One of the worst RFI problems with the RC-850 is the terrible signal it emits right on 29.600 Mhz. All RC_850 units have this problem..
It makes it almost impossible to run a 29.60 Mhz FM simplex radio on any of the auxiliary ports. This RFI occurs about once every second or so when the 8085 processor samples the telemetry inputs on the Voice Response Telemetry board. I have been able to significantly reduce (but not totally eliminate) this 29.600 Mhz signal by installing flat ribbon cable Ferrite RFI suppressors on the large ribbon cable connecting the VRT board to the Main board, and also on the ribbon cable exiting the VRT board to the rear panel connector. I have also had to install a similar ferrite suppressor on the cable connecting to the Analog connector on the rear of our RC-850 units. The ferrite material used in all of these cases is #43 Ferrox material. It is also imperative that you run the RC-850 from its own separate power supply to isolate the +12 volt buss as much as possible from any other radio equipment to keep the RFI to a minimum. Ron WW8RR Sawnee Mountain Repeater Group -----Original Message----- From: Mike WA6ILQ [mailto:[EMAIL PROTECTED] Sent: Monday, December 06, 2004 10:46 PM To: [email protected] Subject: Re: [Repeater-Builder] Re: RC-850 madness At 06:47 PM 12/6/04, you wrote: >Been running an 850 here for 19 years with no trouble frim >RFI. Is this a new install? Anything else recently changed >with your repeater when it started? > >The electrolytic caps will dry out on the boards. Seems like >I heard this could cause problems, although we have not >changed caps on our unit. The 850 design uses a 15khz signal from the master microprocessor clock, feeds it into an audio power amp (an LM386 if I remember correctly) and then rectifies that to make the negative power supply for the audio stages. When the caps dry out the negative buss gets 15khz power supply ripple on it. >I'm sure the day is fast approaching though.... Yep. Use a scope to check the negative supply for 15khz ripple. If your TX has sufficient audio filtering you may have the problem but just don't see it. Every 850 gets it sooner or later - the caps mostly came from the same vendor and in the same time period. The worst case scenario is that the ripple rolls right into the TX and creates spurs every 15khz up and down a chunk of the band... My solution is to simply shotgun the negative supply - I replace every electrolytic, and once that is done I think seriously about doing everything in the positive supply as well. Mike WA6ILQ Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
