From: "Hans Joachim Brandt" <hajo.brandt.dj1zb@t-online.de>
To: <rsgb_lf_group@blacksheep.org>
References: <733942171.20160730141305@chriswilson.tv>
In-Reply-To: <733942171.20160730141305@chriswilson.tv>
Date: Sat, 30 Jul 2016 16:30:00 +0200
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Subject: LF: AW: My active whip antenna has gone noisy and insensitive
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Dear Chris,

I am using an active antenna using an operational amplifier OP27; the
circuit had been published in the german CQ-DL May 2007. This circuit is
employing two protection diodes 1N4148 at the positive gate input (both
cathodes in direction to the plus voltage). Additionally a series resistor
of 47 ohms maximum has been used between the active antenna area and the IC
positive input and another resistor of 12 kOhm between the positive input
and a blocking capacitor (at this capacitor the DC voltage is half the total
supply of 12 volts. The negative input of this IC is connected to the IC
output by an 1kOhms resistor. Until today I have never encountered any
damage of the IC or its input gate. I guess such a gate protection should be
included into every active antenna circuit. Another advantage of using such
an operating amplifier is a supply current of just 10 mA! Sorry to say that
for the moment, due to a change of the computer, I do not have a circuit
copy available for this active antenna.   

HW?

73 Ha-Jo, DJ1ZB


-----Ursprüngliche Nachricht-----
Von: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] Im Auftrag von Chris Wilson
Gesendet: Samstag, 30. Juli 2016 15:13
An: rsgb_lf_group@blacksheep.org
Betreff: LF: My active whip antenna has gone noisy and insensitive

30 July 2016


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  2E0ILY                           mailto:chris@chriswilson.tv

 My        part        time        LF        grabber       is       at
 http://www.chriswilson.tv/grabber.html