[ARC5] Home brew passive CW filter

[Dennis Monticelli]

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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