## Where did the “1.2” come from?

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.

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

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

Jeff Davis
Summer 2014 TAPR PSR Journal Available –> tapr.org/psr/psr126.pdf #hamradio

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

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

## If goTenna can encrypt, why can’t hams?

I’ve written here before about encryption and whether or not amateur radio operators should be allowed to use encryption. I’d like to throw another log on the fire.

I just read an article in RadioWorld that describes the goTenna, a device that uses Bluetooth and the Multi-Use Radio Service (MURS) to allow users with smartphones to text one another even if there’s no WiFi or cellphone link. The goTenna device communicates with the smartphone via Bluetooth and then transmits in the MURS band (151 – 154 MHz).

The goTenna manufacturers claim a range of  a half mile to three and a half miles. That’s probably reasonable. In the city, you’ll get a half mile or so range, while out where it’s more open, you’ll get more range.

Among the “key features” are the following:

• Automatic message retry & delivery confirmation
• Individual & group messaging
• ”Shout” broadcasts to anyone within range
• End-to-end encryption (RSA-1024) & self-destructing messages

I have often thought that handhelds should include some kind of text-messaging feature. I suppose you can send text messages using D-STAR, but it seems like an awful expense to do that. It seems that adding this functionality to something like a BaoFeng would make it very appealing.

Also note that this device encrypts the messages. If goTenna can encrypt, why shouldn’t hams be allowed to do so? I’m really not convinced by the arguments put forth by those who are anti-encryption on my previous blog post. I think that someone—someone more knowledgeable about the topic than me—should petition the FCC to allow encryption in certain situations.

## NASA Looking for Out-of-This-World Mars Communications Services

As you may or may not know, the ARRL has an award called the Elser-Mathers Cup that is to be awarded to the amateurs that complete the first amateur radio contact between the Earth and Mars. It’s been sitting on a shelf at ARRL HQ since 1928.

Well, apparently, NASA isn’t waiting for hams to make this happen. A story in Network World reports that NASA has issued a Request for Information that explores options to buy commercial communications services to support users on Mars.

NASA’s current Mars relay infrastructure is aging, and there is a potential communications gap in the 2020s, which is why NASA wants to explore alternative models to sustain and develop the Mars relay infrastructure. Mars landers and rovers are constrained in mass, volume, and power, all of which contribute to a substantial restriction in the data rates and volumes that can be communicated on the direct link between Mars and Earth.

To address the limitation in direct-to-Earth bandwidth, the Mars Exploration Program has developed a strategy of including a proximity-link telecommunications relay payload on each of its Mars science orbiters. The relay payloads establish links with landers and rovers on the surface, supporting very high-rate, energy-efficient links between the orbiter and lander.

## From my inbox: 100 years of ham radio, spectrum analysis, mesh networks

Celebrating 100 years of ham radioThis month marks the centennial of the American Radio Relay League, the largest ham radio association in the United States. That means it will be a special year for the hundreds who converge annually on W1AW, a small station known as “the mecca of ham radio” in Newington, Conn., to broadcast radio signals across the globe.

Spectrum Analysis Basics – A Resource Toolkit. Learn about the fundamentals with Agilent’s most popular and recently updated application note, Spectrum Analysis Basics – Application Note 150, which is now paired with a toolkit of app notes, demo videos, web/mobile apps, and related material.

When the Internet Dies, Meet the Meshnet That Survives. The art and technology nonprofit center Eyebeam recently staged a small-scale scenario that mimicked the outage that affected New York after Superstorm Sandy hit in 2012. As part of the drill in Manhattan, a group of New Yorkers scrambled to set up a local network and get vital information as the situation unfolded.

