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.
Sunday, March 7, 2010
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!
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.
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:
There are many published resources about the design and performance of NVIS antennas. Here are a few that we discussed recently on the air:
- The Cloud Warmer NVIS Beam - A nice article found by kb4xx.
- A Short Study of NVIS - A concise presentation of the design and performance. Includes antenna radiation patterns to show effects of various design choices.
- Some Notes on NVIS Antennas - This is a link to several very detailed articles by L. B. Cebik. A free web account provides access to a treasure trove of antenna articles by this author.
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.
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.
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