[Premium-Rx] Clean LOs

[Clemens Paul]

Dan,

great information,didn't know this one.
Thanks a lot!

vy 73
Clemens
DL4RAJ

----- Original Message ----- 
From: "Dan Rae" <danrae at verizon.net>
To: "Clemens Paul" <cpaul at gmx.net>; <bcomer at cox.net>
Sent: Saturday, February 12, 2005 8:09 PM
Subject: Re: [Premium-Rx] Clean LOs


> Paul and Brian,
> I don't know of you have seen it but there is a very useful discussion 
> of the 8640B's failings when used for IIP3 measurements at this web site:
> http://www.aoruk.com/comments.htm
> 
> with particular reference to the receiver that he designed, of course, 
> but it does include details of the modification he made to the ALC 
> circuitry of the 8640B that vastly improves the intermod that this 
> causes.  This will allow use of two 8640Bs to measure up to and possibly 
> above +40 dBm IIP3.   This is a very easy modification to make and also 
> easily reversible.
> 
> Regards
> Dan
> ac6ao / g3ncr
> 
> Clemens Paul wrote:
> 
>> Hi,
>>
>> The HP8640B is extremely sensitive to variations in load impedance
>> also with respect to intermodulation.
>> Reflected signals up to 60 dB down cause internal intermodulation.
>> Therefore it's not possible to measure receiver IP3's of more than say 
>> +25dBm
>> even with the best combiners (tunable, with ~60dB return loss) with a
>> pair of HP8640B.
>>
>> 73
>> Clemens
>> DL4RAJ
>>
>>
>>> The 8640 has fairly low phase noise but is not the best especially if
>>> the load impedance is varied and the output division ratio is not very
>>> large.
>>>
>>> 73 Brian
>>>
>>> KF6C/G3ZVC
>>
>>
>>
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>>
> 
>