[ICOM] 751 Vs. 751A

[Adam Farson]

Hi Hsu,

In fact, one of the main reasons for the move to DDS was precisely that - a
reduction in phase noise as compared to classical PLL designs, as well as a
simplification of the high-resolution part of the synthesiser. 

http://en.wikipedia.org/wiki/Direct_digital_synthesizer

I ran the reciprocal mixing test on both radios in 1994. At 14.100 MHz and
10 kHz offset, the IC-781 figure was 102 dB, and the IC-751A value was 96 dB
(still not bad at all.)

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 Hsu
Sent: 16-Feb-11 19:38
To: ICOM Reflector
Subject: Re: [ICOM] 751 Vs. 751A

Hi Adam,
   I do not think the DDS can reduce the phase noisy.
        It just supply a easy way use few parts in PLL system in small steps
it is why only 10Hz step in that time and now 1Hz,even lo-end rig like
FT-817.
But old  PLL  equpments in 1970s to 1980s with bad phase noise parameter, it
is not duo to  without DDS, but because of  the thought of engineers, in
that time , the engineer seems can not know how to optimize  PLL system.
  By the way, Could you to share your test result   parameter  about 751A?
        73!Hsu
----- Original Message -----
From: "Adam Farson" <farson at shaw.ca>
To: "'ICOM Reflector'" <icom at mailman.qth.net>
Sent: Thursday, February 17, 2011 11:06 AM
Subject: Re: [ICOM] 751 Vs. 751A


> Hi Hsu,
> 
> In 1994, I measured reciprocal mixing noise on my 751A and 781. The 
> 781 was significantly better in that area because of its DDS synthesiser.
> 
> Cheers for now, 73,
> Adam VA7OJ/AB4OJ