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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20 December 2009

As promised, a few photographs of the snowstorm of 18-19 December 2009.
 

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.
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.

The path I shoveled to reach the mailbox.
 

Looking down the path in the opposite direction, towards Clifton Road.
 

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.
 

Back yard  view. The two vertical antennas are Z1501C active antennas under test.
 
 
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.

 

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.
 

Channel Master U-bolt package. These are relatively small U-bolts, suitable for a mast of 1.25 inches or less.

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.
 

Note the "kink" at the center and the right side.

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.

Note the holes are not sufficiently spaced to fit the U-bolts.

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.

 

 
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.

 

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.
 

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.

 

 

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.

 


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.

 

 

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.

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.
 
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.
 

 

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.

 

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..  

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.