[1000mp] INRAD Bonus mod VS MkV EDSP CW demodulation.

[John]

Hello Lou,

Thanks for sharing your findings!  I have the INRAD IF and "Bonus" mods
here, however, to date I've been stalling on installing them.

Appreciate if you would send me pictures of your spectrum analyzer displays.
Thanks!

73,

John  W0DC

----- Original Message -----
From: "lhlousek" <lhlousek@nvbell.net>
To: <1000mp@mailman.qth.net>
Sent: Saturday, January 11, 2003 2:48 PM
Subject: [1000mp] INRAD Bonus mod VS MkV EDSP CW demodulation.


> I just made some before and after comparisons of the INRAD "Bonus" mod
which consists of adding a .047 mF cap across C3015 on the audio board.  I
used an audio spectrum analyzer and my ears to make the comparison.
>
> Prior to the mod, the radio exhibited an unacceptable amount of hiss
without EDSP CW demod enabled.  After the mod, EDSP demod is still better
but the RX is reasonable with it off too.  This is most evident listening to
week sigs on quiet bands.
>
> On my rig, this mod only had an effect only in CW mode and then only when
the EDSP CW demod (menu 7-7) was turned off.  On SSB, or on CW with CW Demod
on, there was no affect at all.  I did not look at any digital modes.
>
>
> The audio board is located on the bottom of the rig and C3015 is a
through-hole film cap on the top of and close to the center of the board.  I
had some small clip leads that I was able to attached to C3015 and use to
quickly switch between several values including .022, .033, and .047 uF.
All values substantially reduced high frequency hiss with .047 having the
greatest affect, although not much different audibly or on the spectrum
analyzer than .033.  I chose to go with .047 since it only affects CW and
tacked it onto the bottom of the board.
>
> On CW NOR (1800Hz INRADS) and with EDSP demod off, the passband is tilled
downward toward higher frequency going down about 10dB at ~2400Hz compared
to 800Hz.  This is not really a problem on CW.  There is also a noise floor
that extends well beyond the passband cutoff.  This noise floor is the
objectionable hiss.
>
> EDSP CW demod has the effect of flattening the pass band so there is no
drop-off toward the higher frequencies.  It has a sharp cutoff at ~1800Hz
that also takes out the noise floor above this frequency.  Of course, this
cut-off is introduced in the baseband so signals above this cutoff, but
still within the IF passband, will pump the AGC.  Adjusting the Width
control to align the upper IF passband edge with the EDSP demod cutoff
solves this problem.
>
> Adding the bonus mod has the affect of increasing the downward tilt of the
passband so that it is more like 25 dB over the range 800 to 2400 Hz.  This
still sounded fine listening to actual signals because it only attenuates
the sigs that are far above a signal beat with your side tone.  It also
greatly decreases the noise floor above 2400Hz but not to the same extent as
EDSP demod.
>
> I have a MS Word file with the spectrum analyzer screen shots.  I'll email
it to anyone interested in seeing them.
>
> Lou
>
>
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