The 4-20mA loop used for the water sensor needs a source of 24VDC. This is obtained from the battery (3.6-4.3V) using a DC-DC boost converter which runs only when a measurement is made.
This article discusses related issues. Continue reading IoT water tank telemetry project – part 4
A common theme among online experts is to measure, or ask for measurement of a common mode choke connected between the centre conductor of a VNA’s tx and rx ports. That raises the question of whether |s21| is meaningful, whether it in any useful way characterises the choke as a component of an antenna system.
Direct measurement of common mode current is not difficult, and it is almost always the best way to determine the effect of a choke on common mode current.
That said, analytical and simulation techniques can be of great value in the antenna design process, well before a prototype antenna is built.
An example choke at 7MHz
Lets perform an experiment using NEC to model the effect of a choke in a 7MHz antenna.
The choke used uses 11t on a FT-240-43 ferrite core. The values are from a calibrated model, values confirmed by measurement.
We will use NEC-4.2 with one of the scenarios detailed in the article Baluns in antenna systems, Model 4, but using the choke described above which has an impedance of 3175+j2502Ω at 7MHz.
Above is a simulation of the connection. Zcm of the choke in this case at 7MHz, 3175+j2502Ω, has been converted to an equivalent inductance and resistance to suit the simulator. (Note that the equivalent circuit it valid only for a narrow band, there is no simple wideband circuit equivalent for this ferrite cored choke (more later).) Continue reading Is |s21| measurement of a common mode choke meaningful to antenna systems?
It seems that almost all small DC-DC converter modules listed on eBay with LM2577 in the headline actually use the Chinese XL6009 chip which they may or may not state “replaces LM2577”.
But… is it a replacement? Continue reading XL6009 DC-DC converter chip issue