[sci.electronics] PRO-2004

ewb@raybed2.UUCP (EUGENE BALINSKI) (04/08/88)

 According to the latest (April 88) issue of Monitoring Times there is yet
another modification to the Radio Shack PRO-2004 scanner. Apparently, by
removing another diode (presently un-named), coverage of the 550 MHZ to 770 MHz
band can be restored. I don't know who would would want to listen there as
it's only a TV band, but according to the mag, it will be available.
Monitorong Times is trying to verify the story and will print directions
in an upcomming issue.                                      Good Listening
                                                                  Gene
                                                                WA1UXA

die@frog.UUCP (Dave Emery) (04/09/88)

In article <1156@raybed2.UUCP> ewb@raybed2.UUCP (EUGENE BALINSKI) writes:
>
> According to the latest (April 88) issue of Monitoring Times there is yet
>another modification to the Radio Shack PRO-2004 scanner. Apparently, by
>removing another diode (presently un-named), coverage of the 550 MHZ to 770 MHz
>band can be restored.

	It is possible that there is some way of making the microprocessor
accept frequencies in this range and perhaps even set up the VCO PLL
dividers correctly, but the radio's front end has no bandpass filter for
this range and the tuning range of the first LO VCO as discussed in the
alignment procedure for the 2004 doesn't go low enough.

	I suspect that the very best one could do by fiddling the VCO
adjustments so it would lock lower in frequency (and yet not drop lock at
the 1300 mhz end) is to go a 100 mhz or so below the current 750 mhz 
lower limit with reduced sensitivity.

	I am sure a RF hacker with the right equipment could fiddle the
front end to make it work (a varacter UHF TV tuner with RF amp (some
exist that actually have one or two stages of RF amplification) might
serve pretty well as the front end RF section) - and substituting a
hyper-abrupt junction varacter for the VCO tuning varacter might make the
VCO tune low enough.  Of course there are probably going to be spurious 
problems at the first IF at 608-612 mhz and the  2nd LO (550 mhz).

	I will have to look at the service manual again.  In general it
is useful to be able to tune a scanner slightly out of band (IE override
its internal limits) if the PLL dividers will cooperate.  If anybody knows
the diode involved I'd be curious.

	On another PRO-2004 topic, I have been playing around with
my 2004 with low phase noise (I hope) signals from a precision low phase
noise (FLUKE 6160) VHF synthesizer multiplied to 800 mhz (part of a stable C
band satellite down converter lashup) and I find that it's LO's seem pretty
noisy (ultimate FM quieting on a strong CW signal isn't that impressive at
800 mhz) I don't think it noise from my multiplier or the synthesizer either.

----
David I. Emery
Charles River Data Systems
983 Concord St.
Framingham, MA 01701
Tel: (617) 626-1102
uucp: ...!decvax!frog!die

jack@csccat.UUCP (Jack Hudler) (04/12/88)

Here is a re-post of the article posted last year.

-Jack



From: mgrant@MIMSY.UMD.EDU (Michael Grant)
Newsgroups: mod.telecom
Subject: Restoring Cellulsr Coverage on the Radio Shack PRO-2004 Scanner
Message-ID: <8703162343.AA08357@mimsy.umd.edu>
Date: 16 Mar 87 23:43:38 GMT
Distribution: world
Organization: The ARPA Internet
Lines: 32
Approved: telecom@xx.lcs.mit.edu

In the March 1987 (Vol 6, Number 3) issue of Monitoring Times on page 48,
there is a short article on how to modify your RadioShack Scanner to 
pick up the cellular frequencies.  (This just had to have been leaked
from someone in Tandy sales!)

1. Remove the four cabinet screws and the cabinet

2. Turn the receiver upside down and locate circuit board PC-3

3. Remove seven screws holding board and plug CN-501

4. Carefully lift up the board and locate diode soldered in place below the
   module
   {In the large article, it mentions "a matrix of diodes attached to the
   microprocessor's input port, which is often used to configure radios
   for sale in different markets.  From recent flux on the circuit board,
   it appears that a diode had been added/removed", this is the diode in
   question.}

5. Snip one lead of the diode carefully, leaving it suspended by the other
   lead for later reattachment if desired, such as warranty repair

6. Reverse first four steps above for reassembly.  Radio will now cover
   825-845 and 870-890 MHz and search in 30 KHz increments for no-gap
   760-1300 MHz reception

(Thanks to Jim Marquand and other readers of Monitoring Times)

I do not own a PRO-2004, nor have I ever seen this tried, do it at your
own risk.

-Mike


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