Posted by
KD8NNU on
Feb 04, 2012; 3:02pm
URL: http://elecraft.85.s1.nabble.com/RF-on-power-to-K3-question-tp7254202.html
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.
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.
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.
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.
Should a CAP be placed across the batteries to filter out the HF. If
yes how do I determine what size.
Also if yes for the CAP will this improve battery life.
Also if yes could the CAP have influence that could negatively effect my
use of chargers for floating power.
Again as always, that in advance for your help from this great group.
Cheers
Don
~73
Don
KD8NNU
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