OpenBCM V1.07b12 (Linux)

Packet Radio Mailbox

IW2OHX

[Bollate(MI)]

 Login: GUEST





  
G8MNY  > HIFI     06.11.17 11:31l 96 Lines 4543 Bytes #0 (0) @ WW
BID : 63727_GB7CIP
Read: GUEST
Subj: Technics Rx ST-RT550
Path: IW2OHX<UA6ADV<I0OJJ<GB7CIP
Sent: 171106/0708Z @:GB7CIP.#32.GBR.EURO #:63727 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : HIFI@WW

By G8MNY                                    (Updated Jan 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
넬컴커             旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커           
냅컴켸 o   O  O  O 쿜uartz lock Stereo RDS                 ch TUNE()  /~~~\  
                      旼    ..  3      | 旼 旼 旼 旼26 MODE   |     | 
    [_][_][_] [__]    납   .... 2            쳐     Auto         芙
                     납납 ......1      | 읕   |*읕 읕   Man    |     | 
                           signal FM                    MHz Lock    \___/  
    旼컴쩡컴왯컴커읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸[ ]        
    읕컴좔컴牡컴켸<][ 1][ 2][ 3][ 4][ 5][ 6][ 7][ 8][ 9][ 0][10][>           
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
I was given a faulty one of these tuners, it covers LW, MW & Band 2 with RDS, &
its has 39 memories. I have now got it all going OK.

CLEVER AUTO IF WIDTH
It has an unusual feature regarding the automatic FM IF filter width selection
I have not seen before. If the station is strong enough, it uses the wider low
distortion IF (300kHz), unless there is a nearby carrier. It decides this by
tuning 100kHz first with the narrow filter (180kHz) & if there is a signal
marking the spectrum graphic display with a bar  to the left or right of the
main carrier & then it uses the narrow filter.

PSEUDO SPECTRUM GRAPHIC
The Spectrum Graphics shows the IF bandwidth selected....

  IDEAL          BAD      BAD      BAD                             IDEAL
  STRONG         LF       HF               LF     HF            BUT WEAK
  NO QRM   Sig   QRM      QRM      QRM      QRM    QRM     QRM     NO QRM   Sig
 旼컴  ..  3   旼컴    旼컴    旼컴     旼    旼     旼      旼
    .... 2                      납    납     납      납
   ......1   납      납    납납    납납    납납   납납     납......1
  WIDE         MANUALLY FORCED INTO WIDE    NARROW FILTER MODE SELECTED

I wonder if anyone has any information, tips, do's & don'ts etc. for this Rx?

AM                         태컴컴컴컴컴컴컴커
It had no AM pickup        킴   VHF TUNER   
loop aerial, so I am       냅컴컴컴컴컴컴컴켸
using a large loop from      旼컴컴컴
6m of wire, (about 10uH)   쿴f( ) ( )쿴f
& I tracked the series     쿘W       쿗W
LW & MW aerial & Osc coils 쿹f( ) ( )쿹f
coils to best match this.    읕컴컴컴
                           
                                  旼커
                                  ()
                             AF   읕켸
                            Notch 旼커
                           쿑ilters()
                           ______ 읕켸_______
NO MAINS SWITCH!
As with many modern items there is NO MAINS SWITCH, the standby switch only
really powers off the display.

Much of the power consumption on my UK mains @ 245V 50Hz is due to the large
over run mains transformer (for 2x 110V 60Hz?) & gets hot even on standby with
little load, as does the plastic power supply regulator transistors when on.

POWER MODIFICATION
I modified the mains circuit (the large empty PCB with the transformer was
ideal) with a 2W 1k resistor in series with the mains neutral, & mounted it
well above PCB, I also tuned the mains transformer to 50Hz with a mains 0u15
X type Cap for minimum mains current (PF=1.0).
                          ___________
  Live컴컴컴컴쩡커   ...    Cooler  _____Rx
                )납(     Regulator 
 245V    0u15=== )납(    쿟ransistors
                )납(...  ~~~~~~~~~~~
Neutral컴1k컴컨컴 Cooler
         2W      Transformer

The result was a much cooler transformer all the time & cooler power supply
regulators, & hence less power wastage despite adding the 2W resistor. The
transformer voltage now has 230V on standby (2W consumed) & 220V when on (5W),
there is enough power supply headroom for the cooler running regulators OK, but
the display is very slightly dimmer due to the directly heated fillements.
(longer lifetime?)

HUM
I have done this sort of thing before on another FM Rx, but that case is was
due to acoustic & strong stray magnetic flux leakage hum from the super
saturated transformer causing problems. Again adding an series R reduced both
these completely.


Any feedback would be greatly appreciated.


Y don't U send an interesting bul?

73 de John G8MNY @ GB7CIP.


Read previous mail | Read next mail


 25.05.2018 20:49:52lGo back Go up