From my Twitter feed: Whitebox, four-layer PCBs, propagation service

HamBeat1
Combining Software Defined Radios and Smart Phones: http://t.co/reduPzk6Qn#hamradio #hamr

This is a very interesting project, and I hope that it gains some traction.

mikelectricstuf
How 4 layer PCBs are made http://t.co/R4VNy2yloj

DH1TW
Radio Propagation as a service http://t.co/siVQ8tEDsQ #hamr @k6tu

30 bucks seems reasonable for this service.

From my Twitter feed: software-defined scanner, TAPR in Seattle, the art of electronics

n0rc
How to get started using the #rtlsdr as a scanner for as little as $19http://t.co/VK3qKdpMJS #sdr #hamr

This looks like fun…..Dan

 

HamBeat1
Seattle Will Host the 32nd Digital Communications Conference:http://t.co/0xGJUpjw1C #hamradio #hamr

I should have gone last year, when it was a lot closer……Dan

 

o0ToTOm0o
The Art of Electronics – Horowitz & Hillhttp://t.co/4p2rYYfcvV

A classic! Get it. It’s free……Dan

From my Twitter feed: WWV, smart meters, freeDV

SWLingDotCom
History of WWV and the NIST Time Stations http://t.co/xKWgOX0mwj #shortwave #swl #dx

Concerned about RF effects from smart meter? Check out http://t.co/mht0hvGSrP for technical analysis of meter signals

Been playing with FreeDV? Looks like some very recent improvements have been made. http://t.co/4MtGko4U75 #hamr #DV

From my Twitter feed: JT65, Shack Nasties, hashtags

WB0LCW
@kb6nu The main program is JT65-HFhttps://t.co/Sz8ijw2m - also a handy add-on is jt-alert, found at http://t.co/MrpgL78X

ka3drr
#hamr m0xpd Shack Nasties is bookmarked and I like his sense of humor as a ham radio blogger including tech prowesshttp://t.co/vfxZllp6

hamradioskywave
http://t.co/nGCZt8nz ; Amateur “ham” radio hash tag proposal: #radio #cqdx #hamr_usa #hamr_world

From my Twitter feed: SDR, Hallicrafters, digital voice

KD4E_73
Just found this resource:http://t.co/wlqb30CF Coverage down to 50mHz is possible with one type & down to 22mHz with another.

Wish I had the time to play with these things…..Dan

w7dtg
W7DTG: Another boatanchor receiver demonstration Hallicra…http://t.co/QXZn29Pe

 

Ham_Radio_News
Amateur Radio – FreeDV – Digital Voice Software for Amateur Radio http://t.co/u01JTDMa #hamradio #hamr #dx#swl

I’m still not sold on digital voice, but if it were easy to set up, like say PSK-31, I’d give it a try, at least….Dan<

From the trade magazines – 092612

Three more articles from recent editions of the electronics trade magazines.

HeathkitHeathkit: A right-time, right-place business. Heathkit was a popular electronics company for decades before its demise earlier this year. Former employees Lou Frenzel and Chas Gilmore share some memories and discuss the factors that led to its closing. Lou Frenzel is W5LEF.

In the article, he notes how he was instrumental in developing the Heath/Zenith line of computer kits. At that time, I was a fledgling test engineer working for Memorex (remember them?) making the 8-in. floppy drives that were an option for those computers.

Real-world testing of wi-fi hotspots. This article talks about both the RF testing and data communications testing needed to ensure a good wi-fi hotspot.

How to simulate cable in SPICE. This article covers the two main loss effects related to cables (the skin effect and dielectric losses) and presents a simple cable modeling method for use in standard SPICE simulators.

Extra Class question of the day: Digital signals and communications modes

Morse Code is arguably the original digital mode. Morse code is a digital code consists of elements having unequal length. (E8C01) One advantage of using Morse Code is that it is very narrow bandwidth. The bandwidth necessary for a 13-WPM international Morse code transmission is approximately 52 Hz. (E8C05)

The next oldest digital mode is radioteletype, or RTTY. RTTY uses a five-bit code called Baudot. Most modern digital devices these days use ASCII, which is a 7-bit or 8-bit code. Some of the differences between the Baudot digital code and ASCII are that Baudot uses five data bits per character, ASCII uses seven or eight; Baudot uses two characters as shift codes, ASCII has no shift code. (E8C02) One advantage of using the ASCII code for data communications is that it is possible to transmit both upper and lower case text. (E8C03)

The reason that some ASCII transmissions have only seven bits, while others use eight bits is that the eighth bit is a parity bit. The advantage of including a parity bit with an ASCII character stream is that some types of errors can be detected. (E8C12)

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)

PSK has become a very popular digital mode. One reason for this is that it occupies a very narrow bandwidth – only 31 Hz. One technique used to minimize the bandwidth requirements of a PSK31 signal is the use of sinusoidal data pulses. (E8C04)

An up-and-coming digital mode is JT-65, named after its inventor, Nobel Prize winner and amateur radio operator, Joe Taylor, K1JT. It uses 65 different tones spread over a bandwidth of 175 Hz. One advantage of using JT-65 coding is the ability to decode signals which have a very low signal to noise ratio. (E8C13)

