[ICOM] 751A

[John Geiger]

I will agree that my 756 original with the preamp off on 20 meters is very
quiet.  The NR helps alot also, but probably not as much as the IF DSP in
the PRO series.  Still seems sensitive enough with the preamp off also.

However, it does seem a little noisy on the lower bands, especially 30 and
40 meters.  Do others who have used this rig actually add 6db or so of
attenuation on the low bands?  It seems more than sensitive enough.

73s John NE0P

----- Original Message -----
From: "Adam Farson" <farson at shaw.ca>
To: "'ICOM Reflector'" <icom at mailman.qth.net>
Sent: Wednesday, September 21, 2005 1:57 AM
Subject: RE: [ICOM] 751A


> Hi Blair,
>
> Yes indeed - reciprocal-mixing noise manifests itself as out-of-band noise
> mixing with the noise pedestal of the 1st LO (synthesiser) to raise the
> idle-channel noise level in the IF passband.
>
> The IC-756Pro series use a very up-to-date DDS scheme which yields
excellent
> reciprocal-mixing noise numbers. The Pro2 is a little better than the
756Pro
> in this area, and the Pro3 a little quieter than the Pro2. Even the
> "original" IC-756 DDS is quieter than any of its PLL-only predecessors.
>
> The DSP NR in the 756Pro series improves the S/N at the receiver's audio
> output even further.
>
> Cheers for now, 73,
> Adam VA7OJ/AB4OJ
>
>
> -----Original Message-----
> From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net]
On
> Behalf Of Ynkedragon at aol.com
> Sent: 20 September 2005 11:59
> To: icom at mailman.qth.net
> Subject: [ICOM] 751A
>
> In a message dated 9/20/05 2:21:12 PM Eastern Daylight Time,
farson at shaw.ca
> writes:
>
> << The SSB filtering and PBT operation on the 751A was far superior to
that
> of  its predecessor in my shack . . . . However, I did find that the
751A's
> PLL  synthesizer was somewhat noisy as compared to newer radios using a
DDS
> design (-104 dBc/Hz at 2 kHz offset, as compared to -111 for the IC-765
and
>  -125 for the IC-756Pro2). This led to relatively poor close-in reciprocal
> noise mixing performance. >>
>
> Hi Adam,
>     Regarding the '751A, you mentioned a noisy synthesizer.  Perhaps that
is
> what I noticed--something I had had always attributed to a noisy audio
> chain.
> A good friend had one which I frequently used.  When he upgraded he
offered
> the '751A to me at an attractive price.  I thought about it for an hour
and
> decided against it because of its omnipresent "white noise".  It could
have
> been unique to that particular radio, but I found that listening to the
> '751A became very tiring after just a few hours.
>     FWIW, the '756PRO series [all flavors] seems to lack that
> (annoying-to-me) "white noise" component.
>
> 73,  Blair k3yd
>
>
>
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