Vacuum capacitors are used for high end applications that require high voltage withstand and low loss.
Though they are called capacitors, and simple analyses treat them as a capacitance with some small equivalent series resistance (ESR), there is more to it.
Above is a view (courtesy of N4MQ) looking into one side of a vacuum capacitor. It consists of an outer cup, and a series of 5 inner cups progressively smaller in diameter. The other side of the capacitor has a similar structure but the cups site in the middle of the spaces between cups in the first side.
Continue reading Vacuum capacitors – construction implications for Q
This article is an expose of the internals of a 60dbm.com 0.1-3000MHz Return Loss Bridge available on eBay for around $17 incl post.
Above, the 60dbm.com Return Loss Bridge. Continue reading 60dBm.com 0.1-3000MHz Return Loss Bridge
One of the insane things about some Baofeng hand held radios is that the charger cradle requires 10V DC, and malfunctions on car battery voltage.
The cigarette light adapter that came with a Baofeng GT-3TP was simply a pass through device and the charger did not work properly using the adapter plugged into a car.
The charger cradle electronics should include electronics to charge properly from a car, preferably from 10-16V. The implementation is a half-baked idea.
To solve the problem I have made an adapter cable using a small buck DC-DC converter off eBay (~$2), the converter is adjusted to 10V out.
I have used an Anderson Power Pole connector to suit my power distribution, you could use a cigarette lighter plug or some other plug to suit your needs. The output connector is a 2.5mm DC plug. Continue reading Baofeng charger DC-DC converter
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 enameled 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