Dave,
I appreciate the fact that you sent some specs. This tells me a lot:
"I typically use cormcom EMI/RFI AC line filters. But I've used some
surplus jobs from Fair Radio with similar success. Decades ago I spent a
good amount of time in a lab comparing some of these filters types, even
the K-coms.
Here is the info from one of the surplus filters:
LINE
RNF - 5PI
2X5 AMPS
125/ 50VAC
50 400hz
RTRON CORP
I bought a couple dozen of these years ago. They have been solving
phone RFI problems for many years.
73,
dave
wa3gin"
For point of clarification, Dave, my comments about not using power line
and signal control filters for telephone applications were based upon
filters having the following characteristics:
Operating freq: DC to 60 Hz
Impedance: Unspecified (meaning "uncontrolled") for either line-to-line or
line-to-chassis (ground)
Stop band: 14 kHz to 10 GHz
Insertion loss in the stop band: 100 to 120 dB (measured in a 50 ohm
environment)
The Corcom and Rtron filters come nowhere close to having that amout of
insertion loss. In order to obtain 100 dB insertion loss at 14 kHz, the
filters with which I worked had at least 30 to 40 dB attentuation at 3 kHz,
the upper end of the telco pass band.
So, yes, comments pertain to those items with which we are familiar. You
managed to get some filters that are usable to 400 Hz (that helps a lot)
and which probably don't have more than about 40 to 50 dB attenuation in
the stop band. That is plenty adequate for your application and allows you
the "luxury" of having some low cost "tel line" filters. I truly believe
in going with what works, but we need to be sure that we adequately
describe the working item.
Thanks again for supplying this information.
73, Dale
WA9ENA
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