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Your Connection to the World!!!

Another website you should not miss is:

 W4RNL - Dr. L.B. Cebik's:

LB is a very interesting person to listen to. He missed his calling, as far as I'm concerned... he is a recently retired Professor of Psychology at the University of Tennessee (GO VOLS!!!) in Knoxville, Tenn. That's right, the same school my older son Rusty is attending (and is finally going to graduate from next year!!!) And about that calling: he knows more about antennas and antenna theory, than anybody I know-he would have contributed a lot to the science and the art of antenna engineering, had he chosen that field as his original course of study.

A terrific lecturer, LB often delivers forums on antennas and related subjects at Hamfests all over the South. Go and see the website-it's truly worth the trip!!!

He has a great discussion of the Extended Double Zepp Antenna at: EDZ

There is a terrific series of articles (60+ pages in pdf format, available from the ARRL website, by Walt Maxwell, entitled: Another Look At Reflections. It was published in QST between April 1973 and August 1976 (not continuously.) Just click on the title to hyperlink there. Thanks to Alan, KB7MBI for the tip that it was there!

I would like to recommend the program EZNEC by Roy Lewallen, W7EL. It is now out in a WINDOWS version, and is an extremely capable program for antenna modeling, or just looking at what an antenna should do. His website is: http://www.eznec.com or just click the button below

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I finally 'bit the bullet' and bought Adobe's Acrobat so I could reproduce my Autosketch v7 drawings & schematics here on my website. It took a while to figure out how to get the drawings (they are "drawing.skf" files-which ONLY convert (normally) to Windows Meta File: "drawing.wmf" or Autocad: "drawing.dwg" or Autodesk Drawing Web Format: "drawing.dwf". The problem was that I'm running Windows 2000 Professional (e.g. WIN NT-5)... and from the starting instructions, etc. I thought I didn't have a Postscript driver installed. Searching around the Internet didn't help... and finally I decided to go to CONTROL PANEL > PRINTERS and try and find one on the original WIN 2000 Pro CD. It wasn't there BUT it WAS already installed as a Printer within the PRINTERS Folder. I made that 'PRINTER' the "default printer" and VOILA!!! When I then ran Autosketch v7, opened a drawing, and printed it, ultimately it was saved as the appropriate Acrobat: "drawing.pdf". Worked like a million $$$... and even worked when I sent it to myself as an attachment to an email. Now to put the antenna drawing, with a description, as a hyper-link (button/whatever.)

The 1st antenna drawing shown here is not complete... I need to add a second page of DETAILS. I would appreciate it if anyone who got through all this rhetoric would let me know that the drawing turned out OK at their end. Thanks. Just click on the underlined title for the drawing.

This is a series of very interesting messages that evolved from a question on QRP-L (the email reflector). First, the question:

• From Michael Melland, W9WIS: Found a manual for alignment of my R-71A receiver.  However.... the signal generator settings in the manual are stated in dB"micro".  I don't think it's dBu ... the "u" is actually the micro sign... my HP 8640B outputs in dBm.  Anyone know the conversion from this dB"micro"(?) to dBm or vice versa?
   
  A clue may be the levels themselves.... S9 +40 dB = +74 dB"micro" ..... S9 = +34 dB"micro"

   

• From Adam, VA7OJ/AB4OJ: The reference 0 dBuV at 50 ohms equals -107 dBm; and may be used in all cases to convert dBuV to dBm.

• From Nick, WA5BDU: The dBu (where u is the symbol for micro) apparently means that power level produced by 1 microvolt (1uV) across 50 ohms. That power may be expressed as 2E-14 Watts; or, - (minus)107 dBm. This is because 10 times log(2E-14/1E-3) equals - 107.

  Suppose your receiver S-meter calibration is intended for S9 to occur at +34 dBu. Therefore S9 is at a power level expressed in dBm of 34 - 107 or -73 dBm.  Which is equivalent to 50 uV across 50 ohms. A common standard for S9.
  
  Long story short:  Set your signal generator for -73 dBM and adjust your S-meter calibration for S-9.

   

• From George, W5YR:

  The basic formula for the dB using voltages measured across the same resistance is
                             

  dB = 20 log (V2/V1)

   

  If we let V1 = one microvolt, then a voltage V2 used in that formula will give us the number of dB that V2 exceeds one microvolt. If the result is negative, it means that V2 is less than one microvolt.

   

  The term dBm is used to mean dB relative to one milliwatt of power. Thus 0 dBm is equal to one milliwatt.

   

                      dB = 10 log (P2/P1)

   

  If P1 is one milliwatt, then a power P2 used in that formula will be shown as having a value of so-many dBm since it will be that much larger than one milliwatt. Again a negative value means that P2 is less than one milliwatt.

