Two bare dimmer modules sold on eBay with identical specification and similar price are compared.
Both claim to have zero hysteresis.
Zero hints a lie!
Hysteresis is caused in simple phase control dimmer circuits at low settings because in each half cycle the trigger capacitor starts at a different voltage depending on whether the diac fired on the previous half cycle.
A serious issue with this snap-on effect is that if power is turned off at low power setting and re-applied, the controller may not switch on.
Above is type 1, a very triac basic phase control circuit. The red capacitor and resistor to its left are snubber components, the yellow capacitor, 4.7kΩ resistor to its left and the 500k pot are the phase delay circuit, the diac is just visible above the red capacitor. Continue reading A comparo of two bare light dimmer modules
This article is an expose of the internals of a common Chinese no-name 1-1000MHz Return Loss Bridge available on eBay for around $65 incl post.
Above is the exterior of the device. Specs are sparse: P<23dBm, Directivity>35dB. Continue reading Chinese no-name 1-1000MHz Return Loss Bridge
Though ham radio enthusiasts often rail against CBers, with the eflux of time, it is more difficult to distinguish between the two.
From Innovantennas website, a caption to a pic of one of their antennas explains:
The 10-54MHz LDPA directional antenna at K4ANP. Sadly, Len caught one of the elements and vent it during installation but SWR 1:1.4 thorughout.
The emphasis of the SWR value is mine. They, as antenna ‘professionals’, do not seem to understand the concept of SWR, and that by definition it is a ratio of greater than unity, ie the big number goes first. In fact if they just rationalised the ratio and expressed it as SWR=1.4 it would be briefer, clearer and more importantly, actually correct.
Little wonder hams not really understand what they are buying acquire bad learning from those who might provide accurate information.
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
Lets say we measure the impedance of a 1t wind on a FT240 size core to have Z=13.6+j19.1Ω @ 7.31MHz.
But it has a resistive component, it is not an ideal or lossless inductor.
Nevertheless, we can consider that Z=j*2*pi*f*L, and since Z is complex, a complex values is implied for L. Continue reading Where do µ’ and µ” come from?
This article documents an initial checkout of a Baofeng GT-5TP.
Above is the GT-5TP with its supplied antenna. Continue reading Baofeng GT-5TP – first impressions
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
In a discussion about using a 40m centre fed half wave dipole on 80m, the matter of feed line loss came up and online expert KM1H offered:
Use this to help make up your mind. Add it to the normal coax loss. http://www.csgnetwork.com/vswrlosscalc.html
This is to suggest that the feed line loss under standing waves can be calculated with that calculator.
He then berates and demeans a participant for commenting on his recommendation, bluster is par for the course in these venues.
The calculator in question states
this calculator is designed to give the efficiency loss of a given antenna, based on the input of VSWR (voltage standing wave ratio) and other subsequent factors.
This is a bit wishy washy,
efficiency loss is not very clear. The usual meaning of efficiency is PowerOut/PowerIn, and the usual meaning of loss is PowerIn/PowerOut, both can be expresssed in dB: LossdB=10*log(Loss) and EfficiencydB=10*log(Efficiency). Continue reading Line loss under standing waves – recommendation of dodgy tool on eHam
This article is an expose of the internals of a common Chinese no-name 1-500MHz Return Loss Bridge available on eBay for around $50 incl post.
Above is the exterior of the device. Specs are sparse: P<23dBm, Directivity>36dB. Continue reading Chinese no-name 1-500MHz Return Loss Bridge
I often see comparisons of toroidal inductors of different core dimensions with all other characteristics (eg turns, core type, frequency) held the same.
There seems an implicit assumption by many that the bigger the core, the larger the inductance. There are several failure in that thinking.
The ‘inductance’ of a toroidal inductor is µ*n^2*a/l where:
- µ is complex permeability, µ0+µr;
- n is the number of turns;
- a is the cross section area; and
- l is the effective magnetic path length.
Note that at RF, permeability may be a complex frequency dependent value, and therefore ‘inductance’ will be a complex value.
Many online calculators incorrectly calculate l from core dimensions using a simplistic formula.
Many online calculators treat permeability as a real number that is not frequency dependent, they use initial permeability (µi). Continue reading Comparing toroidal inductors of different core dimensions