[Boatanchors] QEX Dec 1988 W3NQN Article

[Bill Cotter]

I still have the CW and SSB filters from the 
Wetherhold article, and use them to this day. 
Even though I have a K3S and OMNI-VI+ with DSP 
magic, the W3NQN design doesn't have the ringing 
and digital artifacts that DSP filtering 
introduces. However, they don't do anything for 
noise reduction short of reducing the bandwidth. 
Using the W3NQN filters last in the audio chain 
before the headphones seems to be ideal.

73 Bill N4LG

PS: They do wonders for BA receivers that were before DSP.



At 12:30 PM 7/12/2020, Bill Cromwell wrote:
>Hi, I once used a passive L-C audio filter built 
>around those. I may still have it and may still 
>have some more 88 mH toroids ( I once hade five 
>of them). They did a nice job at the time but 
>other filtering schemes run circles around them. 
>They do what they always did and are good for 
>nostalgia:) For on-air use I will take the DSP 
>machines:) I could be talked into parting with 
>my 88 mH toroids assuming I can find them:) 73, 
>Bill  KU8H bark less - wag more On 7/12/20 12:09 
>PM, w5jo at brightok.net wrote: > Someone refresh 
>my memory abut those coils Grant mentioned.  I 
>have 10 > coils that, as I recall, are that type 
>but am short on memory. > > These are toroid and 
>a lot of wire on them, indicating a large > 
>inductance. There are 5 with Red wire and 5 with 
>Green wire.  If I > recall they are 88 and 44 
>mH but I can't be sure. > > Does this ring a 
>bell with anyone?  I inherited them in an 
>estate from a > local ham who was prone to save 
>things like that and I did not look at > them 
>until just after reading message from Grant and 
>Scott. > > Should they be of use, postage will 
>get them. > > Jim > W5JO > > > -----Original 
>Message----- > > While not Wetherhold’s 
>filters, there is a Crud-o-ject filter in a 
>1972 > QST which looks to have a similar 
>bandwidth. > > I built the later SSB Crud-o-ject 
>which I wish I still had, but parted > with a 
>long time ago.  I had it built into a Heath 
>SB-600 speaker.  > These were both basically 
>“noise and crud” filters, but the original > 
>version for CW is relatively narrow.  Someone 
>also produced commercial > versions of 
>these.  It’s too bad that 88/44/22 mH coils 
>have become so > seemingly scarce. > > Grant 
>NQ5T > >> On Jul 12, 2020, at 11:12 AM, 
><whitebear1122 at comcast.net> >> 
><whitebear1122 at comcast.net> wrote: >> >> Hi, I'm 
>trying to get my hands on an article from 
>December 1988 QEX.  >> It is >> not available 
>through the ARRL's magazine Archives.  The 
>article is by >> W3NQN >> titled "CW and SSB 
>Audio Filters Using 88 mH Inductors. >> >> >> >> 
>I'm looking to build LC SSB and CW audio filters 
>for my homebrew HBR-13 >> receiver.  I'd like 
>to narrow up the CW bandpass to something 
>like >> 800-1000 >> Hz. >> >> Thanks.  73, 
>Scott WA9WFA >> > > 
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