Diagnosis of engine coolant temperature gauge issue with a certain vehicle

The subject vehicle is a Land Rover Defender of mixed heritage. The owner describes the engine coolant temperature (ECT) gauge as useless.

The ECT display system is a dashboard gauge and negative temperature coefficient (NTC) thermistor mounted near the engine thermostat. It measures the engine coolant temperature (hence its name) at the hottest point in the coolant circuit… so it gives the best warning that coolant might be approaching boiling point… and which point cooling capacity catastrophically falls and there is a significant risk of permanent engine damage.

It would seem that Land Rover used many different dashboard gauges, but the underlying electrical characteristics were of just two different types. Likewise there appears to be several different sensors.

The following table of coefficients for four common sensors was derived from published measurements by TSD of a single sensor of each type.

Part R25 B25/100
AMR3321 2246 3897
ERR2081 2218 3879
ETC8946 2450 3671
AMR1425 536 4356

These are measurements of a single sample, so average values might be a little different. Additionally, the R25 / B25/100 model is only an approximation. Continue reading Diagnosis of engine coolant temperature gauge issue with a certain vehicle

A handy 230VAC 10A inline power meter based on an inexpensive module from eBay

This article describes a simple and inexpensive inline power meter for use as a test instrument.

CNC routing

The box cutouts were done on a CNC router, but they could be done with hand tools.

Above, calcs of feeds and speeds for the CNC router. The box is actually ABS, but cutting speed for Polycarbonate is the same.

Above is the tool path for one side of the box. The cutouts suit the 7P-2 strain reliefs. The gcode is generated from a custom Python file using a custom library of common shapes that I use. Continue reading A handy 230VAC 10A inline power meter based on an inexpensive module from eBay

Comment on KN5L on balun CMRR – series through impedance fixture

In recent articles, I flagged that on some of John’s VNWA plots he showed flawed impedance calculations using VNWA’s t2s inbuilt function.

The function t2s is documented in the VNWA help.

t2s is a VNWA built in function intended to solve the so-called s21 series through fixture for impedance measurement of two terminal Zx connected between Port 1 and Port 2.

None of John’s test fixtures were equivalent to the circuit above required for valid t2s transformation. Continue reading Comment on KN5L on balun CMRR – series through impedance fixture

Comment on KN5L on balun CMRR – two wire line example

The article Comment on KN5L on balun CMRR dealt with model and measurement of John’s coaxial choke in fixture, dealt with first because it is a simpler model. This article builds on that and models the balun wound with a pair of wires.

Above is the subject balun in fixture.

John’s schematic shows the balun as coupled coils, but that does not capture the transmission line transformation that occurs in the actual device. Again the test fixture is used without explanation. Continue reading Comment on KN5L on balun CMRR – two wire line example

Comment on KN5L on balun CMRR – coax example

One of the ham fashions of proposed solutions to characterising a balun is to find the Common Mode Rejection Ratio (a term carried over from other applications, eg voltage driven operational amplifiers).

(Anaren 2005) explains a method of finding balun CMRR. Anaren gives a definition of CMRR:

Common Mode Rejection Ratio is defined and the ratio between the differential mode insertion loss/gain versus the common mode signal loss or gain.

Note that in a passive system, CMRR in dB will usually be positive, and the larger the better.

Anaren does not mention applying the CMRR statistic to antenna systems. I have commented elsewhere on the lack of utility of CMRR in analysing common antenna systems.

John, KN5L, has published his own solution to balun characterisation in some online forums. Continue reading Comment on KN5L on balun CMRR – coax example

Baofeng BF-T1 (BF-9100) – initial impressions

I purchased two inexpensive Baofeng BF-T1 UHF portables (hand-helds) for use around the yard.

Key features:

  • LiIon pouch single cell battery that may be obtainable longer than proprietary batteries;
  • micro USB charger interface, internal charge / battery management;
  • programmable with CHIRP (channel table only);
  • chanellised operation, lockable keypad;
  • CTCSS support;
  • integrated antenna;
  • small and lightweight (110g with belt clip);
  • inexpensive.

The radio has been in the market for more than three years, so one might hope that design issues have been fixed in ‘mature’ product. Continue reading Baofeng BF-T1 (BF-9100) – initial impressions

Comparing sensitivity figures of an AM receiver and SSB receiver

Receiver sensitivity is commonly given as some signal level, say in µV, for a given Signal to Noise ratio (S/N), say 10dB. For AM, the depth of sinusoidal modulation is also given, and it is usually 30%. In fact these are power ratios in the context of and some nominal reference receiver input impedance.

In fact what is commonly measured is Signal + Noise to Noise ratio, and of course this ratio is one of powers. For this reason, specifications often give (S+N)/N.

This article discusses those metrics in the context of ‘conventional’ receivers and introduces the key role of assumed bandwidth through the concept of Equivalent Noise Bandwidth..

Let’s consider the raw S/N ratio of an ideal AM detector and ideal SSB detector.

Raw Signal/Noise

AM

 

Above is a diagram of the various vector components of an AM signal with random noise, shown at the ‘instant’ of a modulation ‘valley’. The black vector represents the carrier (1V), the two blue vectors are counter rotating vectors of each of the sideband components, in this case with modulation depth 30%, and the red vector is 0.095V of random noise rotating on the end of the carrier + sideband components. Continue reading Comparing sensitivity figures of an AM receiver and SSB receiver

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2×2631540002 – measurement of Zcm

Low power Guanella 1:1 balun with low Insertion VSWR using a pair of Fair-rite 2631540002 suppression sleeves – design workup presented a desk design of a low power balun. This article presents measurement of common mode impedance Zcm of a prototype using a nanoVNA.

Above is the prototype 2631540002×2 wound with 3.5t of RG316. Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2×2631540002 – measurement of Zcm

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – measurement of Zcm

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – design workup presented a desk design of a low power balun. This article presents measurement of common mode impedance Zcm of a prototype using a nanoVNA.

Above is the prototype 2843009902 binocular wound with 3.5t of RG316. Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – measurement of Zcm