FM WAVE PROPAGATION

[audioguru2]

Hi Prateek,
In my country, the AM and FM broadcast bands are for the public, not the military.
The military and others have their own bands.

 

[prateeksikka]

hi audioguru!
i must correct u on this point.in my country too ,F,M and AM bands are not used by army,the bands used by them fall into say 540-1600kHz which we vaguely called AM band (atleast in my country)
but thats what i meant by my point earlier,540-1600 kHZ IS NOT F ULLY AM some frequencies are missing and those are used by army .actual AM is say(hypothetical)
540-670
690-880
930-1600
these are assumed and not actual values values falling out of this range used by military


prateek

 

[prateeksikka]

hi audioguru!
i had started this topic of FM wave propagation because i had recently built an FM RECIEVER AT MY PLACE ,.it was designed to operate at 220Vac which was followed by transformer,rectifier and filters etc.
actually i had no transformer earlier when i was making it, out of curiosity,i connected only 4V dc (with fear in mind) after the filter directly
and you wont believe,one of my electrolytic capacitors of 470uF
exploded like a bomb! i changed it and put a 1000uF in its place i was shocked when i saw it exploding into pieces,however the circuit worked when i put the T/F in place and connected the mains supply
any comments on how it could happen?
prateek

 

[audioguru2]

Hi Prateek,
Sure, backwards polarity from a high current supply is a good way to blow-up electrolytic capacitors. When I worked on the car-radio production line that's how they tested the anti-reversed-polarity protection diode. They put a heavy bucket over the radio and connected reversed polarity. We cheered each explosion a couple of times per day!
You are lucky your radio's semiconductors weren't destroyed too.

 

[prateeksikka]

I KNOW THAT AN ELECTROLYTIC CAPACITOR HAS A POLARITY!
I AM SURE ON THAT POINT !
I CONNECTED IT RIGHT AFTER ALL,I LOST 2 CAPACITORS IN2 HUGE EXPLOSIONS.NEITHER ARISES A QUESTION OF HIGH BIAS BECAUSE I WAS CAREFULLY INCREASING IT WHEN I REACHED JUST 4V IT EXPLODED WITH ALL MATTER COMING OUT OF IT.YMMMMMMMM
CAN THE CAPACITORS BE FAULTY?
PRATEEK

 

[audioguru2]

I dunno.
Reversed polarity is all I can think about that would explode caps with such a low voltage.

I know! AC voltage at a high current explodes them too! Or DC with a high ripple voltage at high frequency.
There is an inverter in our projects section that explodes its coupling capacitors. At first we thought it was because the caps are shown with backwards polarity. Then I realised that the caps have an extremely high AC current that is blowing them. The entire power of the inverter (70W to 100W) is going into those caps.

 

[prateeksikka]

audioguru!
though in any case i have only seen electrolytics caps exploding
ceramic capacitors just turn blackish if i apply high voltage across them
prateek

 

[prateeksikka]

AND I MUST CONFESS I HAVE SEEN A VERY HIGH VOLTAGE CAPACITOR EXPLODE!
IT IS ALMOST LIKE A BOMB WHICH CAN EVEN KILL.THE YELLOWISH PASTE COMES OUT WHICH IS REALLY HOT!!!!!
PRATEEK

 

[audioguru2]

Exploding tantalum capacitors are worse than electrolytics. Molten metal spits all over. Ouch!  ;D

 

[prateeksikka]

hi audioguru!
i think in my case i connected electrolytic capacitor with correct polarity but internally the polarity was reversed. i.e i put the blame on the capacitor manufacturer.is it fair enough as an explanation? how often is it the case?
prateek

 

[audioguru2]

I never heard of a capacitor that has its polarity marked backwards, but I guess anything is possible.