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20 December 2009
As promised, a few photographs of the snowstorm of 18-19
December 2009.
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Snow depth in back yard before the storm ended. Another 2
to 3 inches fell after I took this photo. Total depth in the back yard was
between 21 and 22 inches.
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Font yard snow depth. This is from a sheltered area with
less snow than I measured in the back yard. This photo is from this morning,
after the storm ended. For my non-US readers, I've included a centimeter
reading as well.
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The path I shoveled to reach the mailbox.
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Looking down the path in the opposite direction, towards Clifton Road.
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Even the bird feeder has snow on the roof. The large pile of snow at the left
side of the photo has accumulated on top of the "anti-squirrel baffle." I use
quotes because the squirrels have learned alternative way of accessing the
feeder. Some athletic squirrels will climb up a nearby tree and launch
themselves horizontally several feet onto the feeder. One bird is on the ground
looking for seed knocked out of the feeder by other birds.
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Back yard view. The two vertical antennas are Z1501C active antennas under
test.
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19 December 2009
The Weather Bureau predicted the Washington DC area would
receive 20 inches of snow this weekend, and their prediction is accurate. I
measured 18 inches in the back yard this afternoon, and several more inches fell
after the measurement. Needless to say, Clifton Road has been quiet today. The
Virginia Department of Transportation snow plows have been out all day, but most
people around this semi-rural section of Fairfax County have long driveways.
Although ours is only 90 feet long, one of our neighbors has a 700 ft driveway.
I'll work on the driveway tomorrow and Monday and hope to
get enough snow out of the way that I can put the truck into 4 wheel drive and
at least make it onto Clifton Road.
I'll have a few photos tomorrow.
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19 December 2009
This summer when I worked on designing the Z1501C Active
Antenna mounting bracket, I bought a few different types of U-bolt assemblies
for evaluation. I settled on a "universal" design from Winegard that works with
masts from 1 inch to 2 inches diameter (25 to 50mm). One set of U-bolts I bought
but never opened the package on were from Channel Master, packaged in the
card shown below.
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Channel Master U-bolt package. These are relatively small
U-bolts, suitable for a mast of 1.25 inches or less.
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I needed several small U-bolts today, and I thought of the Channel Master sets I
had on the shelf. The first thing I noted is that the U-bolts have two "kinks"
as can be seen in the photo below. The first is at the center, and an even more
abrupt kink can be seen at the right. I do not believe either is intentional,
but rather represents poor manufacturing.
All four of the U-bolts I had look the same, so it's not
the case that a bad one slipped by quality control.
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Note the "kink" at the center and the right side.
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The kinks are more or less cosmetic blemishes, in that the U-bolt will still
function. It may not conform to the diameter of the mast quite as well, but
there still will be adequate clamping force.The
next problem I found is not so minor, however. The photo below shows the
problem—the holes in the saddle are too close together for the U-bolt to fit.
The left leg is at the outside edge of one hole and the right leg shows the hole
is about one half the leg diameter too small. Looking at the clamp width,
properly sized holes would not leave sufficient material on the ends. |
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Note the holes are not sufficiently spaced to fit the
U-bolts.
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It's possible to squeeze the bolts into the clamp holes, but then
the U-bolt legs are no longer parallel and won't fit properly into holes that
might be drilled in a mounting plate. The photo below shows the magnitude of the
problem. At the saddle clamp, the legs are about 1.75 inches center-to-center,
but at the end the center-to-center spacing is only 1.55 inches or so.
This is unacceptable for anything other than an emergency where you have to have
something clamped and all the hardware stores are shut down.
It's possible, after thinking about it more, that the kinks
are not a byproduct of poor quality control, but were intentionally added as an
attempt to make a badly designed (or mis-manufactured) saddle clamp work with
these U-bolts.
Regardless of the reason, these Channel Master U-bolts are
next to worthless with the provided saddle clamps.
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18 December 2009
I've expanded my
Toroid and Solenoid External
Field page to provide data on toroid Q versus spacing from a typical shield,
with both conducting and non-conducting hardware.
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16 December 2009
I think all the parts required for the Z1501C Active
Antenna and the associated Z1203A DC Power Coupler are either in boxes in my
basement shop or on order.
Before officially releasing the Active Antenna kit, I plan
to have a couple of test builds completed to verify the documentation. I've also
tinkered a bit with a couple of component values and the hardware.
The image below show the AM medium wave broadcast band
signal level with two antennas:
- Green trace is an 80 meter band inverted vee antenna
with the apex approximately 80 feet above ground and the ends about 40 feet
above ground.
- Yellow trace is the Z1501C Active Antenna on a 10 ft
support mast.
Considering the inverted vee is a fairly good
antenna, the Z1501C gives a quite decent account of itself.
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The image below shows the active antenna's clear superiority
over the inverted vee below 500 KHz. This sweep is with the active antenna on a
shorter mast, approximately 4 feet above ground.
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09 December 2009
As promised, in-focus photos of the active antenna are
posted below. I borrowed my wife's Nikon D80 digital SLR camera for these shots
and it certainly represents a quantum leap from the old Nikon Coolpix 950 I use
to document my kit manuals. The Coolpix 950 has one major advantage over the D80
however, as it will focus in macro mode down to a few inches.
