Month: July 2018

Please read and comment, I’m sending this out on the 25th. Thanks!

ORI_ARRL_Letter_1

I attended a ham radio conference over the weekend, and sat at dinner with a couple from that usually-liberal encampment, Palo Alto. But this couple were clearly conservative and Republican. I had identified myself as coming from Berkeley, so I would imagine they understood I was liberal.

At ham radio conferences, I generally talk about ham radio and its issues. I don’t usually get into politics, because I’m lobbying for some changes in ham radio policy, and it simply isn’t productive to confuse issues. Just as I wouldn’t talk about those things when appearing at an Open Source event – it’s more important to lobby people on Open Source policy issues.

But what interested me was the degree of denial I heard. The woman’s husband probably understood that I wasn’t the person to discuss his politics with, and limited his conversation to issues of attracting young people to ham radio, an issue we both felt was important.

His wife had a comment about living in Palo Alto, and this is an exact quote: “My friends say the most absurd things about President Trump. I just ignore it and let them talk.”

She also mentioned that her husband listened to conservative talk shows that “kept her honest”.

Now, the last time I checked, it was pretty clear that President Trump had cheated on his wife with a porn star and a “Playboy bunny” whom he had – as taped by his own lawyer – discussed paying for her silence during the election in possible contravention of national election funding law. He chummed with Vladimir Putin, publicly dismissing a vast pile of evidence from our nation’s security professionals that Putin had authorized interference with U.S. elections, and even high officials of his own party felt a need to contradict Trump about that. And I guess I could write about 100 more things we’ve learned about Mr. Trump that would be equally disturbing.

I didn’t engage her about this. It wouldn’t have been productive.

Somewhere in Palo Alto is a lady who listens only to Fox News, some internet sites, and conservative talk shows. And – I guess like very many people – news that concerns the rest of us that the president is unsavory, various sorts of criminal, and possibly even a Russian agent goes right over her head.

Now I understand how the people of Germany let all of the evil of the Nazis go on with their full acceptance. They had a great capacity for denial, one that we are now seeing in our own nation.

It is difficult to have hope in the face of this.

Unfortunately, I will no longer be able to allow conferences to purchase my airline tickets. I must purchase them myself and be reimbursed. I will purchase the lowest price un-refundable coach-class tickets available for flights of a reasonable duration. These will be insured with cancel-for-any-reason travel insurance which the conference must pay for, and which will protect them from having to pay if I am not able to appear.

The reason for this is that I’ve had a number of bad experiences when I’m not the one who books my travel. The worst was when my wife was hospitalized, and I was not able to change my flight to get back to her quickly. But there have been others, including calling the booking travel agency for help only to find we didn’t have any language in common, not being able to buy my own ticket for my wife because the conference took too long to secure my ticket, and the time a conference stuck me in a city I didn’t want to be in for a long weekend, with no regard to my own plans.

I will usually buy tickets less expensive than are available through a conference’s travel agency. Part of this is because they are un-refundable, but in general I’ve not found institutional travel agencies to be able to access better bargains than available online, if one books far enough in advance.

Note also that when I am traveling for your conference, I am not running my consulting business, and will have no billable time. So, I go through quite a lot of expense to appear there.

OpenResearchInstitute_18_86_Reply1

Here are notes from a fire safety meeting in Berkeley, California.

I wrote a comment in the FCC proceeding to “streamline” rules for small satellites, for Open Research Institute.

Crystal, as currently deployed on Linux, creates rather large executables.  On my system, a zero-length source file results in an executable of 1087016 bytes in size, with a instruction size of 726121 bytes,  2856 bytes of initialized data, and 1263736 bytes of filled-with-zero-on-demand data (“bss”). This is a problem for embedded use. For example, if I could cross-compile to my ESP32 (ignoring that LLVM doesn’t have its instruction set implemented) I would already be using all of the available memory.

If I was to write an operating system kernel in Crystal, I’d want to have a specially-tweaked support library, as Linux has for common C APIs.

Fortunately, it is pretty easy to build Crystal programs without their support library. This will give you a program with no garbage collection, no exception handling, and no support libraries for Crystal’s built-in classes. It is now your job to fill these in to the extent that you want or need to.

Having stripped out the support library, a minimal Crystal program will compile to an executable only a few kilobytes in size.

Before you get too deep into this, be warned: objects won’t work the way you expect, and are probably pretty broken until they get some library support. The program as I show it below leaks memory, and may not allocate memory properly. There is no garbage collection and no exception handling. I may have written bugs. All of this is left as an exercise for the reader, this is Open Source at work 🙂

Here is a simple Hello World program in Crystal, creating and using a class, and printing a message. Compile this with the command:

crystal build minimal.cr --prelude="empty" -p --release --no-debug

minimal.cr

require "lib_c"
require "lib_c/i686-linux-gnu/c/stdlib"
require "lib_c/i686-linux-gnu/c/stdio"

def free(object)
  LibC.free(pointerof(object))
end

class String
  def to_unsafe
    pointerof(@c)
  end
end

class Foo
  def bar
    LibC.printf "Hello, World!\n"
  end
end

f = Foo.new
f.bar
free(f)

The executable emitted by compiling this is only 6304 bytes in size after the symbol table has been stripped. Instructions are 2179 bytes and initialized data 600 bytes, fill-with-zero-on-demand data is only 16 bytes. It loads with three shared libraries: linux-vdso.so.1, libc.so.6, ld-linux-x86-64.so.2 . These are of course much larger than the program. Doing without these libraries is left as another exercise for the reader.

Obviously the above program is meant to build on i686. Modify “i686-linux-gnu” to be your architecture, and if you are on a different OS, the libraries required above may be different.

