owenduffy.net – Page 84 – Mostly electronics…

Exploiting your antenna analyser #17

Optimising a G5RV with hybrid feed

(Varney 1958) described his G5RV antenna in two forms, one with tuned feeders, and the more popular form with hybrid feed consisting of a so-called matching section of open wire line and then an arbitrary length of lower Zo coax or twin to the transmitter.

(Duffy 2005) showed that the hybrid feed configuration is susceptible to high losses in the low Zo line as it is often longish, is relatively high loss line and operates with standing waves. Varney did offer two options for the low Zo line: any length 72Ω twin or coax. Continue reading Exploiting your antenna analyser #17

Last update: 9th May, 2016, 10:37 AM

Fox flasher MkII – high power 2 LED solar powered beacon

Fox flasher MkII – owenduffy.net described an animal deterrent based on an STC 8051 microcontroller and running from a single LiPo cell.

This article describes a further development using a solar cell, shunt regulator, 1S LiPo cell with protection board, and two high power red LEDs.

Above, the unit constructed in a medium size Jiffy box, and a 6V 0.6W PV panel fixed to the top with silicone adhesive. The LDR is fixed to one end with silicone adhesive.

Two SM 1W red LEDs are fitted to opposite sides. They are 120° LEDs, the holes are countersunk to provide for light dispersion and the LEDs clamped to the inside with small brass brackets and heat sink rubber, a little silicone adhesive seals the holes. Continue reading Fox flasher MkII – high power 2 LED solar powered beacon

Last update: 22nd June, 2016, 3:28 PM

Exploiting your antenna analyser #16

Measure inductor using SOL calibration

At Measuring balun common mode impedance I showed a method of backing out the effects of a text fixture using the “subtract cable” facility of Antscope software with the Rigexpert AA-600.

Some analysers (including the AA-600) support SOL calibration of the instrument itself, and some support SOL calibration using the client software (Antscope in this case). This article demonstrates use of Antscope with SOL calibration to measure a small RF inductor which has similar characteristic to good Guanella 1:1 HF baluns.

The text fixture used for this demonstration is constructed on a SMA(F) PCB connector using some machined pin connector strip, and SMA(M)-SMA(M) and N(M)-SMA(F) adapters to connect to the AA-600.

Above is a pic of the test inductor in the test fixture with adapters. The test inductor 6 turns of 0.5mm PVC insulated wire wound on a BN43-202 binocular balun core. Continue reading Exploiting your antenna analyser #16

Last update: 16th October, 2020, 6:59 AM

Improved cooling for the ATR-30

In Improved cooling for the MFJ-949E I described a solution to a problem of demonstrated overheating of the ATU at rated power, indeed at a lot less than rated power.

Though I have never measured the ATR-30 temperature rise, and am probably unlikely to stress the 3kW rated ATU with a 100W transmitter, I have performed a similar cooling modification to the ATR-30.

Continue reading Improved cooling for the ATR-30

Last update: 29th April, 2016, 7:04 AM

On use of enameled wire in transmitting baluns

I have published a number of transmitting balun designs, and none of them use enameled wire. I am sometimes asked why is that so, but more often advised that it is a better solution than the wires that I have used.

enameled wire depends on an insulating coating, and its breakdown voltage depends on the wire diameter, polymer used, the minimum thickness applied, coating cure / bake processes, temperature, humidity etc.

Whilst I have seen specifications promising breakdown voltage of a single round enameled wire in the regions of 5-10kV, and you might hope for nearly double that between a pair of twisted wires, unless you have sourced specific product, new performance may be closer to 2kV. Continue reading On use of enameled wire in transmitting baluns

Last update: 27th January, 2021, 10:27 AM

Exploiting your antenna analyser #15

Measure MLL using the half ReturnLoss method – a spot test with a hand held analyser

At Exploiting your antenna analyser #14 I gave an explanation of the method of approximating MLL of a line section by taking the average half Return Loss with o/c and s/c terminations.

This article demonstrates the technique using the Rigexpert AA-600 analyser in hand held mode.

The task is to assess whether a section of RG58A/U coax has MLL at 3.5MHz similar to specification or not.

The specification loss of 10.13m of RG58A/U has MLL=0.29dB.

Above, the first test with an o/c termination. Return Loss is 0.4dB. Continue reading Exploiting your antenna analyser #15

Last update: 25th April, 2016, 10:16 AM

Assessing the Q of a half wave dipole antenna system – a real world example

Assessing the Q of a half wave dipole antenna system explained that Q can be a valuable indicator of antenna system health.

This article uses a recently published VSWR curve for a 15m half wave dipole antenna system as an example to demonstrate the technique.

The following graph is from a Sark100 style antenna analyser, and it is quite a poor start to diagnostics, but using it draws out what is desired for further analysis.

Above, the captured VSWR(50) sweep. Continue reading Assessing the Q of a half wave dipole antenna system – a real world example

Last update: 25th April, 2016, 10:17 AM

Assessing the Q of a half wave dipole antenna system

Q can be a valuable indicator of antenna system health

The Q of an antenna can be a useful statistic in assessing whether it is operating as it should.

The Q of half wave dipole antenna system on HF depends to some extent on conductor size, its environment (height, type of ground, nearby structures and vegetation, and feed line / matching loss. Nevertheless, it should usually fall in the range of 10 to 13 for good wire dipoles, and if you measure a half wave dipole antenna system to have Q significantly outside that range, it is probably significantly less efficient than it should be. Continue reading Assessing the Q of a half wave dipole antenna system

Last update: 23rd April, 2016, 7:52 AM

Field strength survey of an M40-1 short helical vertical on 40m

This article documents a field strength survey of an M40-1 short helical vertical on 40m.

This test is more a feasibility study of the experimental method and apparatus than an absolute measure of the antenna.

The antenna under test is described at AUT – MobileOne M40-1 40m helical.

Field strength was measured using a small square untuned loop and VK3AQZ RF power meter (RFPM1), and data was captured using A prototype data logger for RFPM1.

Power meter

VK3AQZ RF power meter (RFPM1) described my build and calibration of the RFPM1.

Above is the RFPM1, shown with two probes, but only one probe is required for this procedure, the other is disconnected. The RFPM1 directly reads input power in dBm.

Loop antenna

The loop antenna used was described at (Duffy 2007). It is a small square loop (600mm sides) fed in one corner with a 1:1 voltage balun. Continue reading Field strength survey of an M40-1 short helical vertical on 40m

Last update: 15th March, 2020, 4:25 PM

USB-A to DC 5.5/2.1mm power cable – current carrying capacity

The growing popularity of 5V plug packs and Li-ion power banks with USB A connectors provides a convenient source of power for some projects, and a USB-A to 5.5/2.1mm DC cable is a possible connection option.

Scouring eBay turned up some sources, but one can never assess the quality of the things because usually there are no meaningful specification offered, and lets face it, they are Chinese.

Above are two sample 1m cables that I purchased, the left one for about A$1, and the right for about A$3.50 (posted).

Loop resistance of the cables was measured with Kelvin probes to assess their current carrying capacity from a voltage drop perspective.

DC loop resistance of the one on the right was 0.16Ω, so the maximum current for a 5% voltage drop is 5*0.05/0.16=1.6A… not quite a 2A rating.

DC loop resistance of the one on the left was 3.3Ω, so the maximum current for a 5% voltage drop is 5*0.05/3.3=0.075A… not even a 100mA rating.

This is not surprising, experience with USB-A to USB-micro cables has revealed similar variation, and an explanation why so many of these cables are hopeless in battery charging applications.

Last update: 20th April, 2016, 7:52 AM