Ralph, all,




On 21/07/2020 22:52, Ralph Mowery wrote:

Well actually this is a bit strange, because a ham usually has to pass
an exam, and the theory that has to be learned from that usually includes
the basic principles of HF electronics, including a discussion of things
like L/C circuits, Q factor, skin effect, etc.

But maybe you only did a crash course and pre-learned the 500 questions
and their correct answer, without actually understanding it.

The test of the last 20 or 30 years have been a joke. Anyone with a
memory can pass those without knowing anything.


Well, I have this discussion a number of times.
(I man a infobooth to promote amateur-radio at FOSDEM -a yearly
conference on open-source development in Brussels- so I get to explain
this quite a lot)


In essence, that is not the problem with the exam itself.


When explaining to people why you need to do an exam for amateur-radio,
I compare this to a drivers-license.

A drivers-license is to show that you are technically capable to drive a
car on the public road in a way that is safe for yourself and others on
the road.

This is very similar to the the amateur-radio exam: it is to make sure
that you have sufficient technical knowledge to transmit without
interfering with other radio-users and to make sure you do not blow up
yourself.

The only additional element here is that we are not only allowed to
drive a car, but to also build one ourself; so, you have to show you are
technically able to build a basic model of a transmitter.



So, in essence, the exam still serves it goal: allow all users of the
radio-spectrum operate without to much "bumping into each-other".



But there is very different problem:

The problem is that radio-technology nowadays is nowhere near the
technology when the exams where conceived. I did my exam in 1992 (when I
was in the 2nd year of what would now be a professional bachelor
(digital) electronics).

I do not think that the exam has really changed in that 28 years.

The "problem" is that technology DID really change. Electronics is now a
lot more digital and software, and -especially- the way you do
electronics has changed dramatically.

I think the exam in Belgium now has just two questions one SDR, one
asking of a drawing is a FIR filter and one asking if it is a IIR filter.
(and yes, most people just learn it by heart: "is there is line going
back from the last block of the drawing to the beginning, , it's answer
2. If not, it is answer 1).



In essence, the problem is that the amateur-radio exam requires you to
know how to build a car ... a basic model of a car: chassis, 4 wheels,
engine, breaks, suspension, fuel, ....

However, the reality is that a car build in 2020 is 100 times more
complex than that basic model.
A modern car is filled with hundreds of sensors and as many
microcontrollers that all talk together over any number of CAM-bus.
After all, the goal is that -if the driver hits the break and the
sensors in the wheels notice that the car is losing grip- some device
will take over and -based on the input of a myriad of other sensors
determining the state of the car- and try to keep the car going in a
direction the driver wants it to go.


In amateur-radio terms, almost any device you buy or build these-days is
driven by DSP, SDR, microcontrollers, FPGAs, etc.

We use plutoSDRs to transmit to QO100, arduino's to drive a PLL as a
cheap WSPR beacon in a 3d-printed case and a raspberry-pi as
signal-generator for DATV.


And the exam does not reflect that.
Should it do that? Should there be a question on the amateur-radio exam:
"please provide a general overview of the hardware and software for a
POCSAG paging transmitter using either an arduino + FM transmitter or a
si4332 radio-chip"?

I don't think so. .. that is simply not the goal of the exam.



But, the problem is that, if you do not require this knowledge for the
exam, 99 % of the amateur-radio community is completely clueless on how
modern telecommunication-equipment works internally.
So either they do not care "I'm just an operator and I know how to use
my radio", or they have a very vague idea of how it works.





As explained, my interest here is to learn. Antenna's are not my
speciality (as you can guess). I learned about them in school (which was
good enough to pass the ham-radio exam) but that does not mean I
"understand" it.
In fact, it was a presentation of my former teacher in our radio-club on
the nanovna, the video of a talk by Dr. KC Kerby-Patel at MIT about
antenna's beginning this year and a discussion I had at FOSDEM with a
somebody working in the physics department of a university that made me
for the first time see an antenna in the context of "energy".

I have been playing around with the Java tool Jeff pointed out (I'm also
trying to really understand the article he has provided) and been
playing around with a couple of xnec2 simulations.
I kind-of favour the idea that this loss is pure related to the practice
components (as Jeff and Jeff have said), but I do not understand how
this matches up with a statement that the resistance of a shortened
antenna is less then a that of a full-size antenna.



Concerning the skin-effect, I did read some information on it, and just
tried the tool that John has provided (I already had that formula so it
saves me time having to do the calculations :-) ), but the problem is
that the result does not really say that much.
What does a skin-effect depth of 24.46 μm (copper, 7.1 MHz) say
concerning additional resistance to an antenna-system and how to does
this compare to other resistive elements in the antenna-system and the
overall behaviour?

As said, there is a difference between "having learned" and "understanding".



73
kristoff - ON1ARF