It rained most of the last 12 hours and the antenna made
it through the moisture exposure without a problem. The mast is an old piece of
TV mast, driven into the ground a couple feet.
The main elements of the Z1501C shown in the photographs
are the electronics enclosure (a Hammond weatherproof die cast box), the
inverted "L" shaped antenna bracket, made from 1/8 inch (3.2 mm) aluminum with
punched holes, two "universal" U-bolt and saddle clamps (usable with masts from
1" (25mm) to 2" (50mm) diameter, a 3/8x24 antenna mount and a whip
antenna. The electronic module output is through a short length (approximately 3
feet / 1 meter) RG-174 coaxial cable, terminated in a female BNC connector. Upon
special order I may be able to supply a female "F" connector for those who use
75 ohm TV cable. (There is no performance difference of significance when the
Z1501C is connected with 75 ohm cable instead of the more common 50 ohm coax.)
The standard Z1501C includes all of these items (plus the
electronics inside, of course) with an option of a medium length telescoping
whip or longer telescoping whip or it may be purchased without a whip, so that
you may use an old CB-radio antenna. The telescoping whip antennas are sourced
from Buddipole and are high quality construction.
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One more spectrum analyzer capture with the Z1501C. I connected the HP 3562A
Dynamic Signal Analyzer (spectrum analyzer for this purpose) to the 15.625 KHz
low frequency IF output of an HP 3586B Selective Voltmeter to increase
measurement flexibility. The image below shows the 21.4 KHz signal from NPM in
Hawaii as received this morning on the Z1501C. NPM is around 10-12 dB over the
average noise level, which for late morning on the East Coast of the US isn't
too bad. The narrow spikes are 60 Hz power line harmonics, which plague the low
frequency spectrum unless you live in a particularly quiet environment. |
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08 December 2009
This afternoon, I finished the mechanical work left to
install the Z1501C PCB in the enclosure and mount the enclosure on the bracket.
After a quick checkout, I mounted the assembly outside and connected it to a
Z1203A DC coupler on my test bench.
I took several photos of the finished antenna installed
outside, but I'm embarrassed to admit that the camera's auto-focus locked onto
the background and the antenna is blurred beyond recognition. I'll post new
photos tomorrow.
The image below is of the spectrum 23.8 - 25.8 KHz, the
VLF range I to test low frequency response. The strong signal at the left is
24.0 KHz, NAA Cutler ME. The strong signal right of center is 25.2 KHz, NML at
LaMour, North Dakota The third signal is at 24.8 KHz, about 10 dB over the noise
level. It's NLK in Jim Creek, Washington.
The narrow spike-type signals are power line interference,
spaced 60 Hz. A common mode choke will reduce the interference level, but given
the prevalence of switching power supplies, computers and the like, spectrum
noise pollution is ubiquitous. |
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As an example of other interference, the spectrum plot below
shows WWVB at 60 KHz centered in the display. The wide signal at 59.946 KHz (to
the left of center) is from (I believe) a computer monitor. It's 15 dB above
WWVB's signal, and only 54 Hz away.
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06 December 2009
I built a production PCB for the Z1501C Active Antenna
today, photographing the build and drafting about half of the instruction
manual's step-by-step parts installation section. There's still a lot of writing
to do and I need some parts, but the Z1501C is moving along.
A photo of the assembled PCB is below. The open area in
the lower right labeled T2/T3 is for an optional balanced input transformer, not
used in the normal active antenna configuration.
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05 December 2009
I've added a new page for the
Z1203A DC Power Coupler kit. The
Z1203A's assembly and operating manual is available by clicking
here. It's a 3.7 MB PDF file. I
should be able to ship the Z1203A immediately, assuming I'm not deluged with
dozens of orders (not too likely).
I've added three features to the Z1203A not commonly found
in remote DC power couplers:
- Isolated receiver connection;
- Flexible remote DC power control and
- Active pull down.
Isolated receiver port reduces power line noise from being
conducted to the active antenna. The last two features support the input
protection switching found in the Z10040B and
the forthcoming Z1501C Active Antenna. For more details, see the
Z1203A page or the
assembly and operating manual.
The next kit to be available is the Z1501C Active Antenna,
which will be used with the Z1203A. I'll start building and documenting the
Z1501C tomorrow morning and hope to have the manual finished in three or four
days. The Z1501C kit should be shipping around 7 to 10 days from now. I have all
the long lead time parts on hand, but need to order many of the electronic
parts.
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02 December 2009
As usual, I've moved last month's entries to an archive page, reachable by
clicking here or by the archive links at the top of this page.
In late October, I asked a question of my readers and potential customers on
their construction preferences for new kits and to respond by E-mail. I've kept
the "push button" poll using a service
from www.blogpolls.com asking the
question in this month's updates as well.. |
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02 December 2009
I've finished a first draft of the Z1203A DC power
injector manual this evening. It's 46 pages and has required 50 or so hours of
building, photography and writing. I believe the kit will be available for sale
in the next few days as all that is remains is to proof read the manual
and verify that I have all the parts in stock.
My rule of thumb is that it takes me about one hour to
develop one page of documentation and this manual is certainly consistent with
this experience.
The photo below is from the cover of the manual. |
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