Category Archives: Amateur Radio

Is mobile operation of a ham radio really safe?

The federal government is currently considering the possibility of legislation banning the use of cell phones and texting. I’m mostly okay with that, because, quite frankly, it’s obvious that people aren’t very good at operating a cell phone or texting while driving, a fact which has been reinforced by study after study. But while many radio amateurs accept this conclusion with respect to cell phones, radio amateurs as a whole seem to think that it doesn’t apply to operation of an amateur radio transmitter while the vehicle is in motion. Witness the quotation from ARRL CEO David Sumner:

According to ARRL Chief Executive Officer David Sumner, K1ZZ, it boils down to the difference between simplex — when only one message can be sent in either direction at one time — and duplex — a communications mode, such as a telephone system, that provides simultaneous transmission and reception in both directions. Harrison, citing Sumner's 40-plus years of experience as an Amateur Radio operator, puts it this way: “Simplex, two-way radio operation is simply different than duplex, cell phone use. Two-way radio operation in moving vehicles has been going on for decades without highway safety being an issue. The fact that cell phones have come along does not change that.”

via ARRLWeb: ARRL NEWS: ARRL President Presents League’s Views on Distracted Driving Laws to Safety Advocacy Group.

But here’s the thing that bothers me. This is just a bold assertion: that operation of simplex radios is inherently safer than duplex radios. Here is what the NSC President Janet Froetscher had to say about the subject:

The NSC position is grounded in science. There is significant evidence that talking on cell phones while driving poses crash risk four times that of other drivers. We are especially concerned with cell phone use because more than 100 million people engage in this behavior, with many doing so for long periods of time each day. This exposes these 100 million people and everyone who shares the road with them to this increased crash risk every day. This combination of risk and exposure underlies our specific focus on cell phones.

We are not aware of evidence that using amateur radios while driving has significant crash risks. We also have no evidence that using two-way radios while driving poses significant crash risks. Until such time as compelling, peer-reviewed scientific research is presented that denotes significant risks associated with the use of amateur radios, two-way radios, or other communication devices, the NSC does not support legislative bans or prohibition on their use.

That is not to say that there is no risk associated with drivers using amateur or two-way radios. Best safety practice is to have one’s full attention on their driving, their hands on the wheel and their eyes on the road. Drivers who engage in any activity that impairs any of these constitutes an increased risk. While the specific risk of radio use while driving is unmeasured and likely does not approach that of cell phones, there indeed is some elevated risk to the drivers, their passengers and the public associated with 650,000 amateur radio operators who may not, at one time or another, not concentrate fully on their driving.

This is widely being circulated as vindication of the idea that operation of a ham radio while simultaneously operating a motor vehicle is safe. Unfortunately, I don’t think that is an accurate representation of Froetscher’s position. Froetscher merely said that she was unaware of any scientific, peer reviewed studies that demonstrated a significant safety risk. As we should all know, absence of evidence is not evidence of absence. David Sumner’s assertion that simplex is inherently safer than duplex is just that: an assertion, and is not evidence.

The fact is that humans are very bad at evaluating risks and their own performances at tasks. That’s why we have scientific studies like the ones that we have for operating cell phones. Because there are 100 million cell phones being used literally every day, there is plenty of data to sift through on their potential role in accidents. Even so, it’s taken about a decade for the true extent of the risks involved in cell phone operation to become documented.

There are only about 660,000 or so hams licensed in the U.S. The vast majority of these do not operate mobile. The vast majority of those do probably spend most of their time listening. In such a case, we’d expect that the number of accidents caused to be much lower than those caused by cell phones, even if mobile operation was every bit as dangerous as using a cell phone. The overall instance of accidents may be only 0.1% or less of the levels we see from cell phones. One study estimated that 6000 accidents might have been caused by cell phones in California in 2001. Even if ham radio were as dangerous, we might expect to see only six accidents in the entire year from ham radio operation.

I’m not saying that we should outlaw mobile ham radio operation. Without evidence that it is dangerous, I think it is premature to make it illegal. But I also think that it is inappropriate to confidently assert that we understand what the risks are, and that we actually present no significant risk to ourselves or to others on the road.

