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.
Over on YouTube FairlawnARC.org have uploaded a talk about SDRs and ham radio by Ria Jairam (N2RJ0). The talk is a good overview of the current state of SDRs for ham radio use, and she discusses the various hardware and software options as well as giving many tips for improving your ham station. The blurb reads:
Our speaker was Ria Jairam (N2RJ), a world class contest operator and member of the Frankford Radio Club. Ria discussed the latest technology and offerings from Flex Radio, the HPSDR project (Ananradios), RTL SDR and others, as well as practical tips for contesting, DXing and rag chewing using your SDR. This presentation was held on Friday, October 20, 2017, 1900 hours at the Fair Lawn Senior Center, 11-05 Gardiner Road, Fair Lawn, NJ. The event was open to the public & refreshments were served.
Ria Jairam, N2RJ YLs, SDR & Setting Up A World Class Station
Part 2 - Ria Jairam, N2RJ YLs, SDR & Setting Up A World Class Station
FSQ (Fast Simple QSO) is a relatively new ham band mode for making text QSO’s (contact or exchange of information with another ham) over HF frequencies. It is a low data rate mode similar to PSK31 but with some interesting features like relaying which allows signals to be relayed further via other FSQ stations.
Over at in Melbourne, Australia a Cyberspectrum SDR meetup is held every few weeks. At this weeks meetup @faulteh discusses the FSQ mode and some of it’s interesting features. He also shows how he can transmit FSQ using a Si5351 clock generator and Arduino (with filtering). In the future he hopes to also create a fully automated receive station using a Raspberry Pi and RTL-SDR dongle.
Over the last two weeks the QB50 experiment was launched from the International Space Station (ISS). The experiment consists of 36 cubesats built by various universities around the world, with the main science goal being to make measurements of the thermosphere (an upper atmospheric layer that the ISS orbits in). All the cubesats broadcast their telemetry in the 70cm (420 – 450 MHz) amateur band and they are expected to stay in orbit for about 3 months before falling back to earth. In a previous post we made a point to mention Lilacsat-1, which is one of the most interesting QB50 satellites due to its implementation of a FM to digital voice repeater on board.