[1000mp] Inrad 70Mhz mod for Mark V

[Tom Rauch]

> This is the subject of some controversy.  The quoted opinion is 
> W8JI's.  W2JVN says otherwise (it's his board design).  At least you
> should read both posts (or sets thereof) before you decide.

I think part of the problem is in how the measurements are made. 

Most important is the test spacing of signals. If you put interfering 
signals outside the roofing filter passband, adding 70Mhz gain after 
the wide 70MHz roofing filter will not change overloading. If you 
have signals within the passband of the roofing filters, it will make 
the receiver more prone to overloading.

This all goes back to the poor close-spaced IM performance of the 
FT1000's when the NB gain is left up in FT1000MP, or the 
FT1000(D) in ANY configuration of settings.  If you use a wide test 
signal spacing, you will miss observing that major design flaw.

Since the NB system (even when off) and the 2nd mixer both are 
the limiting areas of receiver close-spaced performance, adding 
gain in front of the 2nd mixer makes little sense for anyone worried 
about close-spaced performance, although it makes some sense if 
you operate CW on quiet uncrowded bands...like ten meters. 

IMO there are better solutions. If you want to reduce the broadband 
noise and not reduce dynamic range, just use an audio filter! 
Otherwise you can add any preamplifier between the antenna and 
the 455kHz IF, and reduce 455kHz IF gain.
73, Tom W8JI
W8JI@contesting.com