Jeff et al,
The JPS NIR-12 audio filters give me lots of great advantages to no filters.
The difference between the audio through the filter and with the filter turned
off is tremendous. Audio straight from the radio with no filter, no matter
which radio I use, is full of "snap, crackle & pop" no matter how quiet the
band. I can't stand to listen to that at all anymore. I refuse to.
With the filter, the audio is much cleaner with no transient noise, not only for
my ears but also to the demodulators - both MMTTY and the HAL DXP-38.
The NIR-12 (no longer made but I found one on E-Bay) has two outputs - one for
the headphones which can be adjusted by the volume control on the front of the
unit and an Audio Out jack with a constant output (independent of the volume
control) that I split two ways to go to the sound card and the HAL unit.
Furthermore, I take audio from the headphones jack on each NIR-12 and bring them
to my Dunestar 2 Radio headphone selector. I can then adjust the audio with the
volume control on each unit for a comfortable level to each side of the
headphone (left headphone for left radio, right headphone for right radio). It
just seems perfect this way. I can even switch either radio audio off with the
Dunestar switch, but rarely do that.
I doubt very much if the DSP of the NIR-12 units has any degrading effect on
MMTTY. When callsigns highlight out of nowhere when I can't even hear them, I
know something must be working. That happened a lot of 15 meters this past
weekend. No noise, but couldn't hear a signal either, but those weak EU
stations were still highlighting.
I used to use the NIR-10, but the problem with that unit is that it has only two
outputs - speaker and headphones. And both outputs are tied to the volume
control on the filter which is not good.
It's unfortunate JPS has gotten out of the Amateur business. Although expensive
in their time, the NIR-12 is a so valuable I cannot think of RTTY contesting
without them (time to look for a spare on E-Bay again).
73, Don AA5AU
-----Original Message-----
From: Jeff Stai WK6I [mailto:wk6i@twistedoak.com]
Sent: Friday, October 01, 2004 2:08 PM
To: Don Hill AA5AU; rtty@contesting.com
Subject: external DSP audio filters (was Re: [RTTY] AA5AU Contest Notes for CQWW
RTTY now on-line)
At 11:30 AM 10/1/2004, Don Hill AA5AU wrote:
>For anyone interested.
>
>http://www.rttycontesting.com/contestnotes/2004_cqww.htm
hi Don - thanks for the writeup! And thanks again for the excellent info on the
rest of your site - it really helped me get my first SO2R attempt going for this
contest.
Question: you have talked about using NIR-12 DSP filters in your contest setup.
What are you really achieving with those filters? And how?
It seems to me that MMTTY is a DSP filter in concert with a RTTY demod, and if
you put another DSP in front of it, you may end up losing some of MMTTY's
effectiveness by removing information that MMTTY could use.
(As far as cleaning things up for my headphones - my ears can suffer, as long as
I am getting the best print...:-)
Or are you using it mainly with your external HAL modem?
Or am I missing something? thanks! - jeff wk6i
--
Jeff Stai jds@twistedoak.com
Twisted Oak Winery http://www.twistedoak.com/
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