A low cost home made USB CI-V interface with open collector and solid Windows drivers

This article describes an inexpensive USB adapter for Icom’s CI-V interface.

There are four common options for USB-serial adapters:

  • Prolific;
  • FTDI;
  • WCH; and
  • Silabs.

This article describes an adapter based on an inexpensive FTDI adapter (~$5 on eBay).

opc478ftdi01

You will need the module, a Schottky signal diode (eg 1N5711), wire and a 3.5mm TRS plug or two. I have connected two plugs, one wired for TS (CT-17) and one for RS (OPC-478x). Continue reading A low cost home made USB CI-V interface with open collector and solid Windows drivers

Voltage and current on a transmission line with standing waves

Folk often ask how to calculate the maximum voltage on an antenna feed line with standing waves, often to get a feel for the necessary voltage withstand of baluns, feed line, switches and relays, and ATUs.

Feeding at a current maximum outlines the method described in detail at (Duffy 2011), but the approach is more complex than a lot of hams want.

A simpler method is to treat the transmission line as lossless, and to simply find the worst case voltage and current that can occur… and design for that, or perhaps do the more detailed analysis depending on the outcome.

A new calculator, Calculate Vmax, Vmin, Imax, Imin for lossless line from Zload (or Yload) and Zo, does just that.

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Above is the built-in example of a G5RV with tuned feeder on 80m with feed point impedance derived from a modelling package. The voltage and currents calculated are those for a long lossless feed line.
Continue reading Voltage and current on a transmission line with standing waves

Exploiting your antenna analyser #12

Is there a place for UHF series connectors in critical measurement at UHF?

Seeing some recent discussion by a chap who was trying to construct a low power 50Ω termination on a UHF series plug, it bought to mind the futility of using some kinds of connector for critical measurement above perhaps 100MHz.

There is a lot of conjecture about the nature of UHF series connectors, whether they act line a simple transmission line section with fairly uniform Zo, whether they are really just a lumped shunt capacitance, whether it is even important at UHF etc.

To illustrate the issue, I have assembled a simple test jig comprising an N(M)-UHF(F) adapter, UHF(M)-N(F) adapter and a 50Ω N termination (which was also used to calibrate the analyser. This set was assembled and plugged onto a calibrated AIMuhf analyser and swept from 1-500MHz… just into the UHF range (which is 300-3000MHz).

UhfTL

Above, the test jig.

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Above is an expanded scale centre of the Smith chart of the sweep. Continue reading Exploiting your antenna analyser #12

Exploiting your antenna analyser #11

Backing out transmission line

Often we make measurements through a section of transmission line, and the measurements are wrt the reference plane, which for many analysers is the connector on the instrument.

Some analysers, or their associated software allow the effects of the transmission line to be backed out.

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Above is a Smith chart view of measurement of a test antenna through some length of RG58. The antenna will have R<50Ω at minimum VSWR, so the angle of the complex reflection coefficient Γ will be close to 180° at the feed point. Antscope uses a different notation, but shows here the angle at the point of measurement to be -15.1°, so we need to increase it by 180–15.1=195.1°, which will take about half that electrical length of line, 97.6°. From TLLC, I calculate the length involved is 7.6m of RG58, which is an estimate that gives a starting point for backing out the cable. Continue reading Exploiting your antenna analyser #11

Is maximum power transfer and conjugate matching simultaneously possible

A reader has asked the question in a transmission line context after reading Walter Maxwell’s teachings on system wide conjugate matching.

In the real world, transmission lines have loss and almost always, the nature of that loss will mean that Zo is not purely real.

The answer to the question depends on whether or not there are standing waves on the transmission line.

Nothing in this article is to imply that a transmitter is well represented by a Thevenin equivalent source. Continue reading Is maximum power transfer and conjugate matching simultaneously possible

Exploiting your antenna analyser #10

Measuring an RF inductor

This article walks through practical measurement of a ferrite toroidal inductor using an antenna analyser.

To be relevant practically, lets use an example from N4SPP’s end fed wire antenna on 3.6MHz. His coupling transformer uses a two turn winding on an FT240-43 core for the nominal 50Ω connection to the antenna system.

We could calculate the impedance of this winding using one of the plethora of online and desktop inductance calculators, but lets first fetch the data from the manufacturer.

Screenshot - 29_12_2015 , 11_05_50 AM

A simple statistic that is widely used is Al, and above, Fair-rite gives Al=1075nH +/-20%. Note that although they give a tolerance of +/-20%, it is not uncommon that manufactured product has greater error, they may have optimistically quoted the standard deviation and it is easy to fall outside that (37% chance). Continue reading Exploiting your antenna analyser #10

Exploiting your antenna analyser #9

Disturbing the thing you are measuring

In all measurements, we need to be careful that the measurement does not disturb the thing being measured.

This article explores an example where the instrument measurements appear wrong.

The story starts with a mobile antenna that the transceiver indicates has very high VSWR over the 40m band, though starts to decrease towards 7.350MHz.

To assist in problem identification / tuning, the antenna connector is disconnected from the radio and connected to the AA-600 analyser and a sweep taken.

Screenshot - 16_12_2015 , 5_03_16 PM

Above is the sweep, but it is quite inconsistent with the transceiver’s VSWR meter readings. The plot above looks good, a little adjustment of the tip would get it down to 7.060… but the transceiver does not see it that way. Continue reading Exploiting your antenna analyser #9

Exploiting your antenna analyser #8

Finding resistance and reactance with some low end analysers

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There are some analysers on the market that do not display reactance X or even magnitude of reactance |X| and possibly resistance, but do display VSWR and magnitude of impedance |Z|. Continue reading Exploiting your antenna analyser #8

Walter Maxwell’s teachings on system wide conjugate matching

Walt Maxwell (W2DU) made much of conjugate matching in antenna systems, he wrote of his volume in the preface to (Maxwell 2001 24.5):

It explains in great detail how the antenna tuner at the input terminals of the feed line provides a conjugate match at the antenna terminals, and tunes a non-resonant antenna to resonance while also providing an impedance match for the output of the transceiver.

Walt Maxwell made much of conjugate matching, and wrote often of it as though at some optimal adjustment of an ATU there was a system wide state of conjugate match conferred, that at each and every point in an antenna system the impedance looking towards the source was the conjugate of the impedance looking towards the load.

This is popularly held to be some nirvana, a heavenly state where transmitters are “happy” and all is good. Happiness of transmitters is often given in online discussion by hams as the raison d’être for ATUs . Continue reading Walter Maxwell’s teachings on system wide conjugate matching

Exploiting your antenna analyser #7

Application to a loaded mobile HF whip

This article explores application of an antenna analyser to a helically loaded 7MHz mobile whip that has an adjustable length tip for tuning.

The task at hand is to ‘tune’ the antenna to a desired operating frequency.

The analyser used is a Rigexpert AA-600, but the article deals more generally with analyser features.

Initial measurement and interpretation

Screenshot - 11_12_2015 , 3_02_53 PM

Above is a plot of R, X, and |Z| measured at the cable connector that plugs onto the transmitter. Ignore |Z|, it is irrelevant and confusing but unfortunately a ‘feature’ of the Rigexpert software that cannot be disabled. Continue reading Exploiting your antenna analyser #7