[ICOM] 751A

[Jan Robbins]

W5JMW John wrote:

> John,I found that lowering the rf gain helps more than anything else.. 
> NO preamp or attn,just use the rf gain to ctrl...73,john
> ----- Original Message ----- From: "John Geiger" <ne0p at lcisp.com>
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Sent: Tuesday, September 20, 2005 9:17 PM
> Subject: Re: [ICOM] 751A
>
>
>> 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
>>>
>>>
>>>
>>> Scanned for viruses by Blue Coat
>>> http://www.WinProxy.com/
>>> ----
>>> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>> Icom FAQ: http://www.qsl.net/icom/
>>>
>>
>> ----
>> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>>
>>
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>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
>
>
Yes, John.  The point that the local Icom reflector pundits don't seem 
to grasp is that Icom specs a setting for IF gain  on the 751A, 765, and 
I suppose other rigs that is designed to show how "sensitive" they are 
and to get GREAT S-meter swings.  All Icom rigs, from at least the 751 
era (735 etc.) are GREATLY improved simply by adjusting IF gain for best 
noise floor.  The notion that a Pro or ProII (I can't speak of anything 
later) has a "better" receiver than a 751A properly adjusted is 
nonsense.  Such people have never properly adjusted their radios, 
whatever their supposed credentials.  A 765 with properly adjusted IF 
gain will behave as well as a 775, which is a HELL of a lot better than 
any Pro.