While there are different ways to distribute high-quality reference-clocks to multiple receivers and transmitters, or to general lab equipment, perhaps the best and easiest is with a Clock Distribution Buffer. The TIS-126 has been designed for this job:
This unit can send a square-wave clock to six output ports. Input and output are 50 Ohm impedance, and the frequency range is from 100 KHz to 100 MHz (and down to under 1 Hz in many cases). The input level can range from -20 dBm to +20 dBm.
This has been in use for a while, combining the multiple outputs of the Beacon Blaster and WSPRSONDE onto one SMA jack, allowing the use of a single antenna. The results have been excellent, so this box is now on the Turn Island Systems website, available for purchase:
Applications for the Filter-Combiner are not limited to the WSPRSONDE. Some have used this to combine the outputs of other QRP (1W or less) transmitters. One person is using the Filter-Combiner in reverse as a general preselector, sending the output of a single multiband antenna to several narrow-band SDR receivers (reducing overload from out-of-band signals).
What about eight bands? I glad you asked that question! Fitting additional bands into the combiner has proven to be a major challenge. A 160 meter port can’t be implemented using available (inexpensive) components — too much inductor loss. Squeezing the 17 and 12 meter bands into the gaps between 20, 15, and 10 meters also requires inductor tolerance and loss well beyond that of readily-available parts. However, if there is demand for it a future combiner could include a 6-meter port.
But single-channel filters can be provided for those “oddball” frequencies.
As you may know, the powerful RX888 SDR receiver is truly a game-changer — especially when used in conjunction with ka9q-radio and wsprdaemonsoftware. This combination provides full HF-band coverage and analysis — much more than I can go into here.
But to obtain the desired frequency accuracy and stability necessary for serious propagation analysis the RX888 does need an external 27 MHz reference clock. Fortunately, the receiver provides a small “U.FL” connector on the board, allowing easy interface to the clock circuitry. However, it’s not as simple as connecting the output of a GPSDO (typically a Bodnar, or the upcoming TAPR reference). The RX888 clock input does not provide a 50 Ohm termination, and requires an AC-coupled reference of around 1V P-P. What is needed at this interface is a DC-block, an attenuator, and a termination.
Rather than string together a bunch of little adaptors, we (Turn Island Systems and TAPR) have come up a single-board solution, as well as a replacement back-panel (so you don’t have to drill a hole in the existing panel for an SMA jack), and a short U.FL jumper cable.
That SMA plug on the right-hand side of the adaptor is not installed for the “Inside the RX888” configuration, but the footprint is there so this board can be used as an external adaptor.
As you can see, the circuit is quite simple. Here’s the schematic:
And it’s pretty easy to cobble together an interface board yourself. Here’s my first attempt, which has been in operation for about a month now. This one isn’t exactly the same (it’s missing one capacitor and the attenuator values are slightly different):
I usually do my prototyping with surface-mount components, but for old-times sake I decided to use my old stash of through-hole parts on this. I’m waiting for delivery of the assembled boards, but if all goes as planned these kits should be available by the end of April.
If you want to use off-the-shelf components to interface between a Bodnar GPSDO and the RX888, I recommend inserting a DC-block at the RX888 external clock jack, followed by a 10 dB attenuator (the links are to probably-OK parts, I haven’t tried these particular ones myself). The attenuator reduces the output of the Bodnar to a more appropriate level, and provides a “good enough” termination at the RX888. Since the board-end of the internal jumper cable is unterminated the 10dB attenuator only provides about 8 dB of attenuation, and this is fine. The attenuator also provides a compromise termination to both the cable from the GPSDO and to the internal jumper.
Note that since Glenn wrote this we have discovered that the coupling / DC-block capacitor is desirable. Also, Glenn has included a switch that allows you to enable/disable the RX888 internal clock. Many of us are not bothering with the switch, but just pulling the internal “enable” jumper clip.
Rob Robinett and I will be co-presenting at the upcoming HamSci Workshop (https://hamsci.org/hamsci2024), our topic being High Resolution WSPR Transmissions for Ionospheric Research.
We will also have a hands-on demonstration of the hardware and software used, including the new WSPRSONDE-8.
