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G8MNY > TECH 12.05.25 07:23z 87 Lines 3819 Bytes #999 (0) @ WW
BID : 32399_GB7CIP
Read: GUEST
Subj: Simple mic clipper for MC60A
Path: HB9ON<DK0WUE<PI8ZTM<CX2SA<EA2RCF<I0OJJ<GB7CIP
Sent: 250512/0715Z @:GB7CIP.#32.GBR.EURO #:32399 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New May 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This modification puts a crude, but very effective clipper into this base mic
when used with & powered from a simple TS50 rig.
EXTRA COMPONENTS
2x Germanium/Schottky Diodes
1 10K small preset pot
1 470R Variable R
CIRCUIT
No preamp
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÂÄÄ<Rig 8V
mic Ä>o + Cut track o<ÄÄRig \³ 1K8
o 1K Ú------------o Mic T2 ÃÄÄ´
³ ÚÄÄÄÄÅÄÄÄ´ÃÄÄÄÄÂÄÄÄÂÄÄÄ¿ ³ +ÄÂÄ>o e/³ ³
³ 39K ³/ _³_ _³_ ³ ³ ³ oÄÄ´ _³_
À´ÃÄÁÄÄ´ T1 /_\ \_/ 10K<Ù ³+ _³_ /_\' 3.6V
³\e ³ ³ pot === /_\ ³
ÃÄÄÄÄ¿ ³ ³ ³ ³ ³ |<-remove
220R 470<¿ ³ ³ ³ ³ Batt ³
ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÁÄÄÄÁÄÄÄÁÄÄ ÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄ
The 3.6V zener diode in the regulated supply is removed by heating & lifting
up one end. This gives the preamp much more headroom to facilitate symmetrical
clipping with the added diodes. The extra 470R mic gain preset is placed over
the tiny 220R. The 2 diodes & are mounted over the preamp in/out switch
connector socket.
The track is then cut to the "Preamp in" position switch & the output level 10k
preset mounted over the preamp in/out switch.
BUTTON PCB
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄ¿
³C ³ ³: Ú' '³
³ T1 UP DOWN SWITCHES T2 1k8 ³ ³:_|ú ú³ |=cut track
³220 Zener³ Ú bk³: ³
³ ³ Ã rd³: ' '³
³ PTT LOCK ³ ³ ÀÄÄÄÄÄÄÙ
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ Batt SWITCH PCB
Setting up is best done with a scope looking at the signal on the diodes, check
that at normal close mic use the diodes clip the peaks off, adjust the 470R mic
gain to suit. Then operate the PTT & adjust output pot (& Rig mic gain) to just
give full power (normal ALC drive) on a loud clipped whistle (almost at zero).
This clipper only works when the mic level is just right, your voice level is
important, so aim for 3x (10dB) clipping level. On air tests gave it a good
clear audio report with clipped audio not too noticeable, but sounds quite a
bit louder.
CONTROLS
Using the Mic Impedance switch, some modulation control is posssable.
PREAMP MIC Z RESULT
out 50k Lowest unclipped (For loud background situations)
out 500ê Normnal unclipped
in 500ê Slightly clipped
in 50k Heavily clipped (For weak signal/noisy band)
WHY CLIPPERS WORK
Peaky Ý Ü ^ Clipped _ _ Resultant /~\ /~\ ^
Mic / \ / \_/~\_ ALC Mic / \_/ \_/~\ after / \ / ALC
Audio Þ ß v Audio ALC level \_/ v
When the worst of peaks are clipped off, the lower level can then drive the rig
with a higher mean level (less ALC action). This results in slightly noticeable
audio distortion, but a MUCH LOUDER SIGNAL. Under weak/poor conditions the low
level distortion products are not detectable, but the louder signal is more
easily read.
Audio harmonics generated will be transmitted if they get through the SSB
filter outside that they are filtered enough in the rig to not be a problem.
This is all very subjective, so heavy clipping should only be used for "weak &
poor contacts", not strong local ones where the distortion becomes wearing to
listen too!
Why Don't U send an Interesting Bul?
73 De John, G8MNY @ GB7CIP
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