On 12/13/2011 12:53 PM, David Herring wrote:
I'd like to ask a few questions.
David,
I hardly know where to begin in responding to your question. First, if
you want a self-supporting vertical antenna for 30-10M, there are some
really good choices that you can buy, that can be easily
Hi Jim,
Thanks for the tip on the AV-640...I'll surely look into that. I am looking
for a self-supporting solution to minimize my impact upon the XYL's view (to
her credit, she's been incredibly patient and understanding about that). The
home brew vertical dipole I'm running now requires guys
On 12/14/2011 8:29 PM, Ross Primrose N4RP wrote:
Is it just me, or does that paragraph have a glaring typo in it
Yep! Thanks. It should read, if we put the choke at the antenna, the
differential loss . . . . .
Jim K9YC
__
I hesitate to step between Dean and anyone else but... it seems to me
that a Balun with good enough common mode choking should fulfill all the
isolation requirements we might have. The isolation any Balun provides
takes place at the point it is inserted, so a Balun built for 50 Ohms
may be
Dean,
The last two paragraphs of your writeup do not seem relevant to the
discussion of balun (CM choke) at the input or output Those paragraphs
deal with operating coax at a very high 60:1 SWR, and neither support
nor agree with the other points.
Consider the following: A situation where
On 12/14/2011 4:59 PM, Don Wilhelm wrote:
The balun has the same loss no
matter where it is placed, so lets assume it is placed at the output.
There we go with that nasty word again (balun) -- we're talking about a
common mode choke, right? :)
The problem is more complex than it looks. Let's
Dean's example is still valid. By placing the CM Choke at the wrong
distance of 20 feet from the tuner, the 3,000 ohm Z presented at the balun
in addition to the extra 20 feet of line can create substantial mismatch
loss (i.e., additional loss due to VSWR). The choke simply adds three feet
On 12/12/2011 5:10 PM, Jim Brown wrote:
Yes, chokes like these would be a great choice for use at the feedpoint
of ANY HF antenna, whether fed with coax or parallel conductor line.
One VERY important exception that I forgot to mention is that common
mode chokes can be destructively overheated
Jim Brown said:
Mon, 12 Dec 2011 17:10:36 -0800
I have not attempted to measure the Zo of the bifilar wound chokes I've
built using #12 and #14 THHN, but Jerry Sevick, in the last of his
books, did wind some using exactly that method and that wire, and he
says the Zo of those he wound
On 12/13/2011 10:43 AM, Dean Straw wrote:
I used a bifilar wound CM choke at the input of the ARRL high-powered tuner
described in late editions of The ARRL Antenna Book. It had 12 bifilar
turns of #10 AWG Formvar wire on a 24-inch diameter OD Type 43 core.
Jerry said that Zo for this sort of
I used a bifilar wound CM choke at the input of the ARRL
high-powered tuner described in late editions of The ARRL Antenna
Book. It had 12 bifilar turns of #10 AWG Formvar wire on a 24-inch
diameter OD Type 43 core. (Nowadays I'd probably use a more optimal
Type 31 mix.) In testing the input
Now, #10 wire is roughly the same size as the inner conductor used in
RG-213. On 10 meters the majority of loss in the bifilar transmission
line wound around the torroid will be I-squared-R conductor loss,
rather than additional dielectric losses that come into effect in
the VHF and UHF
Joe:
Right on -- certain unnamed baluns had a quite reputation as being RF fuses.
But as the suject title above says, I'm still talking about the pros and
cons of placing a CM choke balun at the input or at the output of an
unbalancing antena tuner to feed balanced lines. Both positions are
Aloha Jim, Joe, Alan, Dean and the rest of the reflector,
I'm thoroughly enjoying reading this thread.
I'd like to ask a few questions.
