classic k40 capacitor?

[mutley]

hi all im not new here or new to radio but can somebody who really knows what theyre talking about please explain.

so.... if you bought a used k40 how you even would know if the capacitor in the base is allready blown or faulty?

whats the symptoms?
what happens if you just delete it alltogether?


thankyou!

 

[Robb]

The symptom of a blown capacitor is that the SWR will be high.

And no, you cannot just take it out,; it needs to be there in order to balance the capacitive reactance to the coil's inductive reactance. . .

 

[mutley]

The symptom of a blown capacitor is that the SWR will be high.

And no, you cannot just take it out,; it needs to be there in order to balance the capacitive reactance to the coil's inductive reactance. . .

thanks for the reply but in the event of buying it at some yard sale taking it home and setting it up but NOT. having access to a meter does it recieve any different worse etc?

 

[mutley]

thanks for the reply but in the event of buying it at some yard sale taking it home and setting it up but NOT. having access to a meter does it recieve any different worse etc?

can you test it with a multimeter?
can you even get to it inside the base?
i ignorantly thought it was some gimmic to act like a fuse from a lightning strike etc or to cut noise
seeing as most antennas dont seem to need it.

 

[222DBFL]

Don't take that capacitor out.
Hook up an swr/watt meter in line and check the VSWR. If it's off the charts then the capacitor is most likely blown or you have a bad connector or pinched coax. But like Robb said, it needs to stay.
Like I said, get an swr/watt meter and check the VSWR of the antenna. This will give a good indication of something is wrong. If your VSWR is like 3:1 or more. Then the cap is blown. If it's low, or below 2:1, then it might just need to be tuned. Nothing really special about the classic or anniversary models other than a different color logo. I had one and gave it away. The other sits on the bench as the mag mount base got some water intrusion and started rusting. They are an okay antenna for what they are. There are much better ones out there. JMHO.

 

[midnight special]

one point here is that the cap is not always blown,,, the older k40 the cap was wrapped better and soldered the newer ones is just hooked and soldered,,, when using high wattage these are know to heat up and come loose,,,

 

[mutley]

yes but like i said
i havent got a meter at the moment
so.... does the receive suffer?
can you " hear" a difference?
im not interested in starting a
" i would rather push my chevy than drive a ford" type pi$$-ing contest over antenna brands.

 

[space cowboy]

Receive might suffer depending on how the capacitor has gone bad, but you can easily fry your radio if you broadcast.

 

[Robb]

Get a meter; they are cheap and plentiful. Probably find one at a flea market or even sometimes at a garage sale. One requires the right equipment when playing radio.

The antenna will hear; but the requirements for transmitting on an antenna are higher than for receiving. The radio transmit output requires a proper load in order to be efficient and therefore effective.

If you must, the antenna can be taken apart and the capacitor can be examined to see if it has cracked. It isn't an expensive part to replace or find a replacement for; just troublesome to get to. Make sure you replace it with the same capacitive value that the original one had (don't recall ATM just what it is).

 

[mutley]

Get a meter; they are cheap and plentiful. Probably find one at a flea market or even sometimes at a garage sale. One requires the right equipment when playing radio.

The antenna will hear; but the requirements for transmitting on an antenna are higher than for receiving. The radio transmit output requires a proper load in order to be efficient and therefore effective.

If you must, the antenna can be taken apart and the capacitor can be examined to see if it has cracked. It isn't an expensive part to replace or find a replacement for; just troublesome to get to. Make sure you replace it with the same capacitive value that the original one had (don't recall ATM just what it is).

 

[mutley]

i hear you but " one" has been playing with and hording this junk since around 1978 but i clear stuff out every so often ( as i am again now) and so right now i dont have one
well i do but its built into some radios

 

[Robb]

Well, you will need to get 'one' to be 'one'.
External type . . .

 

[mutley]

Receive might suffer depending on how the capacitor has gone bad, but you can easily fry your radio if you broadcast.

the only radio i ever " fried" was a kenwood hf set accidently txing out of band on 100w.

infact for fun ive deliberately tried to fry - blow up a rig with no antenna and a rubber band on the mic
ive also discovered several times my antenna was missing or the cable cut or unplugged
the result?
no mushroom cloud no huge bang no nothing
not a good idea but no harm ever done

Well, you will need to get 'one' to be 'one'.
External type . . .

so
will it not swr? or is it just easier with the good capacitor?
and theres no way to tell without
checking the swr if its blown or not?

 

[mutley]

Don't take that capacitor out.
Hook up an swr/watt meter in line and check the VSWR. If it's off the charts then the capacitor is most likely blown or you have a bad connector or pinched coax. But like Robb said, it needs to stay.
Like I said, get an swr/watt meter and check the VSWR of the antenna. This will give a good indication of something is wrong. If your VSWR is like 3:1 or more. Then the cap is blown. If it's low, or below 2:1, then it might just need to be tuned. Nothing really special about the classic or anniversary models other than a different color logo. I had one and gave it away. The other sits on the bench as the mag mount base got some water intrusion and started rusting. They are an okay antenna for what they are. There are much better ones out there. JMHO.

thanks for that usefull reply some good onfo there.
when i said classic i was just trying to clarify its a typical old school classic twist off k40 not any of the other styles like a firestick or center load etc

 

[Robb]

An external SWR meter would be the fastest/cheapest way to find out. A better way is to use an antenna analyzer; but that is quite a bit more costly.

I've had two K40's that had bad caps in them. One of them I got that way; the second I popped myself. Seems that they don't like amps that put out more than 250w before they pop. Been there; done that.

Be sure to mount your antenna/mag mount on the center.top of the vehicle before you adjust it or check it. You will find out if the cap is bad if the antenna's SWR can't be adjusted by changing the whip length.