Where did the “1.2” come from?

Recently, a reader asked:

On question E8C06 and E8C07 the formula uses 1.2. Where did the 1.2 come from and what does it represent?

I wasn’t sure what he was referring to since my study doesn’t mention how to calculate that value at all. Instead, it reads:

The bandwidth needed for ASCII digital transmissions increases as the data rate increases. The bandwidth necessary for a 170-hertz shift, 300-baud ASCII transmission is 0.5 kHz. (E8C06) The bandwidth necessary for a 4800-Hz frequency shift, 9600-baud ASCII FM transmission is 15.36 kHz. (E8C07)

I e-mailed him, asking him, “”Is the formula you’re referring to perhaps in another license manual? If so, and if you can send that to me, perhaps I can explain it to you.”

He replied, “This was out of the Gordon West Extra Class book page 81.” He attached a copy of the page, and it did indeed refer to the formula:

BW = baud rate + (1.2 x f shift)

Now, I had never run across this particular formula, but I decided to do a little Googling. What I turned up was interesting. It appears that the 1.2 number basically comes from some version of the ARRL Extra Class License Study Guide. Where they got it from I don’t really know.

In my Google search, I turned up one source that simply says that:

BW = baud rate + the frequency shift

Perhaps someone along the line said, “Well, that’s the theoretical value. Practically, if we increase that by 20% to 1.2 times the frequency shift then the signal will definitely fit in that bandwidth.” I’m just guessing here. I’m not really sure.

I told my reader that, for what it’s worth, there’s a lot of this in amateur radio. The formula used to calculate the length of a half-wave dipole antenna is perhaps the biggest example of this. There’s no real science behind the formula length in feet = 468 / frequency in MHz. It’s just a rule of thumb.

While it may be disappointing that the science behind this is perhaps a bit shaky, the good news is that using these rules of thumbs produce circuits and systems that generally work.

Cleaning off my desk: “F” is for frequency

I make lots of notes as I Twitter and read my e-mail. I have so many notes about interesting things piled up on my desk, that I really need to start cleaning it up and moving the notes either here to my blog or maybe to Evernote.

Having said that, I’ve written in the past about the need for a study guide for kids. We still need something like this in amateur radio, but there are now books and videos that can teach kids about electronics. One of the books available is The Manga Guide to Electricity.

As far as videos go, Adafruit, has published a number of YouTube videos they call the Circuit Playground. I’ve just watched the video “F is for frequency” (see below). It’s really pretty good, and there is a whole series of them. Adafruit also has a coloring book, E is for Electronics, to go along with the videos. If you have kids, you should check them out.

From my Twitter feed: diode ring mixers, TAPR news, SDR SA

Stefano_NVR's avatarDr. NVR @Stefano_NVR
How a Diode Ring Mixer works | Mixer operation theory and measurement: youtu.be/junuEwmQVQ8

 

ke9v's avatarJeff Davis
Summer 2014 TAPR PSR Journal Available –> tapr.org/psr/psr126.pdf #hamradio

 

EDNcom's avatarEDN.com @EDNcom
RT @measurementblue: Michael Dunn tries The $11 spectrum analyzer & SDR ubm.io/1q5JI5W @EDNcom @EDNMichael ow.ly/i/645Dp

 

rtlsdrblog's avatarrtl-sdr.com @rtlsdrblog
BeagleBone Black Image File with RTL-SDR + GNU Radio + More rtl-sdr.com/beaglebone-bla…

Next year, let’s do a “maker” Field Day

A couple of minutes ago, I got an e-mail from John, KD8MKE, who wrote:

I had this crazy idea that you could use a quad copter to hold up a dipole antenna AND power the quad from the ground (to save the battery weight).  Ed pointed out that the cable would weigh quite a bit, which is a good point.  Modern quads are remarkably steady when they are in loiter mode.

I wondered if you had heard of someone doing something like this at a Field day?  Seems like it would be handy if you didn’t have a tree or other structure to use as a peak.

I replied:

I haven’t heard about the use of copters for actually supporting the antennas, but there has been talk about using them for getting ropes into trees.

In the past, people have used balloons to support vertical antennas. With a vertical, you’d need only support the wire itself, not the feedline. A 160m vertical would be about 133 ft. long. How far up can these things go? How long do you think they would stay in the air?

I thought about this for a bit, and it occurred to me that next year we should do a Maker Field Day. The idea would be to incorporate as many “maker” projects as we can think of into it. Copters are a big maker thing, so that certainly qualifies. Another idea that I had for a maker ham radio project is to use 3D printing to make a “cootie key” or a paddle.

What are some others?

From my Twitter feed: SDR, SWL, kits

sdrsharp's avatarsdrsharp @sdrsharp
You want more and better rtl-sdr tools? Consider helping this initiative from Kyle Keen indiegogo.com/projects/a-mon…

 

UlisK3LU's avatarUlis K3LU @UlisK3LU
Western radio broadcasters tuning out (excellent article on the demise of #shortwave broadcasters) via Straits Times shar.es/LgFv9

 

wa1gov's avatar#hamradiopic.twitter.com/oaBaj00Ady

From the trade magazines: free design tools, DSP, education

Top Free DIY Tools Ever Engineer Needs. We’re seeing a relative explosion in free tools for engineering electronics. Some of those online tools prove to be worthless, and it’s back to blind searching or some paid tool. To help sort out the nonsense from the useful online tools, check out this list.

What Do You Know About DSP? Louis Frenzel, who is a ham by the way, reminisces about his experience with digital signal processing (DSP) and recommends a new book for those just learning about DSP.

