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TUCoPS :: Radio :: bc760.txt

Lengthy information on the Bearcat 760XLT scanner





                           - 1 -



                UNIDEN/BEARCAT 760XLT SCANNER:
                       FIRST IMPRESSIONS

                     by Bob Parnass, AJ9S

   Reviews of the new Uniden/Bearcat 760XLT (950XLT) scanner
   have  been published in Monitoring Times and the All Ohio
   Scanner Club's American Scannergram.  I've been using  my
   760XLT  for  several  days  now, and here are my observa-
   tions.

   The 760XLT, also sold as the 950XLT, is a  full  featured
   base/mobile  scanner,  which  makes  use of surface mount
   technology to cram  100  channels  into  a  small,  metal
   cabinet.   Generous  coverage is given to the traditional
   scanner bands, including aircraft, 10 meter FM, 6 meters,
   and  the  800 MHz ranges.  A 10.85 MHz first intermediate
   frequency (IF) is used, versus the 10.8  MHz  IF  in  the
   older Bearcat 300.

   Although Uniden  sales  literature  claims  the  cellular
   telephone  bands  are  excluded,  my 760XLT came equipped
   with this coverage.  Some  scanner  dealers,  like  Grove
   Enterprises,  charge  about  $10  for  the  scanners they
   upgrade with a simple modification  to  restore  cellular
   phone coverage.  Grove no longer offers the cellular res-
   toration modification.  I didn't  buy  the  $35  wideband
   preamplifier or $69 CTCSS decoder options.

   When using the 760XLT with an outside antenna, I  experi-
   enced     intermodulation    distortion    from    paging
   transmitters, as was true with the 40 channel 800XLT.  In
   both  cases,  the  front  end circuitry is probably being
   overloaded (driven into the  non-linear  region)  by  the
   strong paging signals.

   All is not lost, however.  I bought this radio to monitor
   local signals, and no intermodulation products were heard
   when using the 760XLT connected to an indoor antenna.  In
   this  respect,  the  760XLT fares better than the 800XLT,
   which sometimes  experiences  paging  interference  using
   only its internal whip antenna.

   The 760XLT does receive images 21.7 MHz  (twice  the  IF)
   below  the  programmed  frequency.   One can hear pilots,
   actually transmitting in the  118-132  MHz  range,  while
   scanning  the  140-174 MHz band.  Images are nothing new.
   Experience shows that scanners employing  up  conversion,
   with  high IFs, are less likely to suffer image problems.
   Spend the extra money and buy a Radio Shack  PRO-2004  or
   ICOM  R7000  if  you  want  to  search  the 160-170 range











                           - 2 -



   without image interference.

   I have a difficult time monitoring Naperville  Police  on
   470.3125  MHz  using my 760XLT on an indoor antenna.  No,
   it's not a sensitivity problem, the problem is  that  the
   760XLT  hears TV channel 35 audio (601.75 MHz) on 470.300
   MHz, and the wider IF  filter  allows  the  religious  TV
   broadcasting signals to interfere with adjacent channels.

   My calculations confirm that the 760XLT can  hear  601.75
   MHz  TV  on  470.3  MHz due to the phenomenon of multiple
   injection frequencies.1 When the scanner is programmed to
   470.3  MHz,  its  synthesizer  is  generating a signal on
   153.15 MHz.  The third harmonic of 153.15  MHz  is  mixed
   with the incoming signal to produce an IF of 10.85 MHz.

   The TV problem arises because the 4th harmonic of  153.15
   MHz  is also present, and it mixes with the 601.75 MHz TV
   signal to produce 10.85 MHz.2

   Sensitivity on 800 MHz and other bands appears  adequate.
   I  can  still  hear Joliet Police, DuPage County Sheriff,
   and Naperville Fire on 800  MHz  using  a  19  inch  whip
   antenna in rural Oswego.

   The 760XLT and 800XLT squelch controls are sloppy, having
   too  much hysteresis.  I can usually fix this by changing
   a single resistor, but the  surface  mount  construction,
   and  lack of a schematic make modification more difficult
   in the 760XLT.

