[Elecraft] RF on power to K3 question

Sun Feb 5 09:11:17 EST 2012

Hi Fred,

I am asking the question simply because I was warned by another ham to 
consider the possibility of a power spike on the feed to the K3 with the 
choke by another ham.   He was not fully sure and suggested that I post 
the question to the folks who might really know the answer.

Plus if it is good practice to put a CAP across the batteries for the 
way I am doing my power to help with a clean signal, clean power and 
better battery life I want use good practice.

If I had not been prompted by the ham who suggested a CAP I would have 
never asked the question.

Power is an SGC power cube good for 500w.  Antennas are a 2 WL loop for 
160m and a dipole and the shack is on the second floor.

Maybe the answer to the question is so obvious that it just shows my 
total ignorance.  Hey but I do learn slowly at times :-).  Example I now 
work split and if you remember those posts from me on that topic I think 
everyone wanted to hit me in the head with a baseball bat.

Like I indicated right now everything is working real good and I have no 
problems, but I dont want to be in the process of creating new ones.

Cheers
Don

~73
Don
KD8NNU

On Sun, Feb 5, 2012 at 12:32 AM, Fred Townsend wrote:

> Hello Don:
> If you have cured your RF problems I'm not sure why you are asking 
> your
> questions.
> In general adding a choke or capacitors to your power lead shouldn't 
> hurt
> anything so give it a try. I will add detail to your questions below. 
> BTW
> you should indicate how much power you are running and where your 
> antenna is
> located relative to your K3. FT
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of 
> goldtr8 at charter.net
> Sent: Saturday, February 04, 2012 7:03 AM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] RF on power to K3 question
>
> Dear Group,
>
> I have determined that the majority of my RF shack problems were 
> related to RF on the power lead to the K3.   Winding 7 turns thru a 1" 
> clamp on #31 ferrite has cured the symptoms.   With this choke in 
> place everything is even happy on 160m.
>
> So let me explain how I power the equipment and then ask about putting 
> a CAP
> across the power.
>
> The radio and SGC power cube amp are powered by 5 batteries connected 
> in parallel.   I use a very small battery tender connected at all 
> times to keep the batteries at a full charge.    When using the amp I 
> also float a battery charger set to its mid range position with a max 
> of 15 amps of charge to help maintain the system.   From this 
> perspective it works real well for powering the system.  But I wanted 
> to be sure that everyone
> understands how I power the system as I get to my questions below.
>
> Plus there is the normal AC stuff like the PC and so on.
>
> All equipment is grounded to a single point ground on one of the 
> negative
> posts of a battery.
>
> Do you have an earth ground? That is a ground rod. Depending on your 
> setup
> that may or may not help. FT
>
> So now to the RF problem.  If you have followed earlier posts I have 
> been
> chasing RF in my shack for quite awhile and finally started playing 
> around
> with a clamp on meter and that is what tipped me off to the power feed 
> of
> the K3.
>
> With the power feed determined as a problem (there still could be 
> more). One of the tests I did was to remove all of the chargers and 
> disconnect all
> the AC equipment and connect the amp output directly to the dummy 
> load.  RF
> was still present even after I attempted to remove all influences to 
> verify
> if something was putting this on the power leads. So now I believe it 
> is there natively when in TX and is not from a charger
> or PC or other antenna.
>
> That suggests you may have other, as yet, undetected problems. FT
>
> Based on my reading about chokes, I put 7 wraps in the 1" big snap on
> ferrite.  This killed the RF and like I stated in the opening 
> paragraph with
> everything reconnected again the system is now happy at 160m.  It now
> actually works real well.
>
>
> This is good. FT
>
> In discussing what I found with others, I have learned that batteries 
> are
> not filters and all the HF energy goes right thru them. 
> Recommendations have been made to put a ceramic capacitor across the
> batteries to filter the HF out.  I also have been cautioned that there 
> may
> be a problem with a choke on the power feed to the K3 that could put a 
> power
> spike on the feed line that could do damage when turning the radio on 
> and
> off.
>
> So here are the questions.
>
> Can the choke cause a problem with power spikes that could damage the 
> K3.
>
> No. FT
>
> Should a CAP be placed across the batteries to filter out the HF.  If 
> yes
> how do I determine what size.
>
> Adding a cap won't hurt but it probably won't help much either. It 
> might
> make your battery tender happier. It should be pointed out your K3 
> already
> has bypass caps across the input power leads. Take a look at the 
> schematic.
> As for value it is not critical as long as it is a ceramic cap, 50V or
> greater. Since you are working 160M I would start with an 0.1uF. It is
> useful to have a combination of values. If I were working 40M I would 
> add a
> 0.01uF and for 15M and above a 0.001uF. Put them all in parallel. FT
>
> Also if yes for the CAP will this improve battery life.
>
>
> No. FT
>
> Also if yes could the CAP have influence that could negatively effect 
> my use
> of chargers for floating power.
>
> Again, no. FT
>
> Again as always, that in advance for your help from this great group.
>
> Cheers
> Don
>
>
> ~73
> Don
> KD8NNU
>
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