[Icom] Icom 756-Pro II audio/mic input alternatives

Sun, 2 Jun 2002 00:51:54 -0400

Adam I don't know what you know technically and I respect your knowledge
however I am amble to run my Heil HC5 through the W2IHY EQ and noise gate
and get a nicer and more full range of audio by going direct through the
balance modulator than through the front mic input and I tired both and I am
an audio person who can tell the difference between good audio and bad with
no offense intended by the remark. I don't use vox and I set my mic gain
from the EQ and noise gate so I don't lose anything that really is a problem
since I key the radio with a footswitch using the W2IHY EQ and noise gate.
73, Steve
----- Original Message -----
From: "Adam Farson" <[email protected]>
To: <[email protected]>
Sent: Saturday, June 01, 2002 2:23 PM
Subject: RE: [Icom] Icom 756-Pro II audio/mic input alternatives


> Larry,
>
> the low-end audio response is lower at ACC1 Pin 4 (80 ~ 100 Hz at -6 dB)
than at
> the MIC input (250 ~ 300 Hz at -6 dB), but the high end is hard-coded in
the DSP
> firmware. From a look at the speech amplifier (IC451 on the MAIN UNIT
board),
> there is an RC feedback network in the first stage (AMP). This network
looks
> like a high-pass filter, which would account for the steeper low-frequency
> roll-off at the MIC input compared to the ACC1 input. The second stage
(VCA,
> voltage-controlled amplifier) appears to have a flat response. The design
intent
> is probably to cut off low-frequency components of the microphone output
(below
> 250~300 Hz). These components contribute virtually nothing to articulation
at
> the receiver, but rob transmitter power which can more usefully employed
to
> transmit the midband and upper frequency subbands which determine the
> articulation index at the receiver.
>
> If a bass-boost is applied to the mic audio fed to the front-panel mic
socket,
> IC451 will filter out all components below 250 ~ 300 Hz.
>
> The AMOD (ACC1 Pin 4) input bypasses IC451 entirely. The outputs of IC451
and
> the AMOD buffer are fed to the ADC via the DTAF line. The design intent
here is
> probably to pass AFSK signals without distorting the frequency
transitions,
> which have a low-frequency component.
>
> Icom's engineers probably felt that this analogue solution would be more
> cost-effective and less risky (in terms of potential bugs) than separate,
> selectable DSP modulation algorithms for voice and data transmission.
>
> Best 73,
> Adam, VA7OJ/AB4OJ
> North Vancouver, BC, Canada
> http://www.qsl.net/ab4oj/
> Note new e-mail address:
> mailto:[email protected]
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Larry Benko
> Sent: Saturday, June 01, 2002 10:20
> To: [email protected]
> Subject: Re: [Icom] Icom 756-Pro II audio/mic input alternatives
>
>
> Larry,
>
> Using the ACC1 input does lose the VOX  function but does NOT lose the
> PTT
> function.  The SEND line (pin 3 in the ACC1 jack) is the PTT line.
>
> 73,
> Larry, W0QE
>
>
>
> [email protected] wrote:
> >
> > I believe that this topic may have been covered many times, so if you
wish,
> > please email directly as to not clutter up the reflector.
> >
> > Is there another way to feed audio into a pro 2 other than the standard
mic
> > jack/pin config on the front, so that after eq'ing the mic/audio, the
pro 2
> > won't flatten the eq'ed audio and canceling the eq effect. I heard
something
> > about using the acc1 audio input, but there seems to  be some
conflicting
> > information in the manual.
> >
> > Also, If i feed the acc1 with audio, I know I will lose ptt, but will I
also
> > lose VOX.
> >
> > thank you all again..
> >
> > vy 73.. Larry.. N2LH
> >
>
> ----
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>