...first "EMPIRICHAL" TEST of the switching IRF unit ...

Unfortunately in this period there are not very "Busy Contests" around in which one could try to "fish" weak signals below strong ones.
So having not at my disposition any expensive instruments other than my ears, I was tuning on the bands
to get some crowded channels. I found a commercial rtty station on 10100Khc at s9+ signal strength.
This station is almost every day on the frequency, do not know who is it, but I use it as fishing net.
Under this strong signal from time to time can appear a HAM_CW station
I was trying to receive with the IRF and my cw filters 500 and 250.

But every manoeuvre I have done by switching the IRF unit and the rig's filters on\off no improvement came to my ears.
The only visual & listening difference is the increased noise level when switching ON the IRF unit.

Therefore I prefer to switch OFF the IPO preamplifier to get a quiter ground level when IRF is ON.
Instead of going into the rig's IF_gain menu.


Then I remembered that there was a little program "MPFilters" written by K6SE (find it on va3cr.net) and re-installed it.
This program lets to receive without the filters or better said with the wide AM passband on ssb (thru at 6khz)
without going into the "DEEP_Functions" of the FT1000 menu.

In this wide mode tuning around that rtty signal and playing on\off of my simple switching unit I noticed that
below its center starting about at 2000Hz the signal reduction was audible, but unfortunately the cw station was away.
The screen capture below shows how the tones of the rtty station disappear almost completely when switching ON the IRF unit
starting about 2200Hz away from the main channel.
This band-cut was evident only on the low part of the rtty channel not so on the high side of the tones.
Why so I cannot explain, maybe will do someone more technician than me.

*** Audio file *** A short mp3 file has been recorded to show the on\off switching of the IRF unit: roofing-test mp3 The difference will be better understood wearing the headphones. There are 2 sstv stations the high-pitched is the one that is cutted away when inserting the IRF The only way to appreciate the narrower IF window of the IRF with the own ears is to switch the cristal filters off and receiving ssb with the 6khz via the K6SE program. When using the ssb or cw filters is impossible to appreciate any difference. * * *

* * * Here is my Point of View after some months of use of the narrower Roofing Filter. The expectation of better receiving results were great at the beginning , but after having tried the IRF in various modes and conditions I have realized that adding that filter is not sufficient to beat the close channel QRM specially on 40mt SSB. CW & Rtty do not take much advantage of the IRF because the tight filters are already sufficient for a " Ham use ". I suppose that it is a hard battle to obtain a cleaner freq. between 2 ssb stations maybe away only 5 to 8 khcs without modifying deeply the original first IF stages. ... Try to receive in the middle of 2 S9 or stronger stations in ssb ... ... not speaking of those stations ROARing into thier mics at ultra-maximum because They do not see the meters moving ... ... and Their channel is almost 20 to 50 khcs or even wider ... Not even mr. Spock could demodulate a qrp station between 2 such "strong" ssb signals ! Hopefully someone of good will and skill one day shall develop and sell a real *top permormance first IF and Roofing* module to substitute the original in the FT1000mk_Vx models. Untill then we can use the VRF, IDBT, Shift&Width, Noise Reduction and RF_Gain features to improve our receptions. Yes, RF_Gain control : you will be surprised about this ancient and unused option. * * * Of course a good Antenna helps ... most of times * * * In the mean time before we will find a Star_Trek_Enterprise's surplus radio, mount and forget the IRF added june 2005

Part one .