## From my Twitter feed: Trash Talk, Android antenna analzyer, Oinker

DIY Engineering @DIYEngineering
Trash Talk – Trash Talk is a prototype for an inexpensive, mesh-networked, democratic public address system. Each … ow.ly/2Gx8z5

Amateur radio more Space Age than Digital Age gaining popularity reviewjournal.com/life/recreatio… pic.twitter.com/sNti1HxhXD

Matthew Williams @W2MDW
Interesting, and fairly cheap antenna analyzer that has Android support. ebay.com/itm/Sark100-HF…

DIY Engineering @DIYEngineering
Oinker is Twitter for HAMs – Have you ever wanted to send a quick message to your HAM radio buddies over the … ow.ly/2GDOlL

## From my Twitter feed: clear-top boxes, SDR, HSMM

Sverre Holm, LA3ZA @LA3ZA
Show off your project in a clear top tin la3za.blogspot.com/2014/02/show-o…

Victor Laynez @roteno

DIY Engineering @DIYEngineering
Using SDR to Read Your Smart Meter – [BeMasher] was dissatisfied with the cost of other solutions to read his smar… ow.ly/2EcLiT

kc5fm @kc5fm
An Old Buzzard’s Guide to Getting Started with HSMM-Mesh bit.ly/1eL1cQg #ARRL #hamradio

SB QST @ ARL \$ARLB007

ZCZC AG07
QST de W1AW
ARRL Bulletin 7  ARLB007
Newington CT  March 3, 2014

SB QST ARL ARLB007

At the January 2014 ARRL Board of Directors meeting, a resolution was passed which asked for member feedback and input pertaining to the increasing popularity of data modes. The information gathered by  this investigation is to be used by the HF Band Planning Committee of the Board as a means to suggest ways to use our spectrum efficiently so that these data modes may “compatibly coexist with each other.”  As per the resolution, the ARRL Board of Directors is now reaching out to the membership and requesting cogent input and thoughtful feedback on matters specific to digital mode operation on the HF bands.

The feedback may include, but is not limited to, the recent proposal the ARRL made to the FCC, RM 11708, regarding the elimination of the symbol rate restrictions currently in effect.  A FAQ on RM 11708 can be found on the web at, http://www.arrl.org/rm-11708-faq .

The Board of Directors believes that member input in the decision making process is both valuable and important as well as fostering a more transparent organization.  It is to this end that we open this dialogue.

Comments must be received no later than March 31, 2014 to be included in the Committee’s report to the Board at the July 2014 ARRL Board of Directors meeting. Please e-mail your comments to: HF-Digital-Bandplanning@arrl.org

Concerned members may also contact their Division Director by mail, telephone or in person with any relevant information.

## 2014 Tech study guide: station setup

There were two question changes in this section. Question T4A02 was changed from a question about headphones to a question about using computers in the shack. Question T4A05 was changed from a question about band-reject filters to one about using an SWR meter. I’ve added that question to the appropriate section…Dan

When setting up an amateur radio station, choosing the radio itself is the most important consideration, but you must also choose a wide range of accessories, such as power supplies and microphones. In addition, how you set up the station is important for it to operate efficiently.

One accessory that you’ll definitely need is a power supply to provide the DC voltage and current that your radio needs. A good reason to use a regulated power supply for communications equipment is that it prevents voltage fluctuations from reaching sensitive circuits. (T4A03) When choosing a supply, check the voltage and current ratings of the supply and be sure to choose one capable of supplying a high enough voltage and enough current to power your radio.

If you are going to operate with one of the voice modes, you’ll need a microphone. When considering the microphone connectors on amateur transceivers, note that some connectors include push-to-talk and voltages for powering the microphone. (T4A01)

A computer has become a very common accessory in an amateur radio “shack.” All of these choices are correct when talking about how a computer be used as part of an amateur radio station (T4A02):

• For logging contacts and contact information
• For sending and/or receiving CW
• generating and decoding digital signals

If you plan to operate packet radio, you will need a computer and a terminal controller, or TNC, in addition to the radio. A terminal node controller would be connected between a transceiver and computer in a packet radio station. (T4A06) The TNC converts the ones and zeroes sent by the computer into tones sent over the air.

