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G8MNY  > TECHNI   01.03.20 23:25l 222 Lines 11308 Bytes #999 (0) @ WW
BID : 43868_GB7CIP
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Subj: Watson 'Hunter' Counter Mods
Path: IW8PGT<HB9ON<IW2OHX<IR2UBX<DB0RES<ON0AR<OZ5BBS<CX2SA<OK2PEN<N3HYM<
      KA3BVJ<AB0AF<F1OYP<JH4XSY<JE7YGF<GB7CIP
Sent: 200205/1035Z @:GB7CIP.#32.GBR.EURO #:43868 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                              (Update Nov 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

I have bought a damaged one of these small 3GHz handheld counters, & I went
about repairing & upgrading it as there were a lot of components & switch
options possable that were missing on this bottom of the range model.

On point about this counter, it does now actually count what it shows & at VHF-
UHF the resolution (what it counts) may be in 4 8 16 32 64 or 100Hz steps
depending on what the prescaller system is doing.

MODIFICATIONS DONE (in order of importance!)
1/ Add UHF clipping diodes across the BNC socket.
2/ Stop LCD rubbing marks from the lens casing. (& future smashed LCD) 
3/ Add bargraph signal meter.
4/ Add low battery indicator.
5/ Add gate time push button, to give 0.1s 2s 1s & 5s gate times.
6/ Add "no prescaler" RF path to read 1 - 30MHz.

With 5 & 6 you can read 1MHz - 30MHz down to 0.1Hz & 30MHz - 3GHz down to 10Hz.
But calibrating the crystal osc to high accuracy even short term is not easy.

There is only 2 other features according to the LCD graphics..
  a) switchable filter
  b) a period timer.
I did not understand the wiring for a) & I don't think the PCB supports b).

Be warned it as all very small Surface Mounted Devices! So other than the input
clipper protection & LCD case modifications, I do not recommend the other
modifications unless you are fairly competent with soldering SMD components on
a busy SMD board!

            O R I G I N A L                         M O D I F I E D
   .³~~³.                      DC          .³~~³.                      DC
 ÚÄÄÁÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿   ÚÄÄÁÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
 ³                                   ³   ³                                   ³
 ³                                   ³   ³                                   ³
 ³ WATSON Hunter                 o   ³   ³ WATSON Hunter                 o   ³
 ³-----------------------------------³   ³-----------------------------------³
 ³| Frequency         PRESCALE HOLD |³   ³| Frequency         PRESCALE HOLD |³
 ³|                              MHz|³   ³|                              MHz|³
 ³|[] [] [] [] [] [] [] [] [] []    |³   ³|[] [] [] [] [] [] [] [] [] []    |³
 ³|[].[].[].[].[].[].[].[].[].[].   |³   ³|[].[].[].[].[].[].[].[].[].[].   |³
 ³|                                 |³   ³|                   _ - = ð ~  ÚÄ¿|³
 ³|                                 |³   ³| signal    _ - ð ~ ð ð ð ð ð  ³X³|³
 ³|                                 |³   ³| _ - = ð ~ ð ð ð ð ð ð ð ð ð  ÀÄÙ|³
 ³-----------------------------------³   ³-----------------------------------³
 ³ 10MHz-3GHz/50ê Frequency Counter  ³   ³ 1 MHz-3GHz/50ê Frequency Counter  ³
 ³   Power                        Cal³   ³   Power  Pre                   Cal³
 ³     On                 Hold     0 ³   ³    On   Scale      Hold   Time  0 ³
 ³     []                 ³__³       ³   ³    []    []        ³__³   ³__³    ³
 ³                                   ³   ³                                   ³
 ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ   ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

\³/___  ____  ___  _______  ___     \³/___  ___    ____    ___  _________  ___
 À´Preôö100ô ö8ƵCounterôLCD³     À´LimôPre³ o´ö100´o ³ ö8Ƶ Counter ôLCD³
  ÀÄÄÄÙÀÄÄÄÄÙ³ö16³ÀÄÄÄÂÄÄÄÙÀÄÄÄÙ      ÀÄÄÄÙÀÄÂÄÙ\oÀÄÄÄÄÙo/³ö16³ÀÂÄÂÄÄÂÄÄÂÙÀÄÄÄÙ
             ÀÄÄÄÙ  Hold                   ÚÄÁÄ¿ ³ÚÄÄÄ¿ ³ ÀÄÄÄÙ ³ ³ Batt³
                                           ³Det³ À´AmpÃÄÙ       ³Hold  Time
                                           ÀÄÂÄÙ  ÀÄÄÄÙ         ³
                                             ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
FRONT END FAULT
The fault was a blown up front end SMD MIMIC (A06), as there is NO input
protection fitted!

