QEX

Noisy signal to update the noise estimate, Q'. Today's DSP technology allows us to design such a system and make it cost-effective. Fig 1 shows a diagram of a spectral-subtraction system that enhances noisy speech in real time. I implemented it in a commercial product whose key components include 40-MHz TMS 320C26 DSP chips, 8 kbytes of external ROM and 16 kbytes of external SRAM. The algorithm, however, is also suitable for off-line (post-processing) operation on a personal computer. The unit...

Info

3 Testing Rechargable Alkaline Batteries and More By Ed Hare, KA1CV, and Mike Gruber, WA1SVF 17 Spectral Subtraction for Eliminating Noise from Speech Reprinted from 1995 Mid-Atlantic VHF Conference Proceedings American Radio Relay League 28, 29, 30, 31, 32, Cov IV Communications Specialists Inc 32 Down East Microwave, Inc 32 HAL Communications Corp 16 Tucson Amateur Packet Radio Corp 27 Z Domain Technologies, Inc 32

Spectral Subtraction for Eliminating Noise from Speech

A superior DSP technique removes noise from speech signals. If you operate on any of the HF bands you'll quickly notice that they all have one thing in common noise. When signals are strong, noise isn't much of a problem, but as the signal strength drops the noise begins to mask the information contained in the signal. The proliferation of low-cost DSP chips has encouraged efforts to create noise reduction equipment based on digital signal-processing techniques. The concept of noise reduction...

S O Os

5 6 7 8 9 10 11 12 13 14 15 16 SERVICE LIFE HOURS 5 6 7 8 9 10 11 12 13 14 15 16 SERVICE LIFE HOURS Fig 8 The discharge curves for a typical reformulated rechargeable alkaline D cell. Reprinted with permission of the Rayovac Corporation. discharge cycle to last longer than necessary. Fortunately, battery manufacturers have already walked this road, and in the case of the Rayovac Renewal batteries, they selected a load of 2.2 C2 for much of their D-cell test data. The smaller C cells were...

Aw I

Let's hear and see your ideas. By John Sartor. KB3XG, 1214 N Trooper Road, Norristoivn, PA 19403 I needed a band-pass filter to reduce the noise bandwidth of my 3456-MHz receiver lineup. I tried the beg, borrow or steal method with no success. Bill, W3HQT, gave me a copy of a 5760-MHz transverter article which used pipe-cap filters on the mixers. I scaled the dimensions for a 3456 version and it just so happens that a l' a-inch pipe cap works fine. I used a 2-inch square...

Testing Rechargeable Alkaline Batteriesand More

So, do those rechargeable alkaline batteries work The ARRL Lab investigates. By Ed Hare, KA1CV, and Mike Gruber, WA1SVF When we were first asked if the ARRL Lab could produce an article on rechargeable alkaline batteries, it looked so easy. We had previous testing experience with portable gel cells and lead-acid batteries and assumed the rechargeable alkaline products would follow nicely. For the most part, that turned out to be so. There were however, enough surprises, interesting results, and...

U

Fig 1 Schematic diagram of the Ultimate VFO. 14 QEX switch, DDS chip and LCD display via its I O ports. The RIT potentiometer is connected to one of the microcomputer A D ports. U4 is a standard 2-row by 16-char-acter display, and its contrast is adjusted with the use of an external potentiometer. The VFO draws approximately 130 mA at 5 V. U5, the voltage regulator, provides the 5 V, and it requires a heat sink. The VFO frequency can be increased or decreased by holding down the UP or DOWN push...

The Ultimate VFO

Scrap your old VFO for this amazing state-of-the-art design, or use this VFO for the heart of your next homebrew rig. Would you like a VFO that can provide continuous receiver coverage from 0 to over 25 MHz while also controlling your transmitter frequency The ultimate VFO can do that and more. This VFO incorporates RIT, and it displays all frequency information in 1-Hz steps. All you do is tell the VFO what your receiver IF frequency is, then let the VFO take over. The VFO uses a...