[ICOM] 751A

[Adam Farson]

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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