> Hello, i am curious anyone has experience on topband with
the new roofing filter from Inrad for the FT1000(D) series.
> I decided to upgrade my old FT1000 (see also the w8ji
site) and keep it for more years. Also i am not using the
Ft1000 250 hz
> filters because of to much signal loss.. Change into
400hz filters worthwhile ?
Bert,
The significant thing a roofing filter does is remove
signals outside the passband of the roofing filter. Anything
outside the roofing filter passband can only overload the RF
amp and first mixer. It cannot overload things downstream
past the roofing filter.
Anything *inside* the roofing filter passband can overload
anything downstream up to the narrow filter you use, at
which point this repeats again for things further
downstream.
In my FT1000D, the weakest link was the noise blanker (even
with the NB turned off). Adding my diode modification to
fully turn off the noise blanker still allows stages
downstream from the 12kHz roofing filter to be the weakest
link, but not by a very large margin over the early stages.
If you replace a 12 kHz roofing filter with a 5 kHz wide
roofing filter, problems caused by exceptionally strong
signals between +2.5 and +6 kHz away and -2.5 to -6 kHz away
will be reduced. Nothing else would change. In the FT1000D
there would be a noticeable improvement if you have overload
from exceptionally strong signals in those two windows.
Overload is also caused an accumulation of signal power from
many strong stations. In a contest you might have enough
strong stations operating in those windows to reduce dynamic
range.
The largest effect would be in a crowded SSB contest, less
effect in a crowded CW contest, less yet in normal SSB
operation, and the very least effect in regular day CW
operation.
This is why you will get a variety of answers.
73 Tom
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|