A more modern way to operate digital modes, such as RTTY or PSK-31, is to use a computer equipped with a sound card. When conducting digital communications using a computer, the sound card provides audio to the microphone input and converts received audio to digital form. (T4A07) The sound card may be connected directly to the radio, but it’s usually better to connect it through a device that isolates the radio from the computer. This prevents ground loops from causing the signal to be noisy.

Audio and power supply cables in a amateur radio station sometimes pick up stray RF. At minimum, this RF can cause the audio to be noisy. At worst, it can cause a radio or accessory to malfunction. To reduce RF current flowing on the shield of an audio cable (or in a power supply cable), you would use a ferrite choke. (T4A09)

Modern radio equipment is very well-designed, and harmonic radiation is rarely a problem these days. Even so, there may be times when it does become a problem, and you’ll have to take steps to attenuate the harmonics. To reduce harmonic emissions, a filter must be installed between the transmitter and the antenna. (T4A04)

Good grounding techniques can help you avoid interference problems. When grounding your equipment, you should connect the various pieces of equipment to a single point, keep leads short, and use a heavy conductor to connect to ground. Flat strap is the type of conductor that is best to use for RF grounding. (T4A08)

If you plan to install a radio in your car and operate mobile, you have a different set of challenges. One is connecting the radio to the car’s power system. Some amateurs connect their radio with a cigarette lighter plug, but this plug is not designed for high currents. Instead, a mobile transceiver’s power negative connection should be made at the battery or engine block ground strap. (T4A11) The positive connection can also be made at the battery or through an unused position of the vehicle’s fuse block.

Another challenge is noise generated by the car itself. One thing that could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter is that noise on the vehicle’s electrical system is being transmitted along with your speech audio. (T4A12)

The alternator is often the culprit.  The alternator is the source of a high-pitched whine that varies with engine speed in a mobile transceiver’s receive audio. (T4A10) Should this be a problem, there are filters that you can install to mitigate the alternator whine. One thing that would reduce ignition interference to a receiver is to turn on the noise blanker. (T4B05)

## 2014 Tech study guide: digital modes

Three questions in this section were updated. The answer to TD802 was changed from “Automatic Position Reporting System” to “Automatic Packet Reporting System.” T8D05 was changed from a kind of irrelevant question about Techs being able to use data in the 219 to 220 MHz range to one about an application of APRS. T8D11 was changed from a question about the parity bit to one about ARQ transmission….Dan

When hams talk about “digital modes,” we are talking about the ways in which we use a computer in conjunction with a radio to communicate with one another. They all involve sending digital data back and forth to one another. All of these choices are correct (examples of a digital communications method) (T8D01):

• Packet
• PSK31
• MFSK

Packet radio was one of the first digital modes. It is called packet radio because the data to be sent from station to station is separated into a number of packets which are then sent separately by the transmitting station and received and re-assembled by the receiving station. All of these choices are correct when talking about what may be included in a packet transmission (T8D08):

• A check sum which permits error detection
• A header which contains the call sign of the station to which the information is being sent
• Automatic repeat request in case of error

Some amateur radio digital communications systems use  protocols which ensure error-free communications. One such system is called an automatic repeat request, or ARQ, transmission system. An ARQ transmission system is a digital scheme whereby the receiving station detects errors and sends a request to the sending station to retransmit the information. (T8D11)

APRS is one service that uses packet radio. The term APRS means Automatic Packet Reporting System. (T8D02) A Global Positioning System receiver is normally used when sending automatic location reports via amateur radio. (T8D03) Providing real time tactical digital communications in conjunction with a map showing the locations of stations is an application of APRS (Automatic Packet Reporting System). (T8D05)

A popular digital mode on the HF bands is PSK. The abbreviation PSK means Phase Shift Keying. (T8D06) PSK31 is a low-rate data transmission mode. (T8D07)