   Now for a scanner history lesson.  Electra's Bearcat  300
   scanner  was  introduced  in  the  1979-80 timeframe, and
   became  a  favorite  of  scanner  enthusiasts.   The  300
   included  a new "Service Search" feature, whereby several
   FCC allocated frequencies were preprogrammed by the  fac-
   tory.   Users  could  press  one  of 11 keys (for Police,


__________

 1. See "512-657 MHz Reception on Your Scanner," by Bob
    Parnass, AJ9S, in Monitoring Times, February 1985, pg
    19.

 2. The multiple injection frequency problem plagues other
    scanners, like the Radio Shack PRO-30, which can hear
    800 MHz signals in the 390 MHz range, and Bearcat 20/20,
    which can hear 162.55 MHz weather broadcasts in the
    30-50 MHz range.












                           - 3 -



   Fire, Hams, Mobile  Telephone,  Aircraft,  Marine,  etc.)
   and the scanner would scan all the preprogrammed frequen-
   cies for the  specified  service.3  This  was  especially
   handy  when the scanner went along on vacation, making it
   easier to find the local channels for police and fire.

   Bearcat's main competitor, Regency  Electronics,  offered
   their  version  of  a Service Search feature in the K500,
   M400, and D810 models.

   Although the Bearcat 300 has been discontinued,  the  new
   760XLT carries forward the Service Search tradition.  The
   760XLT Service Search covers only Police, Fire/Emergency,
   Aircraft,  Marine, and Weather.  Service Search banks for
   Ham, Industrial, Local Government, Forestry,  Transporta-
   tion, and Telephone have been dropped, although any these
   frequencies can be programmed in the usual manner.  A new
   feature  is "buried" in 760XLT owners' manual, and is not
   mentioned in the advertisements.  The 760XLT provides the
   ability  to  lock  out  preprogrammed frequencies, one by
   one, from the Police and Fire/Emergency services.

   Say you don't want to listen to the  hospital  paging  on
   152.0075  MHz  (rounded  to 152.010), now you can lock it
   out of the Fire/Emergency search.  Locked out channels in
   a given bank can be re-enabled en-masse by depressing the
   LOCKOUT key down for 2.5 seconds.

   I was looking for a scanner operable in the dark, and the
   760XLT  fit  the bill.  The orange LCD display is backlit
   at all times, as  are  the  hard  plastic  SCAN,  MANUAL,
   PRIORITY,  and  HOLD  keys.  The four keys must be lit by
   incandescent bulbs, as they get warm to the touch.  Since
   the  solid  rubber  frequency  keys  are not lit, one can
   operate, but not program the 760XLT in the dark.

   When Uniden acquired the Bearcat line  of  scanners  from
   Electra, they greatly improved the internal construction,
   but started using wider IF filters.  The Uniden  scanners
   are  less  selective than their predecessors, which means
   they are more prone to adjacent channel interference.   I
   would  have  gladly  paid the extra $3 or so for a better
   filter.


__________

 3. The recently enacted Electronic Communication Privacy
    Act (ECPA) makes it illegal to monitor mobile telephone
    calls.












                           - 4 -



   So far, I like the 760XLT.  I paid  about  $290  for  the
   760XLT from Grove Enterprises, Brasstown, NC - good folks
   who use what they sell.



                  MORE COMMENTS ON THE 760XLT

                         by David Woo4

   I purchased the Uniden 760XLT [scanner] recently based on
   your review.5

   I got it sans CMT (cellular mobile  telephone)  coverage.
   It  was  very difficult to implement the Monitoring Times
   conversion for cellular phone.  I had to take both covers
   off  to get pin 20 out of the board.  I was unable to cut
   the pin from the bottom side with any available tool,  so
   I ended up unsoldering the pin and yanking it up from the
   board from the bottom side.

   Once I soldered pin 19 to 20, CMT coverage  did  function
   as advertised.

   The 760XLT definitely has a good deal more spurs than the
   PRO-2004.   Also, the lack of the sound squelch means you
   can't scan through IMTS mobile telephones, which place  a
   carrier on unused channels.

   Your comments on the mushy squelch are VERY true.  If you
   come  up  with  a  modification  like  for  the  PRO-2004
   squelch, scannerdom will certainly appreciate it.

   It is possible to use the frequency up and down  keys  of
   the  PRO-2004  at  night.  If you look at the back of the
   keypad, there is a shield with a hole in  the  middle  of
   it.   Last  year,  Radio  ShackO sold a 12V bulb (60 mA?)
   with pigtail leads.  Unfortunately, they no  longer  have
   it.   I  put  this  bulb in a grommet and glued it in the
   hole.  I grounded one lead and connected the hot lead  to


__________

 4. David Woo, room IH 4G-319, AT&T Bell Laboratories,
    Naperville, IL

 5. See "Uniden/Bearcat 760XLT Scanner: First Impressions,"
    by Bob Parnass, AJ9S, in The Radio Enthusiast, June,
    1988.












