MIME-Version: 1.0
In-Reply-To: <56618AD6.8070205@lineone.net>
References: <CAA8k23Q8YSBO5NE8Qtyt=9TJ8J18tAjLTYFBRxS+LRp+WOHY0A@mail.gmail.com>
	<565D78F1.5060106@lineone.net>
	<CAA8k23RAWbqepp-xGbuED_NQVMek2+u+g_NVW=apCLm95Eskog@mail.gmail.com>
	<3061063.yGTG6Xp9uk@zv5000>
	<56618AD6.8070205@lineone.net>
Date: Fri, 4 Dec 2015 15:30:52 +0000
Message-ID: <CAA8k23T=wey=vXMBmhDGnwaBMm=H9e5+_1_GTTq-=HRcx6=Qhw@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Beware damage from active antennas
Content-Type: text/plain; charset=UTF-8
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Its the output that causes the problem, and anyway ferrite beads were
suggested on the input to my receiver RF amplifier , the LTC5524.
In retrospect I will probably change the distribution of gain in that
receiver.  It doesn't need RF amplification before the mixer
(essentially a Softrock design) and the extra 0 - 20dB controllalble
gain can more safely be allocated to an opamp stage on the baseband
output.    Since I've already combined the I/Q at that point, it only
needs a single gain stage with variable feedback R to set the gain.
  Would also be a good opportunity to include another stage of 1kHz
bandbass filtering.

On 4 December 2015 at 12:45, LineOne <dhchurch@lineone.net> wrote:
> I assume that as this is high impedance and tiny current into the amplifier
> that ferrite beads may not be quite so so effective. I do like them though,
> cheap and easy, removable with no damage.
> If your whip setup is wide-band, would a low-pass filter be appropriate, or
> if single band, how about a series-tuned circuit? These should take the edge
> off any spikes.
>
> Hugh, M0DSZ
>
> On 03/12/2015 16:29, Claudio Pozzi wrote:
>
> On Tuesday, December 01, 2015 11:23:09 you wrote:
>
>> Yes, there are plenty of options for normal Tx/Rx. In fact the
>
>> existing C/O relay in the 137 transmitter provides more than enough
>
>> isolation for that
>
>>
>
>> But I was on a separate active whip at the time, a quite independent
>
>> conenction and irrelevent to real operation at the time. It was the
>
>> fact that the active whip could shove out such an alarmingly high
>
>> level that concerned me - 13V very sharp spikes. And I forgot to
>
>> mention in the previous post, those 13V edge spikes went to both +13V
>
>> and -13V, so technically 26Vp-p
>
>>
>
>> Perhaps the homebrew designs others use aren't so robust in their output
>
>> stages?
>
>>
>
>
>
> For sharp spikes coming out from the cable I suggest some ferrite bead or a
> VK200 choke on the receiver input. I believe they have no attenuation at LF
> frequency.
>
>
>
> 73 de Claudio ik2pii
>
>
>
> --
>
> Claudio Pozzi - rispondere a cla.po@tiscali.it
>
>
>
>
>
>
>
>
> ----
> ZE-Light e ZE-Pro: servizi zimbra per caselle con dominio email.it, per
> tutti i dettagli clicca qui
>
> Sponsor:
> Soluzioni di email hosting per tutte le esigenze: dalle caselle gratuite a
> quelle professionali su piattaforma Zimbra, da quelle su proprio dominio a
> quelle certificate PEC. Confronta le soluzioni
> Clicca qui
>
>