|
President's Message
It's beginning to get a bit chilly outside, time to get that fall antenna work done. Otherwise, it will be so cold you can't tell whether you're still holding the tools or not! Besides, it's easier to get those dipoles up in the trees when there are no leaves to block your view.
I already have one person interested in kit building this winter, there must be a couple more of you out there who would like to build your own HF regen receiver from scratch. I'll be building my own and we'll be learning together. The Desert Ratt III is a design by Paul Harden, NA5N, and has been built by people on the internet QRP mailing list. Total parts cost should be in the $10 to $15 range, you supply your own enclosure (something from Radio Shack would be fine). It's a very buildable design, and I'll guarantee, as always, that your efforts will be successful.
You will notice that we're accepting bids on the two tube HF amps the club owns. We are going to take the profits from their sale, and buy a contest-class amp, probably something like a SB-220. Our goal is to have a fairly robust amp so people aren't afraid to use it. This is not the case with the current equipment.
W1RH has done a great job of scheduling the meetings. December's meeting will have a special guest, Mr. Vince Kajunski, of the Boston FCC office. We will be discussing club finances and the costs of running FARA at the January meeting, so I urge you all to attend.
73,
Peter, KA1AXY
Digital Concepts for the Millennium
By Ed, W1NXC
With the current interest in analog-to-digital conversions (see Bob W1RH's article in the October issue of The Circuit) it becomes necessary to concern ourselves with the introduction of random noise which intrudes at the junction of the analog-digital interface. The elimination of so-called low-end noise can be particularly troublesome but some limited success has been achieved by employing Trellis coding, equipped with a non-coherent phase quantizer to minimize arbitrary Gaussian interference.
While the intrusion of any type of noise in the analog-to-digital conversion process is a problem that must be dealt with, control of the avalanche gain and quantum efficiency of the junction is of prime importance. This calls for careful analysis and design of the asynchronous control interface adapter (ACIA). It may even become necessary to develop an algorithm of the parenthetic regression of the noise source, using an arbitrary Nyquist spectrum to assist in the diagnostic differentiation of the average signal distribution.
Although most amateurs are familiar with noise mitigation procedures, in some instances random phase modulation or jitter is more annoying. This is usually the result of digital circuitry that exhibits a non-uniform quantizer transfer characteristic. It is often necessary to modify the bipolar timing signals which would allow the framing code to block any intersymbol pulses from interfering with the logic circuits. In very severe cases it may even be required to provide redundant interface units which could be controlled by an integrated nodal timing supply.
Finally it should be recognized that at the receiving end of digital circuits, the inverse of the processes used at the transmitting end must be provided, and very careful attention must be employed to minimize degradation of any kind at the analog-digital interface. It is
...Continued from page 1
|
|
