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

Sat, 1 Jun 2002 16:38:53 -0400

adam two question's.nobody compare's transmitter's in hf rig's.in your
opinion the finals in the yaesu ft-920 has the mrf 255's rated at 55 watts @
54 mhz.or the transmitter in the 570d/g toshiba 2sc2879 rated at 120 watts
@30 mhz.Also the mrf 255 are power mos fet.this is a 12 volt final,i was
unaware mosfets can be 12v.anyway which transistor can take more abuse
before crapping out in your opinion.also which radio is the better overall
rig? im very grateful to all your past help on many issues.thanks so much
adam.73

anthony k2vi
----- 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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