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Showing posts from April, 2011

iHAB-4 Launches This Morning!

iHAB-4 a high altitude baloon complete with qrp beacon and student science exerpiments will launch this morning! We helped chase iHAB-2 back in October and had a great time! You can read more about the fb work by W0OTM and team at the iHAB-4 web site.

The posting to GQRP announcing the launch is copied below:

The Iowa High Altitude Balloon project is making it's 4th launch
tomorrow morning at 10Am Central, 1500z, from Cedar Rapids, Iowa.

A major milestone is that science student's cannister experiments will
be carried aloft and analyzed upon recovering the payload.

One of the goals of this launch is to do a remotely triggered cut down
at 75,000 feet, or over the Mississippi River, whichever comes first.
The tether between the payload and the balloon will be severed from a
ground command. A test of the cutdown circuit at low temperature can
be viewed here

As on the last flight, a 2M simplex repeater will be operatiing on
147.500 PL TONE 100.00.


Biot Savart Notes

Still watching MIT Freshhman EM lectures in preparation for quals. Notes and time stamps follow the video.

Biot Savart

C = mu0/4pi = 10 ^ -7

9:40 Magnetic field from current loop

15:00 Dual of current loop magnetic field and electric dipole electric field

Magnetic flux through a closed surface is always 0.

37:30 Leiden jar disassemble and discharge example
Demonstrates corona discharge from metal to the insulating glass
Removing charge from the insulating glass is difficult

MIT Freshman EM... Magnetism ... Studying for Quals

In getting ready for quals next January, I found out that MIT provides several of their courses online. I watched the freshman physics lecture on magnetism today and it's awesome! There are demos of the forces created on wires by magnetic fields, (car batteries are apparently the key to getting this demo right), as well as simple electric motor demos. There are also several everyday applications that make the Lorentz force equation immediately applicable. The video is embedded after the notes.


Force on a wire due to a B field

SSB Internet Reader: History

Studying the Tenna Dipper Deluxe

I saw an interesting new kit from Hendricks QRP Kits yesterday called the Tenna Dipper, (designed by KD1JV). It tells you the 50 ohm resonant frequency of an antenna. Basically, you scan the frequency from the Tenna Dipper until an LED goes out and the read the resonant frequency from the display.
What I thought was even cooler was learning how the kit worked. I’ve included the links I used for research below.

The schematic is available on the Hendricks site as a pdf.

The kit uses a Wheatstone Bridge to cause the LED to go out when the antenna resonates at 50 ohms. The bridge is the workhorse circuit that provides antenna match information. It’s actually fairly easy to understand, check out the explanation at:
Wikipedia Wheatstone Bridge article.

A voltage controlled oscillator, 74HC4046, is used to generate the square wave sent to the antenna.
74HC4046 datasheet [pdf]

A 74HC4017 decade counter is used as frequency counter to feed the kit’s frequency display.
74HC4017 datasheet [pdf]


Another Five Representatives Cosponsor HR 607, NY, PA, AK, GA, and IA

Yesterday two more representatives cosponsored HR 607 which impacts amateur radio frequency allocations in the 70 cm band. They are:

Rep Lowey, Nita M. [NY-18]
Rep Gerlach, Jim [PA-6]]
Rep Young, Don [AK]
Rep Barrow, John [GA-12]
Rep Loebsack, David [IA-2]

If you're an amateur radio operator from one of these districts, you might want to write your representative.

SSB Internet Reader: Technology

Soldersmoke 132 inspired me to look up Donald Norgaard, one of the engineers who worked on and promoted SSB transmission early on. I found a wealth of material about early SSB available on the internet. Here's a list of the more technically minded articles:

Amateur Radio and the Rise of SSB[pdf]: Nice historical overview of SSB. This article references a 1948 QST article, (see below), by Norgaard that has a very nice explanation of phasing SSB.

"A New Approach To Single Sideband", Donald Norgaard, QST June, 1948
This is the article referenced above. If you're an ARRL member, you can pull it from the QST archives.

"Notes on the Design of the SSB Jr. Rig"[pdf] Another article by Donald Norgaard that appears in the GE Ham News. Be sure to check out the FB from N4TRB.

"A QRP SSB Transceiver" by WB9IPA This page has plenty of other links to SSB articles on the web as well as a very interestin…

First Tran-Atlantic SSB Transmission Made in Rocky Point, NY

View TeslaTwain in a larger map> Apparently Long Island is rife with radio history! While listening to Soldersmoke #132 I noticed N2CQR mention Don Norgaard as one of the pioneers of SSB modulation. Interested, I looked up Don, W2KUJ and came across a lot of interesting information on the history of SSB, including a great ARRL article[pdf]. It turns out that the first trans-Atlantic SSB transmission was sent from the RCA Transmitter Laboratory in Rocky Point, NY just a short distance from Tesla’s last laboratory!

Dash! The Dog Faced Ham at MOCCA 2011

We went to the Museum of Comic and Cartoon Art Festival this weekend and met Jeff K1NSS of Dash! The Dog Faced Ham fame! It was great to run into another ham at a comic book fest! Jeff is a super, super nice guy! He supplied us with the first two issues of Dash and three Official Dash Insulators which will go into the backyard dipole just as soon as the new Rockmite is finished.

After we got home, I tore through the first dash book and got half-way through the second. Dash is the story of a dog-faced kid growing up with ham radio. The book chronicles Dash's adventures with vacuum tubes, fox-hole radios, and all sorts of other exciting and arcane technology! The art in the book is pretty to look at and the story is great fun to read! There are plenty of ham radio in-jokes for those in the know, and secret morse code messages as well!

There were a few other cool and pretty things around the fest. I'll add more as time allows:

The Center for Cartoon Studies, from White River…

Spring Turkeys

These guys turned up yesterday.

Higgins: Amateur Radio Operator!

Just finished watching season 3 of Magnum PI and I saw that Higgins is an amateur radio operator with the callsign WP6RNA. I quick search of the FCC database showed that the callsign has never been issued. Higgins callsign in a later season changed to N6DBZ and that callsign is in use now!

Nice Note on the Ham Radio Practice Tests and Congrats to KD8GEH

I just received a nice note about the ham radio practice tests. Great job on your exam Dave!


Just a note to let you know the I used your practice exam and got my extra. Thanks so much for the work! Much appreciated.

Keep up the good work, and the interesting jokes :)

Hope to catch you down the log,

73 De Dave KD8GEH

Groups and Their Graphs: Clarifications of Normal Subgroup Theorem and Test for Normal Subgroup Elements

On page 123 of “Gropus and Their Graphs” by Grossman and Magnus I struggled understanding Theorem 6 and the test it provides. The theorem read more clearly for me with the following substitution:

“the set K that contains all elements of G such that...” becomes

“the set K containing every element of the group G such that...”

The following paragraph that contained the test was easier for me to understand with the following substitution:

“If f maps all elements onto I...” becomes

“If f maps all elements of G onto I...”

Hope this helps! Any comments or questions?