I have found that adding a resistor in series with the fan and a capacitor across the fan will do the same job as an inductor and capacitor without taking up as much space. The value of resistor I use is just enough to drop the voltage by about 1/2 volt. For a fan drawing 0.5A, use a 1 ohm 1W resistor. For other current draws adjust accordingly. It is not critical. The fan speed will not change much - 12vdc fans will run as low as 6-7v normally.
Burt VE2BMQ Captainlance wrote: > *We have found that 12v. fans do cause interference with our link > transmitters for the NYC voting network. The solution we found is taking > one of the 2 power supply chokes from an old Micor mobile radio and > using it in series with the 12v. lead to the fan, add a cap. 2000 mfd or > larger from fan to ground and the level of AC imposed on the power lead > drops from nearly 4 VOLTS to less than 10 millivolts...Resulting in a > totally clean carrier. * > *lance N2HBA* > > ----- Original Message ----- > *From:* Doug Hutchison <mailto:[EMAIL PROTECTED]> > *To:* Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder@yahoogroups.com> > *Sent:* Saturday, April 26, 2008 4:48 AM > *Subject:* [Repeater-Builder] Cooling fan > > Hi, > > Have tried a few ex equipment and CPU cooler fans on a p/a heatsink > but all generate a noise (light buzz) on the transmitted signal. > > Can anyone suggest the correct choice of fan (or what I am missing) to > stop the buzz on the transmitted signal? > > RF choke? Tried cap up to 4700uf little change? > > Thank you, > Doug - GM7SVK > >
