Today I Learned: Berkeley Has Two Ham Radio Clubs; Emperical Evidence and Dipole Conductor Diameter

There are more radio stations than I thought at UC Berkeley. To be specific, there's two. Yesterday, the KD0FNR Rockmite was seen by both of them: the first piece of evidence that changing the conductor diameter of the half wave dipole had a measurable effect. As it turns out, changing the dipole conductor width led to more questions than answers & also better propagation... maybe.

The aerial wires for the Rockmite's dipole have always seemed somewhat vanishingly small to me. I don't have an exact size right now, but if I had to guess, I'd go with them being 24 AWG or about 02 inches in diameter. They're signle stranded wires that break at the BNC to banana plug adapter about once a week, gradually shortening the antenna and raising its resonant frequency.

Out of a suspicion (vague recolection from EM class?) that a higher diameter wire would result in better power output, and some vaguely supporting research materials, I swapped out the single strand wires for a 16 AWG wire yesterday.

The above picture shows the first issue I encountered with the wire. It's too large to be easily inserted into the adapter. As you can see, I figured out a workaround. There were other issues with the antenna mostly revolving around it's increased weight per foot.

The nice thing though, was that the results were immediately different. Not long after changing out the wire, the Rockmite hit two stations in Berkeley: W6BB and NU6XB. The last time it hit one of the stations was several weeks ago. The other station was new to the Rockmite. Both were at Berkeley, and might have been different antennas from the same radio club? I'm looking forward to researching the history of the clubs.

In general, I learned that I have way more to learn. The wire change definitely caused different results. That's good. There a lot of reasons this could be though:

The increased weight of the wire led to it having a feedpoint altitude in the backyard that was about a foot lower. This would have increased the angle of radiation launch from the antenna making it more likely to hit Berkeley.
While it wouldn't have been an issue for the Berkeley spots, (they were made at 14:10 GMT, or 6:10 PST when there's little evidence of ionospheric skip propagation from the home station), the results observed during the rest of the day could have been due to the ionosphere being different from one day to the next.

One final note, I found out this morning that half wave dipoles have an impedance of 72 ohms in free space??? This makes our usual 50 ohm cable choice seem odd. Again, I'm looking forward to doing more research in this regard.

Update:

This makes more sense of the 72 ohms:

If a horizontally polarized ½ wave antenna (dipole) is greater than 0.2 wavelengths above ground, the feed-point impedance will not be noticeably affected. At 0.1 wavelength above ground the feed-point impedance of such an antenna will be closer to 20 ohms, rather than the 72 ohms expected at optimum height. For example, an 80 meter dipole needs to be about 50 feet above ground and away from other objects for best results, and then a 75 ohm transmission line cable would be used. If a 50 ohm cable is desired (to better match with the radio) the antenna height could be more like 35 feet above ground. Experimentation is the best means of determining the best height because one cannot be sure where the true ground level is located (it may be under the earth level).

The Valentine's Day Magnetic Monopole

There's an assymetry to the form of the two Maxwell's equations shown in picture 1. While the divergence of the electric field is proportional to the electric charge density at a given point, the divergence of the magnetic field is equal to zero. This is typically explained in the following way. While we know that electrons, the fundamental electric charge carriers exist, evidence seems to indicate that magnetic monopoles, the particles that would carry magnetic 'charge', either don't exist, or, the energies required to create them are so high that they are exceedingly rare. That doesn't stop us from looking for them though! Keeping with the theme of Fairbank[1] and his academic progeny over the semester break, today's post is about the discovery of a magnetic monopole candidate event by one of the Fairbank's graduate students, Blas Cabrera[2]. Cabrera was utilizing a loop type of magnetic monopole detector. Its operation is in concept very sim

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

Now available as a Kindle ebook for 99 cents ! Get a spiffy ebook, and fund more physics The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems , there seem to be fewer explanations of the procedure for deriving the conversion, so here goes! What do we actually want? To convert the Cartesian nabla to the nabla for another coordinate system, say… cylindrical coordinates. What we’ll need: 1. The Cartesian Nabla: 2. A set of equations relating the Cartesian coordinates to cylindrical coordinates: 3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system: How to do it: Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables. The chain

More Cowbell! Record Production using Google Forms and Charts

First, the what : This article shows how to embed a new Google Form into any web page. To demonstrate ths, a chart and form that allow blog readers to control the recording levels of each instrument in Blue Oyster Cult's "(Don't Fear) The Reaper" is used. HTML code from the Google version of the form included on this page is shown and the parts that need to be modified are highlighted. Next, the why : Google recently released an e-mail form feature that allows users of Google Documents to create an e-mail a form that automatically places each user's input into an associated spreadsheet. As it turns out, with a little bit of work, the forms that are created by Google Docs can be embedded into any web page. Now, The Goods: Click on the instrument you want turned up, click the submit button and then refresh the page. Through the magic of Google Forms as soon as you click on submit and refresh this web page, the data chart will update immediately. Turn up the:

Copasetic Flow

Search This Blog