At 01:23 PM 3/18/05, you wrote:
>Which fan would be better on the GE MastrII, and Motorola Micor
>mobile radio converted into a repeater; 12vdc or 120vac? Thanks in
>advance.
Is your system going to go away if the 120v goes away? If yes,
then 120v AC fans are usable. If you are going to use the battery
backup facility in the Micor, then you will need cooling while on
batteries and that means 12v DC fans. If you need fans at all -
many Micor stations are convection cooled, and only need the
fans if you run them continuous duty (i.e. "lock to talk" mode).
Some folks will tell you that the 12v fans can put noise on
the DC supply and thereby on the TX audio. This is true,
but only if the TX audio circuits aren't filtered properly, and if
the fans aren't filtered properly. You will need to put a filter on
the fans, and the average fan takes much less than a quarter
amp.... usually less wattage then the equivalent AC fan.
Building up a filter for a few fans is trivial - a couple hundred
UFs and an old transformer winding used as a choke. Run
the DC to the choke, then the caps to ground. Put the fans
in parallel with the cap.
All of the audio circuits should be fed by their own filtered
DC power... should be immune to noise on the DC supply
line.
If the fans are audible in the TX audio you need to properly
filter the TX audio circuits first, then add filtering to the fans
as well so that if one filter breaks the system is still clean.
There is no excuse for half-engineered systems. Phil
Lefever, KB0NES made the point quite well in an email
posting when he said: "I hate driving up the hill to fix
something I could have done better the first time around".
Mike
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/
