Hobbyking Swamp Dawg build – #1

SwampDawg01

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

ESC02

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

On-air testing of APRS digipeater with a crafted suite of test records

It is one thing to read code, and perform traces of live traffic to test proper function of a digipeater. This is a more valid technique than injecting test records directly into the software as for instance, viscous digi depends on the neighbour digis. Continue reading On-air testing of APRS digipeater with a crafted suite of test records

Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2

This is a follow up to Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites.

Steve saw the above article and revisited the FT240-52 measurements which he apparently did, and found them wanting: Continue reading Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2

Sevick’s comments on selection of ferrite mix

(Sevick 2001) discusses efficiency of transmission line transformers that use nickel-zinc ferrites in Chapter 11 “Materials and power ratings” applied to broad band baluns.

In Chapter 11 he reports a range of measurements of two different basic configurations, a 4:1 Ruthroff balun and a 4:1 autotransformer and uses nickel zinc ferrite cores of types that are no longer readily available (and none were the K and 52 mixes he is said to have recommended).

The types of transformers he built are ones where core flux (and so core loss) at low frequencies is approximately proportional to the quotient of voltage impressed across the input terminals and number of turns, so core losses can be decreased by reducing voltage and/or increasing turns. These are Voltage Baluns, see Definition: Current Balun, Voltage Balun.

By contrast, the flux (and so the core losses) in Current Baluns is proportional to the common mode current times turns, and in antenna systems, that cannot be simply calculated using back of the envelope ohms law (though pundits often do it), see Baluns – Rule 500.

So Seviks experiments and discussion are not directly applicable to Current Baluns, yet they are cited by manufacturers, sellers, and users as rationale for their designs using nickel-zinc ferrites for Current Baluns. Continue reading Sevick’s comments on selection of ferrite mix