Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.
Another post about frequencies – this time I’ve assembled a DFD4A from Almost All Digital Electronics:
As you can see, it’s spot on – the last digit flips between 0 and 1 every so often, that’s all.
As with the Capacitance Meter I assembled recently, this kit comes with detailed build instructions. Except that this time I didn’t really want to build it, so I got the pre-built version instead, including the connectors and (fully) plastic enclosure. The front plate already has all the right cutouts, and a printed piece of paper (!) glued to the front. Works ok, but I suspect that it’ll get dirty over time.
The unit came with all the parts, I just had to solder a few components and wires in place after inserting all the switches and BNC connectors.
One thing missing was the 9V battery clip – but not to worry, I have a couple of those lying around anyway.
The reason to get this particular unit was its high frequency range of well over the 868 MHz and 2.4 GHz frequencies I may want to measure here at JeeLabs. The main difference with a professional unit is probably the fact that it doesn’t have many input signal options:
- HF measures from 0 to 30 MHz, with 5 Vpp max into a high impedance input
- UHF measures from 10 to 3000 MHz over a 50 Ω input (max 15 dBm)
No way to directly measure the 868 MHz output from an RFM12B, I suspect – i.e. it probably won’t be sensitive enough to measure 0 dBm.
The slow measurement mode continuously collects data for one second, so you get 1 Hz resolution on the HF range and 100 Hz resolution on the UHF range (since that’s essentially just a ÷ 100 prescaler).
The fast measurement mode runs 10 times per second, i.e. a gate time of 0.1s – so this gives 10 Hz resolution on HF and 1000 Hz (1 KHz) resolution on UHF.
It’s a bit odd that the display shows more significant digits than are being measured in all but FAST + HF mode, but no big deal – the current mode is clearly visible from the switch settings.
Knowing that the counter is very accurate (for now – it’ll no doubt gradually drift slightly), it’s time to find out how accurate the TG2511 AWG’s frequency is when not synchronized to the Rubidium standard:
That’s only 0.4 ppm off and well within spec – excellent!