Differential flux leakage in a Guanella 1:1 balun

This article has been copied as reference for a new article from my VK1OD.net web site which is no longer online. The article may contain links to articles on that site and which are no longer available.

I have been asked by a correspondent to comment in the context of my model of a Guanella 1:1 balun wound on a ferrite toroid (Duffy 2008a) on the impact of differential flux leakage as discussed in the ARRL 2011 Handbook on the predicted losses in a Guanella 1:1 balun using a ferrite toroidal core

ARRL

The ARRL 2011 Handbook (Silver 2011  20.23) states [i]f the line is made up of parallel wires (a bifilar winding), a significant fraction of the flux associated with differential current will leak outside the line to the ferrite core. Leakage flux can exceed 30% of the total flux for even the most tightly-spaced bifilar winding.

This might suggest that differential current will contribute significantly to balun core losses and consequently transmission loss. The claim is made without explanation or substantiation, or without making conclusions about any resultant loss. This is the makings of fear, uncertainty and doubt (FUD), and hardly the enlightenment that readers might expect. Continue reading Differential flux leakage in a Guanella 1:1 balun

DYS SN20A out of the box

I was intrigued by the seemingly endless stream of stories of woes with the DYS SN20A (eg RCTimer / DYS Mini SN20a / SN30a / SN40a esc), so I purchased one to see if they are all bad. Of course, impressions of a sample of size one are of somewhat limited value, but it seemed like an interesting thing to do.

Some reports of problems seem to relate to use of BLHeli on the ESCs, and it seems at least one beta release of BLHeli v14 had defects that resulted in serious damage in unprotected tests.

Discussion blames problems on front ends, flight controllers, wiring, motors, ESCs hardware, firmware, and bootloaders… but all these possible causes evident more so with this one ESC does not seem likely or logical. With the quest for more rapid FC loop response, there is a risk of instability and the drive may be working harder with oscillating demand, only logs from a flying craft will reveal what may be happening in that respect.

The test ESC

The DYS SN20A was purchased 14/06/2015 from RCTimer for about US$19 inc post. Not an inexpensive ESC by any means.

The DYS SN20A is described as an “opto” but I doubt it is optically coupled, it is probably just another instance of the fraud in terminology where opto refers to a BECless ESC. (If it were optically coupled, it would almost certainly not be a bidirectional servo interface and the SimonK bootloader would not work… but it did.)

SN20-01Above, the top view of an unwrapped SN20A. Continue reading DYS SN20A out of the box

Review of G3LDO STL (Radcom Sep 2010)

(Dodd 2010) describe a small transmitting loop (STL) and gave some meaningful performance measurements. It is rare to see such measurements and he is to be congratulated.

The loop is an octagon of perimeter 4.7m which at 14.2MHz is 0.224λ so although many will consider it meets the requirements of an STL, the common formula for radiation resistance Rr of a STL fail for perimeter above about 0.1λ (see Accuracy of estimation of radiation resistance of small transmitting loops).

Dodd gives calculations of one of the many simple loop calculators which gives Rr as 0.422Ω, it is probably closer to 160% of that value. This is an important quantity as it has direct bearing on calculated efficiency.

Dodd’s NEC model should have used a better figure for Rr, but it seems unlikely that the structural losses were fully included and its bandwidth prediction will be impaired.

G3LDO01

Above is Dodd’s measurement of antenna VSWR at 20m. This is most useful as it allows estimation of the half power bandwidth of the antenna. In this case, the antenna is not perfectly matched at its centre frequency, the residual VSWR is 1.07. The graph allows scaling off the VSWR=2 bandwidth as approximately 42kHz.
Continue reading Review of G3LDO STL (Radcom Sep 2010)

Helical loading and Calculate small transmitting loop gain from bandwidth measurement

Several correspondents have asked about the application of Calculate small transmitting loop gain from bandwidth measurement to the helically loaded small transmitting loop.

The helically loaded small transmitting loop appears to be the invention of K8NDS and is described at Stealth Antennas for the Radio Amateur and (K8NDS nd). It may not be a novel idea as it was analysed at (Maclean 1978).

Without getting too much involved in the inventor’s specious arguments which attribute magic properties to his antenna, this article focusses on whether / why the calculator will or will not provide valid results for the antenna.

At Stealth Antennas for the Radio Amateur he makes the statement

A solid copper tube “Magnetic Loop” exhibits a certain inductance per foot of the total circumference of the antenna.

The statement seems to belie a basic understanding of inductance, the inductance of a given conductor formed into a single turn loop is not simply perimeter multiplied by some constant “inductance per foot”. Continue reading Helical loading and Calculate small transmitting loop gain from bandwidth measurement

End fed matching – PA3HHO design review

 

A correspondent having read End fed matching – design review raised a similar design by PA3HHO which uses a#43 ferrite toroid as part of an end-fed matcher, see Multi band end-fed (English).

The text and diagram  are inconsistent, but to allow him the benefit of doubt, lets consider the FT240-43 with a 3t primary… this is his lowest loss configuration.

Continue reading End fed matching – PA3HHO design review

Designing a Guanella 1:1 balun using the ‘unknown’ ferrite toroid

At Characterising an unknown ferrite toroid an ‘unknown’ ferrite toroid was characterised. This article uses that information for design of a Guanella 1:1 current balun.

The proposed design uses 11t of small coax wound in the Reisert ‘cross-over’ style.

The impedance of a single turn vs freq was used to predict the impedance of an 11t choke. Such a choke exhibits a self resonance that can be represented as due to an equivalent shunt capacitance. This equivalent capacitance is not easily estimated, and can best be determined by calibrating an analytical model of the choke for the same self resonance as exhibited by a real choke.

Clip 030

Above is common mode impedance from an analytical model of the choke, assuming an equivalent self capacitance of 11pF.
Continue reading Designing a Guanella 1:1 balun using the ‘unknown’ ferrite toroid

Characterising an unknown ferrite toroid

The ‘unknown’ toroid is wound with a single turn and measured with a VNA, an AIMuhf in this case.

LO1230

Of interest in the first instance is the apparent inductance of the single turn winding at low frequencies where typically permeability µ is fairly constant and core loss is fairly low. Continue reading Characterising an unknown ferrite toroid

A method for initial ground loss estimates for an STL

Over recent weeks, I have run literally hundreds of thousands of NEC models of small transmitting loops (STL) over real ground. The objective was to try to discover some simple methods for initial design of a STL, particularly an estimate of ground loss of STL mounted near natural ground. Continue reading A method for initial ground loss estimates for an STL