Here's a tunable coil with an inductance between around 1.9 mH at minimum and 2.9 mH at maximum. The outer coil is around 200 turns of AWG16 wire around a 160mm diameter tube. The rotating inner coil is maybe 60 turns of AWG16 wire around a 110mm diameter 90mm length tube. The inner coil rotates on a 20mm solid rod with 10mm diameter holes through the ends for feeding the wires out. A small geared DC-motor rotates the rod.
Seems to work quite well! This prototype shows about 140 pF of input(or parasitic) capacitance when the tuning capacitor is set to 0 pF. That could probably be improved on by better layout on a custom PCB.
Web-SDR located at Nastola
In particular the power-supply section using a common-mode choke, a Murata BNX025 filter, and low-noise regulators LT1963 and LT3015 seems to work quite well. I also used ferrites (2 kOhm @ 100 MHz) as well as an RC-filter on all supply pins. Perhaps overkill? Performance with the intended AC/DC brick is still to be verified.
Measurements around 10 MHz show a 1 dB compression at over 14 dBm and an IP3 of around 27 to 30 dBm. The gain extends beyond 100 MHz with some gain-peaking.
Some measurements of residual phase-noise with a 3120A phase-meter, at 10 MHz. My earlier distribution amplifier required shielding with aluminium foil as well as powering from a lead-acid battery to achieve a reasonably quiet phase-noise spectrum. These measurements were done with lab power-supplies for +/-12 V to the board and without any shielding.
Finally some measurements of gain vs. frequency with a Rigol spectrum analyzer.
A new pulse distribution amplifier for 1PPS distribution.
The input is fed to a LT1711 comparator triggering at 1.0 V (set by reference ADR423). This edge is buffered by 74AC14 before 1:8 fan-out to output-stages with three 74AC04 inverters in parallel driving the outputs.
Preliminary measurements show around 200ps channel-to-channel propagation skew - to be improved on by further trace-length matching or tuning. More measurements to follow.
A new distribution amplifier design featuring a 1PPS pulse distribution amplifier (PDA) and a 5/10 MHz frequency distribution amplifier (FDA).
1U 150mm deep rack-enclosure from Schaeffer. Prototype PCBs without soldermask or silkscreen from Prinel. Both the FDA and PDA boards have 1:8 fan-out with 9 BNC (optionally SMA) connectors spaced 16mm apart. The boards fit comfortably side-by side on a 19" rack panel. Some funky BNC-cables with unusually large connectors may not fit side-by-side 16mm apart - a price to pay for the compact design. The plan is to use an +/-12 AC/DC brick power-supply (not shown) which fits in the back of the enclosure.
Detailed posts on the PDA and FDA boards to follow.
Holy megacycles Batman! This thing is made for hacking. You telnet into the thing, delete one line in an XML config file, and then reboot. Whiskey-Tango-Foxtrot!?
Here's how the screen looks before and after, and a view of the 120 MHz signal on the scope. There's a bit of amplitude ripple as you sweep up from around 50 MHz.
By default it shows up at 192.168.10.2, so configure your PC eth-interface on 192.168.10.XXX. Now
Should find the device:
-- UHD Device 0
However uhd_usrp_probe suggest upgrading the firmware and FPGA image, so we do that by:
$ sudo /usr/lib/uhd/utils/uhd_images_downloader.py
$ sudo /usr/bin/uhd_image_loader --args="type=usrp2,addr=192.168.10.2"
and after power-cycling the device we now get (in addition to a long description of the RX and TX interfaces or installed daughter-boards):
FW Version: 12.4
FPGA Version: 11.1
To show that it works in gnuradio a simple USRP-source can be connected to a QT GUI Sink (or QT GUI Frequency Sink) that visualizes RX I/Q samples:
The source needs to be configured with "addr=192.168.10.2" and it uses the samp_rate, freq, and gain variables.
The USRP now samples at 100 MS/s, digitally downconverts a bandwidth samp_rate around a center frequency freq, and streams the samples over Ethernet to the gnuradio source node. When setting freq=10e6 and samp_rate=200k (the minimum possible!?) and applying a 10.020 MHz sine-wave to the RF1-input we get this:
With a signal that seems close to maximum amplitude the dB-scale shows a peak at -16 dB, and without any signal applied the noise-floor close to the center frequency dips just below -140 dB rising to -135 dB at 20 kHz offset.
Awesome stuff! The 200 kS/s samples from one I/Q channel produce about 800 kB/s of Ethernet traffic.
Stay tuned for more SDR updates in the near future!