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Author Topic: FT-897D- Does it really need a CW filter?  (Read 1755 times)

Posts: 26

« on: December 03, 2006, 03:19:09 PM »

Hi all!
I have a new FT-897d. Being new to ham / cw I am just starting to work my way thru DSP.
My initial understanding of DSP was that it was for  noise reduction, as against selectivity / adjacent signal rejection achievable with a plug in filter. However, page 27 of the owners manual "DSP CW peaking filter" suggests it 'may be ideal for use under crowded conditions'. This suggests to me that DSP is, at least somewhat, taking the place of a plug in filter. This is all fine on paper but I'm wondering what all you experienced users of this rig have found in your real conditions.

Also, if your answer is, YES, I do still need an accesory filter then which one- 500 or 300hz. I am aware that the 500 is easier to use whereas the 300 is so tight that you can easily speed thru and miss a perfectly good signal. I am also aware that the 300 is better for contesting. I'm not contesting yet but I won't rule it out for the future.

All help appreciated,

73 de Pete

Posts: 247

« Reply #1 on: December 03, 2006, 03:47:17 PM »

 I have the 897 and operate cw only. The "peaking" filter works quite well but has three settings of 240, 120, and 60 hertz. That's a little tight for general use. I got the 500Hz filter as well and use it most of the time that I need a filter at all. For general rag chew qso's I don't use a filter unless someone is severely qrm'ing us. During contests, I use the 500Hz filter most of the time and the peaking filters when needed.

Eric, N3EF

Posts: 26

« Reply #2 on: December 04, 2006, 02:18:44 AM »

Hi Eric,
Tnx for the reply so far. Yes, I noted the 3 DBF filter widths available but they are so narrow I felt sure they were for some purpose other than adjacent station rejection. My experimentation in the meantime has revealed I need a more gentle touch on the dial to get the most out of it.
I guess I'm just now left wondering that if this DBF is so good then why have Yaesu still provided plug-in filter slots and even mentioned the filter accessory at all.
Many thanks for your help on the topic.

   de Pete

Posts: 173

« Reply #3 on: December 04, 2006, 05:50:21 AM »


The biggest reason that Yaesu (and others) still offer optional plug-in filters is that their DSP features are purely audio filters, while the plug-in's are active in the intermediate frequency (IF) chain of the receiver.  The difference in performance is slight if there are no strong signals on nearby frequencies -- either filter will slice off the noise and weak interfering signals.  It is only when there is a strong signal on a nearby frequency that the IF filters help the most.  In these cases, with only the DSP in the circuit, the receiver will likely experience "de-sensitizing."  When this happens, the automatic gain control of the receiver will sense the strong signal nearby and reduce the over-all gain of the receiver.  You will "lose" reception of the weaker signal you are trying to copy.  If you then switch in an IF filter, it will filter out the offending signal before it gets far enough along to affect the AGC, thus allowing you to continue to copy the weaker signal.

That said, while I don't have an FT-897, I do run an FT-847.  Similar in that its DSP is audio only, so I have added the 500 Hz mechanical filter for CW.  A very useful combo.

One thing to check -- you mentioned that you will need to develop a more sensitive touch on the tuning dial.  Did you check the 897's manual for adjustments?  My 847 allows for user selection of the tuning rates for the main and RIT tuning.  Maybe a simple tweak will make it easier.

73 es gud luck!
Steve  WA9FZB

Posts: 26

« Reply #4 on: December 04, 2006, 12:44:21 PM »

Hi Steve,
Thanks too for your reply. I guessed there would be a good reason they would still have the plug-in option and I get what you are driving at.
As for the dial speed, yes I have a number of options. Its probably more a matter of me slowing down. My biggest problem is that I'm trying to stay 100% CW and that activity can be quite scarce at times "down under"(I'm hoping this might change) so I end up just twiddling the dial over a large range and end up frustrated when nothing turns up.

tnx again,
73 de Pete

Posts: 729


« Reply #5 on: December 07, 2006, 01:26:02 PM »

I agree, the settings for the DSP are too sharp, even at the 240 hertz level, for comfortable CW operation.  I did not purchase the Collins filter for my 897 but if I decided to do so, it would be the 500 hertz.  

On my primary rig, a Drake B-line, I use the 1.2 khz position for nearly all my CW work.  Rarely do I find a need to drop to the 400 hertz position on the Drake.  I have done so, but not very often.  

The 897D is a very nice rig, and I am happy I chose it.  I may decide to order the 500 hertz filter, as the 897 is also mostly a CW radio for me.  

Many years ago I was using an R390A which has a 100 hertz (cycle in those days) audio response filter (See?  It's been around a long time - that was in 1959!)  and found it way, way too sharp for anything useful.  Many of us prefer the "filter" in our heads, which prevents the ringing of sharp filters.  

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