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KX3 - Roofing filters

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Pierre

KX3 - Roofing filters

Hello to all.

Maybe that I don't understand the real utility of the roofing filter but I observed this. Last saturday, we were on a SOTA summit using two KX3s about 40 feet appart transmitting CW at 5 W. And even with the roofing filters on, we heard each other's sending as a diffuse noise. I know that changion RX shift to 8 disable the roofing filters, but we were not using that shift.

So, am I missing something about the use of these filters? Are they designed for operations with operators near each other like SOTA activation on a crowded summit ?

73, de VE2PID KX3 S/N 190
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JP O'Connor

Re: KX3 - Roofing filters

Hello Pierre,

It is most likely not a roofing filter issue. Rather it is probably a local
oscillator leakage issue. Set the "RX ISO" menu item to "ON" and I suspect
the problem will significantly diminish, if not disappear. See page 38 of
the current KX3 owner's manual (Rev B4) for this menu item and for a
discussion of when it may be helpful. Be sure to first refer to the "Tech
Mode" section on page 35 to unlock this menu item.

73 de JP WF4Z

On Mon, Jul 23, 2012 at 10:34 PM, Pierre <[hidden email]> wrote:

> Hello to all.
>
> Maybe that I don't understand the real utility of the roofing filter but I
> observed this. Last saturday, we were on a SOTA summit using two KX3s about
> 40 feet appart transmitting CW at 5 W. And even with the roofing filters
> on, we heard each other's sending as a diffuse noise. I know that changion
> RX shift to 8 disable the roofing filters, but we were not using that shift.
>
> So, am I missing something about the use of these filters? Are they
> designed for operations with operators near each other like SOTA activation
> on a crowded summit ?
>
> 73, de VE2PID KX3 S/N 190
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Don Wilhelm-4

Re: KX3 - Roofing filters

In reply to this post by Pierre

Pierre,

The roofing filters may not necessarily help with such strong signal
rejection as you would have had with 2 KX3s transmitting simultaneously
on different parts of the same band.

The usefulness of the roofing filters is to protect the receiver front
end from normal level signals that are within the passband of the
roofing filter, but not within the passband of the DSP filter. The
result is AGC Pumping by the stronger signal which may not even be heard
because the DSP filter cuts it out.

73,
Don W3FPR

On 7/23/2012 10:34 PM, Pierre wrote:

> Hello to all.
>
> Maybe that I don't understand the real utility of the roofing filter but I observed this. Last saturday, we were on a SOTA summit using two KX3s about 40 feet appart transmitting CW at 5 W. And even with the roofing filters on, we heard each other's sending as a diffuse noise. I know that changion RX shift to 8 disable the roofing filters, but we were not using that shift.
>
> So, am I missing something about the use of these filters? Are they designed for operations with operators near each other like SOTA activation on a crowded summit ?
>
> 73, de VE2PID KX3 S/N 190
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Jim Hoge-2

Re: KX3 - Roofing filters

In reply to this post by Pierre

You didn't mention whether the two radios were on the same band, different bands, or odd harmonic bands like 40 and 15. Or, was it on any and all combinations?
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wayne burdick

Re: KX3 - Roofing filters

Administrator

In reply to this post by Pierre

Pierre,

I think what you were hearing was low-level transmit phase noise. The
KX3 has very low phase noise, but with the two radios on the same band
and only 40 feet apart, during quiet conditions, the TX phase noise
floor could be above MDS. Roofing filters won't help with this, but
the KX3's new noise-reduction feature would (coming soon).

Of course if you hear each other's VFOs at close proximity even in RX
mode, you can turn on RX ISO (isolation amp). Adds 10-15 mA to current
drain but drops the VFO leakage by some 70 dB+.

73,
Wayne
N6KR

On Jul 23, 2012, at 7:34 PM, Pierre wrote:

> Hello to all.
>
> Maybe that I don't understand the real utility of the roofing filter
> but I observed this. Last saturday, we were on a SOTA summit using
> two KX3s about 40 feet appart transmitting CW at 5 W. And even with
> the roofing filters on, we heard each other's sending as a diffuse
> noise. I know that changion RX shift to 8 disable the roofing
> filters, but we were not using that shift.
>
> So, am I missing something about the use of these filters? Are they
> designed for operations with operators near each other like SOTA
> activation on a crowded summit ?
>
> 73, de VE2PID KX3 S/N 190
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html