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G8MNY > TECH 25.08.25 15:52l 68 Lines 3337 Bytes #9 (0) @ WW
BID : 39508_GB7CIP
Subj: Passive CW headphone filter
Path: JH4XSY<N3HYM<VE3CGR<GB7YEW<GB7CIP
Sent: 250825/0640Z @:GB7CIP.#32.GBR.EURO #:39508 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 04)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This filter is a plug in adapter that has no batteries but gives very good
performance.
Level
ﾚﾄﾄﾄﾄﾄﾄﾄﾄ10Rﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄｿ 0dBｿ ..
Rig o through o ｳH/Phone ｳ . .
Jack ｳ Socket -10dBｴ . .
<ﾄﾄﾄﾄo DOUBLE POLE C/O oﾄﾄ)ﾄﾄﾄﾄ< ｳ . .
<ｿ \ \ ｳ ﾚ< -20dBｴ . .
ｳ o cw filter o ｳ ｳ ｳ . .
ｳ ｳ u47 ｳ ｳ ｳ -30dBｴ . .
ｳ === 88mH||) 120R ｳ ｳ . .
ｳ ﾃﾄ3K3ﾄﾂﾄﾄﾄﾄｿ ||) ｳ ｳ -40dBｴ . Measured .
ｳ ｳ ｳ ||)88mH ||) ｳ ｳ ｳ . Performance .
ｳ ||) u47ｳ ||)ﾄﾄ1K5ﾄﾄｴ ｳ ｳ -50dBｴ . .
ｳ ||) === ||) === ｳ ｳ ｳ . .
ｳ ||)88mH ｳ ｳ u47ｳ ｳ ｳ -60dBﾅﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄ
ﾀﾄﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄﾙ 0 200 400 600 800 1k 1k2 1k4 1k6 1k8
Frequency Hz
The through position attenuator values of 10R & 120R may need adjusting to suit
your Rig & Headphones to have the same loss as the filter.
The 3 tuned circuits are all made from 0.47uF polyester caps & old telecomm
bifilar wound line loading coils connected in series to make 88mH. The input &
output tuned circuits are series ones matching the low impedance of the LS jack
& Headphones. The middle tuned circuit is a parallel one, but the coil centre
tap has been used as the output load.
The coupling Rs of 3K3 & 1K5 are compromise between bandwidth & loss.
I boxed it up in a small plastic box that was a tight squeeze for the
components so they did not need any fixing. The I/P was a short wander lead
jack & the O/P was a socket in the box. The holes for the cable, switch &
socket, were moulded in with a soldering iron.
In use it will make beacons & CW much easier & less tiring to read. At around
800Hz your ears can resolve about 25Hz in frequency, this filter is much wider
& does not have bad ring effects that some narrow filters do.
As this is a post IF filter large signals in the IF bandwidth outside the CW
filter bandwidth will affect the Rig's AGC & thereby weaken/modulate signals
heard through the CW filter.
Using it takes the hard work out of resolving noisy signals. Switching the
filter out on a tuned in weak signal is very impressive!
-----------------------------------------------------------------------------
Eric ON4CBL says try a long resonant tube of a LS...
RESONANT QUARTER WAVE OF A TUBE BAFFLE GOOD FOR MAKING RESONANT SPEAKER ON CW!
Eg Tube diameter: 0,1 metres, Length: 1 metres
This is a resonant quarter wave at:118,835 Hz
A tube placed over an audio speaker can be used to enhance a specific frequency
such as a CW signal. Use a tube resonated to your preferred cw beat note &
place over the speaker. Other frequencies not at your chosen beat note will be
attenuated. 73 - Eric
Why Don't U send an interesting bul
73 De John, G8MNY @ GB7CIP
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