K30 magnet mobile antenna

[MadisonMod]

Hello. I have a k30 magnet mount antenna. The receive went away and swr went off the chart. I took the magnet off the bottom of the mount and the coax is burnt. It looks like it had a resistor or something Sauderd across the transmit conductor and shield. Does anyone know what this is or why it would be there? I thought the 2 needed to be separated. Maybe for wavelength or match ? Please let me know what you think.

 

[144inBama]

If I'm not mistaken, I "think" it was a ceramic disc capacitor.

 

[Cable Guy]

Maybe a dc grounded, diode shunted antenna?

Edit: maybe that was a diode, not a cap

 

[9C1Driver]

It's a capacitor. The K-40 and K-30 both use them, it's a week link for those antenna's.

 

[Cable Guy]

It's a capacitor. The K-40 and K-30 both use them, it's a week link for those antenna's.

Glad someone with experience with those antennas spoke up. I have no experience with those but with others that are shunted with a diode. Is it safe to assume the capacitor is to change the resonance of the antenna, making it a different length electrically? Or is it a filter of sorts?

 

[BigLou]

I have the K-30 to me it,s junk never did work like other antennas I have had .

 

[The DB]

Glad someone with experience with those antennas spoke up. I have no experience with those but with others that are shunted with a diode. Is it safe to assume the capacitor is to change the resonance of the antenna, making it a different length electrically? Or is it a filter of sorts?

For any length of antenna shorter than 1/4 wavelength, there is a loading coil that will, by itself, get you resonance. However, when you start shortening antennas to this degree, just because you are at resonance does not mean the SWR will also be at a use-able level. Because of this, sometimes, tuning to resonance is not enough to make an antenna use-able with a modern day radio. The capacitor's main job in this case to achieve a reasonable SWR at resonance.

Unfortunately, the capacitors used in these antennas are also a serious week point, to the point that using well less than 25% of the manufacturers maximum power rating are enough to blow many of said caps.


The DB

 

[MadisonMod]

If I'm not mistaken, I "think" it was a ceramic disc capacitor.

Any idea what size? The antenna specs say

For any length of antenna shorter than 1/4 wavelength, there is a loading coil that will, by itself, get you resonance. However, when you start shortening antennas to this degree, just because you are at resonance does not mean the SWR will also be at a use-able level. Because of this, sometimes, tuning to resonance is not enough to make an antenna use-able with a modern day radio. The capacitor's main job in this case to achieve a reasonable SWR at resonance.

Unfortunately, the capacitors used in these antennas are also a serious week point, to the point that using well less than 25% of the manufacturers maximum power rating are enough to blow many of said caps.


The DB

Thank you for the information. What capacitor would you recommend that I put back to make antenna work properly?

 

[The DB]

Thank you for the information. What capacitor would you recommend that I put back to make antenna work properly?

I know the capacitor in the K40 is 130 pF. I don't know anyone wo had taken the K30 apart and haven't found any info on said capacitor online so I am not sure about that one. Likely to get that information, you will have to have someone take apart a perfectly good K30...


The DB

 

[sp5it]

130pF, ceramic, voltage rating as high as you can put inside. Maybe 3kV would fit inside. KEMET C340C131JHG5TA

 

[MadisonMod]

130pF, ceramic, voltage rating as high as you can put inside. Maybe 3kV would fit inside. KEMET C340C131JHG5TA

Thank you sir. I will try and let you know.