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January 2008 Archive


29 January 2008

I've spent the last week researching bias circuits and thermal stabilization for bipolar RF amplifiers. Part of this work involved extensive measurements of various parameters versus temperature. To make these measurements, I had to build a simple thermal-stable heat source, photo below.  I'll describe this and some of my measurements over the next few days.

I received today another acceptance of an article from the ARRL. This one is a simple two-page compendium of data I consistently find myself looking up during construction projects. It will be on the ARRL's web extra page, not in a paper publication. I'll add a note when its published.

Thermal chamber - usable up to 100°C. It holds the set temperature within 0.5°C.
22 January 2008

After the Jan/Feb 2008 QEX hit the mail, more Z100 orders arrived than I had anticipated and hence I ran short on some components.

I shipped all Z100 backorders this morning, and I've sent a confirmation note via E-mail to all customers for whom I could find an E-mail address. Future Z100 orders will continue to be shipped a day or two after receipt, absent some unexpected event.


22 January 2008

I've revised the 1N400x diode page to include data for two additional diode types, and also to show voltage versus current temperature sweep for a 1N4005 diode at different currents. I've also provided extensive temperature versus collector current data for a 2SC1945 RF transistor. The data on this page required about three days, full time work to collect and analyze, by the way and may form the basis of a future article submission for QEX.
22 January 2008

I'm a fan of wooden spring clothespins to serve as "third hands" during PCB assembly. I recently built a couple of Z100s and experimented with spring clothespins to hold the 28-pin socket to the PCB during assembly, as pictured below. The modified clips work better than the paper tape I've used in the past. The modified clips also work well to hold other oversize parts during soldering, such as the Z100's 3.5mm phone jacks and the coaxial power connector.

Top view - standard wooden spring clothespin without modification.

The stock clothespins, however, are a bit too wide for the PCB bottom, as they either bend the end pins or get in the way of soldering the end pins.  The simple solution to this problem is a sharp knife. I first cut about 3/16" (5mm) length from the bottom half. Using a sharp knife, I then whittled down the bottom half profile to form a tapered end. The end is now about 0.2" (5mm) wide and clears the 0.3" DIP width.
Bottom view. This half of the clothespin clip has been modified two ways:
  • Cut 3/16" (5 mm) from the end.
  • Taper the tip end to a flat point about 0.2" (5mm) wide.

These are only suggestions, and it's easy to carve wooden clothespins into custom shapes to hold particular parts to the PCB while soldering.


19 January 2008

We had a couple of visitors yesterday, pictured below. This part of Fairfax County is zoned for minimum lot size of 5 or 10 acres, so there are woods and open fields for wild life. I've seen foxes in our back clearing before, but didn't have a chance for a photo. Yesterday these two were close enough to the house for a decent photo. (Nikon D80 and Nikkor 70-300 mm zoom, with anti-vibration stabilization enabled. Zoom at 300 mm, hand-held.)

Foxes in Fairfax County are a known carrier of rabies, so it's best to keep the viewing at a safe distance, through glass, as was the case here.


17 January 2008

I've been looking at a low power HF power amplifier for the last week or so, and it's been quite educational in many aspects. One of many things it has caused me to look at is whether the standard data sheet for a 1N400x diode is accurate when it shows the forward voltage versus current as a single curve for every member of the family from the lowly 1N4001 through the imperial 1N4007. I've added a page with my findings, viewable by clicking here or via the links at the top of the page.

I've also finished reviewing manuscript edits made to my forthcoming QEX article on carbon composition (and other types) resistors. It should be published in the next QEX, issue, I believe. The article is a significantly expanded version of the information on my Carbon Composition Resistor page.


11 January 2008

I've added a page on the Tektronix P6022 current probe, viewable by clicking here or via the links at the top of this page.

10 January 2008

I've made extensive revisions to the Bill Hewlett and his Magic Lamp page, viewable by clicking here.

08 January 2008

I've added a page discussing incandescent lamps used as feedback elements in the classic Hewlett Packard audio oscillators. You may view the page by clicking here or via the navigation link at the top left of this page.

07 January 2008

I have prepared instructions on how to build a  logic to RS232 adapter for the Z100, in the form of a PDF file, available by clicking here, or via the Documents page.

I continue to recommend FTDI's TTL232R cable, selling for $20 from Mouser ( but if you have a computer with a hardware serial port, you may wish to try the logic to RS232 adapter cable.

I do not intend to provide much assistance to users in programming the Z100.

Home made adapter installed in a prototype Z100 PCB.
Second constant current load breadboard.