DSP filters

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From: Byron8LCZ@aol.com
Date: Fri May 05 1995 - 19:10:59 EDT


Hi Randy,

On Digital Signal Processing units:
I have the JPS NRF-7 - designed for the QSK CW and the SSB operators, had it
two years and use it every day. I leave it in-line all the time. it always
reduces some noise and amplifies all signals. cost about 240, reduces
operator fatique. has peak mode, 2 ssb filters, 2 cw filters, notch mode and
combinations of notch and peak, notch and ssb wide filter, notch and ssb
narrow filter. for the cw op, the only usefull features are peak or cw wide
or cw narrow. you cant use peak and a filter at the same time (major
disadvantage), new unit (NRF-12) has two DSP 40 mhz chip sets to get around
this limitation. Bought this two years ago at dayton.

also have the Timewave 59+, it has added features, filter widths from 25 hz
to 3.4 khz but requires alot of knob twisting and messing around. i found i
dont use it much. if a signals is so weak, i need to play with the knobs, he
probably wont stay in long enough for a qso anyway.
also has audio AGC, movable center freq, high pass or low pass filter
options. and Notch for ssb users. price about 299, bought this last year at
dayton

i just picked up the radio shack DSP it was on sale for 50 bucks and has a 2
watt audio amp and speaker built in. figured i couldnt go wrong for 50 bucks.
havent played with it yet, but have a couple of friends that have it and
thinks its worth the price. they use it for portable QRP work, its has a
bandwidth switch (wide/medium/narrow) and a filter switch (nr,cw,ssb) nr
being noise reduction.

DSP's most interesting feature is the Peak mode, also called Noise Reduction
mode. It reconizes a signal, amplifies it and pushes the noise down, thereby
increasing the signal to noise ratio. this will pull a signal out of the
noise and make a QSO possible, when it wasnt before. amazing.
Next are the digital brick wall filters. if you dont already have a SCAF
filter, this is a great feature to have and will increase your qso rate
during crowned band conditions.

The DSP technology is changing rapidly and the newer JPS NRF-12 has improved
peak function, multiple features (peak and filter together) faster processors
(i think they said it has 40 mhz chip sets, but i'm not sure about that).
variable filter widths and center frequencys. It reduces atmospheric white
noise, auto ignition noise, power line noise, static, computer/TV
interference. It uses both spectral substraction and dynamic peaking noise
reduction. The demo's at dayton sound better then real world conditions but
these filters are quite amazing. I still dont spent much time on 80m, so they
arent a cure all. price is 350. this could be the best unit on the market and
i will probably wind up with one in the near future.

The upside to DSP's is since they work in the audio line, you can use them
with any shortwave or hamband receiver/transceiver. unlike a kenwood I.F.
filter, 150 bucks a pop and it only works in another Kenwood with the same
model number.

The downside, and theres always a downside, is the current draw can range
from 500 ma to 1 amp, since most of these units have a built in audio amp.
makes it tough on batteries for portable use. also, just using a very narrow
filter doesnt always help the situation. signals that bounce off the E2 or D
layers many times, tend to shift in frequency enough to slide in and out of
 a 200 hz filter. I've found with the QRP Plus's digital SCAF filter that the
400 hz bandwidth is the narrowest i can use on DX consistantly. But for local
signals, the 200 hz filter works OK.

I'm sure down the road, DSP will be built into more and more affordable
transceivers (1000-1300 dollar price range), at present, its in the 4400 dolla
r Kenwood and the 2400 dollar Omni-6's.

If you're looking for more info about JPS DSP units, they are JPS@nando.net

72, Byron WA8LCZ Detroit

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Hi Byron..... I didn't keep a copy of the post to qrp-l the other day, but
are you the one who was commenting on DSP filters??? I'm thinking of
buying one in the near future and know absolutely nothing about them e.g.
what's good, what's bad, etc. I only work cw. Any recommendations ?

 


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