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Author Topic: Where do I put the filter?  (Read 359 times)
W5CPT
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Posts: 556




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« on: January 03, 2007, 02:56:32 PM »

In my old age I have gotten re-interested in CW and as I operate more CW the more I think I would like at least one filter in the radio. The radio is an Icom IC-756 (non Pro) and I can put one filter in each of two IF stages.  I am considering a 500 Hz, but where to put it is the question. I can add it to the 2nd IF which is 9 Mhz or the 3rd which is 455 Khz. What advantages to I get by installing it in either? Is there a downside to either?

Your experience will save me from learning the hard way.

Thanks,

Clint - W5CPT
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WB2WIK
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Posts: 20547




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« Reply #1 on: January 03, 2007, 03:30:45 PM »

9 MHz is a better place, as it's closer to the front end; however 455 kHz filters usually have a better shape factor (tighter skirts) because they're easier to make at the lower frequency.

I use narrow (CW) filters in both low frequency I.F.s in my TS-850S (8.83 MHz and 455 kHz), and in that rig, all I.F. filters (4 in each low I.F.) are independently selectable so you can immediately judge effectiveness.  It's an interesting test.

WB2WIK/6
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NS6Y_
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Posts: 0




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« Reply #2 on: January 03, 2007, 08:54:37 PM »

Unless you're really into re-engineering your radio, follow the instructions that come with the filter, it should plug right in. I suggest you get your filter from INRAD, they use the same Collins elements Yaesu does, but they cost much less.

Open radio. Plug in filter. Close up radio. Tell radio the filter is there.
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W5CPT
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Posts: 556




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« Reply #3 on: January 04, 2007, 02:48:49 PM »

N6SY,
You either mis-read or mis-understood the question. I know how to insert a filter. My questions was to learn the Pros & Cons of installing one in the 2nd OR 3rd IF. Steve gave some ideas on the merits of a filter in each location. I do know about the INRAD filters and when I decide it will probably be an INRAD as Icom is very proud of the filters they supply.

Thanks,
Clint - W5CPT
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W9NM
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Posts: 26


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« Reply #4 on: January 05, 2007, 05:56:30 AM »

WB2WIK/6 has the proper answer.  

The earlier in the gain chain you introduce selectivity, the more you reduce chances of IM/overload by strong adjacent signals.  The 9mhz filter should be first.  

The 455khz filter will affect the overall response: steeper skirts -  increasing ultimate refection.  However, the 1st mixer will be in trouble long before most of the benefits of the added 455khz filter can be realized.

Emil
W9NM
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NI0C
Member

Posts: 2383




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« Reply #5 on: January 08, 2007, 09:32:52 AM »

Having used two radios (TS850S and Omni 6) with filter slots in two IF stages, I'd advise using filters in both IF slots.  Cascading filters really makes a difference in reducing noise and increasing ultimate rejection.  You might consider using different bandwidths in each stage to give you some choices of overall bandwidth.  Keep in mind, csacading filters of equal bandwidth results in a slightly narrower overall bandwidth.

73,
Chuck  NI0C


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