VU3SQM directional wattmeter build – #1 laid out the first steps in design review and build of a directional wattmeter.
The parts have arrived and construction commenced.
Above, the PCB populated with the SM parts and soldered. It was soldered in an IR reflow oven. Continue reading VU3SQM directional wattmeter build – #3
VU3SQM directional wattmeter build – #1 laid out the first steps in design review and build of a directional wattmeter.
This article canvasses the issues of the display.
Intention is a digital based display (though not to exclude an analogue meter or bar graph type displays).
So, the output of the AD8307 needs to be digitised.
Let’s first consider the nature of the AD8307.
It is a log detector, so it provides a ‘DC’ voltage proportional to the log of the input signal, but the ‘DC’ voltage can vary very quickly.
The chart above from the AD8307 datasheet shows that the unfiltered response to a burst of RF has a rise time of well under 1µs. Continue reading VU3SQM directional wattmeter build – #2
K0KA made a quite polished presentation published as a Youtube video explaining how to measure balance performance of an antenna system and an ATU.
He did not define what he means by balance… but it will become apparent.
Midway through his video, he measures the ‘balance’ of a Palstar AT5K (though possibly modified) by connecting a symmetric load consisting of two 470Ω 2% resistors in series and connecting the junction to the ground terminal on the ATU.
Above, from KA0KA’s video, his test load. The oscilloscope probes can be seen.
The oscilloscope channel gains are carefully adjusted to be equal.
KA0KA shows two oscilloscope measurements.
Continue reading KA0KA’s Youtube test of ATU balance
VU3SQM offers an interesting directional coupler based on a Sontheimer coupler, and using AD8307 power sensing for a nominally HF coupler. I must say that I am not a fan of Sontheimer couplers… but that is what the board uses.
This article lays out a preliminary design review to assist in selection of appropriate toroids, and ordering of the needed parts.
Above, the top side of a PCB. Continue reading VU3SQM directional wattmeter build – #1
A correspondent wrote seeking explanation of W5DXP’s no-tuner tuner which purports to obtain a near match by adjusting the length of the transmission line using relays or switches of some kind.
The particular device that is of interest is one using a single double pole knife switch as a three position On-Off-On switch.
The accompanying explanations states that this “is a way to use a single DPDT knife switch to obtain one, two, or three feet of ladder-line depending on the position of the switch”. Continue reading An explanation of W5DXP’s ‘line extender device’
This article describes a prototype RF choke (RFC) for use in a power injector for 50Ω coax over range 1.8-30MHz. Power injector / extractors are often used to connect power and / or signalling on a shared common RF coax feed line to accessories such as remote antenna switches and ATUs.
Design criteria are:
The core chose is a LF1260 ferrite suppression bead from Jaycar. It is a medium / high µ core readily available in Australia at $7.50 / 6.
Above is the prototype RFC wound with data cable wire for the purpose of measurement. In application it could be wound with 1mm enamelled copper or PTFE insulated wire (Curie point is lowish at 120°+, but it still benefits from higher temperature insulation). Continue reading An RF choke for a 1.8-30MHz coax power injector – LF1260 core
This article is a review of an inexpensive QRP ATU kit sold widely on eBay and possibly other online stores.
Above is the seller’s pic of the kit. Continue reading Review of inexpensive QRP ATU kit from eBay
A prototype broadband transformer for a End Fed Half Wave operated at fundamental and first, second, and third harmonic is presented.
The transformer comprises a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. The winding layout is unconventional, most articles describing a similar transformer seem to have their root in a single design.
Continue reading End Fed Half Wave matching transformer – 80-20m
Following on from KL7AJ on the Conjugate Match Theorem, KL7AJ on the Conjugate Match Theorem – analytical solution asked the question Is a ham transmitter conjugate matched to its load?
The answer speaks to the relevance of Walt Maxwell’s Conjugate Mirror proposition to ham stations. Continue reading Is a ham transmitter conjugate matched to its load?
KL7AJ on the Conjugate Match Theorem asked the question Should we have expected this outcome?
Let us solve a very similar problem analytically where measurement errors do not contribute to the outcome.
Taking the load impedance to be the same 10.1+j0.2Ω, and calculating for a T match similar to the MFJ-949E (assuming L=26µH, QL=200, and ideal capacitors) we can find a near perfect match.
The capacitors are 177.2 and 92.93pF for the match.
Now turning the network around by swapping the capacitors and changing the load to 50+j0Ω. Continue reading KL7AJ on the Conjugate Match Theorem – analytical solution