As I could not find a replacement device to hand, I used a scrap cellphone
preamp SMD NPN & made up an amp with just an additional bias R (22k). This NPN
fitted over the 4 pad A06 OK, with the bias SMD 22k (selected to give the same
current as the 2nd A06 stage) & placed over the NPN. It all worked well & a QRP
2400MHz Tx was measured OK with the search aerial alongside.

          ORIGINAL                           REPAIRED
      ÚÄ´ÃÄÄÄÂÄÄ+5V                   ÚÄÄ´ÃÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄ+5V
      ³    100ê        °°    °°       ³              100ê        °°    °°
      ³      ³         In    Gnd      ³          ÚÄ22kÄÅÄ´ÃÄ>U2   B  unused
    (o)Ä´ÃÄ´>ÁÄ´ÃÄ>U2               (o)ÄÄÂÄÄÄÂÄ´ÃÁÄÄÄ´<
   BNC³   U1º          Gnd   Out      ³ _³_ _³_       e³          E     C
      ³     º          °°    °°       ³ \_/ /_\        ³         °°    °°
      ÀÄÄÄÄÄÐÄÄÄÄÄ     PCB PADS       ÀÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄ      PCB PADS

1/ To reduce the chance of a re-occurrence, I added 2 UHF clipping diodes wired
across the BNC socket. 1N4148 diodes will do if you have no better.

2/ I had heard of someone breaking the display, this makes the unit a total
write off!
Looking at my display, I could see tell tail marks (lines) where the LCD had
been rubbed by the sharp case lens metal stamping edge.

         C_L_E_A_R__P_L_A_S_T_I_C
 =======<________________________>============
 Embossed`========ð           ð=='
  Metal Case      ^sharp edges^
                 °°°°°°°°°°°°°°°°°LCD
 ________________³__________XTAL_³__________PCB

To remove the sharp edges, use a small modelling knife held parallel to the
case so that the lens can't be damaged. Then firmly drag the blade over the
raised edges, scraping off the sharpest part of the edge. Go all around the
raised lens stamping edge, make sure that there are no proud part that could
put concentrated pressure onto the LCD glass. (e.g. when dropped)

3/ To make the bargraph display work, add a uhf diode to half of D2. I used a
schottky one across just 2 of the 3 SMD diode pads. Note DIODE Polarity! Also
add a 1n instead of adjacent missing R.

       ÄÄÄÂÄÄ+5V                         °°Ä¿
      U2 100ê                              _³_
 Ä´ÃÄÂÄ´>ÄÁÄÄ´ÃÄ>U3 Prescaler       °°  D2 /_\
    _³_                                     ³
    /_\D2                       oÄÄÄÄÂÄÄÄ°°ÄÙ
     ÀÄÄÄÂÄÄÄ>U9 IC                 °°  PCB PADS
        ===1n                     1nÄÁÄ
         Á                          ÄÂÄ
                                    °°

3/ By moving the HOLD push button from mounting holes "SW6" to the left over-
lapping "SW4" holes, there is then room to fit an identical button in "SW7"
position.  (  ( () ) ()   )
            SW4SW5 SW6 SW7

Then you can get the counter to change the gate time from the default 0.2S to
the 3 others possible times & hence the display resolution.

You then have to file the existing case button hole to a long slot. This is
quite simple to do with a set of sharp needle files, but time consuming! I then
cut & filed an ally blank to between the buttons & glued that in place.


4/ This needs 1 small preset pot, 1 SMD NPN (L-4), 2 SMD Rs, & a zener. Looking
at the circuit I found the zener needs a series R to work properly, & I
selected one on test to make my pot have useful setting range.

                 _____           SW2     D1
   +5V <ÄÂÄÄÄÂÄÄ´78L05ÃÄÄÄÄÄÄÂÄÄÄÄÄo\ÄÄÂÄ´<ÃÄÄÄo+ 9-12V
         ³   ³  ³ U10 ³     100k       X   ÚÄv_Û
         ³  10k ÀÄÄÂÄÄÙ  ZD1_³_      +_³_  ³   ³Switched
         ³  R32    ³    2.7V/_\'      _Ü_  ³   ³Power
    U9<ÄÄ)ÄÄÄ´     ³         ³         Ü   ³   ³Jack
         ³    \³   ³   R31   ³         ³   ³   ³
         ³  Q7 ÃÄÄÄ)ÄÄÄ10kÄÄÄ´         X   ³   ³
         ³   e/³   ³         ³         ÃÄÄÄÙ   ³
      C1===  ³     ³    LOW VR1       R2       ³
     100u³   ³     ³   BATT 22k       56ê      ³
        ÄÁÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÙ

The battery does not give > 5V, so the regulator is not actually regulating
when on battery supply! I suspect there should be more than 4 AA cells (but no
room) if the supply needed to be properly regulated for more accurate work the
5x AAA Nicads might work better! The counter is actually quite accurate for its
simple uncompensated xtal system.

