Clifton Laboratories 7236 Clifton Road  Clifton VA 20124 tel: (703) 830 0368 fax: (703) 830 0711

E-mail: Jack.Smith@cliftonlaboratories.com
 

 

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August 2011 Archive

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:

  1. 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.
     
  2. 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.
     
  3. 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.
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.
 

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/

 

 

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.
 

 

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.

 

With five runs of coax cable and rotor cable, there's still ample room for additional cable in just one of the two entrances.

 

 

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.

 

 

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.

 

 
 
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.