[ICOM] IC-7800

[Bill Tippett]

Hi Adam,

VA7OJ wrote:
 >There is no problem making good filters at elevated
centre frequencies. Back in 1977, GTE Lenkurt was making channel filters at
a 36 MHz centre frequency for direct-to-line telephone carrier systems.
These filters were quite costly, but met all Bell System and ITU-R specs and
were actually superb SSB filters. I am confident that filter technology has
made some advances since then.

The Yaesu FT-DX9000 has a 3 kHz roofing filter at a high (but as yet
unknown) IF.

         True for typical voice bandwidths, but there is a problem with
making narrow CW filters at these frequencies.  As Sherwood says, "The
fractional bandwidth of a 600 Hz CW filter at 5 MHz is the same as a 6 kHz
filter at 50 MHz."  To make a 500 Hz filter at 65 MHz would be difficult
and expensive.  W2VJN (Inrad) has been working on a roofing filter for the
Yaesu MP family for some time and has recently come up with a 4 kHz filter.
If 1 kHz or less were easy to do, I'm sure George would have done that.

                                 73,  Bill  W4ZV