1250 kHz bandwidth), but even has an ethernet connection! In other words, you can connect it to your router/switch, and access it with whatever PC is connected to your LAN. Just like the RF Space NetSDR.

Photo: 4Z5LV Alex

The specs aren't out of this world, but neither is the price tag. It will be interesting to see how well it fares compared to my other SDRs, Perseus, NetSDR, Excalibur and Excalibur Pro.

I've just ordered one, and I hope to do some preliminary tests by the end of May. Thanks Tracey Gardner for alerting me.

G39DDC Software For G31/G33 Files Playback

A good thing about Winradio's software is that you don't need the actual receiver. They load into a "Demo mode" if no receiver is connected. It is fully functional, and allows you to play back files without the receiver connected if you wish.

I never seriously considered purchasing the G39DDC Excelsior, but I was keen to check out the software, since it would likely have some improvements over the G31 and G33 software packages. It was a mixed bag.

G39 in Waterfall mode playing back a G33 LF recording

The G39 software has many functions not found on the G31 and G33 software, mainly because it's supposed to support a scanner going up to 3.5 GHz. I had hoped to see a better designed playback function than those found on the G31 (mediocre) and G33 (improved). Indeed I did! The playback bar works very much like those found on the Perseus, Spectravue and SDR-Radio; you can click anywhere inside the bar and the recording will move to that spot instantly. Playing back a recording appears to be easier if you use the G39 software than if you use the G33 (and particularly the G31) software. However, there is still no way to make a small selection of the recording, and loop it. Both Perseus and SDR-Radio feature this very useful tool.

G33 recording/playback controls

G39 recording/playback controls

The last four lines on the G39 control box expands/subtracts by use of the tool box to the right of the file path.

Winradio G3x software has never been the easiest to use for those who want to check offsets from the nominal frequency. The G33 Demod window can be zoomed in to a width of 240 Hz. Maximizing the window enables the user to move in 1 Hz steps. However, the resolution is rather low so doing exact offset measurements isn't very easy. The G39 DDC2 window can only be zoomed to 500 Hz, but the resolution is better, so it is still possible to move in 1 Hz steps. Vertical lines on the display help a lot.

G39 DDC2 window

It would be nice though if there was a way to change the MHz labeling to kHz...

Kongsfjord Mid-Winter Report

Today was my first visit to Kongsfjord in 2012! Checking antennas and replacing the QDFA battery was long overdue, with weather being the limiting factor. Last weekend saw temperatures down to -25 Celsius and winds up to 25 meters per second. The result is razor-sharp ice particles blowing around.  You don't want to work outside in conditions like that. The picture below from Kongsfjord International Scuba School (copyright) should illustrate my point. My house is just outside the left frame.

Today though was mild and relatively calm, allowing me to replace the last beverage lamp cord feedline with a Belden Twinax. Works fine.

The QDFA inspection was rather disappointing. One of the clamps securing the secondary fiber glass rods had snapped, probably as a result of the temperature and wind. Also, two of the loop wires had snapped, probably of the same reason. Lesson learned is that we need more durable wires for our QDFA. And another example of the mechanical challenges loop arrays are in areas with extreme weather conditions and without being able to look after the array on a daily basis. But we live and learn! Maybe next season the QDFA will be operational all winter!

Polar Night

Days are dark at almost 71 North. This picture from my mobile phone was taken last Sunday close to local noon. Usually, December days are a bit lighter because of the snow reflecting the modest light from the sky, but  this autumn and winter has been 3-4 degrees Celsius warmer than normal, so there is very little snow at the coastal areas. It was -1C that day.

The picture faces south-southeast and is taken from the QDFA phaser/power box after I had installed a full-charged 18 Ah battery to the QDFA phaser. It will last for another 3 weeks before needing replacement. The mast to the right is the center of southernmost of the four QDFA deltas (or rather "houses" as they have been redesigned to).

Winradio G39DDC Excelsior

If you want to tune from zero (almost) to eternity, this is it. With a 9 kHz to 3500 MHz tuning range, two independent 4 MHz channels (also available for recording and later playback), excellent specifications and a multitude of tools for signal analysis, this appears to be the heftiest SDR available today. Alas, the price tag will require dedication or easy cash flow, and I am rather sure that I don't want to spend USD 4000 for a receiver today. So don't expect to see a G39 review on this blog.

Image from Winradio.com

But Nils Schiffhauer got his priorities right, and submitted this video to the Winradio G3 reflector. Readers who know the G31 and G33 interface will note that the playback bar is different, resembling that of SpectraVue.

For the average MW DX-er though, such as I, the G39 doesn't do much that the G31 and G33 don't, so it's probably overkill. Would be übercool to have one though.

G33DDC Version 1.68 - An Important Software Update

The first official software update since the introduction of the G33DDC has just been made available, with numerous small and a few very important changes.

In version 1.61, if one tuned around inside the DDC spectrum while recording (and who wants to be stuck on one frequency while recording), the spectrum itself would actually move, making it impossible to play back the recording properly. The demodulated frequency would change with the changing DDC spectrum. I first thought this was a bug but in fact it isn't; it's a feature but with an unwanted side effect. The feature is that one can move the DDC spectrum at will within the 0-30 (or 50) MHz range while recording.

The update makes it impossible to move the DDC spectrum while recording with the .ddc extension. So you are free to tune around inside the spectrum. For recordings with the .rxw extension, moving the DDC spectrum during recording requires the "Insert FDT" function to be disabled. So, if you record a DDC file, or an RXW file with FDT enabled, the spectrum will not move.

Another important change is how the playback bar works. Previously, it was cumbersome to move within playback of a DDC spectrum recording. The playback bar has been redesigned so that the handle or thumb is easier to "grab" with the mouse pointer, and the left and right arrows have been assigned to five-second steps. In addition, if you click on the bar, the recording will move back or forth with what I believe is 1/30 of the length of the file (or files, if they are linked into one larger recording). Of course if you move the handle you can maneuver at will within the recording.

Another thing that has been up lately (though unrelated to the software update) is that DDC files recorded in the .ddc format in one time zone (or during daylight savings time) will not show the correct time when played back in a different time zone (or during "normal" time). This is because the date and time information is not embedded in the file, but merely part of the file name.

This not a problem if recordings are made in the .rxw format, which is Winradio's proprietary format. However, .ddc is the default file extension, so you have to actively select rxw when you start a recording. Press "Browse" and select "RXW" from the file types dropdown. Or simply replace ".ddc" in the file path with ".rxw". The software will remember the file format for subsequent recordings, even if you shut down the program. For scheduled recordings it's a bit more cumbersome as you need to define the file format for each task you add.

The RF Space NetSDR

After having played around with the RF Space NetSDR a few weeks, I thought it was time to share my impressions. A PDF-file is available in the Links section to the right, or you can view it as an html-page here.