Thursday, December 30, 2010

Bell Ringers on Skype Video

Here are two views that I captured during yesterday's Skype video conference, which included a walking tour of Dave's new QTH. Click on each image to see the full-size copy.


The image below shows a close-up of the SoftRock SDR transceiver that Jack is now building.


Happy New Year 2011 to all!

Wednesday, November 17, 2010

Frequency Analysis of On-Air Audio Recordings

I used the FFT frequency analysis feature in my audio editing software to produce some views of audio from several members' transmissions as received on my Heathkit SB-104A. The results are presented in this photo album. Click on the first thumbnail image to display it full size with its caption. You can use the two arrowheads above the image to go backward and forward to compare images. Or you can select the slide show mode and navigate using controls below the photo. All graphs were made with the same settings in the audio software. Two overlay images show a pair of curves on a single slide.

Here are some additional notes:
  • All audio recordings are influenced by the receive passband and audio filtering of my SB-104A 
  • A local peak appears around 3 kHz in all graphs. This is a birdie in my receiver and should be ignored.
  • Each horizontal line represents a 3 dB amplitude step -- a factor of 2 power ratio
  • Each graph is the result of FFT analysis of the speech sample that was recorded, and the frequency content varies according to what slice of time you choose to analyze. Speech is a complex, continuously changing waveform. Pure, steady tones would give more consistent results.
  • My software can present a real-time FFT of the audio as it plays. In that case the frequency display varies continuously as expected for a complex, continuously changing waveform.
  • Increasing the FFT size from the 1024 used in these graphs to higher numbers (2048, 4096, etc.) reveals increasingly fine details, but does not affect the overall shape of the response shown in the lowest (1024) setting. 
John

Tuesday, September 28, 2010

Antique Telephone

Here are some photos from George KW7GAM showing his antique phone. Click on the slide show thumbnail to view the photos full size. George said: 
The old Western Electric telephone needed a few drops of oil on the generator shaft. I had to open it up so I took a couple of pictures.

My Dad brought it up from South Alabama when we were kids in the 1950s. I'm sure it must have been when my future company, GTE, was converting to dial in its Alabama properties. My brother and I had it working back then, and I restored it in the 1970s.

See the little key hanging on a loop of the battery wire that the telephone man used to open the compartment with the secret electronics.

Monday, September 27, 2010

Ten-Tec Hamfest 2010

Phil KB4XX and Tim WA4PTZ attended the Ten-Tec Hamfest on 9/25/10. Here's an excerpt from Phil's email report:

"For those who have never been, this is  what I would consider an “old-fashioned” hamfest… free parking… free admission… free outdoor flea market (bring your own tables (or just open your tailgate) and set up shop).  The flea market takes place in a small gravel parking lot behind the building with overflow up the grassy hillside behind that. Ten-Tec has a big tent set up in front of the building where they show off their wares… with demo stations you can operate."

Click here to see a nice photo set by KE9V. One topic of discussion on this morning's 3740 QSO was the new Ten-Tec Model 599 Eagle transceiver that appeared at the hamfest. Gee, I wonder how they came up with that model number?

Wednesday, August 25, 2010

Huntsville Hamfest Photos

Photos from the Huntsville Hamfest are on the Bell Ringers web site. You can reach that page by going to Group Photos from the Bell Ringers home page, or click here for a shortcut.

You'll find the group photo previewed here, along with other small group and individual photos from N4OLN. A thumbnail below the group photo will take you to a set of 81 photos by W4BXI. These include both people and radio gear. Also featured are a few shots taken at some of the excellent forums. SDR and the FlexRadio display seemed to be popular. I noted that FlexRadio's web site includes a link to the W9OY Software Defined Ham Radio blog. A few of John's photos show slides from the ever-popular forum by David Hathaway on Solar Cycle Prediction.

Also included is this link to the extensive collection of people photos from MCARS.

Monday, August 2, 2010

QSO on 3740

Today's QSO on 3740 kHz included KB4XX and KB4PYR operating from the Smokemont camp at the the Great Smoky Mountains National Park. I captured some of the receive audio at my station south of Birmingham. I did not have my recording software running correctly when KB4PYR was on, but I did capture some of KB4XX, along with W4UOA and KE4ID.

Here are MP3 copies of selected audio clips of the QSO. These are compressed to 32 kb/s and are stored on Google docs, where you can open each file directly or download for listening. My transceiver was not tuned in exactly, so the voice pitch is not quite correct in some cases.

KB4XX occasionally reached S9 at my station, but was mostly in the range of S2 to S6. According to Google Earth, the distance from Smokemont to Birmingham is about 249 miles.

73, John

Thursday, July 22, 2010

More Field Day Photos

Bell Ringers have shared additional Field Day photos for your enjoyment.
Click here to visit a very nice collection provided by Tom KC5UN from the DeKalb Co. ARC event.
Click here to see a report and photos provided by Warren WD4NIT from the Wedixie Club event.
    Thanks to Tom and Warren!

    Sunday, June 27, 2010

    Field Day 2010 at Zamora Temple



    Here are some photos from Saturday afternoon. Click on the slide show at any time to see the photos full size in the web album.

