>>> A KBPF3 can be added to the main receiver, or the sub receiver, or both. <<<
What would be the advantage of adding KBPF3 to both the Main and the Sub?
((((73)))) Milverton / W9MMS
From: Wayne Burdick <n...@elecraft.com>
To: Jeff Cathrow <cathrowinternatio...@hotmail.com>
Cc: Elecraft Digest <elecraft@mailman.qth.net>
Sent: Monday, February 9, 2015 4:23 PM
Subject: Re: [Elecraft] Advantage of KBPF3 in K3?
> if one already has an AM filter in one of the K3's slots what does one need a
> KBPF3 for (in terms of general coverage SWLing)?
>
> Does it allow band selection of the popular SWBC bands in addition to the ham
> bands?
Hi Jeff,
The AM crystal filter is for close-in selectivity (6 kHz) in the I.F. This
filter can be used in AM and SSB modes whether in or out of a ham band.
The KBPF3 is at a different point in the receive chain: at the front end. It
provides band-pass filters several MHz wide to allow copy of SWL ranges between
the ham bands.
Without a KBPF3, there are a number of places between ham bands where
sensitivity would roll off up to 20 dB or so. This is because the K3's normal
band-pass filters are very narrow, covering just the ham bands themselves. This
is a very good thing from a receive performance standpoint; it removes strong
signals that are well out of each ham band that could otherwise cause spurious
or image responses. Unlike the K3, most receivers have really wide band-pass
filters, leaving them susceptible to such interference in the ham bands.
By adding a KBPF3, you'll be able to tune virtually the entire range from 0.5
to 30 MHz (plus 6 meters) with your K3 without significant loss of sensitivity.
The K3 automatically selects the KBPF3 filters when you tune a certain distance
outside a given ham band. This is how we provide MARS coverage (when enabled).
I said "virtually" the entire range because there is one gap: right around the
first I.F. (8.215 MHz). In the vicinity of this gap, sensitivity will be quite
a bit lower because the K3 has multiple traps at this frequency designed to
ensure excellent first-I.F. rejection. Also, the range from 0.5 to 1.5 MHz is
gradually attenuated as you go lower in frequency because of a high-pass filter
that protects the PIN diodes used in the T/R switch. To get around this, you
can bring the signal into the RX ANT jack on the KXV3 option. You might do this
is you were doing low-band (AM broadcast) DXing.
A KBPF3 can be added to the main receiver, or the sub receiver, or both.
73,
Wayne
N6KR
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