That's why on more than one occasion I've said that to evaluate a transceiver's
receiver performance, instead of a couple of HP8663 signal generators, two other
like transceiver transmitters should be used as the signal sources for the
measurements, until that is, our transceivers have the spectral purity of '8663s.:-)
On 3/1/2014 7:17 PM, Joe Subich, W4TV wrote:
Fred,
In general you are correct. However, there is one other effect that
the narrow roofing filters are not going to resolve - garbage from
your neighbors in the form of key clicks, transmitted phase noise and
IMD. I see it every time my neighbor (.66 mi) comes on a band with
his Icom POS ... phase noise an clicks +/- 20 KHz. The K3 handles his
fundamental just fine as little as 500 Hz away but the phase noise and
clicks make any band almost unusable.
73,
... Joe, W4TV
On 3/1/2014 7:59 PM, Fred Jensen wrote:
If you can, help me out here Don ...
These are roofing filters. From my perspective, which is likely wrong,
their job is to restrict the bandwidth presented to the 2nd mixer [and
downstream ADC]. They are of most value when you have very strong [i.e.
geographically close] signals adjacent to the desired signal [That would
be WX6V for me :-)]. The ultimate BW is set by the DSP of course, but a
really strong adjacent signal can begin to activate the HW AGC in the K3
which affects the signal inside your DSP BW, or I think that's true. So,
it follows to me that, if you are plagued by KW neighbors, narrower
roofing filters can reduce that problem. This could be true on FD or
any other closely spaced HF operations ... IF you have two stations on
the same band/mode.
If you are not so plagued, I can't figure out why it really matters. I
have the filter that came with the K3 and I bought one [2.7 and .5, I
don't remember which was which], I've had no difficulties. Jim [WX6V]
and Jack KF6T [equally close] became non-problems when I got my K3 ...
even more so now that Jim has a K3 and phase-noise has disappeared. :-)
I've got to be missing something here, and sadly, it wouldn't be even
close to the first time.
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