Small untuned loop for receiving – simple model with transformer gave a simple model for analysing a loop. If you haven’t already read it, you should. It provides a step towards understanding the YouLoop-2T at frequencies where is is a small loop (perimeter<λ/10).
Above is the Airspy Youloup-2T. Try to put the two turns thing out of your mind, it is misleading, panders to some common misunderstanding, and so does not help understanding.
This is somewhat similar to the simple loop, but now the transformer primary is connected to the loop gap terminals by two parallel sections of 50Ω transmission line, the combination being effectively a 100Ω with similar parameters to the component coax sections. Because of the series connection at the transformer and parallel connection at the loop gap, there is a 1:4 impedance transformation additional to that of the coax sections themselves. Continue reading Towards understanding the YouLoop-2T at MF/lowHF
Last update: 7th July, 2020, 8:03 AM
This article explains the operation of a simple nominally 1:4 impedance transformer using transmission line (TL) elements.
Above is a diagram of the device. The currents shown are differential currents in the coax (ie wholly inside the coax), the current on the outside of the shield is not shown on the diagram.
At very low frequencies it may be intuitive that \(V_1\approx V_2\) and \(I_1\approx I_2\), but as frequency increases, a more exact solution is needed. Continue reading A transmission line 1:4 impedance transformer
Last update: 19th January, 2021, 10:35 AM
I have written several articles on untuned loops for receiving, as have others. A diversity of opinions abounds over several aspects, probably none more than the idea of an optimal load impedance for the loop.
This article analyses a simple untuned / unmatched loop in the context of a linear receive system (ie no IMD) of known Noise Figure. Continue reading Small untuned loop for receiving – simple model with transformer
Last update: 11th May, 2020, 12:35 PM
At nanoVNA-H – Port 2 attenuator for improved Return Loss I explained the reasons for essentially permanent attachment of a 10dB attenuator to Port 2 (Ch 1 in nanoVNA speak).
Above, the 10dB attenuator is semi permanently attached to Port 2 principally to improve the Return Loss (or impedance match) of Port 2, a parameter that becomes quite important when testing some types of networks than depend on proper termination (eg many filters). I should remind readers that the improvement in Port 2 Return Loss comes at a cost, the dynamic range of Port 2 is reduced by 10dB. Continue reading nanoVNA-H – Port 1 attenuator for improved what???
Last update: 4th May, 2020, 7:12 AM
Articles describing how to make a Return Loss Bridge are pretty common, but they don’t often spell out component values that are critical to accuracy.
Above is a schematic for discussion. It is somewhat simplified, but it is complete and will work. Continue reading Return Loss Bridge – some important details
Last update: 5th March, 2021, 7:43 AM