[ICOM] 751A

[Steven Moore]

This discussion reminded me of the listening noise of a bunch of older rigs. I going to forget about buying 
the 751a.

I like my 756pro quite well although the nr sounds hollow and the close in dynamic range seems no better than 
the 950sdx I sold.

I use a clearspeech nr and have for 8 years or so. It is superior to listen to than any of 8 or 9 hf rigs I've 
owned with nr. I use it 100 percent of my operating time.

73
Steve  wd0ct


> 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
>
> << 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