The advent of Category 7 cable, which includes four individually shielded twisted pairs, has introduced grounding to the concerns of the network engineer. The general advice of wire manufacturers, and the general configuration of pre-manufactured cables, is for both ends to be grounded. This is contrary to common knowledge in electrical engineering regarding ground loops and the potential for lightning-induced current.

Some purported electrical engineers assert that a shield grounded at only one end is “not a shield at all”, but an RF filter resonant to RF frequencies at its quarter wavelength, and will induce voltage to internal conductors at that frequency. They neglect to mention that a shield grounded at both ends also has resonant frequencies and can induce voltage to its internal conductors.

No configuration of grounding results in a shield always being a low-impedance path to ground across its entire length, for anything but DC and low frequencies. There will always be high-voltage points and null points across its length, for any frequency with a wavelength approaching or smaller than 4 times the circuit length, where the circuit includes the ground path between both ends of the shield if the shield is connected at both ends.

Grounding both ends of the shield simply increases the circuit length, creating a loop with external conductors, including conductive soil. This makes the circuit more vulnerable to lower frequencies than it would be otherwise, and admits additional possibilities for lightning currents to be introduced onto the shield. And you can’t count on the conductors being balanced such that induced currents oppose each other across the length of the circuit.

You must also consider that conductive soil is not a perfect sink to RF currents. Radio Amateurs learn that soil, unaugmented by radial wires, generally makes a poor counterpoise. The ground system in your building is anything but a theoretically perfect ground plane, and will in general present a high impedance at RF. Induced lightning voltage across the soil is a possibility with nearby strikes.

This is one reason for use of optical fiber, especially in areas where lightning-induced currents or RF interference (emitted or received) is a problem. No problems with electrostatic or magnetic induction when you use optical fiber. But we eventually transition to copper or aluminum at the ends of fiber runs. We must then consider lightning-induced currents and how to shield them.

Lightning frequencies are generally low, and energy is generally distributed across frequencies with a 1/f characteristic: more energy at lower frequencies. In this case, grounding the shield at both ends can indeed cause a shield that would be unresonant if single-point grounded to conduct significant energy. Ferrite chokes and other inductive means of increasing the external shield impedance are ineffective at blocking lightning-induced current, because they saturate.

So, I’ll be using single-ended grounding for my application, if for no other reason than that it removes so many unknowns from the equation. I suggest that those who wish to do otherwise actually attempt to model the circuit for its RF resonance and potential for induction of lightning current, using NEC or similar software.

We’re all used to having dynamically-loaded shared libraries for C and C++ programs. The effectiveness of shared libraries depends on having an API with well-defined types. This is good for C, which allows only one type per argument, and C++, which allows some type flexibility based on abstract types and inheritance.

Crystal, however, is not like this (see my introduction to Crystal). The duck-typing in Crystal is somewhat similar to C++ templates, but without the ugly syntax. A function like this:

def add(a, b)
  a + b
end

… can take any type for a and b, as long as they implement the + method. The code compiled and the return value will be different depending on the types provided. Because Crystal has global type inference, you need to compile the entire program, including the library, every time. That allows types to be inferred through the library code and its return to the caller.

So, shared libraries don’t make much sense in this context. They work because they have a tightly-typed API, which normal Crystal programs wouldn’t, and they assume that modules are independent of each other, which breaks down with modern language features like duck typing and type inference.

The cost is that we have somewhat more memory usage than we might for the equivalent C program. The benefit is that we use less programmer time on development and debugging, and we get increased code correctness because any incompatible type (including nil) is flagged as an error. Ultimately, memory is much cheaper than programmers.

There is also a potential performance increase over C, because there will be less need for the automatic type conversion with which C math operations are liberally salted, and code will be optimized for the type. But any real speed advantage over C has not yet been demonstrated.

Where optimization beyond what Crystal can provide is necessary, we can turn to assembly and Crystal’s foreign function interface. In general, the need for this would be rare.

Over time, it’s struck me that want-to-be-entrepreneurs who spend a lot of time on networking before they have a product to sell are kidding themselves about being entrepreneurial.

The supposition is that you can meet other prospective entrepreneurs who can be of help in establishing and running your own business. I think the reality is that you have to spend a lot of solitary hours on making your product, and the time for networking is when you have something to sell.

The defining moment for me came with my momentary participation in an electronic entrepreneurs Meetup group. Actually, I never attended the first meet-up, but my participation leading into it was educational.

The prospective event was a tour of a local PCB manufacturer. The group leader first scheduled it as an hours-long “networking event” followed by the tour. I protested that I didn’t have time for the networking, and could I just join the group to tour the PCB manufacturer? The group leader allowed this.

I then emailed the PCB manufacturer asking for more information, saying I was a local electronics manufacturer and might like to use their business, and that I’d heard of them through the meetup group.

This is where things started to go wrong. The PCB manufacturer informed the meetup group leader that I’d contacted them independently. Perhaps he was just expressing his gratitude for the publicity, but in general as a business person I’d not give un-involved people details about customer inquiries. It would have been sufficient for him to tell the group leader that he’d had an inquiry, without mentioning my name. I resolved not to do business with this PCB manufacturer after all.

Then, the meetup group leader contacted me, upset that I had contacted the PCB manufacturer without going through him! Obviously, I am a business person and can not allow random people to decide who I do and don’t do business with. So, it seemed this “entrepreneurial meet-up” leader didn’t really have the first idea about what it meant to actually be in business.

I cancelled my reservation for the meetup and exited the group. To this day, I don’t understand the motivations of the people involved.