DL4YHF 50MHz counter on a Chinese TB-244746 PCB

DL4YHF published a frequency counter design based on the PIC16F628.

The design has been modified by many, copied by even more, and usually without attribution.

This article documents one of these copies (TB-244756 printed under the chip footprint), a $6 kit off eBay which comes with no documentation, though the screen mask is enough to correctly place components.

It turns out to be DL4YHF’s “DISPLAY_VARIANT 2”, the variation is that it uses a common cathode display.

Above the built kit with the 7550 voltage regulator replaced with a 78L05. Continue reading DL4YHF 50MHz counter on a Chinese TB-244746 PCB

“No short antenna is more efficient than a resonant-length antenna”

A recent online posting asserted that an antenna is optimal when itself resonant, and fed with a resonant feed line length so delivering a purely resistive load to a source, and further that implementors needed to be careful that a shorter dipole could be offset to some extent by a longer feed line but it would be inferior because:

no short antenna is more efficient than a resonant-length antenna

… but does that stand scrutiny?

An NEC experiment

Lets walk though an experiment using NEC-4.2 models of a dipole of 2mm copper wire at 10m height at 7.1MHz over average ground (0.005,13).

Key assumptions:

  1. source has a Thevenin equivalent source impedance of 50+j0Ω;
  2. feed line is lossless.

The results are sensitive to the model assumptions.

We will calculate the ratio of radiated power to the power delivered by the transmitter to a matched load, let us call it TransmitEfficiency for the purposes of this article. Continue reading “No short antenna is more efficient than a resonant-length antenna”

Small untuned loop with MMIC LNA on 80m

This article documents a small experiment with a quite small untuned loop, and LNA and receiver on 80m to assess its ability to copy signals on the band as well as the station transceiver on large antenna.

A significant factor at 80m is that ambient noise is quite high. Let’s consult ITU P.372-12 for guidance.

Curve E is the median city noise, at 3.6MHz Fa is about 62dB. At a more detailed level, P.372-12 gives the median noise figure for Rural precincts at 51.8dB and that figure is more appropriate to the test location (large block rural residential).

The test was carried in a few spots, at 50-100 m from the main station dipole. Continue reading Small untuned loop with MMIC LNA on 80m

Review: magnetic stirrer with heating plate and digital display XB 85-2

I purchased a laboratory style stirrer / hotplate with PID temperature controller for some experiments.

Above, the 85-2 product from Chinese maker XB.

It certainly looks the part and for under $100 looked impressive value… but was it?

Is it safe?

First thing with ANY Chinese appliance is to test the electrical safety. Prior to a full PAT test, I plugged it in on an insulated work space and waved a non-contact voltage detector over the case. Beeeep! The case is hot. Earth continuity (earth pint to case) is zero, there is no connection. This came with an AU plug… so lets look inside at how they wired it up.

The green yellow earth wire is floating look, the end has been tinned so it was or was intended to be soldered to something. The end of one of the screws holding four rubber feet on is more silver coloured than the others, so it appears to have been tacked on to that. Three issues: the screw tension is cushioned by the rubber foot and pressure to case is low so it would not be a reliable low resistance connection; soldered ground connections can melt off in a fault and are unacceptable practice; and the even this had become disconnected and would not have passed a basic electrical test. Chinese Quality!

So with the cover off, it is apparent just a few months after this May 2017 dated build has been put together with rusty steel. Continue reading Review: magnetic stirrer with heating plate and digital display XB 85-2

Failure to treat impedance as a complex quantity leads to…

A ham recently posted a graph on QRZ to educate his fellow hams on the behaviour of transmission lines under mismatch.

Above is one of his graphs (the red arrow is my annotation). It plots Impedance variation along a mismatched 75Ω transmission line. The curves look graceful, but are they science or just pretty artwork? Continue reading Failure to treat impedance as a complex quantity leads to…

Demonstration of the GR1606B for antenna Z measurement and calcs

This article demonstrates use of a GR1606B RF impedance bridge for measurement of the feed point impedance of a MHz loaded mobile whip. The antenna is roof mounted on a vehicle and measurements are made looking into 4m of RG58C/U, then transformed to feed point impedance using three tools:

Key metrics are:

  • F=7.05MHz
  • R=35Ω
  • ReactanceDial offset=200
  • ReactanceDial=442
  • X=(442-299)/7.05=34.33Ω
  • Z=35+j34.33Ω;
  • Feed line is 4m of Belden 8262 (RG58C/U).

Continue reading Demonstration of the GR1606B for antenna Z measurement and calcs

First full week of Amaysim broadband Internet access

iiNet

Review of 10 months of iiNet broadband Internet access detailed a fairly disappointing performance record of our first NBN based service, a 12/1Mb/s FTTN service from iiNet.

With a perception that online performance had degraded and was unsatisfactory, the results of an automated half hourly file download were consulted to verify those perceptions.

Above is a plot of the 90 percentile and 10 percentiles for each week. Continue reading First full week of Amaysim broadband Internet access

4-20mA Pt100 input for the generic heating / cooling controller

The generic heating / cooling controller (hcctl) is a flexible bang-bang controller based on an ATTiny25.

The controller will accept 4-20mA input if the input is shunted by a 50Ω 1% resistor (2 x 50Ω 1% resistors is a practical implementation) and the 4-20mA sensor is wired between nominal +24 and the input pin. Note that 4-20mA sensors may operate properly on less than 24V (the one used here is a DIN rail mount that works for 10-24V).

 

To demonstrate the capability, a Pt100 RTD is connected to a 4-20mA converter and then to a hcctl test module (see above). The test module is driving a small incandescent lamp which is clipped to the RTD to provide a cycling test.

Continue reading 4-20mA Pt100 input for the generic heating / cooling controller

ESP8266 remote power display for energy monitor – EV3 – 5V display

ESP8266 remote power display for energy monitor – EV3 documented an evolved design for a real power display using emontx3 / emonhub / mqtt. This article documents an adaptation to use a 5V display module (for higher brightness). The ESP8266 is not 5V tolerant, so a logic level converter is needed.

Hardware

The remote power display uses a Wemos D1Pro module, a common 5V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit, and a common 3V/5V logic level converter between them.

Above, the Wemos D1Pro with wires attached to the HSPI and power pins. A 1k pull=down resistor is soldered between the D8 and GND pins under the D1Pro board. Continue reading ESP8266 remote power display for energy monitor – EV3 – 5V display

ESP8266 remote power display for energy monitor – EV3

ESP8266 remote power display for energy monitor and ESP8266 remote power display for energy monitor – EV2 documented a design and some variations for a real power display using emontx3 / emonhub / mqtt. This article documents an evolution to use the ESP8266 HSPI port for much higher speed writing of the LED display, high enough to be later adapted for multiplexed displays.

Hardware

The remote power display uses a ESP8266-12E devkit 1.0 module, a common 3.3V 4 digit 14.2mm seven segment LED module with 74HC595 shift register per digit. The particular LED module has sufficient space to mount the ESP8266 inside the module.

Above, the interior of the module that suits the implementation. Continue reading ESP8266 remote power display for energy monitor – EV3