Author Topic: My active mini whip antenna has gone noisy and insensitive  (Read 1861 times)

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Offline Chris WilsonTopic starter

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My active mini whip antenna has gone noisy and insensitive
« on: July 30, 2016, 01:11:04 pm »
I have a a clone PA0RDT active mini whip antenna atop a wind up mast that used to work well, but has recently become insensitive and very noisy. I will pull it down later and first check the co ax. If I remove its in shack power source the noise stops though, and I have tried it on a battery in case the PSU had gone noisy, but no difference in noise on battery power is seen. The circuit is at http://dl1dbc.net/SAQ/Mwhip/pa0rdt-Mini-Whip.pdf Can anyone say if the front end FET may have gone faulty, or what to check please? Thanks!
Best regards,

                 Chris Wilson.
 

Offline Fank1

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Re: My active mini whip antenna has gone noisy and insensitive
« Reply #1 on: July 30, 2016, 02:00:17 pm »
The J310 is probably shot.
This design is very susceptible to static from storms etc.
You need to add a 100nf cap between the J310 gate and the probe.
Then put 2 diodes from the probe to common.
One diode anode to common, the other cathode to common.
I would use 1N4148 or similar.
these will help prevent damage to the J Fet and should not hurt the signals any.
 

Offline AF6LJ

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Re: My active mini whip antenna has gone noisy and insensitive
« Reply #2 on: July 30, 2016, 02:59:53 pm »
The J310 is probably shot.
This design is very susceptible to static from storms etc.
You need to add a 100nf cap between the J310 gate and the probe.
Then put 2 diodes from the probe to common.
One diode anode to common, the other cathode to common.
I would use 1N4148 or similar.
these will help prevent damage to the J Fet and should not hurt the signals any.

This is usually what happens with those.
Sue AF6LJ
 


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