Posted by
stan levandowski on
Nov 25, 2017; 12:52am
URL: http://elecraft.85.s1.nabble.com/OT-Unplanned-Discovery-tp7636096p7636235.html
Howard, I received the core and the replacement choke earlier today.
I put the core on the 25' RG174 feedline right at the 9:1 UNUN and was
able to wind 10 turns. Then I connected a 33' counterpoise wire to the
output BNC using a hose clamp. This was just a quickie "temporary"
installation as it was getting dark here in NY.
With no other changes made, I tried tuning up on 80, 40, 30 and 20 with
my K2/10 and its internal KAT2 tuner.
My 80 meter SWR which had been 1.1:1 was now an unusable 2.8:1. This
makes sense to me if the choke was now keeping the common mode currents
from using "everything" connected to the K2!! I would EXPECT 80 meters
to have a high SWR for a 33' wire and it did! My 40 meter SWR went from
1.2:1 to 1:1. My 30 meter SWR went from 1.7:1 to 1:1 and my 20 meter
SWR went from 1.1:1 to 1:1. I was only able to make one quick contact
but that was a pretty good one - Corsica - on 20M QRP.
Then I put the new choke you sent me on the DC cable IN ADDITION to the
cracked one that I already had on. I detected NO NOISE at this point.
Switching back and forth from battery to Kx33 did NOT change the noise
level.
Of course, I'm going to keep experimenting through radial placement,
elevation and number of radials but for now, it looks like you solved my
"noise problem."
That's a nifty sized little Kx33 power supply you sell and I'm glad I
didn't give up on it. I'm very pleased with the personal support you
provided to me.
Well, the CQWW starts in 15 minutes and I'm looking forward to a 'no
noise' weekend!
73, Stan WB2LQF
On Tue, Nov 21, 2017 at 03:07 PM,
[hidden email] wrote:
Hi Stan,
That is great news regarding the antenna being outside, it is my
experience and that of many customers that a common-mode (CM)
choke at the feedpoint of an end-fed outside is highly effective
at decoupling the feedline as part of the active antenna.
In my opinion, and those of another expert in the field Jim
Brown, it is money wasted purchasing a CM choke. If you had not
taken a look at his excellent paper on the subject here is the
link:
http://audiosystemsgroup.com/RFI-Ham.pdf
<
http://audiosystemsgroup.com/RFI-Ham.pdf>
Before I was able to measure the performance of chokes I had
purchased both a W2DU and DX Engineering choke myself, and
thought they worked OK, but had no way to tell. Once I started
merely winding coax on mix 31 ferrites, I noticed they worked
better than the ones I bought, and the cores are cheap. I ended
up selling the DX Engineering unit and in it's place I have two
2.4" mix 31 cores stacked (for higher power handling) with 8
turns
of RG-8X, and it is superior. Here is a chart showing how
effective winding as many as 6-14 turns around that core can be,
I
suggest 8-10 turns depending on the size of coax you are using:
I will send you a replacement for the small choke which broke in
shipment, I am sorry for that. I will also send you a 2.4"
diameter mix 31 toroid core so you can make your own CM choke at
the feedpoint. The core is weatherproof, so don't worry about it
getting wet. I look forward to getting reports from you as to
the
progress taming this CM noise pickup, and thank you for your
patience! Ease of choking CM RFI is the real advantage to the
Kx33 you purchased relative to other switchers, it is a
characteristic we worked hard to engineer into the supply.
Cheers & 73,
Howie - WA4PSC
On 11/21/2017 2:30 PM, stan levandowski wrote:
Howard, thank you for the info
and the offer.
YES, I would love to have a new
ferrite. The one that was shipped was neatly cracked in half!
I used it anyway; didn't figure it mattered that much as the
mass was still there.
And YES, I am going to install
additional counterpoises right at the 9:1 UNUN and spread them
out. The antenna is not in the attic, it is outside as a
sloper
from the rear of my townhouse up to the top of a 35' pine
tree.
It's working great so far. Worked Paraguay last night on 20M
and Belgium this morning also on 20M. K2@5 watts.
Do you have a recommendation for
an effective choke at the UNUN? Beads, a coax choke, something
from DX Engineering like their 1:1 isolator??
Thanks and 73, Stan WB2LQF
On Tue, Nov 21, 2017 at 01:28 PM,
[hidden email]
<mailto:
[hidden email]> wrote:
Hi Stan,
Thank you for the reply! Regarding antennas; I feel your
pain! I have had to endure less-than-optimum antenna
setups
many times as well.
One of the aspects of common-mode currents is they are
reciprocal between transmit and receive. In transmit they
cause feedline radiation and a radiation pattern which is
the combination of the desired antenna radiation and the
feedline radiation. In receive the feedline becomes part
of
the receiving antenna pattern, and since it leads right
into
your house, it is receiving any and all of the RF noise in
your place. The Kx33 has very low radiated noise, however
if an antenna is placed close to it hooked to a sensitive
receiver like that in the KX2/KX3, some noise may be heard.
