Speaker wire is so popular as an RF transmission line

I received a sample of speaker wire from a correspondent who asked me to characterise it.

Even if I had the time, a 50mm sample isn’t sufficient to characterise in a meaningful way… but let’s have an abbreviated look which will highlight the pitfalls of this stuff.


First thing to do is measure the conductors, stranding and diameter. There are 14 strands and several measurements fall just below 0.15mm diameter. This is probably nominal 0.15mm with new drawing dies which are a little undersize. Continue reading Speaker wire is so popular as an RF transmission line

Accuracy of AIMuhf system – AIM865A vs AIM882 on a ferrite cored inductor

AIMuhfIn other posts, I have commented on the apparent inconsistency of AIMuhf measurements.

One of the devices I often wish to measure is a ferrite cored choke such as those used for a Guanella 1:1 balun. A small test inductor was made to provide a common device for measurement across instruments, and versions of software, though small, it has similar characteristics to the larger inductors more commonly measured.


Above is the test inductor. It comprises 6 turns of 0.5mm PVC insulated wire wound on a BN43-202 binocular balun core. Continue reading Accuracy of AIMuhf system – AIM865A vs AIM882 on a ferrite cored inductor

Slot.it CA20A rework

The Slot.it CA20A is a sidewinder configuration with the Mabucci style MF08 motor with extended shaft at both ends. The shaft ends extend out to about the mid point on the rear tyres with about 1.5mm clearance to the tyre.

The supplied PT32 tyres are quite elastic, and fly off the rim at high speed, making contact with the extended motor shaft and gouge the tyre, not to mention slowing the car. Continue reading Slot.it CA20A rework

Hobbyking Swamp Dawg build – #1


I couldn’t resist the Hobbyking Swap Dawg as an opportunity to play with SimonK ESC firmware with forward / reverse enabled.

ESC selection and implementation

I selected a Hobbyking F-30A ESC, which might seem a bit of overkill but it is a closed air space which reduces its dissipation capacity. The F-30A have proven themselves reliable with SimonK on a range of BLDC motors. Continue reading Hobbyking Swamp Dawg build – #1

SimonK on Hobbyking 40A ESC 4A UBEC 9261000003

Following on from BLHeli on Hobbyking 40A ESC 4A UBEC 9261000003 – #3, further tests were conducted on the ‘chugging’ ESC.

The 9261000003 is a relatively low cost ESC with 6S rating and fast FETs.

At Simon’s suggestion, the BEMF caps were removed. This eliminated the chugging effect on both the DT750 and 4822-690KV where it had been previously observed. The 4700pF BEMF caps are in a vertical row at the bottom right of the pic above.

I used to routinely remove BEMF caps (a carry over from using WiiEsc), but found on some tests that it made insignificant difference. That might be the case for some motors and smallish caps (1000pF), but in this case, the combination of these challenging motors and largish BEMF caps were incompatible and removing the caps solved the problem. Continue reading SimonK on Hobbyking 40A ESC 4A UBEC 9261000003

Feeding at a current maximum, and three other options

Feeding at a current maximum visited the common practice of designing to feed a multi band dipole with open wire feed at or very near to a current maximum.

I explained that feeding at the current maximum may provide sub-optimal performance on the popular T-match ATU as its losses tend to be worst with low R loads, aggravated by the use of 4:1 baluns for even lower R.

On the other hand, feeding at a voltage maximum might exceed the ATU’s voltage capacity, or perhaps be outside of the matching range of the ATU.

Well if neither of these is optimal in all cases, what about half way between. It has been done, the odd eighths wave feed line on an 80m half wave is another of the recipes you will hear.

Lets explore the options of a half wave dipole at 3.6MHz with four different feed line lengths (Wireman 551). Continue reading Feeding at a current maximum, and three other options

LP-100A manual advice on VSWR measurement

At Where is the best place to measure feed point VSWR I discussed location of the VSWR meter and projection of its reading to another point on a known transmission line.

A correspondent has taken me to task and citing Telepost’s LP-100A manual: Continue reading LP-100A manual advice on VSWR measurement