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

Exploiting your antenna analyser – contents

A convenient list of ‘Exploiting your antenna analyser’ and short subject sub-titles, a table of contents for the series as it grows.

Exploiting your antenna analyser #22 Predicting peak voltage at a point from analyser measurements

Exploiting your antenna analyser #21 K0BG’s advice on tuning mobile whips

Exploiting your antenna analyser #20 – Finding resistance and reactance with some low end analysers #2

Exploiting your antenna analyser #19 – Critically review your measurements

Exploiting your antenna analyser #18 – Measure velocity factor of open wire line

Exploiting your antenna analyser #17 – Optimising a G5RV with hybrid feed

Exploiting your antenna analyser #16 – Measure inductor using OSL calibration

Exploiting your antenna analyser #15 – Measure MLL using the half ReturnLoss method – a spot test with a hand held analyser

Exploiting your antenna analyser #14 – Insertion Loss, Mismatch Loss, Transmission Loss

Exploiting your antenna analyser #13 – Insertion Loss, Mismatch Loss, Transmission Loss

Exploiting your antenna analyser #12 – Is there a place for UHF series connectors in critical measurement at UHF?

Exploiting your antenna analyser #11 – Backing out transmission line

Exploiting your antenna analyser #10 – Measuring an RF inductor

Exploiting your antenna analyser #9 – Disturbing the thing you are measuring

Exploiting your antenna analyser #8 – Finding resistance and reactance with some low end analysers

Exploiting your antenna analyser #7 – Application to a loaded mobile HF whip

Exploiting your antenna analyser #6 – Shunt match

Exploiting your antenna analyser #5 – Measure MLL using the Rin where X=0

Exploiting your antenna analyser #4 – Measure MLL using the half ReturnLoss method

Exploiting your antenna analyser #3 – The sign of reactance

Exploiting your antenna analyser #2 – Reconciling the single stub tuner results

Exploiting your antenna analyser #1 – I often see posts in online fora by people struggling to make sense of measurements made with their antenna analyser

 

Exploiting your antenna analyser #16

Measure inductor using OSL 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 OSL calibration of the instrument itself, and some support OSL calibration using the client software (Antscope in this case). This article demonstrates use of Antscope with OSL 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.

Aa600Fix02

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 BN-43-202 binocular balun core. Continue reading Exploiting your antenna analyser #16

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

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.

HRL01

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

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.

Vswr15m

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

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

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.

RFPM00Above 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

Clip 071

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

A generic run on timer using an ATTINY25

At Improved cooling for the MFJ-949E I described a modification to the ATU to improve its cooling using a fan and run on timer.

The run on timer described was based on a Chinese STC15F104E DIP8 8051 like microcontroller.

Because the programming tools for the STC chips work so poorly, and the lack of documentation of their protocol, there is no simple way to update only the calibration data in EEPROM. I have ported the algorithm to an ATTINY25 which doesn’t cost a lot more but had a much better development environment and a range of tools to allow EEPROM update without overwriting the FLASH image, and as well it will run my bootloader, ATB.

This article describes a generic run on timer based on an Atmel AVR chip, a ATTINY25 though the code will also run in ATTINY45 and ATTINY85.

ROT001

The circuit is very simple, the DC output from the forward power detector is connected to the input pin which turns the BC548C transistor on at input voltage greater than about 0.7V. The high value of base resistor ensures very light loading of the forward power detector.
Continue reading A generic run on timer using an ATTINY25

Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #6

Sixth part in the series documenting the design and build of a Guanella 1:1 (current) balun for use on HF with wire antennas and an ATU.

This article documents measurement of impedance.

Impedance measurement

AEP01

The antenna system is a G5RV with tuned feeders (9m of home made 450Ω open wire). The tuned feeders terminate on the balun described in this series, and it is located on the outside of the antenna feed entrance panel shown above. Continue reading Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #6