Several correspondents refer to my article Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer using medium µ ferrite core for receiving use – 50:200Ω and suggest “I got it wrong, #73 is the proven material choice for such a thing, and a 2t primary is optimal”.
In fact, I did explore #73 as an option, this article presents some key comparisons. The two key statistics shown in this article provided the basis for selecting the design.
Note that the scales are different from plot to plot.
Where the magnetising impedance appears in shunt with an ideal transformer with Zin=50+j0Ω, Insertion VSWR can be calculated.
2t on BN73-202
5t on BN43-202
Continue reading Comparison of BN43-202 / 5t with BN73-202 / 2t for rx only on low HF – small broadband RF transformer – 50:200Ω
The article On the concept of that P=Pfwd-Prev discussed the question of the validity of the concept of that P=Pfwd-Prev, exploring an example of a common nominally 50Ω coaxial cable at 100kHz. The relatively low frequency was used to accentuate the departure from ideal.
This article digs a little further with analyses at both 100kHz and 10MHz.
A plot was given of the components and sum of terms of the expression for power at a point along the line.
Lets look at the power calculated from voltages and currents for the example at 100kHz where Zo=50.71-j8.35Ω and Zload=5+j50Ω.
Above, the four component terms are plotted along with the sum of the terms. Continue reading Transmission lines: departure from ideal Zo
The STC15Fx chips use a simple TTL/CMOS async programming interface that is suited to the common USB-RS232(TTL) adapters. This article describes a low cost programmer that also allows the programming application to Vcc (so initiating the boot loader automatically).
Above is the programmer ($2.50 on eBay) and a small adapter that plugs into the top row of the 2×5 header on the programmer.
DIP-28 are located carefully so that the pins 10-18 are in the socket, the same connections are used for both chip sizes for STC15F104E and STC15F204E. Continue reading Basic programming jig for STC15F104E and STC15F204E chips #3
STC produce the U8W & U8 programmers for a range of their chips.
The thing has a JST 7way XH socket provided for an ISP connection to a target board. It is accessed through a cutout in the acrylic housing, but the cutout is no bigger than the shoulder on an XH plug and one cannot get tools in beside it to pry the plug out without pulling on the wires.
The good thing is that there is an inexpensive “XH plug saver” sold to the RC market, it provides a means of getting a convenient grip on the plug without pulling on the wires.
First step is to mill out the case opening to accommodate the XH plug saver.
Next, add the XH plug saver to the XH plug, and it all works. Continue reading XH plug savers on the STC U8W & U8 programmer
A continuing frustration is garden hose maintenance.
We use reinforced hose that comprises essentially three layers, an inner plastic layer, a braided fibre reinforcing layer and another layer of plastic. Though these layers are bonded in new hose, there is potential for them to separate in service resulting in the reinforcing braid pulling back into the hose length and allowing the hose to expand in diameter at that point (lacking the benefit of the reinforcement). At this point failure of the hose by bursting is inevitable, sooner rather than later.
Some hoses are supplied fitted with factory crimped ferrules, and experience is that they have lasted well except that the fittings are plastic and break if subjected to rough treatment.
User serviceable screw collets fail, either through failure of the collets, or just the outcome of the screw collar loosening and resultant pull-back of the reinforcing braid.
What is needed is a tough and durable coupler with an easily applied ‘permanent’ clamp.
I have conducted a trial of brass fittings modified to remove the screw collar and nylon collet, then used with a stainless steel stepless one ear clamp.
Above at left is the unmodified coupler, and at right the coupler with the collet and screw collar discarded, thread turned off the coupler, and a one ear clamp for installation. Continue reading Garden hose couplers – there has to be a better way
Ferrite cored inductors and transformers saturate at relatively low magnetising force.
#61 material example
Lets work through an example of a FT50-61 core with 10t primary at 3.5MHz.
Magnetic saturation is one limit on power handling capacity of such a transformer, and likely the most significant one for very low loss cores (#61 material losses are very low at 3.5MHz).
Let’s calculate the expected magnetising impedance @ 3.5MHz.
Zm=0.966+j144Ω, |Zm|=144Ω. Continue reading RF transformer design with ferrite cores – saturation calcs
A review of transformer design
In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase is uniform, and the effects of distributed capacitance are insignificant.
Above is a commonly used low frequency equivalent of a transformer. Z1 and Z2 represent leakage impedances (ie the effect of magnetic flux leakage) and winding conductor loss. Zm is the magnetising impedance and represents the self inductance of the primary winding and core losses (hysteresis and eddy current losses). Continue reading RF transformer design with ferrite cores – initial steps
An online expert recently advised:
…The spec for type 43 makes it clear that it should never be used for HF unun construction. It is specifically engineered with a complex permeability that makes the core lossy on most HF frequencies. Since an unun is not a TLT (transmission line transformer) but rather an autotransformer, a low loss core is essential for efficient operation….
Now it contains the very common FUD (fear, uncertainty and doubt) that masquerades as science in ham radio, but without being specific enough to prove it categorically wrong. To a certain extent, the discussion goes to the meaning of
efficient operation. Continue reading An online expert on the unsuitability of #43 for HF UNUNs
A recent purchase of an inexpensive ($6) speaker polarity tester prompted a need for a stand alone driver for speakers.
Above, the tester has a microphone that senses the polarity of the pressure wave and indicates with one of two LEDs.
The tester comes with a CD containing a file that can be used to provide the test signal on a complete system with CD player, but there is a need for a stand alone driver for testing bare speakers or speaker units.
Speaker tick generator (for polarity testing) described a stand alone test pulse generator based on re-purposing a brushless DC motor controller (ESC, used for RC models).
This article describes a simple tick generator using a inexpensive 8051 type MCU (STC15F104E) and a H-bridge IC (TC427).
Above, the prototype was build on a small piece of Veroboard. DC input of 6-15V is applied to the 2.1×5.5mm DC jack, and speaker output is on the screw terminals (nearest to DC jack is -ve). Continue reading Speaker tick generator #2 (for polarity testing)
Fox Flasher MkII and several follow on articles described an animal deterrent based on a Chinese 8051 architecture microcontroller, the STC15F104E.
This is an update after several years operation outside, and some in service modifications to improve performance.
Above is the original basic schematic.
Above is the revised schematic. One only high current LED driver is shown, use as many as needed. The battery charger / protection module is based on TP4056 and DW01 chips and modules sell on eBay for $1 or so. Continue reading Fox flasher MkII update 7/2019