[ICOM] 751 Vs. 751A

[Hsu]

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
> 
> 
> -----Original Message-----
> From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
> Behalf Of Hsu
> Sent: 16-Feb-11 18:00
> To: ICOM Reflector
> Subject: Re: [ICOM] 751 Vs. 751A
> 
> Hi Adam,
>   I found this test  data:  http://www.sherweng.com/table.html
> 
> It told me that IC751A's Lo phase noise is -127dbc/Hz, very good result.
>  But in my experience, the 751A seems a noisy reciver.My friend modify this
> receiver, very good result.
> I guess the noise due to DC-DC converter.
>         73!Hsu
> ----- Original Message -----
> From: "Adam Farson" <farson at shaw.ca>
> To: "'ICOM Reflector'" <icom at mailman.qth.net>
> Sent: Thursday, February 17, 2011 2:30 AM
> Subject: Re: [ICOM] 751 Vs. 751A
> 
> 
>> Hi Dick,
>> 
>> Both the 751 and the 751A have a PLL synthesiser which has fairly high 
>> phase noise by current standards.
>> 
>> 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 Dick Flanagan
>> Sent: 16-Feb-11 09:01
>> To: ICOM Reflector
>> Subject: Re: [ICOM] 751 Vs. 751A
>> 
>> I heard from somewhere (check with Adam) that the 751A was practically 
>> an complete re-design of the 751, ending up with a much better radio.
>> 
>> Dick
> 
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