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G8MNY  > TECH     02.05.22 07:02z 90 Lines 4637 Bytes #15 (0) @ WW
BID : 1240_GB7CIP
Subj: BURNS's MF-UHF Wavemeter TC-101
Path: SP7YDD<SR1BSZ<IW0QNL<ON0AR<GB7CIP
Sent: 220502/0652Z @:GB7CIP.#32.GBR.EURO #:1240 [Caterham Surrey GBR] $:1240_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                               (Correction Sep 12)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Here is a reverse engineered diagram & layout of one I picked up the other day.

FRONT PANEL
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
'旼컴컴컴        '     /~~~~~\  RF in'  It covers 800kHz to 500MHz in 6
  \      Sens Band      _     ()    Bands, with a very accurate set
   \      ( )  (_)  |   ( )   |Phones  of 3x 180 scales.
    o                   ~     (0)  
.읕컴컴컴        .     \_____/       .
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴

LAYOUT
敏컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩔
납                                          납        PROBE
납                                          납          _ 2 turn
납                                          납         ( )Search
납                       1n                 납           Coil
납                      o                  납          
납    L6    L5       D1 ____________        납          
납  =(-)= =(-)=       (___  20pF         납          켌nsulated
납    ~     ~ E   L4    L1  Tuning        납          켮andle
납        L3    =(-)=      쳐컴컴컴캑   1n  납          
납       =(-)=           n_  Cap         납          
납  -   +           SW  /   100pF   D2 o  납          
납旼좔컴좔   pot  ===== L2쳐컴쩟컴켸   22k 납          
납 Meter   憫좋 =====__/    납Vernier ~~납          
납         ___ 컫좌      ====         납          튏oax
읖좔컴컴컴좌컴탠탠컴탠탠컴컴컴컵탠컴컴컴컵컫줄          
  ~~~~~~~~~   굇   굇   ~~~~굇굇~~~~   쳐 \Phones    
              Sens   SW       Tune     In잃            
                                          훤袴袴袴袴袴袴
CIRCUIT
                     SW o컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
Phones                  o컴컴컴컴컴컴컴컴컴컴컴컴컴컴      
 Out         D2   L2a   o컴컴컴컴컴컴컴컴컴컴커            
 ==>컴컫22k쨈<쳇컴(()컴>o컴컴컴컴컴컴컴                  
  __        _       o컴컴컴컴                       
         ===  /|      o                                旼o SW
        1n  ===                                 旼컴))훟
            /100p                        旼컴))컴컴))훟
                                   旼컴))컴컴))컴컴))훟<컴(o Probe
      Sens             D1      旼컴))컴컴))컴컴))컴컴))훟  __ Input
 旼컴>10k       旼컴컴졍<쳐 旼))컴))컴컴))컴컴))컴컴))훟
     log       1n _旼컴        \    \    \    \
50uA  Pot      === \ L1)   )  L3)|/\  )|/\  )|/\  )|/\
Meter             ===  )켸  )켸   )|(  L4)|(  L5)|(    )|(L6
880R            20p\  ))켸 )L2b  )|(    )|(    )|(    )|(
     82R       쳐컴컨컴컨켸       /쳐   /쳐   /쳐   /쳐
               Strip Loop                              Earth
 좔컴컴좔컴좔컴좔컨컴컴컴컴컴컴컴좔컴컴좔컴컴컨컴컴컴좔컴컴컨컴컴
                     500-200  200-57  57-18  18-6   6-2.2  2.2-0.8MHz
HOW IT WORKS
The input from a 2 turn loop probe feeds low impedance test signals to the "TV
Belling Lee" input socket. The 6 pole 2 bank switch is actually a 4 bank band
change type with 2 earthing contacts banks on the unselected bands. The lower 4
bands the ferrite cored preset coils L3-L6 are quiet conventional with a 1 turn
drive primary, the layout not too important for the low frequencys.
                                                                    _
The tuning capacitor is a constant frequency snail shaped type,   /~ ~\
with offset shaft. A constant C/angle would be no good really!   읕O컴켸

For the VHF range L2 is a thick wire loop split into two by the switch. Layout
is everything to getting the right L & stay capacitance for the indicated
frequency on this range.

On the same tuning cap there is a UHF 20pF section & a 2cm long copper strip
folded across it that forms L1. The coax drive tap is placed 25% from ground, &
the diode D1 detector on the 50% top of the U bend. Layout & small size at UHF
is needed for stable calibrated scale.

Note that in this circuit the germanium/Schottky diodes D1 & D2 are in series
on UHF range! But this does not affect the sensitivity much with the 50uA
meter. Input power (e.g. direct connection or PA pickup) should be limited to
below 100mW if the diodes are not to be dammaged, as there is quite a bit of
voltage step up!

Also look at my TECH buls on "Piston Absorption Wavemeter", "AKD's VHF/UHF
Wavemeter WA1", & "RF Field Indicator FL-30AH".


Why Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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