subrx and filters

[Juha - oh6os]

Hello,

I am thinking to buy KRX3. The main K3 I have 2,8 kHz and 400 Hz filters. What I need to subRX? Is 2,7 and 500 good choice and do I need KFLMATCH?

juha - oh6os
K2#4781
K3#2100

[Thomas Horsten]

Hi Juha,

If you are going to use it for Diversity RX, the best option is to
have the same set of filters on both receivers. That way the
characteristics of the two receivers are the same in the presence of
strong adjacent signals. If you have the 400hz filter on the main rx,
and 500 on the sub, and there is a strong signal 450 hz away, you will
lose sensitivity in the sub receiver.

At least this is how I understand it, others might be more
knowledgeable than me!

73, Thomas 2E0ETT

On 9 March 2011 12:29, Juha - oh6os <[hidden email]> wrote:

> Hello,
>
> I am thinking to buy KRX3. The main K3 I have 2,8 kHz and 400 Hz filters.
> What I need to subRX? Is 2,7 and 500 good choice and do I need KFLMATCH?
>
> juha - oh6os
> K2#4781
> K3#2100
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/subrx-and-filters-tp6153441p6153441.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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[Mike Markowski-2]

Juha,

Yes, I would recommend having both matching filters in your subreceiver.

In my main receiver I have filters for 13/6/2.8/0.4 kHz.  In the sub I chose
only 2.8/0.4 kHz filters and am happy with the choice.  I've found no need (so
far!) for AM & FM filters in the sub.

Here's why I like the 2,8 and 0,4 kHz filters.  For dx, I put the sub on the dx
op's transmitting freq and tighten up the filter to 400 Hz or less.  Then I have
the main receiver opened up to 2.8 kHz or even wider on occasion.  Using
software on my laptop, the freq spectrum is displayed - a poor man's P3! - and
my tx freq is chosen after discovering the dx op's listening pattern.  I also
turn up the audio on the sub (dx's transmit freq) relative to the main so that
I'm sure to hear when my call finally is answered.

The 2,8 comes in handy for SSB in a similar way, but I use the still wider
filters of the main to hear the pileup.

So far, this works so well that I'm not sure I need a P3.  But I'm open to being
convinced otherwise.  After all, can you ever have enough gadgets?  :-)

73,
Mike ab3ap

On 03/09/2011 07:29 AM, Juha - oh6os wrote:
> Hello,
>
> I am thinking to buy KRX3. The main K3 I have 2,8 kHz and 400 Hz filters.
> What I need to subRX? Is 2,7 and 500 good choice and do I need KFLMATCH?
>
> juha - oh6os
> K2#4781
> K3#2100
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[Jim Brown-10]

On 3/9/2011 6:48 AM, Mike Markowski wrote:
> Yes, I would recommend having both matching filters in your subreceiver.

One variation on that.  While your technique of using the wide filter to
listen on the DX frequency is a good one, the lower cost 2.7 kHz filter
accomplishes that just fine. The only reason for MATCHING filters
between the two receivers is for diversity reception, where the phase
characteristics of the filter can make a difference. Every time I've
used diversity reception I've had a much narrower filter engaged.

My radios have 2.7 kHz, 1.8 kHz, 400 Hz, and 250 Hz filters. You only
need the 1.8 kHz and 250 Hz filters if you're a serious contester.
Otherwise, the 2.7 kHz and 400 Hz filters are a very good choice. My
neighbor, K6XX, an engineer who works for Elecraft, advises me that it's
good to have a 2.8 kHz filter on the MAIN board, so that you are
transmitting through it.

73, Jim K9YC
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[Robby.VY2SS]

Juha,

I have 2.7, 1.8, 500 and 250 in my main RX.
In the subRX I have 2.7 and 400hz.
DSP is usually 200 to 350 hz.
Diversity works fine.
In fact it's amazing!

-Robby
VY2SS

[Juha - oh6os]

Many thanks for replies.

I made ordering and took 2,8 and 400 filters. The same as main rx. I think that is best choice, if I will be interesting diversity receiving in the future.

juha - oh6os