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February 2008 Archive


29 February 2008

February has turned into a month I wish I could forget. My father passed away on the 11th, just a month short of what would have been his 88th birthday. The funeral service was held on a raw cold, rainy day and I came down with the flu. Yesterday was the first day that I've been close to normal and when my wife and I returned home from grocery shopping, we found our house had been burglarized. One of the items lost was my basement notebook computer that held my Swordfish and Delphi software files and my printed circuit board layout software, including custom components.

I hope to get back to a semblance of normality over the weekend.


11 February 2008

I've been working for the last week on the small HF amplifier review. I've finished laying out a PCB with a high quality temperature controlled bias generator for bipolar transistor amplifiers, with independent adjustment of slope an intercept. More details on this later, and it will likely form the basis of a QEX submission.

I'm contemplating another run of the Z10000 buffer amplifier, in both the K2 and Universal versions. The price will be $34.95, covering the kit with all parts, double sided PCB, SMA cable and postage within the US. Availability in late April.

The Z10000 is of use to anyone contemplating using a Softrock as an inexpensive panadapter, as it's important to keep the strong local oscillator signal radiate by the Softrock out of your receiver's IF strip.

If you are interested, please drop me a note. Whether I go ahead with a second run depends on the interest level. It's not economical without a couple dozen orders and even that's marginal. I've added this note to the sticky updates.

More information on the Z10000 by clicking here (assembly manual) and here (K2 specific).

05 February 2008

I've made and analyzed three different ferrite transformers for use in the 10 watt HF amplifier I'm analyzing. Because this has continuing interest, I've added a page with the data, available by clicking here or through the link at the left side of this page.

01 February 2008

As usual, I've moved the January 2008 page to archives, reachable by clicking here, or via the navigation table at the top of this page.

In electronics, as in life, it's often not what you don't know that gets you in trouble, but rather the things you think you know but in fact are wrong. I ran into that yesterday when I add a 1N5711 Schottky diode to clamp the reverse base voltage across a 2SC1945 transistor RF power amplifier.

When I measured the reverse  voltage clamping level, I expected it to be around 0.5 volts or less. After all, a Schottky diode has a drop around 0.4 to 0.5 volts, compared with a standard silicon diode's 0.7 volts, right? When I measured around 1.2 volts across the 1N5711, I first thought I installed a 1N4148 silicon diode instead. The diode was clearly (well, clearly after using a magnifying glass) marked 1N5711.

That lead me to look at data sheets for several diodes and to measure the forward current versus forward voltage of four diode types. Because this subject is likely to be of continuing interest, I've added a new page with my data and analysis. You may view it by clicking here, or via the link at the left side of this page.

If you want the one-sentence summary: A 1N5711 Schottky signal diode does not always have 0.4 V forward voltage and in fact the forward voltage drop across a 1N5711 Schottky diode and a 1N4148 Silicon diode may be quite similar as the forward current exceeds 10-20 mA.