A drive test of RTKLIB accurate GPS

Accurate GPS positioning has been of interest in automating data collection in field strength surveys of antennas on HF. To be useful, the positions need to be accurate to 100mm.

RTKLIB is an open source program package for GNSS positioning.

A number of experiments were conducted using a U-Blox LEA-6T assembly with integral small patch antenna (cost ~A$40) and RTKLIB v2.4.3(b8) using a base station feed from Geoscience Australia (with thanks). The test location is about 200km from the reference station at Symonston ACT.

LEA-6T01

Above, the LEA-6T and a RS-232 to USB adapter are strapped to a roof rack bar with stretch film. The high mounting position gives good view of the sky.

 

Screenshot - 30_06_16 , 12_50_35

Above is a position plot of about an hour with the vehicle stationary (though in Kinematic mode) beside the house. Sky view was slightly restricted by the house and a line of tall trees to the west.

firefox 30/06/16 , 15:36:58 http://owenduffy.net/map/20160630.htm 20160630 - Mozilla Firefox

For the most part the track is smooth, but there is one section where the track in a more heavily treed section is markedly jaggy.

Atten APS3005S – a better thermostatic fan control

The Atten APS3005S is a 0-30V 5A linear DC power supply.

Atten-hcctl00

This later model includes a thermostatically controlled fan which at moderately light currents short cycles (10s on 20s off) and is very annoying… especially since it sits above my desk.

This project describes application of the generic heating / cooling controller (hcctl) to control the fan, reducing the short cycling nuisance.
Continue reading Atten APS3005S – a better thermostatic fan control

Exploiting your antenna analyser #22

On a transmission line with standing waves, the voltage varies cyclically along the line, and is dependent also on power.

This article explains a method to use an analyser to predict the peak voltage level at a point for a given frequency and power based on measurement or estimation of complex Z or Y at that point using a suitable antenna analyser.

The problem

Lets say you have some critical  voltage breakdown limit and want to use your analyser to find any non-compliance at the proposed power level.

Let us assume that the not-to-exceed voltage at that point is 1000Vpk. Let’s allow a little margin for variation due to factors not fixed, let’s actually use 800Vpk as the limit. We will use the maximum permitted power in Australia, 400W.
Continue reading Exploiting your antenna analyser #22

Silver vs alkaline button cells

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).

IMG_1591

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

Micro SD card premature failure

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).

IMG_1599

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

End Fed Half Wave / Inverted L / Half Wave Dipole

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 (0.005,13): 10m;
  • lossless balun / matching device.

Key differences:

  • ground connection: Inverted L = 2Ω, End Fed Half Wave = 100Ω; and
  • effective common mode choke used on the dipole.

 

Clip 202

Above is the modelled gain for all three. Continue reading End Fed Half Wave / Inverted L / Half Wave Dipole

Chinese counterfeiters at it again – EZP2013

Some while ago I purchased a EZP2013 device programmer on eBay.

EZO2013

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

The magic of End Fed Half Waves (EFHW)

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).

Screenshot - 21_06_16 , 14_55_56Above 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 End Fed Half Waves (EFHW)

Exploiting your antenna analyser #21

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.

K0BG’s pitch

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).

 

Clip 201

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