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G8MNY > TECH 19.10.06 16:03l 106 Lines 5020 Bytes #999 (0) @ WW
BID : 51596_GB7CIP
Read: GUEST DL1LCA DL8FBH
Subj: Simple AF test osc
Path: DB0FHN<DB0MRW<OK0PPL<DB0RES<TU5EX<HS1LMV<SV1CMG<VK6HGR<GB7YFS<GB7CIP
Sent: 061019/1216Z @:GB7CIP.#32.GBR.EU #:51596 [Caterham] $:51596_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Oct 06)
(8 Bit ASCII Graphics use code page 473 or 850)
At my local club for a construction contest we made up several
Velleman test osc kits. They all worked OK, but the output shapes
were very poor, so I have had a go at re-designing mine....
THE ORIGINAL
The circuit used a 555 astable osc & then used various cascaded CR
filters (1 Cap combination actually shorting the 555 square wave edges to
ground!). A seperately biased NPN was used as an active filter to help
the sign wave filtering & the options then linked into an outut NPN
emitter follower. There were 4 shapes available all at different levels.
NEW DESIGN
I kept the 555 & set the frequency more to 1kHz by changing the main
timing R to 22k. (NB square wave ratio of 1:1 needs charge R (1k+22k)
to equal the discharge R (22k)! The large square wave is attenuated
6:1 & biased up to work the NPN at the same DC leval as the other
waveforms.
The other waveforms are self biased from the filtered square wave.
ÚÄo\oÄÂÄÄÄÂÄÄÄÄÄÂÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ ³ 1k ÚÄÄÁÄÁÄ¿ 5k6 SQUARE ³
³+9v ³+ ³ ³ 4 8 ³ ÚÄÄÄÂÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo ³
ÄÁÄ === ÃÄÄ´7 555 ³18k ³ TRIANGLE ³
± 25u³ 22k ³ 3ÃÄÁÂÄÄ)ÄÄ18kÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo ³/
³ ³ ÃÄÄ´8 ³ 2k2 ³ ³ SINE <Ä´BC547
³ ³ ÃÄÄ´2 ³ ÀÄÄ)ÄÄÄÂÄÄ)Ä4k7ÄÂÄ10kÄÂÄ22kÄÂÄo ³\e 10u
³ ³ === ³ 5 1 ³ 4k7 ³ ³u1 ³ === ³ ÃÄ´ÃÄ¿
³ ³47n³ ÀÄÄÂÄÄÂÙ ³u22³ === ³ 22nÀÄÄÄÄÄ)ÄÄÄÄÄÄ´+ 47k<ÄÄ>
³ ³ ³ 10n=== ³ ³ === ³ 47n=== 10n=== 4k7 Pot O/P
ÀÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÁÄÄÁÄÄÄÄÄÄÁÄÄÄÁÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄ>
To get the 1/6 height triange wave I used an 18k & u1, & gave an without
too curvey slopes. Then I did the same a 2k2 & u22 as an initial filter
CR to set the higher level needed for the sine wave feed to an active
butterworth 18dB/octave filter, that used a doubling of values to give a
good filter shap. This gives a total of 24dB/O filtering for the sign
wave on the initial square wave harmonic levels.
Only 1 NPN transistor is used in this circuit now. I changed it's
emitter resistor to reduce current & the 1uF supply cap to 25uF & also
the output feed cap to 10uF for as no droop square wave.
Power comnsumption is now a lower 11mA, & the circiut will operate OK
on 12V.
Output level is dependant on supply, but all about 1V P-P on 9V.
USES
The main use is for AF work, where tones can be injected into AF stages.
The 3 waveforms have different uses..
SQUARE WAVE used with a scope to quickely determin the AF bandwidth..
._ _________ _.
³ ~-._ ³ ³ Very ³ ³ _.-~ ³
³ Poor~³ ³ ³ flat ³ ³ ³ Too ³ ³
³ LF ³ _³ ³Responce³_______³ much ³_ ³
³ _.-~ LF ~-._ ³
_____ ~ 100%³ ³ . ~
/~too ³ ³ ³ ³\.____
³little ³ ³ ³ ³ 30% 20% ³ Too ³ ³
HF \_ ³ ³ ³ ³ | 13% ³ much ³ _----Ù
~~~~~ ÀÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁ HF ³/
1kHz 3kHz 5kHz 7kHz
Spectrum
The spectrum is very anoying to the ear as it contains only odd
harmonics that attenuate by there harmonic number fraction.
TRIANGE WAVE used with a scope to look at Amplifer crossover &
peak & other non linearity.
/\ crossover /\ ideal /\ peak
/ \_ _/ / \ straight / \compression
\ / / \ sides / \ /
\/ \/ \/
/~\ symmetrical asymmetrical /\ asymmetrical
/ \ clipping /~~~~\ clipping / \compression
\ / \ / / \ /
\_/ \/ \/
The spectrum is like a Sqware wave, just lower odd harmonic levels.
SINE WAVE used with a scope or AF spectrum analyser (sound card) or
just ears to judge level of unwanted harmonic generation in a piece
of af kit.
_
/~ ~\ Note the smooth dB ³ ³
| | curves of the level ³ ³
³ ³ ³ sinewave, with a ³ ³ Litttle/no
| | perfect inverted ³ ³ harmonics
\_ _/ image & no harmonics. ÀÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ
~ 1kHz
Accurate constant level variable frequency sine wave oscilators are
used to determin the true frequency responce.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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