In the article The system wide conjugate match stuff crashes out again I worked through an example proffered in an online discussion to show that Walter Maxwell’s teachings on system wide simultaneous conjugate match do not tend to occur in practical systems.
Why are hams so obsessed with conjugate matching?
The answer is on the face of it quite simple. Continue reading The transmitter matching problem
At A thinking exercise on Jacobi Maximum Power Transfer #2 I posed the question of a metric for the mismatch at the L2L1 junction in the following network where the calculated values L2L1_lZ is the load impedance at the L2L1 junction (looking left as Simsmith is unconventional), and L2L1_sZ is the source impedance at the L2L1 junction (looking right). The left three components are the fixed antenna representation.
Common practice is to speak of a “source VSWR” to mean the VSWR calculated or measured looking towards the source, and very commonly this is taken wrt 50+j0Ω which may be neither the source or load impedance but an arbitrary reference. Continue reading A thinking exercise on Jacobi Maximum Power Transfer #3
At A thinking exercise on Jacobi Maximum Power Transfer I posed an unanswered Q2:
Keeping in mind that C2 and L2 are an adjustable matching network, usually adjusted for minimum VSWR as seen at the source G. So, the questions are:
Does the system take maximum available power from the source G when the load impedance seen by source G is equal to the conjugate of its Thevenin equivalent source impedance (ie C2.Z=G.Zo in Simsmith speak)?
Does that ‘matched’ condition result in maximum power in the load L?
Above for reader’s convenience is the model conjugate matched at the GC2 interface. The calculated Po figure (lower right) is the power in the load L to high resolution. Continue reading A thinking exercise on Jacobi Maximum Power Transfer #2
nanoVNA-H v3.4 is out, and I don’t yet see significant problem reports.
When I compare the circuit with v3.3 (which I have), apart from new battery charger IC etc, the changes are in three areas:
- decoupling power to the mixers;
- increasing the drive to the mixers; and
- higher attenuation of input on the rx port. Continue reading nanoVNA-H – rework of v3.3 PCB to v3.4?
At The system wide conjugate match stuff crashes out again I discussed the failure of Walt Maxwell’s teachings on system wide simultaneous conjugate match using an example drawn from an online expert’s posting.
The replicated scenario with matching with an L network where the inductor has a Q of 100, no other loss elements is shown below. (Quality real capacitor losses are very small, and the behavior will not change much, the inductor loss dominates.)
Above is a model in Simsmith where I have adjusted the lossy L network for a near perfect match. I have used a facility in Simsmith to calculate the impedance looking back from L1, often known as the source impedance at a node but in Simsmith speak the calculated L1_revZ on the form, (ie back into the L network) from the equivalent load. Continue reading A thinking exercise on Jacobi Maximum Power Transfer
At nanoVNA – measurement of two 920MHz LoRa antennas I mentioned my growing frustration with the USB interface on the nanovna, particularly the tendency to reset the nanoVNA with the slightest wiggle and the frustration in trying to use the resulting mess.
I have previously cleaned both plug and socket a couple of times, the last time was after some board modifications and flux residue was washed from the board keeping the USB socket dry, then the USB socket was flushed with clean solvent and blow dry.
The USB problems have become apparent only recently and rapidly got worse. Continue reading nanoVNA-H – v3.3 USB problems
The article IoT – exploration of LoRa – part 3 showed some components of a simple LoRa system.
This article reports measurements made on two antennas used in the prototype system.
Above is a view of the prototype system. Continue reading nanoVNA – measurement of two 920MHz LoRa antennas
One of the many nanoVNA cloners makes an interesting little inexpensive demo board with a selection of components, filters etc to develop familiarity with the nanovna.
Above is a pic of the demo board and the supplied jumper cables. The demo board may not include information relevant to using the cables and connectors supplied. Continue reading nanoVNA – that demo board and its U.FL connectors
Recent discussion with a correspondent about the design issue of the so-called Co-Co collinears, vertical collinears made with alternating sections of common coax ranged onto the conflict between the phase velocity of the wave on the inside of the coax and the wave on the outside of the coax, and the difficulty in aligning both the outside standing wave pattern for optimal pattern, and the internal phasing to feed those sections with optimal phase. Continue reading Coaxial Collinear – dielectric loading the outer conductor
At https://groups.io/g/nanovna-users/message/9185 a user posted a measurement made with his nanoVNA of a length of coax with termination.
Above is his initial reported measurement of
an approximate 350′ length of coax with a known good dummy load on the opposite end. 350′ is 106.7m. Whilst this chart is less value than a Smith chart rendering, understanding the nature of things allows us to infer the Smith chart. Continue reading nanoVNA user post provides an interesting example for study #1