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November 2009 Archive

 

29 November 2009

I've spent the last several days drafting the assembly and operations manual for one of my new kits, the Z1203A DC power coupler. The Z1203A couples DC power to a coaxial feeder to power a remote amplifier such as the Z10040B, or a remote active antenna such as the forthcoming Z1501C active antenna.

The manual is about 85% completed,  to be finished when the enclosures arrive in the next couple days.

To write a manual, I follow a "build, photograph and write" process. I built the first Z1203A printed circuit board several months ago when the PCBs arrived. During the first build, I made a couple pages of handwritten notes with a rough construction order and notes and took a dozen photographs.

The purpose of the first build was to verify the PCB layout and compare performance against the prototype, not to develop the manual. The second build this week used my earlier notes but I found several places where a slightly different order made more sense. And, this time I completed all the connecting cables in their finished format, or at least finished up to the point where the enclosure work is required.

After installing each  group of components, I photograph the board and write the associated instructions. I repeat this process until finished. This step-by-step process works well for me as it breaks up the writing and building into small chunks.

By the time the manual is finished and this Z1203A is completed and installed in the enclosure, I'll have spent about 40 hours in the process. (This 40 hours is just the assembly and manual writing time, and does not include the original design, prototyping, schematic capture, PCB layout, etc.) The 40 hours breaks down to about two to three hours in actual soldering iron work and the remainder in photographs and writing.

The Z1203A is a 100% through-hole part kit and I believe an average builder will be able to assemble it in two to three hours.  About half that time to stuff the printed circuit board and half to build the connecting cables and install the cables and PCB into the enclosure.

The photo below is of the Z1203A printed circuit board I built this week.

 

 

23 November 2009

My sheet metal supplier is planning on shipping one batch of my enclosures Wednesday, with the remainder a few days later. With some luck, therefore, I will be ready to start shipping three new kits in the next couple weeks. I will have to write the manuals, build one unit and photograph it, etc.

I've also revised the Z10040B manual adding Appendix F to provide measured performance information on the "high gain" option, where the standard 1:11:4 transformer winding (11 dB gain nominal, 10.4 dB typical measured gain) is replaced with a 1:29:6 winding (15.6 dB gain nominal). The bottom line is a realizable gain of 14.6 dB, but a reduction in 3rd and 2nd order intermodulation performance and a reduction in the upper -3 dB bandwidth. These trade offs for increased gain may be acceptable to some users.

 

23 November 2009

I've made a small change to the Z10000B-U manual to reflect corrected resistance reading at the DC input pad. The corrected reading is 100K ohms to infinity, depending on your multi-meter voltage output when in ohms mode. The main thing to look for is the absence of a short circuit to ground, as the most common assembly error will be a solder bridge to ground.

 

20 November 2009

I've had a promise from my sheet metal supplier that he would work at finishing my enclosures tomorrow, Saturday. I hope that nothing interferes with his plans.

I recently had a customer request a Z10040B Norton Amplifier to be built with higher gain than the normal 11 dB design. It's possible to increase the gain, within reason, by altering the transformer turns ratio. For the details on how this works, see the circuit theory section of the Z10040B manual, along with the underlying Norton amplifier patent reproduced in the manual. With a 1:29:6 turns ratio, approximately 15 dB gain can be achieved. The down side to the increased  gain include lower upper 3dB frequency limit and degraded intermodulation performance. I'll add details to the Z10040 page over the next few days.

I've also prototyped a new filter,  the Z10100 AM Broadcast notch filter. The Z10100 is intended to be used where a single AM medium wave broadcast station must be reduced in level by 50 dB or so without affecting reception of other AM stations. In the amateur radio context, the Z10100's advantage over the Z10020 band reject filter is much better 160 meter band performance. As the Z10100 becomes closer to production, I'll add a page. The table below summarizes the differences.

 
Parameter Z10040 Band Reject Filter Z10100 AM Notch Filter
Frequency Rejects 450 KHz - 1750 KHz 3 dB bandwidth is typically 150 KHz, between 500 and 1700 KHz, center frequency set at time of filter construction.
Rejection Depth 80 dB minimum at deepest part of stop band, typically > 90 dB. Typically  50 dB
Impedance 50 ohms; 75 ohms on special order 50 ohms; 75 ohms on special order
Intended Use Where multiple strong signals in the medium wave broadcast band must be suppressed, or one very strong station requires high reduction. To reduce a single medium wave AM signal. Other AM signals experience minimal reduction in signal strength. For amateur radio use, very low loss at 1.8 MHz is a major plus.
Typical insertion loss at 1.8 MHz (160 meter amateur band) Standard Z10040B approx. 3 dB; 160 meter optimized version approx. 1.5 dB.

Insertion loss significantly improves by 1825 KHz.

For center frequency < 1600 KHz, approx. 0.5 dB.
Price $77.50 plus options (if ordered) and shipping Preliminary $97.50 plus options (if ordered) and shipping.
Power Level Receive Only - 100mw max Receive Only - 100mw max

 

The Z10100 prototype rejection, center frequency 1340 KHz. 50 dB rejection bandwidth is approximately 30 KHz.
 
 
08 November 2009

A report recently was posted on the Elecraft reflector noting anomalous SWR values displayed on a K3 transceiver when a Telepostinc LP-100 vector wattmeter sensor was installed on the K3's output connector. 

In order to independently assess this report, I ran a series of tests with my K3 and LP-100 wattmeter, with the results at SWR Accuracy

 

04 November 2009

One bit of amateur radio lore is "a toroid inductor is self-shielding" and hence does not have an external field to interact with other inductors or with nearby conducting objects such as the enclosures.

Like many fables, there's some truth in this statement, but it's far from being 100% correct. In building a prototype notch filter recently, I ran across a case where there was not enough room to space toroid inductors to minimize unwanted coupling and hence found shields between adjacent inductor necessary. This lead me to make some simple measurements to demonstrate the difference between the external fields of a toroid and solenoid inductor. I've added a new page Toroid and Solenoid External Field with more information.

 

02 November 2009

I've added an update to my Softrock page with temperature stability data on my 7 MHz Softrock Lite I receiver. The page is available by clicking here and the new data is near  the bottom of the page.

I've also shortened the kit construction poll questions at the top of this page to avoid odd text wraparound. If you haven't voted yet, please do so. If you have voted, thank you.

 
02 November 2009

My sheet metal supplier reports some progress, with the Z1203A DC power coupler enclosure in production. There's a reasonable chance all the metal work will be finished during November, but no promises as it's not within my control.

 

01 November 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.

Late last month, 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 received five responses, three for surface mount and two for through hole. To make responses easier, I've constructed a "push button" poll using a service from www.blogpolls.com asking the question. I'll leave it at the top of the updates page at least this month and possibly longer.