On May 6, 10:08*pm, wrote:
On May 6, 2:41 pm, RHF wrote:





wrote:
On May 5, 9:41 am, "D.K." wrote:
Hi all,
I'm considering to upgrade my receiver ICOM R75 with CW narrow *filters. My
main interest is NDB listening in the LW band.
There are 2 possiblities:
a) ICOM FL101 (CW narrow 9mHz IF, 250Hz) + ICOM FL53A (CW narrow 455kHz,
250Hz)
b) INRAD 121 (CW narrow 9010.6kHz, 250Hz) + INRAD 122 (CW narrow 455kHz,
250Hz)
Which combination is the better one *in terms of quality and efficiency.
Price does'nt matter.
Any advice is welcome!
Thanks in advance

D. Kremp
France

For my AR7030, I just put in a 250Hz Kenwood crystal filter in the
last IF. Does it really help to change two IF filters?

When I was doing beacons, I followed up with *a FFT program (ARGO). It
provides both a narrow band filter (the FFT bin itself) and a visual
manner to see the Morse code.

M... Sushi,

Should not the Two separate IF Filters of the same Band-Width : one for
the 1st IF and one for the 2nd IF create a Series RF Signal Path
resulting in a better combined Filtering Shape Factor then one along;
plus improve the Ultimate Rejection of the RF Signal Path.

Shape Factor : 2.0 & 2.0 = 1.4

Ultimate Rejection : 60 dB & 60 dB = 90 dB

~ RHF
.

- I suppose, but the AR7030 only switches the last filter.

The Icom IC-R75 allows both the 1st and 2nd IF Filters
to be switched.

- And wouldn't that be 120dB ultimate rejection?

In a perfect Circuit yes.

Here is my attempt as measuring the Kenwood CW filter in my 7030:
http://www.lazygranch.com/images/radio/cwfilter.gif
After a while, the signal was in the noise. Granted, I don't recall
exactly how I did the measurement. I used a RF generator that has 1Hz
steps, which is what you need for the crystal filter because it is
very sharp. I used a HP8903 to measure the audio level. I used the
speaker output because at the time I didn't have a DIN connector to
use the line output.

I suppose I should have cranked up the RF to the point where the 7030
preamp isn't used. That would push the noise floor to the minimum.

- While we are at it, why not a filter to roll off the MW and above.

IIRC - Some Shortwave Radio & Receivers use a
Tuned Front End or Limit Band Pass Filters that
Block Out of Band Frequencies

The Grundig Satellit 800 Millennium Radio
comes to mind : HPF & LPF & BPF &
SW Switching BPF & FM Tracking Filter
http://ph.groups.yahoo.com/group/Sat.../view/17ab?b=9
http://ph.groups.yahoo.com/group/Sat...ab?b=7&m=f&o=0