There is a danger if connecting the counter to an earthed supply while having
the BNC connected to other earthed kit. This is because the nicad battery
charging is via a negative change power switch arrangement. During insertion
the 12V will be placed across the 5V battery until the switch breaks the
negative battery lead. This may only last a very short time but currents >5A
can flow & could damage leads, PCB track & eventually the battery! [good for
battery for a few seconds :-) ]

               LAYOUT        BNC
      DC                   .³~~³.
 ÚÄÂÄÂÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÁÄÄÁÂÄÄÂÄ¿
 ³o³ ³  ³  VR1  ____       ³____³  ³o³  U1 & U2  Input Preamps
 ³~  ³  ³      ³ U7 ³           U1  ~³
 ³   ÀÄÄÙ      ÀÄÄÄÄÙ                ³  U3  3GHz ö100 Prescaler
 ³                            D2 U2  ³
 ³                                   ³  U4 & Q3  No Prescaler bypass amps
 ³  ÚÄÄÄÄÄÄÄÄ¿   ____            __  ³
 ³  ³        ³  ³ U6 ³      U4 ;³U3³:³  U5  Gated ö8 & ö16 prescaler
 ³  ³   U9   ³  ÀÄÄÄÄÙ         'ÀÄÄÙ'³
 ³  ³        ³          Q2           ³  U6  Overflow Counter decoder
 ³  ÀÄÄÄÄÄÄÄÄÙ  ÃÁÁÁÁÁ´      Q1      ³
 ³ X1           ³ U5  ³           _  ³  U7  Gate pulse counter
 ³        Q7    TTTTTTT         :³_³]³
 ³                               U10 ³  U9  Counter IC & display driver
 ³                                ___³
 ³                           Batt³___³  U10  5V regulator
 ³_                                 _³
 ³o³                               ³o³  X1  4.19407MHz Crystal
 ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÙ

5/ A far more complex modification is to add the 2 HF amplifiers, missing for
the no prescaler mode, & move/add the missing switches to control it.

 +5VÄÄÄÄÂ      7,3,2ÚÄÄÄÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
      100ê      ÚÄÄÄÁÄÄÄ¿100ê  6k2  ____       ³
   ÄÄ´>ÄÅÄÄ´ÃÂÄÄ´U3 ö100ÃÄÄÁÄ´ÃÄÁÄ´< Q1 ÃÄ330êÄ)ÄÄÄÄÂÄ+5V
   U2º  ³    ³ 1ÀÄÄÄÂÄÄÄÙ4        e³    ³      o    ³       oÄÄÄ>U9
     Ð  ³   100k   5³7             Á    ³      o <ÄÄÙSW3ÚÄÄ>o
        ³    Á      Á  ÚÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÙ        Á
        ³             R13    R14        ³  1,7,9ÚÄÄ+5V
        R      ÚÄÄÄÄ¿ 310ê   100k   ____³ ÚÄÄÄÄÄÁÄ¿11
       2k2    100k  ÃÄÄÁÄÄÄ´ÃÄÁÄÄÄ´< Q3 ÀÄ´ U5 ö8 ÃÄÄÄ>IC U9
        ÀÄÄÄ´ÃÄÁÄÄ´<     C12      e³     2³   ö16 ÃÄÄÄ>COUNTER
           C9    U4 ³e             Á      ÀÂÄÄÄÄÄÄÙ12
                    Á                      Á3,4,5,6

Again instead of a mimic amp U4 I used a biased HF NPN (L-4). But I found that
I had to add a series R of 2k2 to C9 so that it did not load U2's output to
pre-scaler IC U3. I re-used the changeover power switch SW2, as the SW3
changeover & I found a smaller make switch for the SW2 power switch. Again I
had to make new hole in the case for SW3, & drilled then filed a matching
rectangular hole.

N.B. Below 1MHz the counter software stops the display from counting. And there
are tricks done in the count, so the resolution is not that displayed! eg. at
10MHz there are only 0.4Hz steps on the 10 sec gate, not 0.1Hz.


See other tech buls "Old Venner Counter Type TSA3334", "PIC Freq Counter Mods",
"Marconi Counter Type 2434A", "198kHz Off Air Standard", & "Off Air Lock for
Ref Osc" & "Calibrating Frequency".


Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP



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