8-pole vs. 5-pole roofing filters?

[Bill W4ZV]

NT1Y:
 >What's the performance difference between the 8-pole and 5-pole K3
roofing filters?

         Good question, but the answer is more than simply
bandwidth and shape factor.  You need to know its performance
*in the radio^ with IMD and BDR measurements.  As ARRL
discovered with Orion's 500 Hz 8-pole filter, it had much
worse IMD than the stock 1000 Hz 4-pole.  Granted this had
much to do with a poor circuit design but there is no
substitute for *in radio* measurements, since the gain
distribution for a 5-pole versus 8-pole MUST be different
due to different insertion loss which can affect overall
IMD/BDR performance.

 >For crowded-band CW performance am I better off with a 5-pole 200-Hz
or a 8-pole 250-Hz filter?

         Given no IMD/BDR issues, probably the 250 because of
better skirt selectivity, but you really should look at the
individual filter response plots to know for sure.

 >Also, do I need separate roofing filters for the main and sub-RX?

         Yes, 5 slots available in both.

                                         73,  Bill  W4ZV

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[Gregg W6IZT]

Interesting to note that the 250 hz 8 pole filter actually has a -6 dB bw of
370 kHz.



-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Bill Tippett
Sent: Thursday, May 03, 2007 9:13 AM
To: [hidden email]
Subject: [Elecraft] 8-pole vs. 5-pole roofing filters?

roofing filters?

         Good question, but the answer is more than simply
bandwidth and shape factor.  You need to know its performance
*in the radio^ with IMD and BDR measurements.  As ARRL
discovered with Orion's 500 Hz 8-pole filter, it had much
worse IMD than the stock 1000 Hz 4-pole.  Granted this had
much to do with a poor circuit design but there is no
substitute for *in radio* measurements, since the gain
distribution for a 5-pole versus 8-pole MUST be different
due to different insertion loss which can affect overall
IMD/BDR performance.

 >For crowded-band CW performance am I better off with a 5-pole 200-Hz
or a 8-pole 250-Hz filter?

         Given no IMD/BDR issues, probably the 250 because of
better skirt selectivity, but you really should look at the
individual filter response plots to know for sure.

 >Also, do I need separate roofing filters for the main and sub-RX?

         Yes, 5 slots available in both.

                                         73,  Bill  W4ZV

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