Addendum: Ben makes an additional point which I think is worthy of mention. The ARRL is in part justifying their opposition to bans on mobile radio by suggesting that amateur radio serves a vital purpose in supporting emergency communications. I think this is a somewhat odd claim to make, since it should be fairly obvious that the overwhelming majority of emergencies are reported by calling 911 on the cell phone. Many states have exemptions for mobile cell phone use in times of emergencies: you can report an accident while calling 911 while your car is in motion. The ARRL could choose to suggest to its members that only emergency communications be carried out while the car is in motion, but instead, they suggest that the possibility of using a mobile radio to report an emergency justifies their free use for routine communications while the vehicle is in motion. I agree with Ben, I don’t think this is a reasonable “best practice” suggestion.

One slightly convincing argument that I haven’t heard, but which I can imagine someone making is that without the incentive of being allowed mobile operation, radio amateurs won’t install mobiles in their vehicles, and therefore we lose a valuable resource for reporting accidents and dealing with emergencies. This is an argument which I might seriously consider, and could be made compelling with the right sort of quantifiable evidence to determine the tradeoffs of different regulatory strategies.

Codec2 – Open Source Low Bit Rate Speech Codec

David Rowe is working on a very cool project that should be of interest to hams with an interest in digital communications. He’s creating an open source, low bit rate speech codec. His target is a usable 2400 bps codec that is free from patent issues, and that can be used in situations similar to the patented algorithm AMBE that is currently used in D-Star networks. He’s not quite at the point where he has a full codec yet, but he’s begun to make some code available that can encode and decode using his sinusoidal encoder. He’s also writing up a lot of the theory behind the encoder on his blog, which is frankly a bit beyond me, but not a huge amount beyond me, which means that it’s very interesting reading.

Codec2 – Open Source Low Bit Rate Speech Codec

David has also done some very interesting VOIP work, including a high quality echo canceler. His blog is always worth reading.

Upcoming launch of SumbandilaSat

It looks like the launch of the South African amateur satellite is on track!

The launch of SumbandilaSat is on track for 15 September 2009. In an interview with SA AMSAT, Johan Erasmus, SunSpace systems engineer speaking from Baikonur, said that the satellite travelled well and that all system performed to specification during the testing phase. Tests were carried out in the clean room at the Baikonur launch facility in Kazakhstan. “All payloads operated well and we were able to test the amateur payload from a little distance away. The parrot, voice repeater and the voice beacon responded well.

Via AMSAT South Africa Homepage

As soon as we get a confirmed launch, I’ll try to get some audio and/or work the bird. Stay tuned!

Addendum: The launch didn’t go off today. From AMSAT-SA’s website.

Due to high winds at the launch site and some telemetry issues on the rocket the launch has been delayed for 24 hours and will now take place on 16 September at around 15:45 UTC.

That’s about 9 hours from now. Fingers crossed.

Decoding packet….

It’s late, so I am not figuring this out, but I seem to be getting quite a bit of ripple in the output of this demodulator. I bet that it is because I don’t know what I am doing. Oh well. More for later, I guess.

Picture 3

FET Transistor Homemade From Cadmium Sulfide Photocell.

I’ve blogged about the experiments of Nyle Steiner before, but just recently got back to his Spark Bang Buzz website again, and found that he’s added a couple of interesting bits. In particular, he shows how to modify a common Cadmium Sulfide Photocell to act like a field effect transistor. The voltage gain provided is quite small (about 1/10) but the power gain is better and the principle is quite interesting. Check it out.

FET Transistor Homemade From Cadmium Sulfide Photocell.

Passing the Amateur Extra test by guessing…

The Amateur Extra test is 50 questions, multiple choice, with 4 answers per question. A passing grade is 35 or more. A few minutes of programming this morning, even before I had any coffee yielded that the exact probability of passing was:

      4677523340461106447
------------------------------
158456325028528675187087900672

or about 1 in 33.9 billion.

This wasn’t that interesting of a question, but to solve it, I hacked up a quick but limited implementation of rational arithmetic in Python. I was wondering if there was a better way to implement this in Python so overloading would “just work”. I didn’t know how, and the problem was simple enough, so I didn’t try. Here’s my solution.

