The ideal situation IMHO is the Full Sherwood MOD for the R-4C.
It has a switch so I can keep it wide if I want (and use NB), or use
SSB or CW Roofing filters to keep unwanted adjacent signals from
de-sensing the RX.
It works super!
Almost as well as my Ten-Tec Orion II
73,
Lee, KC9CDT
-----Original Message-----
From: Garey Barrell <[email protected]>
To: Drakelist <[email protected]>
Sent: Sun, Feb 20, 2011 9:47 pm
Subject: Re: [Drakelist] Roofing filter
The R-4A HAS a 'roofing' filter, as do the R-4, R-4B and R-4C. It's
T6,
right after the 1st Mixer.
If you want a flexible receiver, it needs to be wide enough to pass
both
sidebands of a signal to allow the Passband Tuner to work. It also
needs to be wide enough to pass impulse noise without stretching or
delaying it to allow the Noise Blanker to work. You can keep it wide,
and steepen the skirts for some improvement, by adding additional
poles. However, this increases the group delay to the point that the
Noise Blanker is no longer effective as the pulse and blanking signals
arrive at different times!
For a special purpose receiver, you can make it narrower if you wish,
only ONE sideband's width (2.4-2.7 kHz) or narrower still (600 Hz), and
give up useful Passband tuning and/or a Noise Blanker. There are
situations where that is desired, such as high density, low band
contesting, but is rarely of much value in today's relatively uncrowded
bands.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Neil M Califano wrote:
Where in a schematic would a roofing filter be located?
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