[ICOM] Fwd: Re: Hope to see a roofing filter for the IC-775DSP

[Steve N4LQ]

sri. I was looking at the sub rx's 45mhz 1st IF. The main rx's 1st IF is
indeed 9 mhz as it was in the old Triton and Omni D series  if I'm not
mistaken. Looking at the block diagram at
http://www.doug-smith.net/orion.htm. Of course I realize the Orion has a lot
more filtering after that 1st IF than the Triton did! In a way it does seem
kinda retro though.
Oh well, why are we discussing orions on an icom reflector anyway?

Steve N4LQ
----- Original Message ----- 
From: "Carl Moreschi" <n4py at earthlink.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Saturday, September 11, 2004 10:55 PM
Subject: Re: [ICOM] Fwd: Re: Hope to see a roofing filter for the IC-775DSP


> Steve,
>
> The first IF in the Orion main receiver is 9 mhz.  That's really the
design
> point that makes the Orion have the great close-in specs.
>
> Carl Moreschi N4PY
> Franklinton, NC
> ----- Original Message -----
> From: "Steve N4LQ" <n4lq at iglou.com>
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Sent: Saturday, September 11, 2004 9:52 PM
> Subject: Re: [ICOM] Fwd: Re: Hope to see a roofing filter for the
IC-775DSP
>
>
> > Jan:
> > Isn't the first IF of the Orion at 45mhz and the roofing filter is 9
mhz?
> So
> > the "narrow roofing filter" is not really ahead of that first IF if I am
> > thinking straight. I believe the 9 mhz "roofing" filter is the same,
exact
> > filter used in the Omni VI, Omni V, Paragon, Corsair and others so it's
> > really nothing new when viewed in that light. I think you'll find that
> > TenTec put the roofing filter a few floors down from the roof.
> > Hey....That 238 tuner will make a great roofing filter!
> > 73
> > Steve N4LQ
> > ----- Original Message -----
> > From: "Jan C. Robbins" <swanman at cfu.net>
> > To: "ICOM Reflector" <icom at mailman.qth.net>
> > Sent: Saturday, September 11, 2004 9:36 PM
> > Subject: Re: [ICOM] Fwd: Re: Hope to see a roofing filter for the
> IC-775DSP
> >
> >
> > > The front ends of most radios these days--that is, ahead of the first
> > > IF--are wide open, typically 13 to 20khz minimum.  If everything in
that
> > > passband gets to and into the first IF, it grabs the AGC, and makes
weak
> > > signals uncopyable (it also blows by the IF filters, increases phase
> > > noise, etc., but we don't need to get into all that).
> > >
> > > One of the BEST ways to improve ANY receiver is to place a filter
AHEAD
> > > of the first IF that is no wider than is absolutely necessary to copy
> > > the signal YOU want to copy--250hz for CW or RTTY, for  example, or
> > > 1.8khz for SSB (in the days before DSP, many receivers did exactly
that;
> > > it is a fact that DSP has produced a deteriation in receiver design).
> > > What a roofing filters do, as Ten-Tec learned a long time ago (and
Orion
> > > does better than anything now on the market), is exactly that: shut
down
> > > the "window" by which signals get into the reciver in the first place.
> > > That means that almost nothing you DON'T want into the reciver ever
GETS
> > > into the reciver, so the entire RF strip and everything else after
that
> > > narrow opening does its job correctly.
> > >
> > > You might want to check on Rob Sherwood's analysis of how to evaluate
> > > receivers and what matters most in them.  Rob knows more about
reciever
> > > performance than almost anyone alive, and has been quite generous in
> > > sharing what he knows with the rest of us.  I've listed the Sherwood
> > > Engineering website below.
> > >
> > > What you'll find is that Rob not only rates receivers by how narrow
the
> > > front end is, but also how it gets there.  The BEST way to get there
is
> > > a narrow, tracking preamplifier--as in an R390A.  Almost nonexistent
in
> > > radios today (no, the Icom 7800 doesn't match up). But the Orion is
the
> > > best second best by far.  He also makes it clear that ANY
> > > radio--including esp. the messy Icom Pros--that rely entirely on IF
DSP
> > > AFTER the front end cannot possibly perform at the level of radios
that
> > > don't.  One of the reasons why NO "pro-type" front end radio ends up
> > > even above the median in receiver performance.
> > >
> > > Here's the Sherwood Engineering website; sorry this has been so
> > long-winded.
> > >
> > > > http://www.sherweng.com/
> > >
> > >
> > >
> > > Durwydd MacTara wrote:
> > >
> > > > What is a "roofing filter" and why are they desireable?
> > > >
> > > >
> > > >
> > > >  "Carpe` Diem!"
> > > >             Durwydd MacTara
> > > >
> > > >
> > > > ----
> > > > Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> > > > Icom Users Net: Sundays, 1700Z, 14.316 MHz
> > > > Icom FAQ: http://www.qsl.net/icom/
> > > >
> > > >
> > >
> > > --
> > > "There is no end to what you can accomplish
> > > if you don't care who gets the credit."   Anon.
> > >
> > >
> > > ----
> > > Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> > > Icom Users Net: Sundays, 1700Z, 14.316 MHz
> > > Icom FAQ: http://www.qsl.net/icom/
> > >
> >
> > ----
> > Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> > Icom Users Net: Sundays, 1700Z, 14.316 MHz
> > Icom FAQ: http://www.qsl.net/icom/
>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
>