How to make 88mH bifilar filter coil

[G0ILN]

Hi,
I am trying to construct a pasive audio CW filter and I require 88mH bifilar coils . has anyone any info on how to make up such coils ?
what toroid do I require . how many turn and what diameter wire etc.

This is a filter for my ageing Ft817 that is being bought out of retirement!

Many thanks
Richard G0ILN

[W9GB]

R-

This part was plentiful in 1970s ... the part was used in telephone industry.
http://www.charlesindustries.com/loa...il%20cases.pdf

This is a UK telecom usage.
http://62.49.17.234/technical/Teachi..._Explained.pdf

They do appear on eBay and hamfests now and then ... Otherwise it is a winding chore.

w9gb

[G0ILN]

Thanks for the reply.The UK website is the same guy I got the passive filter circuit from!and I hadn't read this particular thread.
Many thanks for your help.

Richard

[W9GB]

ARRL Handbook has had articles on Building Audio Filters using 88 mH coils for a number of years.

Ed Wetherhold's Passive CW Audio Filter, ARRL Handbook

Building W3NQN's Famous CW Filter
http://w3nqn.com/build.html

Since this 88 mH is at AUDIO frequencies (300 - 3,000 Hz), the torrid cores are very simple ...
Some mfg. even used magnetized steel washers !

These 88 mH coils were featured in many amateur radio magazinr articles (1960s and 190s) for usage in audio filtering (CW, SSB) as well as RTTY filtering !

Charles Industries, who sells 88 mH coils, is in the NW Chicago suburbs (Rolling Meadows, IL).
Distributors for that 88 mH coil.
http://www.charlesindustries.com/distributors_tele.htm
The company was formed from Rockwell International’s Wescom division and Alcatel’s T1 and channel bank product lines (AT&T, Bell Labs, Lucent, Western Electric heritage).
They are one of many surviving telecom or electronics firms from the area's golden age with Western Electric manufacturing from 1890 to 1984.

[N2EY]

The coils commonly used by hams are telco surplus and are not bifilar. They are toroids with two windings - 88 mH in series, 22 mH in parallel. There are similar coils which are 44 mH series and 11 mH parallel.

73 de Jim, N2EY

[WA7PRC]

An active filter would work MUCH better... sharper skirts, easy to change the center frequency, bandwidth, and gain/loss. And NO ringing.

[W0BTU]

An active filter would work MUCH better... sharper skirts ...

A heck of a lot less work than shoving all that wire through a toroidal core, too! :-)

[W9GB]

Alexander Graham Bell "invented" Twisted-Pair cabling
http://en.wikipedia.org/wiki/Twisted_pair

Nikola Tesla was first to "document", in a patent filing, Bifilar winding/coil.
http://en.wikipedia.org/wiki/Bifilar_coil

John, G8MNY appears to be using common 88 mH cores sold by telecom equipment mfg.

You can contact Ed Wetherhold, W3NQN
http://w3nqn.com/contact.html
about various audio filter articles that he has written in the amateur radio literature.
The cover of the 2004 ARRL Handbook featured Ed's most recent CW filter build and kit.

W3NQN still offers a "kit of parts" and assembly instructions on his web page.
http://w3nqn.com/build.html

Active filters and DSP can be used -- BUT simplicity of design has a role.
If not, then why don't we see everyone using SteppIR Yagi and vertical antennas?

==
w9gb

[WA7PRC]

W3NQN still offers a "kit of parts" and assembly instructions on his web page.
http://w3nqn.com/build.html

Active filters and DSP can be used -- BUT simplicity of design has a role.
If not, then why don't we see everyone using SteppIR Yagi and vertical antennas?

The W3NQN filters are not easily changed to a different CF, BW, and Q. At $70 for the kit, they're also not inexpensive.
An active filter can be built using parts from RS for much less cost, and have adjustable CF, BW, and Q. Proven circuits abound. The technology is decades old.

We don't see everyone using SteppIr yagis and verticals for various reasons. The biggest reason (for this ham) is the astronomical cost vs return. My Force12 C-4XL does VERY well, for 1/4 the cost.

[KO6WB]

Another vote for an active filter verses the passive filter. The active filter will ring if you narrow the BW too much but generally it is much better. There is no loss and can have gain, it's readily tunable and variable Q. The current draw is quite low and the performance high. It's light weight and easy to construct using readily available parts. A step up from an active filter is to get one of the DSP units. These excel at CW operations, RTTY and data and can make a world of difference in these modes. The DSP will help in phone operations but not as dramatic of an improvement on the narrow modes.
You can make a DSP unit if you want. There are circuits out there that cater to that approarch and it has become much easier to build them provided you have super vision. There are some examples that use older through the hole components.
The 88mH approarch is effective and if you still want to use that method then you'll find the information GB has given you to be very useful.
BTW one of my first homebrewed projects was a active filter for CW. I used it on an ARC5 receiver. If anybody wants to know if that was good idea I would have to advise you not do that. Looked good in theory but in practice it was a pain.
Hope this helps
73
Gary