Bell Ringers Map

Here is a snapshot of a map (updated 2/18/2010) that includes most of the Bell Ringers who appear on 40 or 75 m.  Click on the image to magnify or to download. In this view I've left off the details of cities and roads to provide a less cluttered view of were our members are located.

The placemarks are defined in a KML file that can display in either Google Earth or Google Maps (for viewing in a web browser). Let me know if you'd like to see a different view or if you want to make some yourself using a copy of the KML file.

Radios with Micromachined Resonators

An article in the December 2009 issue of IEEE Spectrum describes how precision micromachined mechanical components, especially resonators, can provide performance superior to that of electronic components for key functions in wireless handsets (e.g. cell phones).  Two valuable characteristics of such components are:

• zero or very low consumption of battery power
• very high Q in resonant circuits (e.g. > 10,000 at 1.5 GHz)
  

 Dr. Nguyen argues that electronic solutions, including software defined radio designs, are not likely to be practical for wireless handsets due to their requirements on battery power. He points to the presence, in today's cell phone designs, of certain electro-mechanical components:

• thin-film bulk acoustic resonators (FBARs), 
• surface acoustic-wave (SAW) resonators, and 
• quartz crystals.

He predicts that future designs will incorporate MEMS components to overcome the challenges of purely electronic approaches to radio front ends. He reports that handset makers and DARPA are funding work in this area. For additional background on this work, with lots of nice illustrations and article links, visit Dr. Nguyen's web site which includes this link to a research summary.

Saturday Net on 7230 kHz

The signal reports among participants in the Saturday, 26 Dec 2009 net confirmed the continuing lack of propagation at distances of less than about 250 miles. Without a map in front of me that shows the locations of participants, it is hard to visualize the relative distances and directions among stations. Below is a map view showing the participants' locations and a dark shaded area representing the approximate zone of "no copy" (aka donut hole) relative to Birmingham. Click on the image to magnify.

To represent the ability of various stations to hear each other I produced another view with color-coded lines between many (but not all) pairs of stations. Red signifies good copy and blue signifies poor or no copy. In general, stations that are at least 250 miles apart were able to copy each other, although this distance threshold seemed to be growing as time progressed beyond the 0900 CST start of the net. W4BXI reported poor copy of K9JWJ although they are 307 miles apart. I used purple to mark that path.

Hopefully, this picture will improve as sunspot cycle 24 gets going!

Museum of Radio & Technology

Visit the Museum of Radio & Technology in Huntington, WV. Their web site includes:

• A virtual tour slide show with 175 photos that include antique radios and other technology on display
• A tour of major display areas that includes captions for many of the items in photos

 A local TV news report provides a brief video tour and commentary on some of the exhibits.

Thanks to W8OI and KA4ZCO for sharing the info about this remarkable museum!

Antenna Wire Candidates

W4BXI recently shared some samples of antenna wire candidates for review and discussion. I've stripped back the tough insulation on the telco wire types to reveal the conductors and check their wire gauge. Below are photos of the samples, with captions. Click on any photo to magnify.

This first photo shows two similar drop wire types, both with copper-clad steel conductors. Telco #1 appears to be 16 ga, based on my adjustable wire stripper. Telco #2 is 19 ga, based on measurement with a telco wire gauge that has calibrated openings for 19, 22, 24, and 26 ga. The insulation is tough, but manageable with a sharp knife. The copper cladding still looked like copper after my scraping with a knife.


This photo shows two identical or very similar drop wire samples. Both have 2 pairs of 24 ga copper wire. Non-metallic (probably Kevlar) strength members are located near the outside edges of the outer jacket. The wires are located between the strength members. The outer jacket insulation is very similar to the that of the first two samples.


This last photo shows two types of single-conductor stranded wire. #4 has 7 strands of 24-ga bare copper, THHN insulation that is resistant to gasoline & oil. #5 has many strands of tinned copper wire.

Lineman's Test Set from 1940's

From WA9JNM:
You might like these pictures of my grandfather's telephone lineman box. He worked as a lineman during the 1940's in southern Indiana. The darn thing still cranks out the
voltage around 30 volts. 73's Steve

What is that single sideband?

Today's discussion on the air was good for stimulating the brain cells as we considered what a single sideband RF signal really consists of. The components of a classic AM signal example using a single, steady audio tone are familiar and are well-represented in the ARRL Handbook and numerous textbooks. In my copy of the Handbook, the chapter on Mixers, Modulators and Demodulators derives the result of mixing (multiplying) a carrier and a modulating frequency. The result is shown as:

AM signal =

sin 2f_ct + ½ m cos (2f_c - 2f_m)t - ½ m cos (2f_c + 2f_m)t

where: f_c is the carrier frequency, f_m is the modulating frequency

You recognize the first term as the carrier, the second term as the lower sideband and the third term as the upper sideband.

A simple view of single sideband would discard the carrier term and one of the sidebands. This could be implemented, for example, using a sharp filter. Examining the term that is left shows a constant sinusoid (cosine function) at a frequency above or below the original carrier frequency by an amount equal to the constant modulating frequency.

During our discussion I postulated that if I transmit a pure (single frequency) audio tone on my SSB transmitter and did not tell you where I was tuned (e.g. 3740 kHz), you could not tell, by tuning your receiver, what audio tone frequency I was transmitting. This is supported by an illustration in the Modulating Sources chapter of my copy of the Handbook. It shows a spectrum analyzer display with a single peak and an oscilloscope view of a constant amplitude RF envelope. The caption labels it as “an unmodulated carrier or single-tone SSB signal”.

Another way of saying this is: Suppose another ham tunes up with a carrier at 3738 kHz. What do you hear at 3740 kHz on your SSB receiver on LSB? You hear a 2 kHz audio tone. Now suppose I transmit a 2 kHz audio tone on my SSB transmitter on LSB on 3740 kHz. If you are listening on LSB on 3740 kHz you hear a 2 kHz tone. The effect is the same.

In the absence of more rigorous analysis, I maintain that a constant pure audio tone transmitted on SSB is equivalent to an unmodulated carrier. Of course, the real world equipment generating such a signal will add some distortion, making it not precisely identical to an unmodulated carrier. Also, a voice waveform is highly complex, with multiple varying frequencies and amplitudes.

The more rigorous treatment of SSB (example) uses math that is equivalent to the phasing method of generating SSB. It is a notch up in level of complexity compared to what is presented in the Handbook. It is also the basis of many communications systems that we take for granted today: broadband Internet access, digital TV, cell phones, etc.

Comments?

John WA5MLF