[Elecraft] Capicator Size for filtering across battery power

[Fred Jensen]

Not quite ... the capacitor goes as close to the rig as you can manage. 
  Putting it "across the batteries" does nothing, the batteries are 
already a far massively larger capacitor than anything the boom box guys 
next to you at the traffic signal ever dreamed of.  Your goal is to 
"smooth out" the IR drop in the power circuit to the rig, and you can 
only do that from the load end.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

On 10/8/2012 5:18 PM, KD8NNU wrote:
>
> Gents,
>
> Thanks for all the information regarding my request for how to size a
> capacitor across my batteries to fix my perceived problem of RF.
>
>>From what I understand is that this is just the normal current flow during
> voice peaks or digital peaks when transmitting and not RF.
>
> So my options as I understand them are to put a large cap like the car
> stereo guys do across the batteries.   These are large cap's and since I
> have both the amp and radio on the same batteries I will need two cap's one
> at each device.
>
> If I have this wrong then please correct me.
>
> Again as always thanks for the replies on the topic as there was more behind
> a simple question than I realized.
>
> Thanks
> Don
>
>
> ~73
> Don
> KD8NNU
> -----Original Message-----
> From: Mel Farrer
> Sent: Monday, October 08, 2012 5:24 PM
> To: elecraft at mailman.qth.net ; jim at audiosystemsgroup.com
> Subject: Re: [Elecraft] Capicator Size for filtering across battery power
>
> Good points Jim,
>
> I would like to add a clarification and results that I use.
>
> 1.  On point 2)  I would rather power the accessories on the battery end of
> the rig power cord as the voltage regulation will not have the rig IR
> losses.
>
> 2.  On point 4) I have used a 5 Farad cap with 3 inch leads to the rig.  It
> does the best of trying to cancel out the IR losses on voice pikes and does
> a great job.  This is the one used by the car monster audio amps.  Cost is
> around $50 direct and less on eBay.
>
> Mel, K6KBE
>
> --- On Mon, 10/8/12, Jim Brown <jim at audiosystemsgroup.com> wrote:
>
>
> From: Jim Brown <jim at audiosystemsgroup.com>
> Subject: Re: [Elecraft] Capicator Size for filtering across battery power
> To: elecraft at mailman.qth.net
> Date: Monday, October 8, 2012, 12:52 PM
>
>
> On 10/7/2012 7:06 PM, David Moes wrote:
>> That is interesting.    I suspect that they are reacting to the
>> elecromagnetic field created by rapid current fluctuations in the DC
>> lines rather than picking up RF.
>
> NOT electromagnetic fields, just simple Ohm's Law.  There's IR drop on
> the power cable between the battery (or power supply) and the rig, and
> if the rig is running full power, peaks of at least 20A, with an
> envelope that follows SSB modulation.  If you are powering accessories
> from that same battery and have audio connections between those
> accessories and the rig, the IR drop (modulated SSB envelope) will
> appear between the chassis of the accessory and the chassis of the K3,
> and will be added to the audio.  That will SOUND like RF feedback, but
> it is NOT.  W8JI told me about this several years ago.
>
> There are at least four good fixes for this issue.  I've set up and
> tested all of these, and all of them work.
>
> 1) Don't power accessories from the same supply that feeds your rig.
> Instead use a separate wall wart for them.
>
> 2) Power accessories from the same supply, but use a simple power
> splitter (Y-cord) at the RIG end of the power cable to get the accessory
> power.
>
> 3) Power the accessories from the battery or big power supply, but bond
> from chassis to chassis of all interconnected equipment with short, fat
> copper.
>
> 4) Power the accessories from the battery or big supply, but use a
> monster capacitor across the terminals right at the rig.  When I say
> monster cap, I'm talking at least 10,000 uF. That's big, and it ain't
> cheap.
>
> 73, Jim K9YC
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