I have written a few articles on fixtures for adapting the device under test (DUT) to an antenna analyser’s coax jack.
Antenna analysers come with a range of connectors, the UHF connector is very popular, perhaps less so are N-type, SMA and BNC.
I use a range of fixtures made to suit specific applications, but the most flexible are the two shown in the following pic.
Above are two adapters: Continue reading Antenna analyser – what if the device under test does not have a coax plug on it?
I recently came across an article Signal level measurement with PowerSDR and external transverters in which Carol (KP4MD) details a set of measurements of a Flex 1500 transceiver and Electraft XV144 transverter.
Carol gives the following table of measurements and calculated results.
|Table 1. Transverter Measurements
|50 Ω expected
Lets focus on the 144MHz measurements. Continue reading Noise Figure measurement of a converter / transverter
(Franklin 1924) described a technique to cophase sections of a long antenna by “concentrating alternating half wave length portions of the wire within a small space, by winding such portions as inductance coils or by doubling such portions back on themselves so that there is practically no radiation from these portions”.
Let’s explore his second option, as unlike the first, it does work reliably.
Above is an NEC-4.2 model with current shown (magnitude and phase). The stubs conductors are all defined from top to bottom. Continue reading Franklin antenna – how does it work?
A reader of End Fed Half Wave matching transformer – 80-20m asked if a good transformer could be made with with a FT114-43 core.
The original transformer above comprised a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. Continue reading End Fed Half Wave matching transformer – 80-20m – LO1238 variant
A reader of End Fed Half Wave matching transformer – 80-20m asked if a better transformer could be made with a stack of 2 x FT240-43 cores and using half the turns.
The original transformer above comprised a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. Continue reading End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant
The Ferrite permeability interpolations calculator performs interpolations of tables of complex permeability data.
From manufacturer’s curves
Some of the data is derived from manufacturer’s published complex permeability curves. The plot above shows the Ferroxcube’s published curve for 3C81 material, and points at which it was digitised to extract a table of µ’ and µ”. Continue reading Online calculator of ferrite material permeability interpolations – more detail
Recently I have had difficult reaching the local DMR repeater on 70cm, and needed to check that the antenna system had not deteriorated.
I took a baseline measurement with an AA-600 after some refurbishment work in Jan 2018, and was able to compare a current sweep to that baseline.
Above, a wide Return Loss sweep of the Diamond X-50N with feed line compared to the baseline (the thin blue line). Continue reading Diagnosing a possible antenna problem by comparison with a baseline
A chap seeking details for a matching inductor for his 5/8λ vertical on 20m reported “my AA54 RigExpert analyser gives the following reading (SWR 8,2). (R 81,5). (X -158) ” measured looking into a “length of rg58 about 15-20 cm” and asked “is the inductor coil going to be enough or will I need an L match to bring the real resistance to 50 ohms”. Continue reading Matching a 5/8λ ground plane – a single stub tuner example
Some time ago I wrote some articles on so-called Coax Traps, and an example design of an Inverted V dipole for 80 and 40m.
A coax trap (before cross connection).
The whole subject of trapped antennas elicits a lot of online discussion that is often more about semantics than understanding. Continue reading Trapped dipole
I am asked about my use of the term
Distortionless Lines from time to time, often in the vein of
they don’t exist, so why discuss them?
The concept derives from the work of Heaviside and others in seeking a solution to distortion in long telegraph lines.
The problem was that digital telegraph pulses were distorted due to different attenuation and propagation time for different components of the square waves.
Heaviside proposed that transmission lines could be modelled as distributed resistance (R), inductance (L), conductance (G) and capacitance (C) elements.
In each incremental length Δx, there is incremental R, L, G and C. Continue reading Do Distortionless Lines exist?