#!/usr/bin/env python

def gcd(a, b):
    if (a < b):
        a, b = b, a
    while b != 0:
        a, b = b, a%b
    return a 

class Rational:
    def __init__(self, a, b):
        self.a = a 
        self.b = b 
    def __str__(self):
        return "[%d / %d]" % (self.a, self.b)
    def pow(self, p):
        return Rational(pow(self.a, p), pow(self.b, p))
    def mult(self, r):
        tmpa = self.a * r.a ;
        tmpb = self.b * r.b ;
        d = gcd(tmpa, tmpb)
        return Rational(tmpa//d, tmpb//d)
    def imult(self, i):
        tmpa = self.a * i ;
        tmpb = self.b ;
        d = gcd(tmpa, tmpb)
        return Rational(tmpa//d, tmpb//d)
    def add(self, r):
        tmpa = self.a * r.b + r.a * self.b
        tmpb = self.b * r.b 
        d = gcd(tmpa, tmpb)
        return Rational(tmpa//d, tmpb//d)

p = Rational(1, 4)
q = Rational(3, 4)

def fact(n):
        c = 1 
        while n > 1:
                c = c * n 
                n = n - 1 
        return c 

def comb(a, b):
        return fact(a)/(fact(b)*fact(a-b))

total = Rational(0, 1)

for t in range(35, 51):
        x = p.pow(t).mult(q.pow(50-t)).imult(comb(50, t))
        total = total.add(x)

print "Exact probability is",  total
print "Only about 1 in", total.b // total.a, "will pass"

Beginnings of an SSTV demodulator

So, armed with the SSTV link that I dug out yesterday, and with a couple of hours this morning to tinker, I started working on an SSTV decoder. It’s not much different than the APT and WEFAX decoders I had written before, but they used amplitude modulation of an audio subcarrier, and most (all?) SSTV modes are based upon frequency modulation. But the only real difference is instead of recovering the amplitude of the carrier, you recover the change in phase. I’ll write this up in more detail sometime when I feel like writing, but here’s some example “demodulations”. The first comes from the header:

yyy

This is from the beginning of the recording of my Robot36 encoded picture. It starts with the so-called VIS code, which has 300ms of 1900hz audio, 10ms of 1200hz audio, and 300ms of 1900hz audio. You then see the mode indentifier, which begins and ends with 30ms of 1200hz, and with the identifier having ones and zeros encoded as 1100hz and 1300hz audio respectively. Neat!

Looking at a later part, we get this:

xxx

This shows scanlines from the image. Between the two tallest peaks, you see two scanlines. The two longer stretches are the intensity information, the two shorter, the R-Y and B-Y color channels.

It won’t be too hard to convert this into a picture, but I’ve been mucking with this too long today. Stay tuned for more developments.

Addendum: The bandpass filter in these examples was probably not positioned optimally (centered on 1500Hz, rather than 1700Hz). I’ve corrected it.

KR7A SSTV Demodulator

Don’t you hate it when you remember seeing a webpage but can’t remember exactly how to get there? This one took me a bunch of judicious web searching to finally uncover again. It basically details how you might go about making an SSTV demodulator, some of the details of which I was a bit sketchy on. This page not only gives you the answer, but shows some of the mathematics that makes you have some confidence that what you are doing is right. I’m too tired to figure it out tonight, but I’m archiving it for later:

KR7A SSTV Demodulator.

SSTV from the ISS, August 3 and 4

The ISS should be operating SSTV on August 3 and 4, using the Robot36 mode. I’ll go ahead and see if I can catch some pictures from space that way. Should work well, after my success with AO-51.

SSTV Aug 3 & 4 | ISS Fan Club.

Addendum: If you want to test your SSTV software before hand, you might want to use a recording that I made. Go here and fetch the linked .wav recording, and use it to test your SSTV software. It will also help you know what an SSTV signal sounds like.

Success: Robot36 encoder works…

Picture 1

Well, it works! Using the information in the paper I linked earlier in the day, I spent some time and managed to code up a Robot36 SSTV encoder. Above, you see the image decoded by Multiscan on my Macbook. Here’s a link to the .wav file:

  • I would often look at the Brainwagon link on the SolderSmoke blog and just sigh. It had been so long!…