[ARC5] Home brew passive CW filter

Thu Apr 28 13:19:14 EDT 2016

I have a 1-page bibliography of 88mH toroidal inductor info/projects.
I don't know who collected these. It came in one of Lloyd's magic
flatrate box thingies.

Can scan and post if anyone is interested. Must be 50+ articles here.

73, ian K3IMW

On Thu, Apr 28, 2016 at 10:12 AM, Dennis Monticelli <
dennis.monticelli at gmail.com> wrote:

> I think the pole count argument stems from using pole to really mean
> pole-pair.  The crystal filter has increased the use of the shorthand term
> by calling an IF or roofing filter 6 pole when in fact it had 6 resonators
> (pole-pairs) within.  Nowadays when I hear the word pole in the context of
> a filter I almost automatically think "pole-pair."
>
> Dennis AE6C
>
> On Thu, Apr 28, 2016 at 9:02 AM, J Mcvey <ac2eu at yahoo.com> wrote:
>
>> Just about anything would be better than the raw ARC5 BW on 40 and 80
>> meter CW.  Even the simple LC would be great if I get a better inductor for
>> the task. an actual loaded Q of 5 might be good.
>> The main thing is that it can't be overly narrow...
>>
>> I don't want anybody to hire Cray computing time to optimize to nth
>> degree or anything, but thought that someone may have made a working
>> passive already.
>> If not, no big deal!
>>
>>
>>
>> On Thursday, April 28, 2016 11:00 AM, Mike Feher <n4fs at eozinc.com> wrote:
>>
>>
>> Well, you would have to have some design parameters in mind first. Like
>> passband width and ripple, transition band width, and ultimate stopband
>> attenuation. Also, do you still want to go all passive? 73 – Mike
>>
>> Mike B. Feher, N4FS
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960
>>
>> *From:* J Mcvey [mailto:ac2eu at yahoo.com]
>> *Sent:* Thursday, April 28, 2016 10:53 AM
>> *To:* Mike Feher; 'Dennis Monticelli'
>> *Cc:* 'ARC-5 Maillist'
>> *Subject:* Re: [ARC5] Home brew passive CW filter
>>
>> anybody got specifics to build a multi-pole filter ? It would save me
>> having to calculate it myself!  I don't think a real narrow filter would be
>> practical on an ARC5 radio because the band spread isn't sufficient enough
>> to tune it easily. .
>>
>> On Thursday, April 28, 2016 8:46 AM, Mike Feher <n4fs at eozinc.com> wrote:
>>
>> I know you want to sound smart and you did not say if that was loaded or
>> unloaded Q. Regardless, he was talking about line transformers and finding
>> a smaller one and that is what I responded to. Two toroids already means
>> two poles, which was one of my suggestions. If it was for me I would just
>> design a nice Elliptic filter for the task. 73 – Mike
>>
>> Mike B. Feher, N4FS
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960
>>
>> *From:* Dennis Monticelli [mailto:dennis.monticelli at gmail.com
>> <dennis.monticelli at gmail.com>]
>> *Sent:* Thursday, April 28, 2016 12:44 AM
>> *To:* Mike Feher
>> *Cc:* J Mcvey; ARC-5 Maillist
>> *Subject:* Re: [ARC5] Home brew passive CW filter
>>
>> FYI.  I have a homebrew CW receiver that uses two small toroids (approx
>> 5/8") and fine wire.  The Q for each filter is 5 at 700Hz.  Q is a function
>> of wire resistance, the permeability of the core material and the loss
>> factor of the core.  Small size can be good or bad depending upon these
>> factors.
>>
>> Dennis AE6C
>>
>> On Wed, Apr 27, 2016 at 9:22 PM, Mike Feher <n4fs at eozinc.com> wrote:
>> For the same inductance a smaller transformer will have a higher R
>> reducing the Q. You will need more poles and if possible some zeros to make
>> a decent filter. 73 – Mike
>>
>> Mike B. Feher, N4FS
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960
>>
>> *From:* ARC5 [mailto:arc5-bounces at mailman.qth.net] *On Behalf Of *J
>> Mcvey via ARC5
>> *Sent:* Wednesday, April 27, 2016 11:14 PM
>> *To:* ARC5 at mailman.qth.net
>> *Subject:* [ARC5] Home brew passive CW filter
>>
>> Someone suggested making a filter using a 70V line transformer. I had
>> been looking in the junk box for something with high inductance, so I
>> tested the primary side of a line transformer using the common and 0.62W
>> taps. Sure enough,  it was useable at 8.5 H  To resonate that at 700Hz , it
>> needs .006 mf, I used a .0047 in parallel with a .001 mf.
>> That got me a measured resonance of 725 Hz on the first try! Sometimes
>> theory works!
>>
>> The test load was 7500 ohms:
>> input 1.85V
>> output at resonance was 1 v
>> Taking the 1 v max, I found -3 db points at 600Hz and 880Hz yielding  a
>> BW of 280Hz  which is a Q of about 2.6.
>>
>> It works pretty well, but I am going to try to find a physically smaller
>> transformer to try to  reduce the insertion loss.
>>
>> Haven't tried it on a real radio or signal yet, but looks promising.
>>
>>
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>
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