If the Beacon Blaster 6 is to be used with a receiver on a shared antenna, an external Transmit/Receive switch will be required. Some T/R switches provide automatic sensing that switches modes when the transmitter starts. This can work well, especially given the relatively low-power output of the BB-6.
But there are advantages to an externally-controlled switch, usually driven by the “PTT” output of the transmitter (this is often an “RCA” or phono jack.) This output is generally a contact-closure (relay or transistor) to ground, which connects during transmit.
The BB-6 T/R Switch Interface provides this control signal. Installation will require that a 10mm (or 3/8”) hole be drilled in the BB-6 rear panel, and the attached control wires be plugged onto an existing header on the BB-6 control board.
BB-6 firmware version 2.4.0 or later is required.
The T/R Switch Interface is offered free of charge to all owners of the BB-6, so please let me know if you want one.
(the image above shows a 1/4W resistor where a small surface-mount resistor should be. Turns out I didn’t have the proper value on-hand when building the test unit.)
Announcing the next stage in Beacon Blaster evolution: The WSPRSONDE 8!
This is still in development, but the initial prototypes look very promising. Similar in many ways to the BB-6, this has the same type of frequency-flexible 1W Digital (square wave) outputs, the same GPS and 10 MHz clock reference inputs, 9-24VDC input, and USB configuration port. The WSPRSONDE-8 supports both WSPR and FST4W-120 modes.
Spurious output levels greatly reduced. The BB-6 was designed to meet a spurious output level of -40dBc or better. The WSPRSONDE-8 uses a different modulation technique to provide close-in spurs typically better than -90dBc
A single-board design that eliminates the many subassemblies and interconnections inside the BB-6. This is a rugged system.
The WSPRSOND-8 provides ultimate frequency accuracy and stability limited only by the external 10 MHz reference.
WSPRSONDE-8 shown with 6-band filter/combiner and Bodnar GPSDOClose-in spurious typically better than -90dBc (20-meters shown here, spurs -96dBc)Using the 6-band filter/combiner, the harmonic outputs are typically better than -60 dBc (20 meter output shown here)
I’ve been running this code (or the previous version) for a few weeks now, and it runs well. The latest version of wsprdaemon is able to calculate spectral spreading for WSPR as well as FST4W, so there’s little reason not to switch over to WSPR.
There are some upgrades to the configuration commands and I will be soon editing the user’s guide to show this, but the old commands still work: just add “MODE WSPR” to the start of your config.txt file. Then reload the file (or restart the BB-6) and you’re now running WSPR!
We’ve had at least five Beacon Blaster 6 boxes running during last week’s solar eclipse (plus another custom beacon design that used the BB-6 motherboard.) A lot of good propagation data was captured using these and other beacons.
I’ve got two BB-6 prototypes running, one in Friday Harbor Washington (WB6CXC, Grid CN88) and another in Occidental California (WB6CXC, Grid CM88). These were both transmitting on 80, 40, 30, 20, 15, and 10 meters, connected through a prototype Six-Band Filter/Combiner.
Here’s the setup in Occidental:
Prior to the eclipse, in order to verify the BB-6 “baseline” performance I set up a little monitoring system. This way we can confirm the validity of remote measurements of frequency, amplitude, or spread.
To do this I used a QRP-Labs “QDX” transceiver, running as a receiver on the 20 meter band. Some external shielding and cable-clamp chokes were needed to attenuate the strong local signal, as even with a dummy-load in the QDX antenna jack the receiver was initially overloading. The QDX was then connected to a computer running the wsjtx program to decode my FST4W-120 transmissions. wsjtx saves a log file showing the time-stamped parameters of every decoded transmission.
For additional monitoring the “-40 dB Tap” output of the Combiner was connected to a spectrum analyzer, which was also plugged into the computer. I first used a “SignalHound SA-44B” analyzer, but wanting to free up that device for other measurements I switched to the amazing “tinySA” (which also has an available computer interface program.)
The Bodnar GPSDO which provides the 10 MHz clock to both the BB-6 and the QDX has a monitoring program that displays internal PLL and GPS satellite status — this was also on the screen.
Finally, the BB-6 USB serial port was connected to the “Putty” terminal emulator. Here’s how it looked:
