| |
G8MNY > TECH 25.11.12 11:46l 79 Lines 2713 Bytes #999 (0) @ WW
BID : 1862_GB7CIP
Read: GUEST
Subj: PA & PSU Fan Noise
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 121124/2105Z @:GB7CIP.#32.GBR.EU #:1862 [Caterham Surrey GBR] $:1862_GB7C
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Sep 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have often noticed fan noise from PSUs & powerful RF PAs, this can be quite
distracting on Rx & the fan is normally not necessary in Rx mode.
FAN QUEITENING
Quiet fans are made & usually have feathered slots in the blade leading edges.
normal Quiet
_.-Ä-._ _.-Ä-._
| | | =<
\ /Leading \ =< Deep
\ _ / Edge \ _=< V Slots
/~ ~\ /~ ~\
There is little loss in efficiency but nearby stationary support bars now
produce a softer blurred sound pulse considerably reducing the blade pitch
noise.
FAN SPEED
Permanently reducing the fan seed will reduce the noise & for some over cooled
systems this works well. But for applications where maximum cooling is
occasionally needed a variable speed solution is appropriate.
There are several options.
1/ Underrun the fan in Rx mode.
This needs a series R that shorted out when on Tx. This can be done with a
relay contact on a mains fan & to keep the R power down the mains fan should
be Power Factor tuned, Or use a lower mains voltage,
+12VÄÂÄÄÄÄÄ¿
LÄÄÄÄ¿ ÚÄÄÁÄÄ¿ _³_ LÄÄÄÄÂÄÄÄÄÄ¿230V
Fan ³Relay³ /_\ ||)_____\
ÃÄÄ¿ ÀÄÄÂÄÄÙ ³ OR ||)150V ³
R / ÃÄÄÄÄÄÙ ||) Fan
NÄÄÄÄÁÄÄÙ PTT NÄÄÄÄÁÄÄÄÄÄÄÙ
2/ Temperature sense.
By adding a thermal switch a DC or maina fan can be kept off or running slow
most of the time.
ON OFF
LÄÄÄÄ¿ MODE SPEED UP LÄÄÄÄ¿
Fan MODE Fan
³ ÃÄÄ¿
/Thermal R /Thermal
NÄÄÄÄÙ Switch NÄÄÄÄÁÄÄÙ Switch
(With suppression)
3/ Variable controlled DC a fan.
This offers the quietest fan control.
+12VÄÄÂÄÄÄ¿+
FAN ===100u
³___³__
³ e\³_Old PNP
\³ /³ Germanium
ÃÄÄÄÙ In heatsink
e/³Tab
0VÄÄÄÙ NPN
If an old germanium PNP it not available it can be a suitable NTC thermistor
& the NPN can have a hold off R base to emitter to set the operation
temperature. The cap is needed on DC fans to handle the pulse currents &
make the motor start better. A permanent quiet run R can be put across the
NPN if wanted.
See TECH Bul on "Variable Speed Fan for AF PA"
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
