Topband: FT-2000 for serious TB DXing?

[Michael Tope]

----- Original Message ----- 
From: "Raoul Coetzee" <raoulc at smmcape.co.za>

> It is also important to note that not everybody lives in a high density
> Amateur Radio area/country. Those lucky Amateurs would be very happy with
> the radio, I suppose.
> If you look at Tom's list after clicking on the 'sorted by IM3 'and 
> looking
> at no 5 on the list, this a "stock" FT1000MP MKV
> WITHOUT an Inrad roofing filter but with  the very simple NB mod done.I 
> have
> done this easy to perform mod but I would still like to ask why is the 
> radio
> better without the Inrad roofing filter installed? Is it because of the
> amplifier that is included? This report is the one reason I have not
> considered the roofing filter, also,I live in a relatively low HAM
> area.(About 5 in a mile radius and not very activey at all.)
>
> Tom, have I lost the plot?
> 73
> Raoul ZS1REC
>

Raoul,

If it really is the 2N5179 amplifier on the roofing filter board and not
some other subtle thing like an upstream mixer or amplifier termination
impedance problem then it should be a simple matter to reduce the
gain of that 70 MHz amplifier to unity (with a pad) or just eliminate the
amplifier altogether.

Assuming the above adjustment brought the 2MHz IMDR back into
parity with the FT1K MK V with W8JI noise blanker mod, I wonder
if any of the other numbers would be any better? If the roofing filter
was simply a band-aid for the noise blanker problem, then the answer
might be "no". After the noise blanker is fixed, if the 1st mixer is the
limiting factor, I suppose then the roofing filter might not offer any
improvement in dynamic range.

BTW, Tom's data for the MK V doesn't seem to indicate whether the
pre-amp is on or off (IPO).

73, Mike W4EF................