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August 2011 Archive
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02 August 2011
I've been taking the evenings off for the last month or
so, and consequently have not recently updated this web site.
In the next week or two, I will provide details on the
following:
- The Z1501D active antenna is replaced with the Z1501F
model. The F antenna has several incremental improvements over the D model.
The F version is the same price as the D antenna. However, the F antenna
requires higher operating voltage than the D and consequently is intended to
be used with the Z1203B DC coupler, not the Z1203A coupler. The B coupler is
$20 more than the A coupler. I have a few Z1501D and Z1203A parts on hand
and can deliver the D/A antenna and coupler, but I recommend it only where
it is essential that the antenna operate on 12V DC, such as where battery
power is used for portable operation.
- New low pass filter, the Z10024A, intended for VLF/LF
use. The filter can be provided in a variety of cutoff frequencies, with
models already supplied with 518 KHz, 125 KHz and 50 KHz frequencies.
- New elliptic high pass filter, the Z10023A, with
extremely sharp transition between 1700 KHz and 1800 KHz, intended for
maximum loss at frequencies in the upper part of the AM broadcast band while
providing loss loss at 1800 KHz and above.
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11 August 2011
One project keeping me busy this month is cleaning up my
antenna test range. In the process, I tried a few ideas that worked well enough
to recommend to others.
First is coax cable selection. For my active antenna work,
I use CATV-type RG-6 cable because it's what many customers use. It's reasonably
priced and F connectors are easy to install and, if done properly, are
weatherproof.
My experience with quad shielded cable has not been
good--installing F connectors are a real chore. It's next to impossible to slip
the Snap-N-Seal connector over the cable to the correct depth—where the center
conductor insulation bottoms against the connector end and the center conductor
extends slightly beyond the connector end. I found this to be true for both the
special Snap-N-Seal connector for quad shielded cable and the "universal"
Snap-N-Seal connector intended to work with all RG-6 cable types. (I know
there's a special flaring tool to expand the braid and jacket that is said to
resolve this problem, but I have not tried one.)
For this project, I decided to go with tri-shield cable,
Belden part number 7915A, with two foil shields and 80% copper braid shield.
Belden 7915A has a solid copper center conductor, important for improved low
frequency performance and reduced IR drop for DC power supplied over the coax
cable. It's direct burial cable, although it's not flooded.
The correct Snap-N-Seal F connector for this cable is
SNS-6, and the Snap-N-Seal BNC connector for this cable is SNS1P6BNC.
What a difference; both the F and BNC connectors install
very easily.
I bought the cable and Snap-N-Seal connectors from TS
Electronics
http://www.tselectronic.com/index.php
I should note that Snap-N-Seal connectors require a
special installation tool and are not the normal crimp-style connectors.
The cable I bought has a white jacket, and it's also
available with the traditional black jacket.
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Second, I bought a label maker, a Brother model PT-1400
capable of printing on up to 1" wide tape. One feature of the PT-1400 permits
rotated, repeated text which may then cut and wrapped around wiring and cables.
The photo below shows a label applied to a length of the
7915A cable.
The type TZ laminated tape used by the PT-1400 is
available in several formulations, and for wrapping cable and wire, the
"flexible tape" version should be used.
TZ tape is said to be weatherproof and UV stable.
I bought the label maker (I went with a refurbished
printer, and it looks like and works like it's brand new) from PTouch Direct at
http://www.ptouchdirect.com/
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To bury one or two small diameter coax runs, a
narrow slit made with a lawn edger can be used. In this case, I had five runs of
RG-6 and an 8-conductor rotor cable to bury. I hired the landscaping service
that cuts our grass to trench in the cable, as it was more work than I cared to
undertake. The technique used worked well. They used a gasoline powered edger
and cut two narrow parallel slits about six or eight inches apart. Then, a
square ended spade was applied at about a 45 degree angle to cut a wedge shape
from one of the slits. The wedge was then levered up and a small amount of dirt
removed from the bottom and the cable laid in place. The turf flap was then
folded back and pressed in place.
The coax run is about 125 feet and it took two men about
an hour and a half to complete the job.
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We have a walk-out basement and to make an entrance
for the cables, I cut two holes through the siding and support 2x10 using a hole
saw. The cable entrance is 2" PVC pipe with 90 degree elbows, held in place with
silicon caulk. Similar arrangements were added to our house for furnace air
intake and exhaust and hot water exhaust, and the PVC has held up well in that
application. |
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With five runs of coax cable and rotor cable,
there's still ample room for additional cable in just one of the two entrances.
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At the antenna end, I also labeled all the cables.
To provide for maximum flexibility, I terminated all five coax runs with male F
connectors near the mast base, and connected them to the associated antennas
with jumper cables and a double female F connector.
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The coax cables are all identified with labels. The
splices are wrapped with silicon rubber self-fusing tape, which is the best
sealing method I've found other than adhesive-lined shrink tubing.
The coax cables are held in two 10 place tubing clips. The
tubing clips are not expensive - $1.50 or less - and make a nice way to hold
small diameter coax in place. The coax can be pulled loose or snapped into
place. McMaster-Carr carries this as part number 2216T13 Multiline Plastic Clamp
for 1/4" Outside Diameter, 10 Slot.
The self-fusing tape is McMaster-Carr part 7643A471 (Same
as 7643A75) High-Temp Self-Fusing Silicone Rubber Tape Rectangular, 1" Wide, 12
Yds Long, .020" Thk, Gray.
http://www.mcmaster.com/
To use the tape, start on one end and apply tension while
wrapping, to the point where the tape stretches in length and shrinks to about
half its original width.
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23 August 2011
Quite an interesting event today - an earthquake in
Virginia. Present reports put it between a 5.8 and 6, centered in Mineral, VA,
about 125 miles southwest from Clifton.
I was working on the computer on the second floor and
experienced quite a shaking, to the point where I thought the house was going to
collapse - my wife and I ran out the front door until it was clear the event was
over.
Looking things over, fortunately no damage appears to have
occurred. A few books fell out of the bookcases, pictures hanging on the wall
are no longer straight and a couple pieces of test gear hit the floor in the
basement. No real damage that I can see at the moment, for which I am grateful.
I've spent quite some time in California on various work
projects over the last 30 years and have experienced several small tremors -
about the same effect as you would notice from a large truck passing 50 feet
from you. This one was much, much different. At first, I thought it was a
military helicopter -- we frequently have low height flybys from military
helicopters and they will shake the house. A few seconds into it, however, it
became apparent that it was not a helicopter flight and the shaking intensified
and I could hear things hitting the floor as well as hearing noise from the
house structure. The entire shaking, from start to end, could not have been more
than 15 or 20 seconds, and perhaps less. But it certainly got my attention.
The east coast is a low risk for seismic activity, and
accordingly the building codes do not mandate earthquake resistant construction
to the degree that is found, for example, in California. |
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