    Also click here for photos by Carl.

    Let me know if you have photos from other Field Day sites that may be of interest to our group.

    73,
    John WA5MLF

    Saturday, May 15, 2010

    Hank's HF mobile antenna

    Here are some photos that show what Hank uses to talk to us while traveling around the southeast.

    Tuesday, May 11, 2010

    Bell Ringers on Google Map

    Here is the most recent version of the Google Map that I assembled using Google Earth. You can click on the link below the small map to get a large view where it is easier to pan and zoom and click on the placemarks.

    With the Google Earth version of this map you can also get distance and bearing between any two points. Click here to download a copy of the Google Earth map for use within the Google Earth program on your PC.


    View Bell Ringers - 02-2010 in a larger map

    Wednesday, May 5, 2010

    Audio Recordings on 75 m

    Here are some audio clips from our QSO on 75 m this morning. Click on each call sign to access the MP3 audio file.
    These are short segments from a much longer recording. Let me know if you want to hear more.

    Wednesday, April 28, 2010

    250 mW Tuna Tin into a 730-ft. doublet

    This item caught my attention when skimming KB6NU's Ham Radio Blog. See the April 14 article here and scroll down to the topic "Another QSO of note".

    W3TIM is the operator of that QRP rig with broadcast-style balanced antenna tuner. His page on QRZ.com includes the same photo of the tuner and a nice photo of his Tuna Tin rig.

    Tuesday, April 27, 2010

    SSB Audio Compression

    This morning George KW7GAM asked for reports about how his audio sounded on 3740 kHz with and without compression. Click here for the audio recording made from my transceiver. The screen shot above shows the audio waveform as displayed in Cool Edit 2000, with text labels added to identify the two compression states. Click on the image for a larger view.

    The appearance of more black space in the right-hand, uncompressed portion of the audio waveform supports the expectation that average audio power is lower for that state. The software allows for selecting a portion of the waveform for statistical analysis. Here are some data for the two portions of the overall waveform:

    Compression ON OFF
    Minimum RMS Power: -37.89 dB -39.54 dB
    Maximum RMS Power: -10.5 dB -11.23 dB
    Average RMS Power: -17.56 dB -19.63 dB
    Total RMS Power: -16.48 dB -18 dB

    The two histograms below also show the difference. The graph for compression ON (lower left) shows a greater number of samples near the high amplitude (right-hand) side of the graph, while the graph for compression OFF (upper right) shows more samples spread across the amplitude range. The X-axis of these graphs provides the amplitude scale in dB relative to some reference not explicitly stated by the program.

    Tuesday, April 20, 2010

    W3DZZ Multi-band Antenna 80-40-20-15-10m

    This antenna has been discussed several times since W4BXI tested it at his antenna farm. Click here for a nice short article by G8ODE that covers the physical and electrical properties, including some radiation pattern plots. A detailed analysis of the antenna by ON9CVD (with discussion of trap component values, impedance and performance) is available here.

    Friday, April 2, 2010

    Antenna Tuner Matching & Feedline Lengths

    This is a recurring popular topic in our morning QSOs on 75 m.  Multiband operation of a single antenna system results in a wide range of impedance at the transmitter end of the feedline. The Hamuniverse web site provides this article with a discussion of some common scenarios that can result in a very high impedance being presented to an antenna tuner. A few good thumb rules are provided along with a table of feedline lengths to avoid and lengths that are acceptable.

    The table focuses on the 160, 80, and 40 m bands. It is worth noting that the listed lengths to avoid are computed for one frequency on each band. For example, the 130 ft and 260 ft lengths to avoid on the 160 m band relate to 1.8 MHz (assuming a feedline velocity factor of 0.95). At 2.0 MHz you may want to avoid feedline lengths of 117 ft and 234 ft. Thus, considering the entire 160 m band you may want to avoid feedline length ranges of 117 - 130 ft and 234 - 260 ft. Similarly, on the 80 m band you may want to avoid length ranges of 58 - 67 ft, 117 - 135 ft, and 175 - 200 ft. On the 40 m band you may want to avoid 32 - 33.5 ft, 64 - 67 ft, 96 - 100 ft.

    A table footnote says that "some trimming or adding of line may be necessary to accommodate higher bands". If one desires to use the antenna on ALL bands through 10 m, the set of feedline lengths needed to satisfy the guidelines on all bands may become more restrictive. Careful testing on all desired frequency neighborhoods should reveal any problem areas for matching. Then, hopefully, minor adjustments of the feedline length can accommodate the range of the antenna tuner.

    Wednesday, March 31, 2010

    W4AXL Tour

    Thanks to W4BXI for the great pictures!

    Saturday, March 20, 2010

    Dayton Hamvention 2010 “Amateur of the Year"

    Congratulations to Jim Stafford, W4QO, BellSouth retiree (1993) and Bell Ringer # 164, public service advocate and well-known QRP enthusiast, who has been named Dayton Hamvention 2010 Amateur of the Year.

    Thanks to Phil, KB4XX, for notifying us of Jim's award.

