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IC8POF's Roofing Filter Experiences * * *
This page shows the TRUTH on the differences between
the Yaesu and the Inrad Roofing Filters mounted into the FT1000 mkV Field rig.
*** One thing is to be WELL known: the Inrad Roofing Filter does not substitute the rig's original ***
it is placed at the output of the original 12Khz roofing filter (18 to be good).
This is not the best solution, but the simplest compromise between simplicity and performance of the drop-in kit.
The two curves have been collaged by cropping the screen during a S9 wide band white_noise injection into the rig.
The bandpass reduction and attenuation of the Inrad roofing are impressive.(n2)
As the base line of the SDR receiver is not a clean line the resulting measurements are not very accurate,
but still enough readable to make signals comparisons.
The differences between the roofing filters are very well recognisable, but the narrow window of the IRF is very difficult
to appreciate simply by listening only at signals.
The above half pic shows the Inrad response and the lower half shows the Yaesu one.
The black column, 2.5 Khz wide, shows where the SDR radio is looking for the IF signals and what we listen at the audio end.
The two signal samples show many interesting infos:
1) The YRF has a width of more than 15Khc at about 6db sides and is not as straight as it we would imagine.
2) the IRF has a width of less than 5Khc at the 6db sides with a loss of about 10db on the signal bandpass and more than 15db
attenuation on the remaining yaesu bandpass window.
3) The ssb signals are not centered on the higher part of the IRF but they are on one side.
It means that to copy better an ssb signal we must re-center it with the IF SHIFT control.
3b) the gain of the IF stage should be kept to a medium value to have both roofing gains in a good performance.
4) It is a MUST to mount the IRF via a switching unit, as its bandpass is too tight for a general use.
The complete switching project is at this link.
Switching from wide to narrow eliminates the lower sstv signal high-pitched.
As written already in the "Roofing-switcher" page the only way to appreciate the bandpass reduction
is to use the roofing switching unit and the K6SE mp-filters program found on va3cr.net web pages.
Any improvements or suggestions will be appreciated.
Write to my email on ic8pofATyahoodotcom (copy,paste and correct)
the Switchable Roofing Filter page
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© v.1.9 giugno 2007