Over on YouTube user Adrian M has uploaded a video where he compares the HF amateur radio digital voice mode known as FreeDV against other common voice modes such as USB, AM, FM and QPSK. To perform the test he uses a PlutoSDR, a GNU Radio program and a GUI called qradiolink.
FreeDV is an open source amateur radio digital voice mode that uses Codec2 compression. It's designed to compress human voice and works with narrow bandwidths and with weak signal power.
In the demonstration Adrian reduces the TX power slowly for each mode, so you can see what the voice sounds like at high and low signal power. The FreeDV mode is not high fidelity in terms of audio quality, but the voice remains able to be copied at low power when the other modes could not.
Transmit and receive FreeDV 1600 and 700C with SDR hardware
Previously we've been posting about the NanoVNA which is an open source VNA project by @edy555 / ttrftech that has recently become extremely affordable at less than US$50 for a fully assembled unit thanks to Chinese manufacturing (or a little more if you order it via Amazon).
Over on the NanoVNA groups.io forums we've seen discussion about a NanoVNA hardware version 2.0 being in the works and it could be ready as soon as January 2020.
The nanoVNA [v2] will eventually reach 3GHz (and at a similar price to version 1).
It's going to be based on the adf4350 + si5351.
The 3 mixers are replaced with one higher spec mixer (ad8342) that is switched between the 3 channels.
A variable gain amplifier is added at baseband using one opamp and switched feedback resistors for improved dynamic range.
The Audio codec is removed and the stm32 built in ADC is used instead.
The performance should be comparable or better to V1.
Info about the baseband VGA design: A RFIC switch is used to switch the shunt resistor in the feedback path. The switch is basically "transparent" because the off state capacitance is in the femtofarad range (it is an RF switch) which is negligible at the IF frequency. The on state resistance is small compared to the resistors being switched in. Since the amplifier gain is mainly dictated by the feedback network, and the switch is "transparent", there is nothing other than the tempco of the physical resistors that can cause a temperature dependence. The RFIC used is the same as for the receiver RF switch, and it turns out all the maxscend switches do not have the shunt diode problem (most RF switch ICs have parasitic diodes from RF input to ground which will start to conduct at lower frequencies), so it has no theoretical lower frequency limit and can be applied at the IF frequency. This is a big improvement over using normal analog switch ICs which have capacitance in the pF range.
Info about linearity: The code will perform a calibration of each VGA step on boot up. Since there is no temperature dependence the calibration only needs to happen once.
The layout designer has also posted, noting that the price will remain the same (roughly $50), but there will be several improvements including a wider frequency range, better dynamic range, and an improved PC interface.
Hi, NanoVNA V2 layout designer here. Here is what I know:
V2 won't have a bigger display because it is too expensive
frequency range will go to at least 3.5GHz; PLL limit is 4.4GHz.
ADF4350 is used because of cost reasons; ADF4351 is more expensive by a factor of 5.
The layout is already fairly packed, so modular is not possible without a huge form factor.
Layout and shielding are much improved for higher dynamic range.
Price will be around the same as the existing NanoVNA. The design is already cost limited, so we can not do anything that will further add cost.
PC interface will be completely reworked. A binary protocol will be used similar to the xaVNA (we are going for full compatibility with the xaVNA PC software). If you are writing custom PC software for the Nano, please make sure the USB interfacing part is well abstracted away and easy to change.
The development timeline is going to be pretty long (by Chinese standards at least). We will iterate on PCB layout to get the best dynamic range. I think we might see initial (quantity limited) sales in ~3 months.
The NanoVNA Version 1.0
Just as a footnote, we received several emails from readers who wanted to make sure we note the credit edy555 should get. Originally edy555 had planned to produce his own units, but due to a Chinese ham enthusiast who had good intentions the design became popular and was soon cloned. We note that the NanoVNA v2.0 does not appear to be affiliated with edy555.
We are pleased to announce the release of SDR# r1717 with the Telerik User Interface.
This is quite a big jump from the old UI components that will allow us to add many fancy features in the upcoming revisions. For now, the functionality of the software was ported "one to one" with full support of the existing plugins. A new Plugin API for the tool bar was added which allows plugin developers to add/remove special buttons for quick access.
Despite a slightly longer loading time at the startup of the application, many performance improvements should be noticed in run time, especially the CPU usage. The package is now distributed with a set of skins/themes you can select in the control panel under "Display". Later on, we will add custom skins loading capability so you can customize the look and feel of the whole program.
Please note that some themes have slower rendering than others. You will have to experiment until you settle with something that is acceptable for the eye candy and the CPU usage / UI reactivity.
Some older plugins may not support the "Dark" themes and will have some rendering problems. The last unskinned version of SDR# will be still available for download in case you really need it. In any case, plugin developers are invited to support the new skins by either using Telerik UI components or at least setting the display properties of the old components so they render properly.
Last month we posted a collection of reviews about the MLA-30 which is a budget magnetic loop antenna designed for receiving HF signals. The overall consensus from the reviews was that it worked decently for the price, but of course could never live up to the high end loops that cost hundreds of dollars.
Recently Martin (G8JNJ) reverse engineered the active circuit used on the loop from photos taken by M0LMK and has made some observations on it's performance, noting that it's design isn't very good. First he notes that the amplifier chip is a Texas TL592B two stage video amplifier which isn't that great for this application. His measurements show an OIP3 of 20dBm, a P1 saturation of -3dBm and a noise figure of 12dB.
