I purchased a new digital caliper recently (no, they are NOT vernier calipers, though modern usage seems to have misused the term vernier to the point of it having no value).
A pic of the back reveals their recommendation for a battery, it is in the upper right corner of the pic “Battery 1.55V”. This is really subtle and a departure from previous practice of marking them more clearly SR44.
The nominal voltage of a silver button cell is 1.55V, an alkaline is 1.5V. Continue reading Silver vs alkaline button cells
I bought a couple of ‘generic’ micro SD cards on eBay about a year ago. They were not much cheaper than brand name cards, and though only speed 6 rated, were available locally for quick delivery. I have a vague recollection that it might have been a RPi product supplied with NOOBS on it (I have a couple of SD adapters with the RPi logo on them).
These were both used in RPi B systems and worked without fault for the last year, though they are not running full time (perhaps a couple of hundred hours of use).
During a Raspbian sofware update, both cards failed with the same problem, they effectively became read-only cards. Continue reading Micro SD card premature failure
The popular End Fed Half Wave is all things to all men, but this article compares an End Fed Half Wave, Inverted L, and Half Wave Dipole with some common parameters:
- frequency: 7.1MHz;
- flat top length: 20m;
- Height above ‘average’ ground (σ=0.005, εr=13): 10m;
- lossless balun / matching device.
- ground connection: Inverted L = 2Ω, End Fed Half Wave = 100Ω; and
- effective common mode choke used on the dipole.
Above is the modelled gain for all three. Continue reading End Fed Half Wave / Inverted L / Half Wave Dipole
Some while ago I purchased a EZP2013 device programmer on eBay.
There were literally scores of sellers, and they all looked the same, and some variation in price from about US$25 to US$50… which is not unusual.
I used the thing a few times, and it was clearly a very poor product so I replaced it with a SOFI SP-8B which cost close to US$50 on Aliexpress including a bunch of (6) adapters. Continue reading Chinese counterfeiters at it again – EZP2013
Work continues on the quadcopter using Cleanflight on a NAZE32 flight controller. Continue reading Some automation to supplement Cleanflight-configurator
I have noted recently the increasing popularity of the so-called End Fed Half Wave antenna, though the term often includes harmonic operation of the antenna.
It seems that at the heart of common ham understanding of this antenna system is that some kind of two terminal feed device creates a scenario with current on the nominal radiator, and zero common mode current on the feed line. If that feed device is small, its contents bears little influence on the current distribution on the feed line and radiator (the device behaviour approaches that of a simple circuit node).
Above is the kind of current distribution envisaged by many. The equivalent source is shown at the end fed feed point The red curve is the magnitude of current, the horizontal line represents the nominal radiator, and the vertical line represents the common mode conductor formed by the feed line. The feed line is often of arbitrary length, arbitrary route, and it may connect to real ground via an arbitrary impedance. Pretty much everything about this antenna system is random save the length of the nominal radiator. Continue reading The magic of the End Fed Half Wave antenna / EFHW
A correspondent wrote about the apparent conflict between Exploiting your antenna analyser #11 and Alan, K0BG’s discussion of The SWR vs. Resonance Myth. Essentially the correspondent was concerned that Alan’s VSWR curve was difficult to understand.
For convenience, here is the relevant explanation.
By definition, an antenna’s resonant point will be when the reactive component (j) is equal to zero (X=Ø, or +jØ). At that point in our example shown at left, the R value reads 23 ohms, and the SWR readout will be 2.1:1 (actually 2.17:1). If we raise the analyzer’s frequency slightly, the reactive component will increase (inductively) along with an increase in the resistive component, hence the VSWR will decrease, perhaps to 1.4:1. In this case, the MFJ-259B is connected to an unmatched, screwdriver antenna mounted on the left quarter panel, and measured through a 12 inch long piece of coax. This fact is shown graphically in the image at right (below).
Note that the graph is unscaled, and that frustrates interpretation. The text is also not very clear, a further frustration. It is easy to draw a graph… but is the graph inspired by a proposition or is it supporting evidence. Continue reading Exploiting your antenna analyser #21
Desk study of opportunity to improve linearity.
At Chinese AD8307 power measurement module #2 I showed measurement of the linearity of an AD8307 based RF power meter.
The specification linearity is +/-1dB, which is poorer than one might like in a power measuring instrument.
The diagram above from the AD8307 datasheet shows the internal architecture, including 9 stages of cascaded log detector cells that attempt to give a log response over around 100dB range. The issue is that in the transition region between detector cells, error is worse than well inside an individual detector cell’s range.
Above is a sweep from -65 to -6dBm at 10MHz after calibration of slope and offset. The linear fit to the blue curve shows slope is 20mV/dB and intercept 1.8015 for 0dBm means the offset is -1.8015/0.02=-90.08dBm. Log conformance is 0.2dB (well within spec at this frequency, temperature etc).
Continue reading Chinese AD8307 power measurement module #4
Seeing the promotion of a clear adhesive with cure initiated by ~400nm UV light from a LED source, one’s mind wondered to its application for attaching temperature sensors to heatsinks etc.
A sample of Kafuter K-300 was tested.
Above is the test jig, a 1N4004 diode is attached to the corner of a scrap of 1.6mm thick aluminium sheet using the adhesive which was cured with UV light and then allowed 10 hours further to strengthen (if that helps). Continue reading UV cure adhesive for temperature sensors
A very long time ago, I purchased a W2AU 1:1 balun on the maker’s claims that it was good from 1.8 to 30MHz.
These were very popular at the time, but as voltage baluns they achieve good current balance ONLY on very symmetric loads and so are not well suited to most wire antennas.
Above is W2AU’s illustration of the internals.
Mine barely saw service before it became obvious that it had an intermittent connection to the inner pin of the coax connector. That turned out to be a poor soldered joint, a problem that is apparently quite common and perhaps the result of not properly removing the wire enamel before soldering.
Having cut the enclosure to get at the innards and fix it (they were not intended to be repaired), I rebuilt it in a similar enclosure made from plumbing PVC pipe and caps, and took the opportunity to fit some different output terminals and an N type coax connector.
Above is the rebuilt balun which since that day has been reserved for test kit for evaluating the performance of a voltage balun in some scenario or another. Continue reading W2AU 1:1 voltage balun