[ICOM] 756PRO3 - popping sound?

[Gunnar SM3DVN]

Adam,

The "perfect radio has still to be developed"...

73, Gunnar SM3DVN


----- Original Message -----=20
From: "Adam Farson" <farson at shaw.ca>
To: "'ICOM Reflector'" <icom at mailman.qth.net>
Sent: Wednesday, February 27, 2008 7:20 PM
Subject: RE: [ICOM] 756PRO3 - popping sound?


> Hi Bert,
>=20
> There was a specific problem in the 756Pro which was caused by ripple =
from
> the noise blanker getting onto the supply rail feeding the audio =
output
> stages. There was a fix for it.
>=20
> http://www.ab4oj.com/icom/756pro_nb/main.html
>=20
> This issue was corrected in the 756Pro2.
>=20
> I have never heard these popping sounds on my Pro3. The sounds =
described may
> also be partially due to artefacts generated by the distant =
transmitter.
>=20
> The choice of AGC attack time in a DSP-based radio is very tricky. In =
the
> presence of a very strong signal, where the AGC has to slew very fast =
over
> an extremely large range, some overshoot can occur under certain =
conditions.
> This can be minimised by reducing front-end gain (preamp off, =
attenuation,
> RF gain etc.) and by careful adjustment of the AGC menu. I would =
certainly
> not regard this as a reason not to purchase the Pro3.
>=20
> See also http://www.ab4oj.com/icom/ic7700/agc.html
>=20
> Cheers for now, 73,
> Adam VA7OJ/AB4OJ
>=20
>=20
> -----Original Message-----
> From: icom-bounces at mailman.qth.net =
[mailto:icom-bounces at mailman.qth.net] On
> Behalf Of Bert Almemo
> Sent: 27-Feb-08 05:46
> To: 'ICOM Reflector'
> Subject: [ICOM] 756PRO3 - popping sound?
>=20
> Hi guys,
>=20
> The following message came in on another reflector. Anyone heard of =
this
> problem on the PRO3?
>=20
> 73 Bert, VE3OBU
>=20
> =3D
>=20
> The original Icom 756 Pro receiver had an anoying popping sound that =
would
> show up at the start of each morse element when listening to strong CW
> signals.
>=20
> The 'pop' was mentioned in the QST product review in 2000 as as
> "characteristic of direct conversion receviers employing audio-based =
AGC
> systesms" and "the pro has a habit of introducing pops on the make of =
each
> CW element".
>=20
> Before purchasing an Icom 756 Pro III, I was told (by Icom) that the
> 'popping' issue was addressed, but that's not the case. The problem =
still
> exists and is especially obvious with fast AGC settings. It's not too =
bad
> with the internal speaker, but it certainly shows up with headphones =
and
> some external speakers.
>=20
> Suggestions appreciated...
>=20
> No virus found in this outgoing message.
> Checked by AVG Free Edition.=20
> Version: 7.5.516 / Virus Database: 269.21.1/1297 - Release Date: =
25/02/2008
> 09:22
>=20
>=20
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/