G8MNY > TECH 16.12.25 15:00l 95 Lines 4811 Bytes #199 (0) @ WW
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Subj: AM TRF Radio
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Sent: 251216/0755Z @:GB7CIP.#32.GBR.EURO #:47323 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Nov 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
In a recent construction contest, we all had to build this QUASAR project kit
No 3063 "One Chip AM Radio". Here I have redrawn the circuit in a more logical
way.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÂÄÄÄÄ>+9V
4K7 5K6 ³ ³
ÃÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ ³/BC +³100u
1K ³ ³ ÃÄÄÄ´ 548 ===
ÚÄÄÄÄÂÄÄÄÄ´ ³ 10K _³_ ³\e ³
100K ³ ³ ³ u47 ³ \_/ 6R8 ³
Rod ³ ÚÄÄÁÄÄ¿ ÃÄÄÄ)Ä´ÃÄÄÂÄÄ150KÄÄ´ ÚÄÄÄÄÄÄ)ÄÄÄÄÄ´ ³+ 100u
ÚÄÄÂÄÄÄ)Ä´MK484³ ³ ³ ³ ³ 820K _³_ ÃÄÄÄÄ)Ä´ÃÄ>LS
||( ³_ ³ ÀÄÄÂÄÄÙ ³ ³ ³ ÚÄÄÄÄ´ ³ \_/ 6R8 ³
||( ³/| ³ ³ ³ ÃÄÄ¿ ³ ³/ ³ ÃÄ´ÃÄÄÄ´ ³/e ³ 8ê
||( === ³ ³ === ³ _³_ ÀÄ´BC548 ³ ³n47 ÃÄÄÄ´ BC ³
||( /³ ³ ³ u1³ ³ \_/ ³\e ³ u47 ³ ³/ ³\558 ³
ÀÄÄÁÄÄÄ´ ³ ³ === ³ ³ 10K<Ä´ÃÄÄÁÄÄÄÄ´ ³ ³
160pF ³ ³ ³u47³ _³_ 100 ³Log BC³\e ³ ³ ÚÄ>LS
=== ³ ³ ³ \_/ ³ ³Volume 548 ³ ³ ³ ³
u47ÀÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÁÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÁÄ>0V
Construction was easy, about 30 min to do a good job. Most kits work OK.
The Tuned Radio Frequency Rx is fairly sensitive, but the high RF gain in this
not flat and there is a tendency to get RF oscillation at the high frequency
end of the band. Selectivity is surprisingly good. N.B. the IC runs at 1.2V
maintained by the 2 diodes. 1.5 of an LED is a bit too high. The 1k load & 100k
bias are said to be the optimum values for the IC's detecting & AGC action.
The AF amp is very poor, why they did not use an IC I don't know. The 1st class
A stage in run on next to no voltage so it distorts. The following class A
driver stage has too little standing current to drive the output NPN BC548 to
deliver +ve current swings into the 8 ohm LS.
There is no LW option, Ideally a 2nd coil on the ferrite rod is needed.
MY IMPROVEMENTS
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÂo\ÄÄ>+9V
³ ³ bootstrap 1K ³ ³ ON
4K7 ³ ÚÄÄÄÄÄÄ´ ³ ³
ÃÄÄÄ¿ ³ +³ 3k3 ³/BC +³100u
1K ³ 10K === ÃÄÄÄ´548 ===
ÚÄÄÄÄÄÄÂÄÄÄÄ´ ³ u47 ³ ³15u _³_ ³\e ³
100K ³ ÃÄÄÄ)Ä´ÃÄÄÂÄÄ150KÄÄ´ ³ \_/ 6R8 ³
Rod Cd ³ ÚÄÄÁÄÄ¿ ³ ³ ³ ³ ÃÄÄÄÄÄÄ)ÄÄÄÄÄ´ ³+100u
ÚÄÄÂÄÄÂÄÄ)ÄÄ´MK484³ ³ ³ ³ ÚÄÄÄÄ´ 820K _³_ ÃÄÄÄÄ)Ä´ÃÄ>LS
||( ³_=== ³ ³ÀÄÄÂÄÄÙ ³ ³ ³ ³ 10K ³ \_/ 6R8 ³
||( ³/|³ ³ === ³ ³ ÃÄÄ¿ ³ ³/ ³ ÃÄ´ÃÄÄÄ´ ³/e ³ 32ê
||( === ³ ³ ³n82³ === ³ _³_ ÀÄ´BC548 ³ ³n47 ÃÄÄÄ´BC ³
||( /³ Rd ³ oLW ³ u1³ ³ \_/ ³\e ³ u47 ³ ³/ ³\558 ³
ÀÄÄÁÄÄÁÄÄ´ \ ³ ³ === ³ ³ 10K<Ä´ÃÄÄÁÄÄÄÄ´ ³ ³
160pF ÃÄÄÙ ³ ³u47³ _³_ 100 ³Log BC³\e ³ ³ ÚÄ>LS
=== ³ ³ ³ \_/ ³ ³Volume 548 ³ ³ ³ ³
u47ÀÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÁÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÁÄ>0V
Oscillation at HF end of MW.
By adding a light damping CR across the tuned circuit stops the oscillation,
the Cd is kept very small, a 10pF, & Rd = 330k did it OK without degrading the
performance.
1st AF amp distortion fault.
Running this AF amp from +9V gives lots more unclipped gain, but the
unregulated DC feed can lead to instability with a high gain output stage, so I
cut the track to the pot and added a 10k in series to attenuate the gain a bit.
Bootstrap.
I added a bootstrap to the output by changing the 5k6 for a 1k from +9V & a 3k3
to the NPN base, with the centre tap connected to a new cap to the output NPN /
PNP. This provides a lot more +ve output drive current, without increasing the
standing current and also increased the gain.
LS.
Using a higher 32 ohm LS reduces the LS current by 4, but I did not have one
and had to make do with the 8ê, which worked OK once boxed up.
LW.
Adding a switched 820 or 910pF gave tuning over 1 LW station @ 198kHz OK. I put
it across the unused 60pF tuning cap section and switch both in circuit to gain
the max tuning range. It is not very sensitive done this way, switching the
coil to a bigger one would me much better!
ON OFF
I added an ON-OFF switch too.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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