[CQ-Contest] Roofing filter improvements?

[Jukka Klemola]

John,
The so-called roofing filter potentially enhances your radio's front
end behaviour from signals more than about 4 or 5 kHz away from the
frequency you listen to.

In case you have real signals coming on top of the signals you want to
hear, I mean on the signal you want to copy, no frequency-based filter
will get it out.

The only cure would be to use a directional antenna to pick up the
signal you want to copy.

The mechanism is the antenna would attenuate the interfering signal.


The roofing filter will give you results most typically in situations
where you have a signal like S9 + 40dB or so, something like 5 up and
you want to hear a DX on the frequency despite the strong signal is on
.. on the frequency of about 5 kHz up or so.
The roofing filter improvement starts to show when the DX signal would
be about 60dB down from the strong signal.

More than 60dB down from the interfering signal, roofing filter will
typically help more.

But when the interfering signal is closer than 3kHz, no real
improvement should take place due to roofing filter.


But:
in case the strong signal spreads around - that is, emits on the
frequency you want to copy the other station, there is no other cure
than antenna.


Occasionally the interfering signal is about in the same direction as
the signal you want to copy.

Then there is no real escape than patience and will to develo skills
to copy the small signal from the ramble all strong signals produce.

Copying some of the far away weak stations require some antennas and
sometimes luck.
Regardless the radio, filters and improved front end electronics.


73,
Jukka OH6LI

2010/11/10 John Geiger <aa5jg at ...com>:
> I have a mid level, late 90s rig on the way that has had the INRAD roofing filter installed in it. This is supposed to be a 5 to 6khz wide roofing filter, not some of the real narrow ones we are seeing today.  What kind of performance improvement are others seeing with these roofing filters?  Is it likely to turn a mid level rig into something usable in crowded contest and DXing conditions?  The rig will also have a 250hz CW INRAD filter and a 1.8khz INRAD filter installed.
>
> 73s John AA5JG