                           - 5 -



   the switch on back of the volume control.   Enough  light
   comes  through  the  yellow keys so that the up/down fre-
   quency keys can be found in the dark.

   I didn't do the 400 channel conversion, so I  don't  know
   if  enough  light  would  come  through  the commercially
   available keypad overlay  that  was  sold  in  Monitoring
   Times.



                    AVOID TROUBLE WITH THE
                   760XLT ANTENNA CONNECTOR

                     by Bob Parnass, AJ9S

   The Uniden/Bearcat 760XLT rear panel is outfitted with  a
   Motorola-type auto radio jack.  Around the outside of the
   jack is a plastic lip.  This arrangement works well  with
   the  supplied  telescoping antenna, but can cause trouble
   if the scanner is used with an SO-239 adaptor,  like  the
   Radio ShackO #278-208.

   The 760XLT's plastic lip prevents one from inserting  the
   adaptor  far  enough  for the center pin to make reliable
   contact.  This will result in a serious  loss  of  sensi-
   tivity.

   The solution is simple.  Using  a  flat  file,  carefully
   file  the  plastic lip down uniformly by about 1/16 - 1/8
   inch.  Don't spill the filings into the radio.

   Now the adaptor can be inserted farther into the  antenna
   jack.




























                           - 6 -



              PROBLEMS WITH UNIDEN REPAIR SERVICE

                     by Bob Parnass, AJ9S

   As I wrote in a previous article, I usually  fix  my  own
   scanners.   However,  when a new radio fails, it's incum-
   bent on the manufacturer to make good on the warranty.6

   My experience with Uniden's Customer  Service  department
   may  represent  how  they  treat other customers.  If so,
   then Uniden's purchase of Regency and Bearcat scanners is
   a setback for consumers.

      o June 12: I bought a brand new Uniden 760XLT scanner.
        On getting the scanner home, it was clear this radio
        had memory problems.

      o June 14: After speaking with Chris at Uniden  Custo-
        mer  Service, I sent my new scanner to Uniden to fix
        under warranty, and was  quoted  a  15-20  day  tur-
        naround time.

      o August 29: Over two  months  and  several  telephone
        calls  later,  I received a replacement scanner that
        was also defective.

      o September 1: Spoke with Judy at Uniden who asked  me
        to  send  back the scanner and promised to ship me a
        new one immediately on receiving mine.  I  sent  the
        radio back the next day.

      o September 16: Receive confirmation from Uniden  that
        they got my scanner, but they won't ship another one
        until October 6!

   If answering customer phone calls is any measure of  ser-
   vice,  then Uniden has a long way to go.  When the Custo-
   mer Service telephone is not busy, I have counted  up  to
   18 - 26 rings before it's answered or I give up.

   To be fair, the representatives were  usually  courteous.
   But  they  were  quick  to  promise, and I learned not to
   believe what they said.  Nobody there seemed  willing  to
   "own the problem."


__________

 6. See "Confessions of a Scanner Collector," by Bob
    Parnass, in Monitoring Times, August 1988.












                           - 7 -



   Twice, in  vain,  I  asked  to  speak  to  a  supervisor.
   Representatives  Chris  and  Judy  took my name and phone
   number, but my calls were never returned.  Neither  would
   representatives  refer  me to anyone outside the Customer
   Service department.

   This poor treatment makes me hesitate to recommend Uniden
   service when scanner owners seek my advice.

   To make smaller scanners,  manufacturers  are  now  using
   tiny  surface  mount  components  in their new generation
   models,  including  Uniden's  600/760XLT  and  100/200XLT
   series.   This  makes  it  near  impossible for even good
   repair shops to fix them.

   The bad news for scanner owners is  that  they  now  have
   fewer  options  for  repair  service.   The  bad news for
   Uniden is that Radio ShackO and AOR also sell scanners.












































                           - 8 -



            760XLT 800 MHZ AND CTCSS MODIFICATIONS

                  Peter pas@jupiter.ic.cmc.ca
             Canadian Microelectronics Corporation

   Hi. A note to BC760XLT scanner owners. I recently  agreed
   to  modify  one  for  a  friend a found the following two
   notes of interest.

