shows shows an AET USB-S-1.84 RF Source comb generator (so called
because its frequency spectrum looks like a comb on the display of a
spectrum analyzer) and a small charger powered by two AA cells intended
for charging mobile phones and USB devices. Although intended to charge
USB devices until the batteries are exhausted, it makes a great 5 Volt
USB power supply for many devices including the comb generator shown.
During operation, the charger draws about 380 mA from the AA cells
while powering the USB powered comb generator. That could translate to
5 or more hours of operation per pair of AA cells. The unit also seems
to run well on a pair of AA nickel metal hydride batteries although I
have not tried to see how long NiMH batteries will power the charger.
The test setup is shown in Figure 2. The charger is connected to the
comb generator using a small cable furnished with the charger and the
comb generator itself is directly coupled to the input of the scope to
achieve the fastest possible edge rates by avoiding dispersion and loss
in coaxial cables which slows edge rates. A close-up of the test setup
is shown in Figure 3.
Figure 2. Test Setup With Charger and Comb Generator
Close-up of Power Source and Comb Generator
Figure 4 shows the
fast portion of the output of the comb generator. There are slower
features on the output that can be seen on a longer time scale, but the
part of the waveform shown is the source of most of the harmonics in
the output of the generator. The pulse has about a 1 1/2 Volt amplitude
with a rise time of a little less than a nanosecond. The generator is
working well powered from the charger.
Figure 4. Plot of USB Powered USB Comb Generator Output
I have seen this charger at Costco and Staples. It is widely available
from other outlets as well. This charger would work well for field work
where USB devices need to be powered up, such as the comb generator RF
source shown above.