   

  I suspect that the answer to your question is to be found on the front panel of your signal generator - it is on my HP 606A. Look at the scale on the attenuator control. It probably shows that 0 dBm is associated with the 0.3 volt scale of the output signal level meter. The actual voltage across 50 ohms - the output load for the generator to read as calibrated - is 0.22361volts as read on the 0.3-volt scale when the attenuator is set to the 0 dBm position.

   

  Power is voltage squared divided by resistance.  So,

   

                              (0.22361^2)/50 = 0.001 watts

   

  or one milliwatt expressed as 0 dBm.

   

  If you set your output level to 0 dBm and everything is properly calibrated, then your output rms voltage will be 0.22361 volts across 50 ohms. A level of -10 dBm will be 10 dB less than that so using the first formula above,

   

                  -10 dB = 20 log V2/0.22361

   

  Solving for V2 gives  0.0707 volts, again across the same 50 ohms. Checking by computing the power, we get

   

                      (0.0707^2)/50 =  0.0001 watt

   

  or 0.1 milliwatts, which is exactly 10 dB less than one milliwatt.

   

  Your example of S-meter readings doesn't tell us anything about the relationship between dBuvolt and dBm but it does tell us how your meter is calibrated. Calculate 34 dB above one microvolt using the first formula above and you will know how many microvolts it takes to make the meter read S9. You will get 50 microvolts. Note that the difference between S9+40 dB and S9 is exactly the difference between +74 dB and +34 dB.

   

  This is interesting stuff, but it is easy to get confused with the different dB references. Just keep in mind that the decibel ALWAYS states a POWER ratio, regardless of whether that value was calculated from voltage, current or actual power values. The formulas above will allow you to find a voltage or power relative to whatever reference is used.

   

  By the way, just to keep the record straight, the pro-audio people use the "dBu" but it has nothing to do with microvolts! It is defined as

   

                      dBu = 20 log V2/0.775

   

  where 0.775 volts is the voltage across 600 ohms required to give one milliwatt or 0 dBm. Thus 0 dBu = 0 dBm if 600 ohms is the resistance involved. If not, then they are not equal but 0 dBu is always 0.775 volts regardless of the resistance involved, as long as it is "high."

  Finally, there is a great PDF table from DARC, at:

  <http://www.y06.de/y06/tools/dbm.pdf>

  

I saw this antenna in a publication somewhere several years ago, when UA1DZ passed away. The dimensions only. The drawing is mine. I haven't built one... but it's another one of those projects you'd really like to try, if only you could get the time. I am going to do a 2nd "details" page soon.

There is a lot of controversy surrounding the Double Bazooka. Probably its bandwidth claims have been exaggerated. I debated even listing it... but you know what? I used a 75M Double-Bazooka for years, with what I consider to be a great deal of success.

I know at least one genuine expert who is certain that a shielded antenna at DC ground is not any quieter than your ordinary dipole. I'm reasonably convinced that there exists math that 'proves' this-based on the explanation I heard/read. However, my own experience with this antenna over a number of years strongly disagrees. Here's the story...

Several years ago, I ran an afternoon Army MARS SSB net just above 4 MHz at 4PM or 5PM local time here in Georgia. You know just how noisy 75M can be in the still-bright sun at that time of day: awful!!! I put that Double Bazooka up specifically looking for help with the summer noise levels. It was a max of maybe 30 ft in the center, down to about 6 ft on the ends.

It was terrific. You could switch to the G5RV and back, and easily hear the serious difference. I found that I was often the only one who could copy some of the weaker (usually out of state) stations. I often copied LA, MS, AL, & SC check-ins-even in the summer. Occasionally, when the band was particularly bad, I was the only one able to consistently copy the entire net roster.

Bottom line? I don't know why it was quieter, I just know it was. It seemed to get out just about as well. So, for local (<1000mi) QSOs, it sure was a winner for me.

This design came to me from the late WA4EZN, Lucky.

P.S. I sure wish I could have compared it to a FW horizontal loop. I might even put up the pair, and see who wins!

These two antennas were designed-and patented (patent: US 6,452,553) by Chip Cohen, N1IR; and came to me through Cliff Donley, K8TND, who built them. The first: a "Serpiensky FRACTAL Bow-Tie" is for 2M and up. The second: a "GODSEYE 7-SQUARE FRACTAL" is for 450 kHz - 1 GHz. Cliff reports excellent results from both antennas. Both selections below yield the PDF Drawing.

*** Coming Soon: A 20M or 30M Fractal Vertical ***