Variometer

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.

PA0RDT Mini-Whip antenna

Antenna in a bottle installed on the roof today. Stay tuned for a future web-SDR...

An article, some theory, some notes on grounding, some comparisons,

There's also a modernized circuit by PA0NHC

Frequency Distribution Amplifier 2017.01

1:8 frequency distribution amplifier based on LMH6702 and LMH6609 op-amps.

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.

 

Pulse Distribution Amplifier 2017.01

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.