This is another of my hacks (the fourth in a row...) for the AOR AR3000 scanner. This time I tampered with the front end board, in order to remove an annoying click which is heard throughout HF, and is due to crosstalk between digital command lines and signal input. This click is heard a) on the line audio output on the DIN-8 connector, which is unmuted, and b) on the loudspeaker, once my "demuting" mod is carried on (sorry for the self reference, but...). My mod does not eliminate the click completely, but almost. Before the mod, a click is heard whenever issuing a command (this includes turning the tuning knob), throughout the range 0.1-50 Mhz (remarkably strong below 10 Mhz); afterwards the click is almost cancelled above 1Mhz, and easily overwhelmed by signal above 0.5 Mhz. I didn't find a way to do, quickly, better than this. In this way, the tuning wheel may be spun giving "almost" the feel of an analogic vfo... You'll enjoy the whhhooshhh on the unsquelched output during free scan... Also, the click noise won't mask weak signals while scanning. The other limits of the front end of the AR3000 (intermodulation, blocking, birdies) will now be fully appreciated. One day I'll buy a real shortwave radio. The click is due likely to leaking of the digital signal on the command board, and ultimately to the pcb tracks layout. Sometimes I have the impression that the AR3000 must have been conceived as a high end receiver, but projected in a rush with a lot of mistakes - check the superetherodine conversion pattern, for instance, and you'll find out that all the range 940-2036 Mhz is sent trough the same prescaler filter, despite that this implies NO image rejection on some frequencies and despite that steering signals for additional SHF filters exist on board... What I've find to work is the following: -one signal has to be routed via a shielded wire rather than via a long pcb track. -two capacitors can be added between two digital lines and ground. True, you're not exactly supposed to short a CMOS output to ground with a 4.7nF capacitor, you'd rather make an RC filter to the next input... it works so don't bother. What I'm describing here refers properly to my old 1989ish AR3000. I have also the schematics of the 1991ish 3000A: the circuit seems exactly the same, so I suppose the problem. The mod is easy but tampers on SMD - shall I insist once more that I TAKE NO RESPONSIBILITY for how you may screw your scanner up? Just a bit of theory: command signals for the front-end are fed _serially_ by the cpu, and parallelized by three 4094 shift registers (IC1-3) connected in cascade. When the cpu wants to change something on the front end, it sends a string of command bits, a clock for moving them across the registers, and then a strobe pulse to make the outputs active. We'll put a capacitor on the clock line, we'll route via shielded wire the overflow of IC1 which goes to the input of IC2, and we'll add a capacitor on that line too. Operation: ---------- -disconnect the power cord, unscrew the and remove the covers, and go to the front end, which is the upper board. You may want to unscrew it in order to solder the capacitors on the lower side, though you can do all the job on the upper side, without unscrewing. If you unscrew it, you'll have to plug off J1 (the antenna connector), J1 on the lowermost board (the front end output, which is soldered on the front end and called there J4). Labels are printed on the board. You'll also have to be gentle when turning upside down the board, and to be careful not to deform the coils. -the track to replace with a shielded wire is the one which connects pin 9 of IC1 with pin 2 of IC2. This track runs mostly on the upper side of the board. The upper part starts on the upper board just beside pin 4 of connector J5, and runs mostly parallel to the backpanel until past the central screw, close to the relais, where it sinks back to the lowest side (no drawings, please). This has to be cut in two places, as close as possible to the board crossing points. Scrap them with a sharp tip. Solder a shielded wire between the two points. The shield can be grounded practically anywhere, as the ground track covers most of the side. The wire can be fastened to the board with a drop of hot melt. -Solder a 6.8nF capacitor between this track and ground. I found it easiest at the relais end. (it could be up to 33nF, more than that would prevent normal functioning). -solder a 4.7nF capacitor (up to some 15nF) on the clock line, i.e. between pin 1 of J8 and ground. I found it more confortable on the SMD side, just at the pin of the connector, but the clock track is also available on the upper side. It sinks to the lower side just beside pin 9 of J8, between J8 and the electrolitic capacitor C80, and is surrounded by a convenient ground track. -rescrew, reconnect connectors if you disconnected, close the unit and enjoy. A final note: I'm indebted to Henry Laviers <hl1@acpub.duke.edu>, who sent me a copy of the service manual two years ago, and to Marc Gauw <marcgauw@simplex.nl> who forwarded me the schematics of the 3000A (which should be available and orderable from aor-uk, just to prevent requests to us). I'd like to very much hear comments or to know if anyone has tried other hacks on the same box. Please email me. Enrico Segre, segre@polito.it PS: check out also my previous 3 hacks for improving the audio bass fidelity, narrowing AM to 6kHz, and removing the cpu muting - they should be in the same directory of this one.