" drawings within this website. If you need the
Adobe Acrobat Reader,
from the Adobe Website by clicking on the Adobe box immediately below:
Your Connection to
Take a look at my CORROSION TOPICS
page. Lots of unfortunate mistakes and cures. Complete with closeups!!!
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
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.
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
has a great discussion of the Extended Double Zepp
There is a terrific series of articles
(60+ pages in pdf format, available from the ARRL
website, by Walt Maxwell, entitled:
It was published in QST between April 1973 and August 1976
(not continuously.) Just click on the title to hyperlink there. Thanks to
for the tip that it was there!
like to recommend the program EZNEC
by Roy Lewallen,
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
or just click the button below
'bit the bullet' and bought
so I could reproduce my Autosketch
drawings & schematics here on my website. It took a while to figure out how
to get the drawings (they are "drawing.skf"
files-which ONLYconvert (normally) to Windows Meta File:
or Autodesk Drawing Web Format:
The problem was that I'm running Windows
2000 Professional (e.g.
and from the starting instructions, etc. I thought I didn't have a
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"
When I then ran Autosketch v7,
opened a drawing, and printed it, ultimately it was saved as the appropriate
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
antenna drawing shown here is not complete... I need to add a second page of
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,
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"
VA7OJ/AB4OJ: The reference 0 dBuV at 50
ohms equals -107 dBm; and may be used in all
cases to convert dBuV to dBm.
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
Long story short: Set your signal generator
for -73 dBM and adjust your S-meter calibration
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
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
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
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
Solving for V2 gives
0.0707 volts, again across the same 50
ohms. Checking by computing the power, we get
= 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
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
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
Finally, there is a great PDF table from
I saw this antenna
in a publication somewhere several years ago, when
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.
a lot of controversy surrounding the
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...
years ago, I ran an afternoon Army
MARS SSB net just above 4 MHz at
4PM or5PM 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
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.
terrific. You could switch to the G5RV and back, and easily hear the
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.
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.
I sure wish I could have compared it to a FW horizontal loop. I might even
put up the pair, and see who wins!
antennas were designed-and patented (patent: US 6,452,553)
Chip Cohen, N1IR;
and came to me through Cliff Donley,
K8TND, who built them. The
first: a "Serpiensky
is for 2M and up.
The second: a "GODSEYE
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 ***
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