     1.  It was shipped with a how-to on the  cellular  res-
         toration  mod  that appears more comprehensive than
         those I've seen posted on rec.radio.shortwave or in
         Bill  Cheek's  scanner modification handbooks. Here
         it is.

         WARNING: If you don't know enough about electronics
         and about what you are about to do, you might toast
         your radio and if you toast your  radio,  you  only
         have  yourself to blame; you can't blame me or any-
         one else! Also, the moment you  twist  a  screw  to
         remove  a cover, your warranty is gone! Also, moni-
         toring of  certain  services  in  certain  freqency
         ranges is prohibited in certain areas.

         WARNING #2: Read the warning above again.

           a.  The following applies to models  manufactured
               during 1989 (HI code date suffix) or later.

           b.  Place radio  so  the  front  is  facing  you;
               remove top cover

           c.  You are looking at the FOIL side (other  than
               surface  mount components and a large upside-
               down Sanyo IC) of the PCB. Locate this  Sanyo
               IC.  A long row of solder pads just above the
               Sanyo  IC  identifies  pins   1-32   of   the
               microprocessor.  Pin 1 is on the left and pin
               32 is on the right.

           d.  Using  a  sharp-pointed  tool,  cut  the  two
               traces  leading to pin 26 of the microproces-
               sor IC. There is a trace  coming  from  above
               pin 26 and a trace coming from below pin 26.

           e.  Solder-bridge pins 19 and 20 together of  the
               microprocessor IC.

           f.  Solder-bridge pins 26 and 27 together of  the
               microprocessor IC.












                           - 9 -



           g.  This part is tricky  to  identify  without  a
               diagram.  Directly  above  pin  27 is a three
               terminal, surface-mounted transistor  device.
               The  lower terminal of this device used to be
               connected to pin 26 of the microprocessor  IC
               until  you  did  step d) above. Solder-bridge
               together the two left-hand side terminals  of
               this device.

           h.  This part is also tricky to identify  without
               a  diagram.   Locate  the  trace that travels
               from pin 19 of the microprocessor IC  to  pin
               26  of  the  microprocessor  IC. Near pin 26,
               this trace will have been cut as per step  d)
               above.  Along the length of this trace, there
               are two devices that are  physically  mounted
               over  it.  Of  these  two  devices,  the two-
               terminal device on the left-hand  side  is  a
               4.7k  chip resistor marked "472" on it. It is
               mounted over the trace in  an  area  approxi-
               mately below pin 20 of the microprocessor IC.
               Carefully remove this chip resistor and  tape
               it  to  the inside of the scanner cover, just
               in case...

           i.  Put the radio back together and try to  enter
               845.  If  845.000  appears on the LCD, you've
               done the mod successfully.

     2.  A $60 option for  the  BC760XLT  is  a  CTCSS  tone
         decoder  board that plugs directly into the scanner
         board. Catalogues  indicate  you  must  purchase  a
         $10-$15  switch assembly in order to enable/disable
         the CTCSS option. You  do  not  need  to  buy  this
         switch if you are comfortable enabling the CTCSS as
         follows:

         WARNING: Read the first and second warnings above.

           a.  Following installation of the CTCSS  card  on
               the  component side of the circuit board, you
               will have used two  row-pin  connectors  (one
               that  the CTCSS board plugs directly into and
               one for a ribbon cable leading from the CTCSS
               card).  This  leaves  a  third, five pin, row
               connector unused in the general area  of  the
               CTCSS  card.  This  is  where  the "required"
               switch is supposed to plug in.

           b.  Locate this 5-pin connector on the FOIL  side
               of  the PCB and mentally number the pins 1 to











                           - 10 -



               5, from left to right (with the  radio  front
               facing  you).  The CTCSS option is enabled by
               connecting pin 5 to pin 2. I did this by run-
               ning  a  wire  from  pin  5 to the top of the
               surface-mounted component directly above  pin
               5  (which  is  connected to a large foil area
               which is connected to the (mentally numbered)
               pin  2). Use your fine soldering skills to do
               this however you like.

           c.  On power-up, the string "CTCSS"  will  appear
               on  the  bottom right of the LCD display. The
               instruction guide tells you how to  punch  in
               PL tones to use the CTCSS option.

   I did the above two mods and have found the radio  to  be
   working  flawlessly. Your mileage may vary. Now I have to
   return the radio to my friend... but without some further
   "testing" of course... :-)




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