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G8MNY > TECH 19.10.06 18:10l 126 Lines 5789 Bytes #999 (0) @ WW
BID : 51621_GB7CIP
Read: GUEST DL1LCA DL8FBH
Subj: Simple AF test osc UPDATED
Path: DB0FHN<DB0MRW<OK0PPL<DB0RES<ON0AR<GB7CIP
Sent: 061019/1511Z @:GB7CIP.#32.GBR.EU #:51621 [Caterham] $:51621_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. (N.B. square wave ratio of 1:1 for no even harmonics
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´6 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 shape. This gives a total of 24dB/O filtering for the sign
wave on the initial square wave harmonic levels. That is about -50dB @
3kHz, or better than 0.3% distortion all in, as the 3rd harmonic should
be the only significant one.
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..
Ú._ ________ _.¿
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 _.-~ ÀÄÄÄÄÄÄÄÄÙ LF ~-._ ³
À~ ______ , ~Ù
/~ Too ³ ³\.______
³ little ³ ³ ³ Too ³ ³
HF \_ ³ ³ much ³ _-----Ù
~~~~~~ HF ³/
Level³ ³100%
³ ³
³ ³
³ ³ A.F. SPECTRUM
³ ³ 33%
³ ³ | 20%
³ ³ ³ ³ 14% 11% 9% 8% 7% 6% 5%
ÀÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄHz
1k 3k 5k 7k 9k 11k 13k 15k 17k 19k
The spectrum is very anoying to the ear as it contains non musical odd
harmonics that only slightly reduce by their 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
\ / \ / / \ /
\_/ \/ \/
Level³ ³100%
³ ³
³ ³ A.F. SPECTRUM
³ ³
³ ³
³ ³ 10%
³ ³ ³ 4% 2% 1%
ÀÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄ Hz
1k 3k 5k 7k 9k
The spectrum is like a sqware wave, but lower odd harmonic levels at
their hamonic number fraction squared.
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.
_ Level ³ ³
/~ ~\ Note the smooth dB ³ ³
| | curves of the ³ ³
³ ³ ³ sinewave, with a ³ ³ Litttle/no
| | perfect inverted ³ ³ harmonics
\_ _/ image & no harmonics. ÀÄÁÄÄÄÄÄÄÄÄÄÄHz
~ 1k
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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