OK, guys, I've got it now (makes a ton of sense now that I think about it). I
don't do a lot of SWL anymore but I might want to add one to my K3 sometime for
the fun of it.
Thanks very much for all of your replies and feel free to close this thread now
that it has been answered well.
73, Jeff, NH7RO
> Subject: Re: [Elecraft] Advantage of KBPF3 in K3?
> From: n...@elecraft.com
> Date: Mon, 9 Feb 2015 14:23:10 -0800
> CC: elecraft@mailman.qth.net
> To: cathrowinternatio...@hotmail.com
>
> > 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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