Category: Amateur Radio

The sign of Return Loss

I was browsing a ham forum recently when I came across a Return Loss plot apparently from a ham grade miniVNA Tiny.

Lets just remind ourselves of the meaning of the term Return Loss. (IEEE 1988) defines Return Loss as:

(1) (data transmission) (A) At a discontinuity in a transmission system the difference between the power incident upon the discontinuity. (B) The ratio in decibels of the power incident upon the discontinuity to the power reflected from the discontinuity. Note: This ratio is also the square of the reciprocal to the magnitude of the reflection coefficient. (C) More broadly, the return loss is a measure of the dissimilarity between two impedances, being equal to the number of decibels that corresponds to the scalar value of the reciprocal of the reflection coefficient, and hence being expressed by the following formula:

20*log10|(Z1+Z2)/(Z1-Z2)| decibel

where Z1 and Z2 = the two impedances.

(2) (or gain) (waveguide). The ratio of incident to reflected power at a reference plane of a network.

Return Loss expressed in dB wrt a real reference impedance will ALWAYS be a positive number in passive networks.

Return Loss according to the miniVNA Tiny

clip-220

Above, the miniVNA Tiny presents Return Loss as a negative value. Continue reading The sign of Return Loss

Last update: 1st July, 2019, 5:45 AM

Is the premises main earthing conductor ok as a lightning down conductor

Upon reading Rationale for sizing of lightning down conductor a correspondent asks whether his premises 4mm^2 main earthing conductor ok as a lightning down conductor.

Intended purpose of electrical installation ground electrode

The usual source of current on the premises main earth conductor would be a fault energised by the incoming supply. To understand the implications, lets review the supply system. Continue reading Is the premises main earthing conductor ok as a lightning down conductor

Last update: 22nd September, 2016, 1:14 PM

Rationale for sizing of lightning down conductor

The lightning ground conductor shown at Mast ground rework might at first seem excessive, this article sets out the rationale.

GroundRod02

The connection to a 2.4m copper clad steel driven electrode (under the green cover) is 35mm^2 copper.

The nature of lightning protection sizing

Lightning protection sizing is a risk management regime driven by the mechanisms of lightning and variation in distribution.

It is not surprising then that regulatory standards in different distributions broadly use similar design methods but set different practices for implementation in the jurisdiction.

So, let’s go standards shopping… what we are looking for is guidance on the energy (or work) that is directed to heating the down conductor, and choosing a conductor size that will sustain not just a single stroke, or an average stroke, but most events that may include many strokes in a short period of time. Continue reading Rationale for sizing of lightning down conductor

Last update: 23rd September, 2016, 12:33 PM

Command adapter for JRC NFG-170 NFG-230 ATU

EA2BQH described an adapter to use a JRC NFG-170 / NFG-230 ATU.

The description is in Spanish, and a Google translation doesn’t help me much, his published HEX file for a PIC12C508A helps more.

Building the device and observing the output, it seems to have two input pins and when one is high OR the other is low, it sends a ASYNC command string at 1200Bd on its output pin. The command string is repeated every 2.5s if the input condition remains. This string appears to command the ATU to review / retune.

The 12C508A is a very old chip, still available, but in low cost form, an OTP.

I have written some code for a PIC12F510 from the ground up to do a similar thing as far as I can see, and built an adapter for testing by VK1EA.

Redesign

My redesign uses different pins to the original to better cater for ISCP and to utilise weak pullup as much as feasible. IN1 is pin3 (GP4), IN2 is pin4 (GP3), TX is pin5 (GP2). IN1 OR /IN2 causes the adapter to send the configuration command. The output (TX) is open collector.

