[Elecraft] K3 for Broadcast Band DX

[Wayne Burdick]

Hank,

When you're in or close to a ham band, the broader KBPF3 filters are not used; the K3's narrow ham-band filters are used. This applies to both the main and sub receivers. The KBPF3's filters are only used when you're far enough outside a ham band to result in noticeable loss of sensitivity.

So in answer to your question: No, you don't need to worry. When the KBPF3 is not in use (main or sub), it is completely out of the circuit, having no impact on filtering.

By the way: the K3's narrow ham-band filters are one of its biggest assets. Most transceivers these days, even superhet designs, use very broad filters intended to cover multiple bands. The K3 (and K3S), in contrast, use filters that just cover the ham band of interest, providing high degree of rejection of out of band signals. This has a secondary benefit in reduction of "IP2" (intermodulation products resulting from the mixing of strong signals prior to the band pass filter array).

73,
Wayne
N6KR




On Jun 8, 2015, at 2:14 PM, "Hank P" <pfizenmayer at q.com> wrote:

> Along this subject of BPF3 - When I assembled my K3 with sub rx - I put the
> BPF3 in the sub rx  - on the assumption that it might degrade the out of
> band main rx protection with some filter  blow by  if I put it in the main
> rx path. Now I wish I had put in in the main rx so I could use the P3  out
> of the ham bands- especially below 160)
> 
> Was this a false worry ? (I live in a hot bed within 3 to 4 miles of several
> contesters / dxers with HUGE signals at my place - two of whom can put 50 to
> 100 mv of signal here on 160 - easy to see both on a scope on antenna)
> 
> I am going to buy the new KXV3B and will have to take the sub rx out to
> install and that would be a good time to move that filter if its not an
> issue.
> 
> Hank K7HP
> 
> 
> 
> -----Original Message----- From: Joe Subich, W4TV
> Sent: Monday, June 08, 2015 12:25 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 for Broadcast Band DX
> 
> 
>> Therefore, at this juncture, the K3 is totally not up to the job when
>> it comes to broadcast band DX hunting. What's up here?
> 
> As documented here literally dozens of times, the TR switch contains a
> high-pass filter with a 1600 KHz cutoff to protect the PIN diodes and
> keep them from generating interference due to strong broadcast band
> signals.  If you want to receive the broadcast (and MW bands) with full
> sensitivity, 1) install the BPF3 receive filter *and* 2) use a separate
> receive antenna connected to either the RX ANT IN jack or the XVTR IN
> jack.
> 
> 73,
> 
>  ... Joe, W4TV
> 
> 
> On 2015-06-08 3:04 PM, Carl Jón Denbow wrote:
>> I sometimes like to do a little Broadcast Band DX, takes me back to my
>> high schools days with my GE transistor radio under the pillow.  I think
>> some of you know the story. ;-)  At any rate, I have the general
>> coverage module installed in the main receiver, but I have found the
>> sensitivity of it in the broadcast band to be horrible.  I can hook up
>> my Palstar R40 and get a 40 over signal from a station, but with the K3
>> hooked up to the same antenna that station is an S4  --  just barely
>> over the noise level.  This is a station 100 miles way that I could
>> receive on that old GE transistor radio at what would have at least been
>> an S9 signal.  Therefore, at this juncture, the K3 is totally not up to
>> the job when it comes to broadcast band DX hunting.  What's up here?
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