    Sunday, March 7, 2010

    N0SAP Mobile

    Here are a few photos sent by N0SAP, showing his mobile CW setup. Sap did not explain if he has a hands-free adapter for the CW rig! Hi.
    Reply from Sap: 'I am working on the hands-free adapter next using mind control.  "SAP"  N0SAP'


    Bell Ringers & TPARCA at BirmingHAMfest 2010

    Here are a few photos from the BirmingHAMfest. I'll post a copy of the group photo with names and callsigns in the group photos section of the Bell Ringers web site. Many other photos are available on the MCARS web site at this link.


    Attendees at our Saturday forum included: David KC4SBP, George KW7GAM, Carl W4UOA, Bob WA4PWA, Pat W4QAT, Ed W4DGH, Fletch W4BBW, John W4BXI, Hank K4HM, Selene KG4RMT, Ron N4DLE, Dennis N4NR, Hjordis KI4TVB, Ben W4CT, Bill KB4PYR, Phil KB4XX, Myra K3PGH, John WA5MLF.

    Bob WA4PWA told us about a fascinating new device that interfaces his cell phone with his hearing aids. It is the iCom communications interface from Phonak.

    David KC4SBP was looking for folks who worked for Southern Bell at the Hurt Building. I suggested that he should also explore the MaBellHams group on Yahoo.

    Dennis N4NR gave us a brief history of the WireNet, a bulletin board predecessor to TPARCA.org. The active community from all continents of the world enjoyed sharing information and programs on WireNet, which also provided Internet email before the RBOCs started their ISP units. We are indebted to Dennis and Jerry Pruett (SK) for establishing the foundation of today's TPARCA.org.

    Wednesday, February 24, 2010

    130' vs 110' for Multiband Doublet Antenna

    See this document for a first pass analysis of the antenna choices that W4BXI is considering.

    Saturday, February 13, 2010

    W1TP Telegraph & Scientific Instrument Museums

    Friday's snow in Birmingham was not sufficient to keep folks away from an excellent presentation by Bell Ringer #263 about the history and technology of the German Enigma cipher machine. A reference in Keith's presentation contains a video that reenacts the use of the machine during WWII. 

    A visit to the W1TP home page reveals a treasure trove of information and photos of interest to collectors and historians. The focus is on telegraph equipment and scientific instruments and the Enigma. One of his web pages contains some nice photos from the 2009 Dayton Hamfest.

    Enjoy!

    Tuesday, February 9, 2010

    75 m Loop Antenna at W4UOA

    Corrected version -- original had results for double the intended loop length.
    Here is some analysis of a loop antenna proposed by W4UOA. The following slide show presents impedance vs frequency for several bands. Resistance and reactance are plotted in the upper half of each slide, and impedance magnitude and phase are in the lower half. Click on any slide to view it in the source album. Additional magnification is available using the magnifier icon in the Picasa album view.



    The radiation patterns below show the typical progression in frequency, with more lobes and lower angle of radiation as frequency increases. There is a large amplitude difference between the peaks and nulls in the patterns at higher frequencies.



    The antenna elements and support wires are the silver lines. The feedline is blue. The color-coded radiation pattern was left at original scale to show its relationship to the antenna structure. The program allows zooming the pattern much larger, such that the antenna structure is engulfed. Viewing at any azimuth and elevation angle, in increments of 5ยบ, is available. Standard 2-D plots are also available.

    The predicted performance of this antenna seems consistent with other published analyses of loop antennas, and does not appear to be adversely affected by un-grounded metallic support wires.

    Thursday, February 4, 2010

    Radio Estate Sale for Oren Anderson, W4HDF

    KE4ID is in the process of posting items for Oren's estate sale. You can view available items on this page of the Birmingham Crystal Radio Group web site. Check back often to see additional items as they are added.

    Thursday, January 21, 2010

    NVIS Antenna Resources

    NVIS antennas have been a very popular topic among our members recently. A very interesting view of NVIS potential is found in the Hourly Area Predictions web page shared by ki4sgu. Use the pull-down menu under General Charts For Global HF and select Atlanta, then click the display button. The resulting color-coded chart indicates recommended frequency ranges for HF radio communication with the Atlanta area. It seems to conform fairly well with our morning QSO experiences on 75 and 40 m.

    There are many published resources about the design and performance of NVIS antennas. Here are a few that we discussed recently on the air:
    We look forward to additional reports from members who are experimenting with these antenna designs.

    Monday, January 11, 2010

    Impedance of Twisted Pair Wire / Cable

    A recent morning discussion by our group on 75 m included the use of twisted pair wire or cable for certain HF antennas. There were questions about the impedance of twisted pair wire at HF. Since Jack KE4ID is building a 2-conductor Beverage antenna using "field phone wire", Bill KB4PYR suggested that he use a noise bridge to estimate its impedance at the HF range of interest. A good article about Beverage construction is this one by W8JI.

    Today Jack advised that his noise bridge measurements show the impedance to be about 100 ohms in the 80 m frequency band. The results were the same whether or not a current balun was included at the source. The 100 ohm value of impedance at radio frequencies is consistent with many web pages that can be found using the search string "twisted pair cable impedance". One example source is the article Twisted pair cables.