Outrageous! Experience is no qualification to teach EEs. This is another column by Louis Frenzel. He writes:

It is obvious that the colleges do not value industry experience when it comes to hiring professors….It seems to me that professors with real world experience could teach the fundamentals in context and to explain what is really important and what is simply nice to know. Experienced teachers would be able to teach students things they ordinarily do not teach in school. They could tell their design war stories and explain that troubleshooting is just as important to know as design. I think that an MSEE with ten good years of experience is more qualified to teach than a no-experience PhD.

Use VLF to detect lightning

Yesterday, my friend Ed, KD8OQG tweeeted:

vielmetti's avatarEdward Vielmetti @vielmetti
a lightning detector, picking up lightning signals on VLF (!) blitzortung.org/Documents/TOA_… @kb6nu @hoopycat #hamr

Ed is a bit of a severe weather geek, and is often Tweeting when severe weather rolls through the Ann Arbor area. So, it’s only natural that he would be interested in the Blitzortung project. The Blitzortung website describes the project this way:

Blitzortung.org is a lightning detection network for the location of electromagnetic discharges in the atmosphere (lightning discharges) based on the time of arrival (TOA) and time of group arrival (TOGA) method. It consists of several lightning receivers and one central processing server. The stations transmit their data in short time intervals over the Internet to our server. Every data sentence contains the precise time of arrival of the received lightning discharge impulse (“sferic”) and the exact geographic position of the receiver. With this information from all stations the exact positions of the discharges are computed. The aim of the project is to establish a low budget lightning location network with a high number of stations. The price for the hardware used is less than 200 Euro. The sferic positions are free accessible in raw format to all stations that transmit their data to our server. The station owner can use the raw data for all non-commercial purposes. The lightning activity of the last two hours is additionally displayed on several public maps recomputed every minute.

Blitzortung.org is a community of station operators who transmit their data to the central server, programmers who develop and/or implement algorithms for the location or visualization of sferic positions, and people who assist anyway to keep the system running. There is no restriction on membership. All people who keep the network in operation are volunteers. There is no fee and no contract. If a station stops pooling its data, the server stops providing the access to the archive of sferics positions for the user of that station. A detailed description about how to participate to the network and how to setup an own receiver can be found in the following document.

The website doesn’t say how much a setup costs, but does says, “If you are interested to setup an own station then you can get the latest printed circuit boards and the programmed micro controller from us. If you are not from Germany, Austria, or Switzerland you can even get a complete controller kit, a complete amplifier kit, ferrite rod antennas, and a GPS module for cost price, if desired.”

The Cloud is an interactive lamp and speaker system, designed to mimic a thundercloud in both appearance and entertainment. Using motion sensors the cloud detects a user's presence and creates a unique lightning and thunder show dictated by their movement.

The Cloud is an interactive lamp and speaker system, designed to mimic a thundercloud in both appearance and entertainment. Using motion sensors the cloud detects a user’s presence and creates a unique lightning and thunder show dictated by their movement.

Ryan Burns, one of Ed’s followers and head of A2 Geeks, suggested that he get a Cloud and hook it to the detector. According to the Cloud’s website, “The Cloud is an interactive lamp and speaker system, designed to mimic a thundercloud in both appearance and entertainment. Using motion sensors the cloud detects a user’s presence and creates a unique lightning and thunder show dictated by their movement.” We would, of course, have to get a version without the motion sensors so that we could interface our lightning detector.

I volunteered that we could mount the detector’s antenna to the tower at the Hands-On Museum. Ironically, I think that we’d have to use a lightning arrestor on the feedline should we actually mount it outside.

From my Twitter feed: wire splicing, SDR, BCB loop

kd0bik's avatarJerry Taylor @kd0bik
How-To: Splice Wire to NASA Standards fb.me/3BMl1CsL0

 

rtlsdrblog's avatar<b”>rtl-sdr.com @rtlsdrblog
Using and RTL-SDR and RTL_433 to Decode Various Devices rtl-sdr.com/using-rtl-sdr-…

 

ke9v's avatarJeff Davis @ke9v
@AA7EE goes mad scientist with his Tuned Loop for BCB –> aa7ee.wordpress.com/2013/11/17/a-t…

From my Twitter feed: new EchoLink for Mac, SDR

dusty_s's avatardusty_s @dusty_s
EchoHam (formerly EchoMac) update in Mac App Store” <- glad to see an update! feedly.com/e/G5x1odQW

 

dangerousproto's avatarDangerous Prototypes @dangerousproto
OHM2013: Hacking the radio spectrum with GNURadio goo.gl/krngx7

 

VA3BCO's avatarBrian (VA3BCO) @VA3BCO
Are we Getting Closer to a Touchscreen SDR HT? >#hamr #hamradio wp.me/p4GMgg-28

From my Twitter feed: Tindie, resonant speaker

blackrockcastle's avatarBlackrock Castle @blackrockcastle
@WIRED: An inside look at Tindie, a thriving new marketplace for DIY gadgets wrd.cm/Rlnkbt pic.twitter.com/pZzItSsUpz@ado_collins

 

n1pce's avatarJohn Ryan @n1pce
April 2014 CQ Plus – Adding Volume With a Resonant Speaker youtube.com/watch?v=nLFPAj… via @YouTube

 

kc5fm's avatarkc5fm @kc5fm
My New Favourite Social Network Is Ham Radio | Business Insider bit.ly/1k5fGIx #ARRL #hamradio