If you were to choke the feedline at the feedpoint/balun
and add an additional counterpoise wire in the attic to
help
balance the antenna currents, you would achieve two goals:
the antenna pattern would no longer be disturbed in receive
or transmit by unwanted feedline currents, and your receive
could potentially be much quieter than even now running
from
batteries. I make this last point because even running
from
a battery I guarantee there are devices in your house which
generate RFI like LEDs and fluorescent lights, not to
mention the numerous little chargers we all seem to have
scattered around for phones, toothbrushes, etc. and your
counterpoise/antenna is close to them.
As is obvious from its size, the ferrite included with the
Kx33 is designed for 3-5 turns of the DC cable only. I
would be glad to send you at no charge a more substantial
ferrite core which would allow multiple turns of coax, just
let me know if you are interested.
Cheers & 73,
Howie - WA4PSC
On 11/20/2017 3:56 PM, stan
levandowski wrote:
Howard,
I certainly didn't mean to impugn your company or its
product. I think I made that clear in the second of the
two
posts I made to the Reflector. I fall into the category of
hobbyist ham and self-educated and I simply wanted to
remind
fellow Listers that noise problems could literally be right
under our noses and *not* because of crummy propagation or
easily blamed on our neighbors.
In my case, yes I have an end fed antenna with a 9:1 UNUN
and yes it uses the coax shield as a ground return and
absolutely yes there are common mode currents involved.
However, Howard, when I disconnected the Kx33 power supply
from my K2 and connected the SLA battery using an 18 inch
twisted pair, there was then NO connection other than the
paddle cable, the battery connection and the antenna
connection for the common mode currents to "...seek a
current path through whatever is attached to the rig..." as
you stated. It wasn't until I UNPLUGGED the Kx33 that the
noise went away. I can only assume that the Kx33, while
powered up, was sending RFI out via it's AC and/or DC
cables
which were lying on the floor about 5 feet away from the K2
even though unplugged from the K2
Please also note that in my post, when I reconnected my old
Samlex 1235M, I also had noise. And the darn computer
supply added noise also.
I will fall on my sword here and admit that I've had high
noise for the last couple of years, ever since giving up my
old fashioned analog supply but I never realized it. I
never made the connection. I was a lousy problem solver
and fell into the trap of ASSuming it was either my attic
antenna picking up all kinds of stuff inside the house, or
just the falling propagation conditions. And I lived with
it and still made contacts. And that darn Laptop of mine
was ALWAYS plugged in and turned on for QRZ.com, the
reverse
beacon network, or just so I could use Notepad with N1EA's
"MILL" font to copy CW (I'm a former Navy Radioman and it's
easier to type CW).
But I have to say here that now that I'm totally on
batteries, it's amazingly quiet. I'm hearing QRP signals
that were previously lost in the noise. After living with
baseline S4 noise for so long, this is like heaven!!
I'm not going to return the Kx33. It's the right size,
puts
out a full 14 volts and I'm confident I can ultimately
solve
the problem with the proper chokes, physical placement and
perhaps even some shielding.
I'm retired and we live in a townhouse. Installing a
proper
ground is not possible for me. It would be so far away
that
the connection would just be antenna. For safety I
disconnect my antenna when not operating.
73, Stan WB2LQF
On Mon, Nov 20, 2017 at 01:35 AM, Howard Hoyt wrote:
Hi Stan,
One thing we have learned in supplying thousands of Kx33s
to hams is the importance of minimizing or eliminating
common-mode currents in the antenna system. The
transverse mode RFI output of the Kx33 is extremely low
and has never been the cause of noise to our customers,
but if the antenna system has significant common-mode
potential, it will always seek a current path through
whatever is attached to the rig...through the power
supply, your body, as well as grounds. The outside of
the
coax shield, the rig, the power supply and AC mains are
all in a series path for common-mode currents.
The most direct cure is to place a high common-mode
impedance in the antenna feedline. The DC power lead on
the Kx33 is smaller in diameter than most RF coax lines,
so it may be easier to form a choke on that cable. You
mentioned "YES, I HAD CHOKES ON ALL SUPPLIES, CABLES,
WIRE." The exact core material used and number of turns
is important in constructing common-mode chokes. Jim
Brown, K9YC has excellent tutorials on this subject:
http://audiosystemsgroup.com/RFI-Ham.pdf
<
http://audiosystemsgroup.com/RFI-Ham.pdf>
Another measure which will shunt common mode currents
away
from other paths is a low impedance ground on the rig.
Something else I want to mention, as it is an issue which
has cropped up recently: There are several sellers on
both
eBay and Amazon stating "Pro Audio Engineering Kx33
power
supply" in their ads, but no supplies other than those
sold directly from us are the actual Kx33. We know this
because we worked with one such customer to resolve noise
issues and it turned out the unit he had was not a Kx33.
eBay and Amazon both state they can not do anything,
since
the other vendors are claiming they use our part number
and name only to state an equivalency, which they most
assuredly are not. Our Kx33 has less than 70 pF of input
to output coupling vs. 1000 pF or more for most other
supplies, making it far easier to choke common-mode
currents. This was the most difficult spec of the supply
to arrive at, but considering we knew it could be used
with temporary antenna systems with common-mode potential
it was important to achieve.
As we unconditionally guarantee everything we sell,
please
contact us at
[hidden email]
<mailto:
[hidden email]> and I am
sure we can help you eliminate this noise or refund your
purchase price.
Cheers & 73,
Howard Hoyt - WA4PSC
www.proaudioeng.com <
http://www.proaudioeng.com>
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