Xref: utzoo rec.ham-radio:4508 sci.electronics:2744 Path: utzoo!mnetor!uunet!husc6!mailrus!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!necntc!frog!die From: die@frog.UUCP (Dave Emery) Newsgroups: rec.ham-radio,sci.electronics Subject: Re: PRO-2004 Message-ID: <2168@frog.UUCP> Date: 9 Apr 88 05:34:00 GMT References: <1156@raybed2.UUCP> Reply-To: die@frog.UUCP (David I. Emery) Distribution: na Organization: Charles River Data Systems, Framingham MA Lines: 45 Keywords: MORE MODS !! Summary: Not too likely 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