Over on my wb6cxc.com blog I have posted about SDR dynamic range and some related Turn Island Systems products that are in the early prototype stage: a Filter-Preamp with a 60 MHz antialias filter optimized for 88-108 MHz FM broadcast band rejection, and a completely new multiband receive filter-bank which (in many cases) will reduce MW and SW broadcast band overload . I hope to have these fine-tuned and available very soon!
I invite you to participate in the development discussion:
There are several prototype versions of the 9BFC in operation, and they work just fine when connected to a decent multiband antenna.
BUT – when connected to a high SWR antenna (as is sometimes necessary in the field) the internal surface mount inductors can get disturbingly warm. The prototype 9BFC used a mix of surface mount and toroid inductors.
So, I am announcing the brand new all-toroid version of the 9BFC!
The 9BFC covers the 80, 40, 30, 20, 17, 15, 12, 10, 10 and 6-meter ham bands. This design has demonstrated its resilience and performance under all load conditions, and so has become the production version of the 9BFC.
So when you want to get a signal out, even when working with too-short or otherwise mismatched antennas, the 9BFC is now available: https://turnislandsystems.com/product/nine-band-filter-combiner/
And of course it works great with a well-tuned multiband antenna!
I’ve been trying to avoid this one because winding and adjusting all those toroids is tedious and time-consuming, but this thing just makes so much sense that I had to do it. The Nine-Band Filter-Combiner (9BFC) is yet another filter-combiner for use with the WSPRSONDE and other QRP transmitters, and it allows a single multi-band antenna to be driven by multiple transmitters. It combines inputs on 80, 40, 30, 20, 17, 15, 12, 10, and 6 meter ham bands. You don’t have to use all the inputs; leaving any unused ones unconnected is just fine.
The 9BFC design is quite a bit more critical than the previous 6-band combiner, as the added 17 and 12 meter bands are extremely close to the 20, 15, and 10 meter bands. This tight spacing requires rather narrow filter passbands, and there is always a tradeoff between filter bandwidth, inductor “Q”, and filter loss. In order to keep the 9BFC loss to a reasonable level, commercially-available surface-mount inductors as used in the 6BFC are not adequate for these five closely-spaced bands. Instead, I am using iron-powder toroids (T50-6 variety) for those frequencies. The 80, 40, 30, and 6 meter filters do use surface-mount inductors.
Not only are these toroids tedious to wind, but the inductance of each of the ten toroids must be carefully adjusted to provide the proper filter shape and impedance match. Adjustment is done by spreading or compressing the windings while observing the filter response with a Vector Network Analyzer — this process requires some iteration since each channel has two toroids and they do interact. Once adjustments are complete the windings are secured with fingernail polish.
Of course, your antenna has to support the bands in use. When using the eight-output WSPRSONDE and the EFHW-8010 (end-fed half wave, 80-10 meters, from myantennas.com) I am using all the 9BFC inputs but the 6 meter port. It works quite well (my two WSPRSONDE locations are shown here, Friday Harbor WA, and Occidental CA). I have a separate 6-meter antenna for the Occidental site.
It’s alive!!! The new WSPRSONDE v2 WSPR/FST4W multichannel transmitters are rolling off the Turn Island Systems assembly line:
There are a few changes from the previous batch of WSPRSONDEs:
There are a few other minor changes on the circuit board — things like Board Revision ID, allowing for future forward and backward compatibility.
But the WS-v2 is otherwise identical to the units that have been deployed on at least 2-1/2 continents. It continues to generate the clean, precise, and stable signals so necessary for accurate measurement of ionospheric propagation effects.
Along with this new hardware release comes updated WS firmware, with new features and options.
This has been in the works for a while now, and I am very pleased with the finished product!
If you are interested in some details of the WS-v2 assembly process, here is a short video of the Turn Island Systems CNC mill preparing a blank aluminum faceplate for the WS.
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.
For details, see the product link: TIS-126
Five units are ready to go (four of them shown here).
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.
More details here:
https://turnislandsystems.com/wp-content/uploads/2024/01/BB6-TRS.pdf
(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.
But the WSPRSONDE-8 adds these new features:
The WSPRSOND-8 provides ultimate frequency accuracy and stability limited only by the external 10 MHz reference.
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!
Get the new Version 2.3.1 upload here:
The assembled Shelving/LPF boards were delivered yesterday, and the “missing” inductor was delivered today (one inductor was not in stock at JLCPCB so I had then assemble it without that one part; I ordered that inductor from DigiKey). Amazingly fast service from JLCPCB! So I soldered on that inductor and the SMA connectors and did some testing:
This board has options where the shelving filter can be bypassed, so I tried that first. The results were much better than I had expected:
This essentially matches the performance of the LTSpice simulation (which used the Coilcraft inductor models, not the similar Murata inductors on the board. This shows a reasonably sharp rolloff with better than 60dB stopband attenuation. I am seeing no obvious inter-stage coupling (which can be a concern when using unshielded solenoid inductors.)
Here is a closer look at the roll-off performance. The loss at 1MHz is essentially zero, while the -3dB point is about 28 MHz. We may want to push this corner frequency a bit higher…
There are some spurious responses above 240 MHz. I suspect that these won’t be a problem because the SDRs that will be using these filters will already have an anti-aliasing filter that should adequately knock down these frequencies. I could guess that these come from inter-stage trace inductance, but that’s just a guess:
With the shelfing filters in place, the low-frequency attenuation is about 20dB:
There is also extra attenuation above 25 MHz, which suggests that we shift the shelving mid-point frequency slightly lower to reduce higher-frequency attenuation.
In conclusion, I am quite pleased with the overall design and layout of this board. Tweaking the frequencies (if necessary) will be trivial.