On May 7, 10:47 am, RHF wrote:
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 Filterhttp://ph.groups.yahoo.com/group/Satellit800/photos/view/17ab?b=9http://ph.groups.yahoo.com/group/Satellit800/photos/view/17ab?b=7&m=f...
.

The AR7030 uses a HPF once you are above the MW band. I don't know
about the latest versions, but my old 7030 switches in the HPF inside
the MW band. That is, it was designed before the band was expanded.

The beacon band is low enough that you could probably roll your own
LPF ladder filter with reasonable success. Yet another project....