Of interest, he explains that the creator of this loop has designed it poorly as the impedance match of the loop to low pass filter is very wrong, resulting in a very poor amplitude/frequency response. He shows how the response can be improved with a few termination resistors, but is still not great.
MLA-30 Frequency Response. Ideally should be flat.
If you're interested in a cheap magnetic loop antenna, Martin suggests DIYing the M0AYF design which he says works a lot better.
We note that the "YouLoop" design is also in the works as a product that will apparently sell at close to manufacturing cost. The YouLoop is a passive loop idea by the creator of the Airspy that consists only of a simple 1:1 transformer and coax cable as the loop. It works best with high sensitivity radios like the HF+ Discovery.
Corrosive (KR0SIV) from the SignalsEverywhere YouTube channel has uploaded a new video that explains and shows HD radio being decoded with an RTL-SDR.
If you are in the USA, you might recognize HD (Hybrid Digital) Radio (aka NRSC-5) signals as the rectangular looking bars on the frequency spectrum that surround common broadcast FM radio signals. These signals only exist in the USA and they carry digital audio data which can be received by special HD Radio receivers. Back in June 2017 we posted about how [Theori] was able to piece together a full HD Radio software audio decoder that works in real time. Later developments saw additional data such as traffic data and weather info extracted from HD Radio too.
Corrosive's video also shows a comparison between analog and HD Radio audio. We note that the "HD" doesn't stand for high definition, so audio quality is not really better than the analog stream. He also notes that the HD Radio data stream can contain multiple audio channels, and often they are not the same as the analog station it surrounds. One example he shows is a Simulcast AM radio station being rebroadcast via HD Radio.
Leif (sm5bsz)'s series comparing the Airspy HF+ Discovery against various other SDRs such as the Perseus, SDRplay RSP1, Airpsy HF+ Dual, Airspy + SpyVerter and AFEDRI SDR-Net continues again, with parts 3, 4, and 5 now having been uploaded to YouTube. In previous posts we covered parts 1 and 2.
The comparisons are very technically inclined, so may be difficult to follow for those unfamiliar with radio theory. We have highlighted the time stamps where he discusses the results.
In conclusion, for all tests the Perseus always comes out on top, with the HF+ Discovery coming a close second. Generally third best is the HF+ Dual, then the AFEDRI, followed by the Airspy+SpyVerter and RSP1.
Part 3: Here performance with real antenna signals is compared. Attenuators are used to make the noise figure 26 dB of all radios at the output of the 7 port resistive splitter. This video is for dynamic range on 7.2 MHz.
Results @ 30:20
rx7compare-part3
Part 4: Here performance with real antenna signals is compared. Attenuators are used to make the noise figure 27 dB of all radios at the output of the 7 port resistive splitter. This video is for dynamic range on 14 MHz.
Results @ 16:04
rx7compare-part4
Part 5: Here here second order intermodulation is studied.
Over on YouTube user Tech Addict Attic has uploaded a video demonstrating what lightning strikes look like on the radio spectrum. To receive the pulses he uses an RTL-SDR and a simple wire antenna located on his roof. He notes that the pulses show up at HF frequencies, and continue all the way up to the broadcast FM band and above.
When lightning strikes it emits a wideband RF pulse that can be detected several miles away by radios. On a software defined radio spectrum display the pulse shows up as a quick horizontal blip. Detecting this blip is how lightning detection websites like blitzortung.org work, although they use their own radio hardware.
In the past we posted about another user who also demonstrated lightning pulses using his RTL-SDR V3.
It is well known that almost all electronic devices unintentionally emit unique spurious RF signals when in operation. By using an SDR like an RTL-SDR to record the spectra from electronic devices, it's possible to build up a database of known emissions. We can then detect when an electronic device is active by comparing the live spectrum to spectra stored in the database.
In a previous post we covered Disney's EM sense which is an experimental smart watch that automatically detects what electronic device the wearer is touching. With EM Sense they use an RTL-SDR and a database of raw pre-recorded spectrum data. To detect what the wearer is touching the live signal from the RTL-SDR is correlated against the database, and the closest match is returned.
José's script does something very similar, however instead of correlating with raw spectrum data he instead uses the waterfall image that is generated by rtl_power and heatmap.py. The rtl_power program allows an RTL-SDR to scan the frequency spectrum over a wider bandwidth by rapidly scanning ~2.4 MHz chunks of bandwidth at different frequencies. Heatmap.py is a program that turns the scanned data from rtl_power into a heatmap image of the spectrum.
To add an entry to the database, the electronic device is placed 7-8 centimeters away from the RTL-SDR, and a heatmap image recorded between 24 - 921 MHz is saved to disk. This can be repeated for multiple electronic devices. Each image will record the spurious signals from the electronic device, resulting in a unique heatmap image per electronic device.
Once the database has been created, you can then place any of the devices found in the database next to the RTL-SDR, and record a heatmap for 20-30s. That heatmap will then be compared against the images in the database using imagemagick which is an image analysis and manipulation library. The electronic device associated with the closest matching image in the database will be returned.
In his experiments he tested various electronic devices like an iPhone and was able to successfully determine when it was nearby.
Various electronic device spectra waterfall images recorded in the database
