Over on YouTube channel Rate My Radio has uploaded a set of three videos showing how to use an SDRplay RSP2 as a low cost spectrum analyzer to measure the inter modulation distortion (IMD) performance of lower end hardware TX capable radios. The test can only be performed on radios that have IMD performance less than that of the RSP2, so very high end amateur radios cannot be tested.
The process is to use audacity to play two audio tones into the transmitting radio under test, and then the SDRplay is used to receive the output. On the SDRuno software you're then able to see the third order and higher IMD products. Later he also performs white noise IMD tests as well. Below is the video description:
We cover 2 Tone Testing, White Noise Testing, and how the later can be particularly useful in terms of station monitoring. Naturally, we show the effects of 'all knobs to the right' :)
Jarrad also covers how with just an SDR Play and a 'rubber ducky' antenna, station performance can be monitored in real time.
Why would a Ham want to do this? The answer is simple: To defend their station performance against that on air Expert, who got their ticket when you needed to send CW at 50WPN, who served in the military radio unit for 20 years, has 3 engineering degrees and worked as a professor at both MIT and Havard, not to mention the times they lectured at Cambridge & Oxford.
With an SDR Play and a bit of simple math, any OM can put such experts in their place.
Below we only post the third video of the three part series. Links to Part 1 and Part 2 are available in those links, or on his channel.
Cubesats are small shoebox sized satellites that are usually designed by universities or amateur radio organizations for basic space experiments or amateur radio communications. Typically they have an orbit lifespan of only 3-6 months.
Cubesats typically transmit signals at around 435 MHz, and they are powerful enough to be received with a simple home made antenna and an RTL-SDR. To help with this Thomas N1SPY has created a YouTube video where he shows exactly how to construct a cheap eggbeater antenna made out of a few pieces of copper wire and an SO-239 UHF connector. Later in the video he demonstrates some Cubesats being received with his antenna, an RTL-SDR and the SDR-Console V3 software.
Earlier in the month the International Space Station (ISS) was transmitting SSTV images down to the earth for anyone to receive an decode. The ISS does this several times a year to commemorate special space related events, such as the day Yuri Gagarin (first man in space) was launched.
In the video Thomas explains why the ISS does this, how to track the ISS, and then he demonstrates actually receiving and decoding the signal. Thomas uses an Airspy HF+ to receive the signal on 145.8 MHz, however an RTL-SDR could do the same job. For decoding he uses the MMSSTV software.
A few weeks ago we posted about the MFJ1708SDR automatic relay switch and how it can be used to combine an RX only SDR with a transmit capable radio. An automatic antenna relay switch is used to automatically ground the SDR's antenna input whenever the TX capable radio transmits in order to protect the SDR's front end from blowing up due to high TX power.
In this YouTube video Pete Sobye shows us the MFJ1708SDR working together with an Icom IC7300 HF radio and an SDRplay which is being used as a panadapter. For software Pete uses HDSDR and Omnirig which allows the PC to control the IC7300.
Icom IC7300 panadapter MFJ-1708SDR, SDRPlay, HDSDR and OmniRig
A question that comes up often is how to combine an RTL-SDR, or any other RX only SDR with a transmit capable amateur radio. It's not possible to connect the RX only SDR together with the TX radio via a standard splitter because the TX radio's power will most likely blow up the SDR with it's powerful output. To solve this problem you need either a manual switch that will switch out the SDR when transmitting which requires absolute discipline to not accidentally transmit in the wrong switch position, or an automatic relay switch.
Over on YouTube channel HamRadioConcepts has given a good overview and demonstration of the MFJ-1708SDR Transmit/Receive automatic relay switch, which is a good product that solves this issue. It is also a fairly budget friendly option, coming in at only US$79.95 over on the MFJ website. HamRadioConcepts notes that the switch automatically grounds out the SDR whenever the PTT on the radio is pressed, and also has a fail safe that will automatically detect a transmission and ground the SDR if PTT is disconnected.
MFJ-1708SDR Transmit/Receive Switch For SDR Receivers
In early February we posted news about the release of a program called GridTracker. GridTracker is a live mapping program for WSJT-X which is a software decoder for low power weak signal ham communications modes such as FT8, JT4, JT9, JT65, QRA64, ISCAT, MSK144 and WSPR. Although these are low power modes, the protocols are designed such that even weak signals can potentially be received from across the world. Mapping the received signals can be interesting as it may give you an idea of current HF propagation conditions.
Thanks to RTL-SDR.com reader Henry for letting us know about the release of a new piece of Windows software by Tag Loomis (N0TTL) called GridTracker. GridTracker is a live mapping program for WSJT-X which is a software decoder for low power weak signal ham communications modes such as FT8, JT4, JT9, JT65, QRA64, ISCAT, MSK144 and WSPR. Although these are low power modes, the protocols are designed such that even weak signals can potentially be received from across the world. Mapping the received signals can be interesting as it may give you an idea of current HF propagation conditions.
GridTracker is a Windows (XP or above) companion program for WSJT-X. It listens to WSJT-X or JTDX decodes and displays them on a map.
A great way to visualize communicating amateurs around the world!
Display on a large second monitor in your amateur radio club, hamfest or as a demonstration in a classroom. Everyone gets excited when they can see what you’re doing!
You can also load your ADIF log files from WSJT-X, Qrz.com, LoTW, PSKReporter and others to get a visual view of ‘stations worked’, stations that can hear you and more!
It might be an interesting project to set up a permanent GridTracker display using an RTL-SDR V3 in direct sampling mode, or RTL-SDR with upconverter. Low cost x86 single board PCs that can run Windows 10 such as the LattePanda, UP board or Udoo might be possible candidates for host hardware.
Henry warns us that the software is still new, so it may be a little buggy.
Over on YouTube user radio innovation has uploaded a brief screen capture showing his Raspberry Pi 3 and RTL-SDR dongle being used as an always-on monitor for low transmit power based signals such as FT8, JT65 and JT9. These signals are transmitted by ham radio enthusiasts for the purpose of making contacts, and determining propagation conditions. This is a good application for an RTL-SDR and Raspberry Pi 3 as it enables cheap monitoring of these signals without the need to tie up a full sized ham radio.
To do this "radio innovation" runs Linrad on the Raspberry Pi, which is a program like GQRX that interfaces with the RTL-SDR dongle. Then the WSJTx software is used to decode the signals. He writes:
Remote Desktop screencapture of my Raspberry Pi3 monitor receiver on 40m amateurradio band with WSJTx and decoding FT8,JT65 and JT9. Receiver hardware is RTL-SDR(tcxo) + simple converter and homemade bandpass filter.