Pawsey Balun – what is it good for?

The Pawsey Balun (or Pawsey Stub) is described as a device for connecting an unbalanced feed to a balanced antenna.

Above is a diagram of a Pawsey Balun used with a half wave dipole (ARRL).

Pawsey Balun on an asymmetric load reported model results in an asymetric dipole antenna, and showed very high common mode feed line current.

Pawsey Balun on an asymmetric load – bench load simulation showed that although the Pawsey balun is not of itself an effective voltage balun or current balun, it can be augmented to be one or the other.

So, you might ask what they do, what they are good for, and why they are used. Continue reading Pawsey Balun – what is it good for?

Last update: 9th May, 2019, 8:23 AM

Pawsey Balun on an asymmetric load – bench load simulation

The Pawsey Balun (or Pawsey Stub) is described as a device for connecting an unbalanced feed to a balanced antenna.

Pawsey Balun on an asymmetric load reported model results in an asymetric dipole antenna, and showed very high common mode feed line current.

This article looks at two test bench configurations modelled in NEC.

The configurations are of a horizontal Pawsey balun for 7MHz constructed 0.1m over a perfect ground plane. The ‘balanced’ terminals are attached to the ground plan by two short 0.1m vertical conductors which are loaded with 33 and 66Ω resistances. At the other end, the horizontal transmission line is extended by two different lengths and connected to the ground plane using a 0.1m vertical conductor. The two extension lengths are almost zero and a quarter wavelength.

Zero extension

The total horizontal length from the ‘balanced terminals’ to the grounded end of the transmission line is a quarter wavelength for the Pawsey balun and a further 20mm making approximately a quarter wavelength in total.

Above is a plot of current magnitude and phase from 4NEC2. The current on the two vertical conductors containing the 33 and 66Ω loads is quite different, and the product gives load voltages that are approximately equal in magnitude and opposite in phase. Continue reading Pawsey Balun on an asymmetric load – bench load simulation

Last update: 8th May, 2019, 7:28 PM

Pawsey Balun on an asymmetric load

The Pawsey Balun (or Pawsey Stub) is described as a device for connecting an unbalanced feed to a balanced antenna.

Above is a diagram of a Pawsey Balun used with a half wave dipole (ARRL).

Whilst these have been quite popular with VHF/UHF antennas, the question arises as to how they work, and whether they are effective in reducing common mode current IIcm) for a wide range of load scenarios. Continue reading Pawsey Balun on an asymmetric load

Last update: 10th May, 2019, 3:33 PM

Nagoya NA-771 2m/70cm antenna

Around 10 years ago, a friend gave me a Nagoya NA-771 2m/70cm antenna to suit hand held radios for the purpose of testing it. He had bought two of them on eBay for around $10 each.

These are often sold without specifications, but where specifications are given, VSWR is given as 1.5, though not stated as maximum so should perhaps be read as typical.

This article looks at 2m performance alone.

2008 purchase

Above is a VSWR sweep around the 2m band.
Continue reading Nagoya NA-771 2m/70cm antenna

Last update: 7th May, 2019, 2:27 PM

Capacity test of aftermarket NB-6L batteries #2

I purchased a further two replacement batteries type NB-6L for a Canon camera from yet another supplier.

Above, the batteries are labelled 1000mAh. They appear to be well made externally, and fit charger and camera fine.

Note that these have different labeling to that shown in the eBay listing. It is naive to expect that the supplied item matches either pics or description, bait and switch is a standard Chinese technique. Continue reading Capacity test of aftermarket NB-6L batteries #2

Last update: 3rd May, 2019, 3:52 PM

A balun puzzle – discussion

A balun puzzle asked several questions of this VK5AJL balun which was cited online.

  • Under what circumstances is the current into one terminal of the secondary significantly different to the current out of the other terminal of the secondary?
  • Is this in fact a better current balun than voltage balun under some conditions? What?
  • Is it a good voltage balun?

Continue reading A balun puzzle – discussion

Last update: 1st May, 2019, 5:54 PM

Capacity test of aftermarket NB-6L batteries

I purchased two replacement batteries type NB-6L for a Canon camera.

Above, the batteries are labelled 1050mAh. They appear to be well made externally, and fit charger and camera fine.

Note that these have different labeling to that shown in the eBay listing. It is naive to expect that the supplied item matches either pics or description, bait and switch is a standard Chinese technique. Continue reading Capacity test of aftermarket NB-6L batteries

Last update: 3rd May, 2019, 3:57 PM

Measuring balun common mode impedance – #3

A correspondent having read my series Measuring balun common mode impedance – #1 related difficulties with his Rigexpert AA-230Zoom.

The articles showed some techniques for measuring common mode impedance of a current balun.

The following examples are of a test choke wound on a BN43-202 binocular core, and the results are quite similar to what might be expected of a broadband HF current balun. The measurements were made with a Rigexpert AA-600.

Above, the measurement result using RigExpert’s newest software Antscope2. Continue reading Measuring balun common mode impedance – #3

Last update: 12th April, 2019, 7:09 AM

Small common mode choke for analyser antenna measurements using 2843000202 (BN43-202)

The project is design, implementation and test of a small common mode choke for use with an analyser for antenna measurements.

The choke must have medium to high Zcm from 1 to 30MHz. It is intended to be used with analysers supporting SOL calibration, so effectively any impedance transformation within the fixture is compensated and the reference plane is the load side terminals of the device.

The candidate core is a low cost #43 binocular ferrite core that is fairly easy to obtain.

Above is a first pass check of the likely Zcm at 1.8MHz using a Fair-rite 2843000202 (BN43-202) binocular core. These chokes have relatively low self resonance frequency so a value for Cs is supplied that delivers self resonance at around 5MHz. Zcm at 1.8MHz needs 8-9t, 8.5t will be used (ie the twisted pair enters one end of the binocular and leaves the other end for convenient layout). (8.5t is not strictly correct, but it is a close approximation in this case.)
Continue reading Small common mode choke for analyser antenna measurements using 2843000202 (BN43-202)

Last update: 8th April, 2019, 7:27 AM