Spread-spectrum communication is a wide-bandwidth communications system in which the transmitted carrier frequency varies according to some predetermined sequence. (E8C08) Direct sequence is a spread-spectrum communications technique uses a high speed binary bit stream to shift the phase of an RF carrier. (E8C11) Frequency hopping is a spread-spectrum communications technique alters the center frequency of a conventional carrier many times per second in accordance with a pseudo-random list of channels. (E8C10) Spread-spectrum techniques causes a digital signal to appear as wide-band noise to a conventional receiver. (E8C09)

Extra Class question of the day: operating HF digital modes; error correction

Perhaps the most popular digital mode these days is PSK31. PSK stands for “phase shift keying.” One of its main advantages is that it had a very narrow bandwidth—only 31 Hz. In fact, PSK31 is the digital communications mode that has the narrowest bandwidth. (E2E10)

One of the ways is achieves this narrow bandwidth is that uses variable length coding. That is to say, characters have different numbers of bits, depending on how frequently they appear in normal text. PSK31 is an HF digital mode that uses variable-length coding for bandwidth efficiency. (E2E09)

Another type of modulation commonly used on the HF bands is frequency-shift keying, or FSK. RTTY, for example uses FSK modulation. FSK is a type of modulation that is common for data emissions below 30 MHz. (E2E01) One type of FSK modulation is MFSK16. The typical bandwidth of a properly modulated MFSK16 signal is 316 Hz. (E2E07)

Amateur transceivers use two different methods to modulate a signal using FSK: direct FSK and audio FSK. The difference between direct FSK and audio FSK is that direct FSK applies the data signal to the transmitter VFO. (E2E11) When using audio FSK, audio, typically from a computer sound card, is used to shift the frequency of the transmitted signal.

To tune an FSK signal, one often uses a crossed-ellipse display. You have properly tuned a signal when one of the ellipses is as vertical as possible, and the other is as horizontal as possible. When one of the ellipses in an FSK crossed-ellipse display suddenly disappears, selective fading has occurred. (E2E04)

PACTOR is one digital mode that uses FSK. It also uses the ARQ protocol to detect errors. Because of this, PACTOR is an HF digital mode that can be used to transfer binary files. (E2E08) How does ARQ accomplish error correction? If errors are detected, a retransmission is requested. (E2E05)

Another way to detect and correct errors in a data transmission is forward error correction. The letters FEC mean Forward Error Correction when talking about digital operation. (E2E02) Forward Error Correction is implemented by transmitting extra data that may be used to detect and correct transmission errors. (E2E03)

No matter what type of modulation you use, data transmission over an HF radio link is very slow. 300 baud is the most common data rate used for HF packet communications. (E2E06) In fact, due to bandwidth limitations, 300 baud is the maximum data rate.

Many of the digital modes were designed to allow keyboard-to-keyboard operation. That is to say, that operators can type messages back and forth to one another, almost as if they were having a conversation using SSB. Winlink, however, does not support keyboard-to-keyboard operation. (E2E12)

Extra Class question of the day: VHF and UHF digital modes; APRS

One of the most commonly understood concepts in digital communications is the baud. A baud is not equal to a bit per second, except for very simple systems. Rather, the definition of baud is the number of data symbols transmitted per second. (E2D02) A data symbol may represent multiple bits.

The baud rate is a measure of how fast a digital communications system can transmit data. Under clear communications conditions, 300-baud packet is the digital communication mode that has the fastest data throughput. (E2D09)

In the past ten years or so, we’ve had an explosion of digital modes become available. JT65 is one example. JT65 is a digital mode especially useful for EME communications. (E2D03) JT65 improves EME communications because it can decode signals many dB below the noise floor using FEC.(E2D12) FSK441 is a digital mode especially designed for use for meteor scatter signals. (E2D01)

One of the most popular digital modes is the Automatic Packet Reporting System, or APRS. AX.25 is the digital protocol used by APRS. AX.25 is more commonly known as packet radio. (E2D07) Unnumbered Information is the type of packet frame used to transmit APRS beacon data. (E2D08)

APRS stations can be used to help support a public service communications activity. An APRS station with a GPS unit can automatically transmit information to show a mobile station’s position during the event. (E2D10) Latitude and longitude are used by the APRS network to communicate your location. (E2D11) 144.39 MHz is a commonly used 2-meter APRS frequency. (E2D06)

Amateurs that enjoy satellite communications also use digital modes. For example, store-and-forward is a technique normally used by low Earth orbiting digital satellites to relay messages around the world. (E2D05) The purpose of digital store-and-forward functions on an Amateur Radio satellite is to store digital messages in the satellite for later download by other stations. (E2D04)

TAPR announces Digital Communications Conference details

Where: Atlanta, GA Sheraton Gateway Hotel Atlanta Airport 1900 Sullivan Road Atlanta, GA 30337

When: September 21 – 23, 2012

Website: www.tapr.org/dcc

Technical / Introductory Sessions Schedule http://www.tapr.org/pdf/DCC_2012_Schedule.pdf

Technical Sessions Friday – Saturday: Introductory Sessions

Saturday Night Banquet Speaker & Topic: http://www.tapr.org/dcc#banquet
DCC Saturday Night Banquet Speaker will be Bdale Garbee, KB0G talking about the “Sharing the Joy of Making.

Sunday Morning Seminar Speaker & Topic: http://www.tapr.org/dcc#seminar
DCC Sunday Morning Seminar will be a hands-on tutorial using Gnuradio  to design and implement software defined radios on your laptop presented by Tom Rondeau, KB3UKZ, the leader of the Gnuradio project.