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The tone reduction in the 599ZX always works.

Noise reduction

The Noise Reduction feature is not the panacea that I had envisioned, li a signal is weak, it definitely helps. Noise reduction is just that: The noise is reduced, but not gone. Most weak signals are made more readable when activating this feature. However the signal must he just above the noise and not in it. The audio is a little more harsh (not distorted) when using Noise Reduction. However, if the audio is distorted, the noise reduction actually makes the audio worse. My guess is that the software doesn't recognize distorted audio as speech and removes parts of it, causing even more distortion (all the more reason to keep your transmit audio as clean as possible!),

I tried the noise reduction feature on 2-meter FMt Signals that were barely above the noise were made more readable. They too were made a little harsh-sounding by this feature.

I also tried the noise reduction on lightning static crashes, It did help some on SSB, but apparently there is ver> little you can do to fight those large bursts of energy.

AM line-noise reduction

This feature is absolutely amazing! I occasionally do some DXing on the AM broadcast band and even though power lines in our neighborhood are buried, I am sometimes plagued by 60 Hz line noise. This noise completely covers weak signals and is at best a minor annoyance on all but the very strongest signals.

To test this feature, I tuned in a weak signal on the AM broadcast band that had so much 60 H/ noise on it that spoken words could not be understood, Activating the AM l ine Noise Reduction feature produced a perfectly clean signal, There was no sign of 60 Hz line noise. This feature is different from the Random Noise reduction described above. It can be set to either 50 or 60 H/ (user selectable) and only removes noise pulses at the selected frequency. The manual notes that this 32 73 Amateur Radio Today • May 1997

feature won't work on SSB. and it doesn't, but there's no explanation why.

Data modes

There is not a single mode but many different ones. They include RTTY AMTOR, FACTOR. G TOR, HF Packet. CLOVER, SSTV, WEFAX, I did not tr\ any of them so I can't tell how much the599ZX improves operation—hut if operation in the other modes is any indication. the 599ZX w ill really help in these.

Test mode

This mode reconfigures the 599ZX into several different pieces of lest equipment. They include a sine-wave generator, a two-lone generator, a peak and true RMS voltmeter, and PL (CTCSS) decoder/encoder.

"Alt you hear is a very short ping when the interfering carrier comes on, and then no more carrier! Very neat!"

The sine-wave generator produced a very clean sine wave on my oscilloscope. The le\el and frequency are both adjustable and are displayed on the LCD,

The two-tone generator produced the two tones that can be used for transmitter adjustment. The level is adjustable.

A peak and true RMS voltmeter are available simultaneously. The range is limited to 2000 mV (2 volts).

The PL decoder is an interesting feature. I connected the 599ZX to a 2-meter rig and began kerchunking the area repeaters (and yes, I identified with my call!). The unit will display the PL frequency in Hz and the level in millivolts. The 599ZX can be used to determine the PL frequency of a private repeater providing that you can hear stations on the input or if the repeater transmits its own PL. The 599ZX can also generate PL tones. Sincc most VHF and UHF rigs now-come with PL isome can even detect the PL frequency of the transmitter), the only uses I can see for this feature are (l) your rig's PL has failed; (2) you're using an old rig without PL (admittedly clunky and expensive-- but it would work): or (3) you need PL to access a 10-meter repeater with your HF rig.

These features are interesting but I don't know where or when I would use them. However, they are there if you need them.

While I was shopping for a DSP I found out that one of the other brands offered an audio spectrum analyzer function when coupled to a PC. I would have expected the 599ZX to include this function since it is the most expensive unit available. I would definitely trade the AC voltmeter and tone generator functions for an audio spectrum analyzer. Most people have an audio generator, oscilloscope (to set the ieve?) and frequency counter (to set the frequency), but how many ot us have a spectrum analyzer? I have access to one at work, but most hams don'i have one, either there or at home. I hope software upgrades will include this option.

Low-pass/high-pass filter

The I liter high-pass and low-pass cutoff frequencies arc individually adjustable. They were most effective when the low pass was set to 3000 Hz and the high Pass to 300 Hz. The manual said that they could be used in plaee of a SSB filter. I adjusted these controls in an attempt to reduce some of the interference from nearby stations when using SSB, but audio DSP is no substitute for a good SSB filter in the receiver's IF My HF transceiver has IF shift and this does help in many situations.

DSP in the work environment

I work in an aerospace test laboratory where we do vibration testing, among other things. Vibration testing consists of putting the test item on a shaker (serv similar to a speaker but much larger). The shaker is driven by a large amplifier (approximately 50.000 watts) over a frequency range of 5 to 3000 H/. Vibration sensors ¿ire attached to ihe test item at locations where parts may go into resonance at certain frequencies. These sensors are not frequency sensitive and return signals from the vibration frequency. rattles, fuel or air passing through the test item and any other source of noise-

During testing we sweep the frequency of vibration over the 5 to 3000 Hz range. We plot the outputs of the sensors vs. frequency to see where certain areas or parts go into resonance. Very often the rattles, fuel and air noise completely covcr the vibration signal. To filter out all this extraneous noise we use DSP tracking filters. They have a moving narrow bandpass window that tracks or follows the excitation frequency. Without them all we can see is noise—no signal is visible. With them we are able to identify very weak signals buried deep in the noise. At times the signal can be as much as 20 dB below the noise!

It's worth it

At $370, the Timcwave Technology 599ZX is the most expensive of all DSPs available, but you're getting your money's worth and a lot more. The 599ZX has the fastest processing time, so there is no delay in output when you tune the dial. You listen in near real time (18 ms). The six memories are a definite plus—-you can switch modes at the push of a button instead of having to adjust many knobs hoping that you have them all set properly. It is also very nice having all of the values and the mode displayed on a backlit window rather than trying to figure out the settings by looking at ihc pointer on a knob. The 599ZX has provisions for connections to two radios—a definite plus if you plan to use the DSP with more than one. There is no need to switch connectors—you just push a few buttons to switch radios.

I am very pleased with the DSP-599ZX. In several weeks it has enabled me to make DX contacts that would have been impossible without it. Other contacts that would have been difficult without it were made much more enjoyable, Every feature that I was able to test worked as stated in the manual. There were no operating quirks or compromises, The design and operation of the unit was well thought out in every area. For further information, contact Time wave Technology, Inc+, 2401 Pilot Knob Rd., St. Paul MN 55120. Phone (612) 452-5939; FAX (612) 452-4571; E-mail [email protected]. Their Web site is at http://www.timewave.com, Be sure to tell them 73 sent you! E9

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