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Author Topic: Narrow filters for a Kenwood TS-480 SAT  (Read 12786 times)

Posts: 108

« on: November 25, 2011, 06:01:45 PM »

I am thinking its time to install a filter in my rig.  I operate mostly CW, psk, rtty and ssb.  My question is for those running 480's, would the 270 hz be too narrow to run comfortably with cw, psk and especially rtty, or should I invest in a 500 hz filter instead?  I will probably end up eventually buying two filters for my rig, but only have the money for one right now.

I've never operated a rig with filters before so I'm wondering how much can I expect the narrow filters to cut down adjacent signals compared to the AF DSP that is built into the radio.  I noticed even though I narrow down the DSP filter, strong adjacent signals can still nearly wipe out the signal I'm trying to pull in.


KB7FSC - Wane

Posts: 100


« Reply #1 on: November 25, 2011, 06:37:20 PM »

I have used both 250 Hz and 500 Hz from various different manufactures,  but for casual operation I prefer 500 Hz filter over 250 Hz,  because I mostly do slow speed CW , and many of the station I communicate with uses older radio , their frequency often drift as time pass, and 500Hz is easier to tune,  only time I prefer 250 Hz filter is when there are a lot of noises from near by electronics power line , etc,  then 250 Hz remove more noise than 500 Hz filter,  my first choice would be 500 Hz , but I also like option of having 250 Hz as secondary

Posts: 12

« Reply #2 on: November 28, 2011, 12:51:25 AM »

Hi Wane... For CW you really need two good filters. One 500 and one 250. When on CW tuning around the band you will always use the 500. To tune through all that noise with no filter is a real pain. When you tune in a station as good as you can with the 500 then you switch down to the 250 for the best clarity. The idea is to narrow the frequency as much as possible to eliminate the noise so you can hear those faint stations.
    An example would be astronomy. You find something you want to look at with a pair of binoculars because they have a wide field of view. Its easy to see a lot of things and then zero in on one thing. Then you use a telescope which has a much higher magnification yet much narrower field of view to get a clearer picture of the object.

  If you can only afford one filter right now go for the 500.

Rosario/ AA2CB

Posts: 2808

« Reply #3 on: November 28, 2011, 02:24:19 AM »

  If you can only afford one filter right now go for the 500.

I agree, FWIW.  A 250 Hz filter is really useful in contests, with cheek-to-jowl signals.  For most work, 500 Hz is fine.

An IF filter is _way_ better than AF DSP.  It is placed _inside_ the AGC loop, so strong signals outside the passband don't affect the receiver's gain.

One thing you could try to work a weak signal that's near a strong signal (I think the TS-480 has a narrow AF DSP filter):

. . . Set a narrow bandwidth on the AF DSP filter (250 Hz or so);

. . . Center the weak signal in the AF filter's passband;

. . . Turn off the AGC;

. . . Reduce the RF Gain so that the strong signal doesn't overload the receiver.

You may be able to get good copy on the weak signal.  I've run many RTTY contests, and normally have AGC _off_ to stop the strong signals from modulating the weak ones.

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