Mine is a 100 watt station, but with aspirations of getting a KPA-500
eventually. I have a Palstar BT1500A Balanced L Antenna Tuner feeding a
vertical dipole
Jerry Sevick used a monster T400A-2 toroid, #2 powdered iron, 4 inches in
diameter, intended to be the 4:1 up transformation for the back of high
power tuners. (Sevick, Understanding Baluns 2003, CQ Communications, pp
60-61) I have run these some times with brick-on-key 1500 watts and never
On 12/13/2011 11:48 AM, Alan Bloom wrote:
Is that a valid assumption? I thought that much of the loss in coax is
due to the dielectric loss of the insulation. That implies that the
bifilar winding should have less loss than coax.
This is a very common misconception, and it is VERY wrong
Jim Brown wrote:
On 12/13/2011 11:48 AM, Alan Bloom wrote:
Is that a valid assumption? I thought that much of the loss in coax is
due to the dielectric loss of the insulation. That implies that the
bifilar winding should have less loss than coax.
This is a very common misconception, and it
I used to think that dielectric losses were a significant factor until
someone pointed out the attenuation data for various transmission lines
between 2 and 500 MHz. The plots for all the various transmission lines are
straight lines. If dielectric losses were involved, they should curve toward
On 12/13/2011 2:47 PM, Ian White GM3SEK wrote:
The reduction in loss is almost entirely due to increase in the diameter
of the center conductor (because that conductor has the largest current
density and hence the highest skin effect losses). The foam dielectric
is merely something that*has*
Balun at Input or Output of Antenna Tuner?
Dean Straw, N6BV (Senior Assistant Technical Editor, Retired) December 12,
2011
I have been lurking on the Elecraft Reflector monitoring the animated
discussion about where to place a balun -- at the input or the output of a
tuner. I was going to jump
Dean
Nice analysis of the issues. K9YC also presents baluns done with wire pair
rather than coax, RG213 or otherwise. Might not they be a better solution
than coax when constructing a CM choke for driving windowline?
Jim ab3cv
__
Poor choice of words: first I fell into the balun habit rather than CM
choke on the first usage. Second: bifilar wound CM choke would have been
a better description for the alternative mentioned.
Jim ab3cv
__
Elecraft mailing list
Home:
I would avoid coaxial cable in any situation where there can be a large
impedance mismatch because of just the losses mentioned. Even though low
power might not burn up 3 feet of coax, that's still a chunk of power thrown
away.
The ideal CM choke at the OUTPUT of a tuner feeding a balanced line
Also note that in the case of the KPA500, we will be matching SWRs of
10:1 or less, which results in less loss for the short coax choke mentioned.
73, Eric
www.elecraft.com
On 12/12/2011 2:00 PM, Ron D'Eau Claire wrote:
I would avoid coaxial cable in any situation where there can be a large
This is 41.2 W per foot
and at that level the RG-213 would get very warm and could even melt,
especially if the choke were confined in a small box with no circulation
of
cooling air.
If a balun of like reactance were instead wound in bifilar fashion using two
parallel wires, rather than
I meant to say KAT500..
73, Eric
www.elecraft.com
On 12/12/2011 2:05 PM, Eric Swartz - WA6HHQ, Elecraft wrote:
Also note that in the case of the KPA500, we will be matching SWRs of
10:1 or less, which results in less loss for the short coax choke mentioned.
73, Eric
www.elecraft.com
FWIW, where there is 1 db of loss in a matched line, a 2:1 SWR adds an
additional 0.2 db loss, a 4:1 SWR adds about 0.8 db loss. A 10:1 SWR results
in an additional 2.5 db loss.
Ken WA8JXM
On Dec 12, 2011, at 5:00 PM, Ron D'Eau Claire wrote:
I would avoid coaxial cable in any situation
Dean,
Nice analysis.
One can take it a step further. Assume your 3 foot RG-213 balun that
dissipates about 8% of power or about 40W for 500W input. It would contain
some 36 beads and would weight perhaps 2 pounds.
An input balun with identical choke impedance would be a single bead with 6
turns
On 12/12/2011 2:06 PM, Paul Christensen wrote:
However, the bifilar winding is not really like a wide
conductor-separated transmission line so, perhaps mismatch losses are less
than the same length of RG-213, but more than open or balanced lines.
I have not attempted to measure the Zo of the
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