CAKE Notes for Nov 25, 2017
Those attending today were Richard W1WUH, Fred KJ6OOV, Eric KK6IZY,Warren
NR0V, Glen KG0T and Ron W6WO. This is truly a group with such a wide range
of knowledge that two hours of concentrated discussion could only scratch
the surface of any one topic. Fred showed a professional VHF folded dipole
which he rescued from a dump. It was part of an array of dipoles that
incorporated impedance matching achieved with sections of coax within the
tubing. As many know Ron can become unBalUnced when coax is involved and
must resist beating his chest. Forgive but how would you answer this.
Given two sections of cable, one twin lead and the other coax. Which
could be described as a balanced transmission line? Answer at the end of
The conversation today had much to say about connectivity. Ron bemoaned
the need to have special cables and connectors, for example the 8pin DIN
connector on a typical radio and the USB connector now standard on PCs.
One day we woke up and parallel ports were gone followed by serial ports
what next, fiber Bluetooth ?. Glen made a kind offer to explain and
assist. Eric showed a diabolical mix of connectors associated with power
supply and other subsystems in his PC. The tour of his Lenovo P51 thinkpad
laptop was quite simply astounding.
Both Eric and Warren described some of the precautions they take to
safeguard their data. Warren mentioned his recent work developing
software to take care of anomalies affecting High Performance SDR
behavior due to the buffering and reading of data packets. Warren is a
true pioneer, builder and problem solver.
Now to the question. The answer is both as they are inherently balanced.
The twin lead is obvious but ideal coax will carry exactly differential E
and H fields internally ie balanced conditions. Consider a 50 Ohm coax
terminated in two 25 Ohm non radiating resistors in series with their
junction connected to some reference point. No common mode current will
flow back to the source via the reference point. It is radiation from an
unbalanced system or antenna (most are to one degree or another) and the
shielding property of the outer conductor that causes common-mode feedline
current and radiation. An even more engaging question is, if it does why
should we care ?
Our next CAKE date is Dec 9 which is the date for our Club dinner at 6 PM
stay tuned for details
73 Vibrate effectively