JrcAtu01

 

Above, a view of the adapter from chip side encapsulated in heatshrink and a patch of double sided adhesive foam to fix it in the ATU. Pin3 is wired to ground, Pin4 (IN2) is green, TX is yellow, ground is black and VDD (5V) is red. The TX pin is wired to pin 6 of the opto isolatorC next to the input terminal block TB1 on the ATU. (It may be possible to cut a track and insert the module after the opto isolator. Continue reading Command adapter for JRC NFG-170 NFG-230 ATU

Last update: 1st September, 2020, 7:38 AM

Demonstration video of Cadweld Oneshot Plus ground rod connection

I showed in Mast ground rework the use of a Cadweld Oneshot Plus thermite weld of the ground conductor to the ground rod.

Responding to reader interest, I have made a little video demonstrating the process.

cadweld21

Above is a pic of the demonstration piece with crucible and slag broken away. Continue reading Demonstration video of Cadweld Oneshot Plus ground rod connection

Last update: 21st September, 2016, 6:40 PM

AD9850 / AD9851 initialisation using PllLdr

A note on using PllLdr with AD9850/51 DDS chips.

PllLdr is a generic microcontroller to load a PLL chip’s configuration registers using SPI. SPI is used by many PLL and DDS chips, data format and content varies from chip to chip.

ad5890module

The AD9850 powers up in parallel load mode, and AD gives advice on how to get it into serial load mode (as you would use with PllLdr). Continue reading AD9850 / AD9851 initialisation using PllLdr

Last update: 27th June, 2020, 7:44 AM

ADF4351 / PllLdr checkout

PllLdr is a generic microcontroller to load a PLL chip’s configuration registers using SPI. SPI is used by many PLL and DDS chips, data format and content varies from chip to chip.

This article documents checkout on an ADF4351 PLL chip. The ADF4351 is a wideband INT-N / FRAC-N synthesiser with integrated VCO, output covers 36-4400MHz (continuous).

The test was made on an inexpensive module purchased on eBay for about A$33 posted.

ads4351-pllldr01

Above is the test frame. At the left is a PllLdr prototype running on 5V, then a 4 channel 5V/3.3V  level converter, the ADF4351 module and at the right a power supply board. The level converter is not needed if the PllLdr chip was run on 3.3V, it was used to test a ‘worst case’ scenario.

adf4351-01

Above, a close up of the board.

adf4351-02

As can be seen, the connectors are not designed for the 0.8mm PCB used, and the right hand connector has not been connected to the track. Chinese ‘quality’.

The onboard 25MHz crystal oscillator was used as the reference, but a 10MHz reference from a GPSDO could be used for high accuracy. Continue reading ADF4351 / PllLdr checkout

Last update: 15th September, 2016, 11:52 AM

Effective RF resistance of a braided solenoid – Gilbert’s coil measurements

(Gilbert 1996) gave a set of measurements of impedance of several inductors wound as a single layer close spaced solenoid of RG-213 coaxial cable.

Of particular interest is the measurements of the 6t solenoid as there are several measurements well below the self resonant frequency of the inductor.

Key geometry details used in this analysis are:

  • cable OD 10.287mm;
  • conductor OD 8mm;
  • mean solenoid diameter 117.4mm (ASTM D-2729 pipe + RG-213);
  • cable length 2.213m; and
  • solenoid length 6*10.287mm.

clip-218Above is a plot of Gilbert’s measurements from 1 to 5MHz, and curve fits.
Continue reading Effective RF resistance of a braided solenoid – Gilbert’s coil measurements

Last update: 14th September, 2021, 12:05 PM

Mast ground rework

When I moved here about eight years ago, I quickly installed a small mast and associated ground system for the station. The grounding of the mast itself for lightning protection was a temporary solution, and less temporary than planned. This article documents the rework.

GroundRod01Above is the temporary solution. A 2.4m copper clad ground rod was driven into the clay, and a couple of short 25mm^2 tails connected to the mast tube. The long term solution was to be tidier and allow the mower / brushcutter to be used to trim grass without fouling the earth rod or cables.

The plan is to cut to bent top of the earth rod, drive it below ground level, and make a new tail of 35mm^2 (#2) cable and Cadweld it to the ground rod. Continue reading Mast ground rework

Last update: 23rd January, 2017, 9:08 PM