On Sat, Dec 31, 2011 at 9:35 PM, Don Wilhelm w3...@embarqmail.com wrote:
Keep in mind that the length of an unmatched feedline is critical to the
success or failure of such a system. That is a factor that is seldom
mentioned in posts that say a particular antenna works well and loads
well -
Those of you using open wire feed lines. How do you keep RF out of the
shack? 73 George/W2BPI K2/100
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Post:
fine... balanced.
Good Luck and Happy New Year!!
--... ...--
Dale - WC7S in Wy
From: w2b...@aol.com
Date: Sat, 31 Dec 2011 11:25:54 -0500
To: Elecraft@mailman.qth.net
Subject: [Elecraft] open wire feeders
Those of you using open wire feed lines. How do you keep RF out of the
shack? 73
Open wire (or 'parallel conductor') feed lines connected to a reasonably
balanced load do NOT radiate (or receive noise, etc.)
The currents, hence the electric fields, around each wire are opposite and
equal at all points, even though the line may have a high SWR. Those equal
and opposite fields
George,
Short question, long answer follows --
Do to constraints at home, I no longer use open wire or ladder line
feeders, but when I did use them, I found several things were true if
you did not want them to radiate (and create RF in the Shack).
My first rule is to use balanced antennas -
Don...
Many hams - as I have done/do - use coax to get out of the house,
connect it to a balun, and then connect twinlead from the balun to an
antenna. There is a lot of commentary on this setup, but perhaps another
time through would be helpful. The questions arise:
- if the coax is short,
The coax will be exposed to whatever SWR is on the feedline. The SWR will
vary as a function of line length, characteristics, antenna length/height
and frequency of operation. If you know the SWR you will be seeing then you
can use coax loss calculators available online to see what the impact of
I have often had a voltage loop at the rig end of my open wire feed line and
have never experienced a problem with stray RF, even though a neon bulb
lying near the ATU blinked as I sent CW.
HOWEVER - I do use a homebrew link-coupled ATU with open wire line. It lacks
the dual-differential tuning
Robert,
When that is done, I recommend doing several things:
1 - prune the balanced feedline until the feedpoint impedance is close
to the characteristic impedance of the coax. You may not be able to
accomplish that on all desired bands, so plan to switch in extra
feedline to accomplish that
Would it were that all baluns were the same. There is a limit to how
much blocking can be put between the balanced line and the coax. What most
people fail to account for in the balanced line business is how much COMMON
MODE current and voltage there can be. Unbalanced current on the feedline
I have a balanced fed balanced length dipole. The dipole sits atop
40' of rope guyed fiberglass pole. 55 feet on each side. About 45 feet
of 450 ohm balanced line comes into the far end of the back side of the
house into one of my 7 , um, junk/storage rooms! There I have a 4:1
balun, which
I don't have a problem with it at all, even with a kw. RG213 goes 8 feet
to a window feed-thru, then to a balun, then 75 feet of 450-ohm line.
The only problem I had was when I installed a second antenna (a 40m
vertical dipole) and fed it with ladder line as well. Then tuning settings
on my first
Ron,
Thank you for the references. I found the information very interesting to
say the least. Parts here would be an issue, but the construction and
methods to check and adjust the tuner were most valuable. Now just to have
some drawer space! As Don had mentioned in an earlier post, getting
Hi,
Wow, gorgeously constructed tuner by WZ5Q. I wish I had one. But is the
center tap of the secondary really connected to the coax input ground as
indicated in the schematic?
AB2TC - Knut
Bill K9YEQ wrote
Ron,
Thank you for the references. I found the information very interesting to
...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of ab2tc
Sent: Saturday, December 31, 2011 2:01 PM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] open wire feeders
Hi,
Wow, gorgeously constructed tuner by WZ5Q. I wish I had one. But is the
center tap of the secondary really
Actually, that is a *brute* tuner, capable of mega kilowatts! Something
a bit scaled down is more practical IMHO. BUT the design is exactly
what I was referring to.
The design principle is the same, but I have always used dual section
capacitors so the shaft is at RF Ground potential (no
On 12/31/2011 11:34 AM, Don Wilhelm wrote:
It is just as easy to use two parallel lengths of coax with the shield
grounded and the balanced feedline connected to the two center
conductors. That will produce a shielded balanced line that you can
bring into the shack just like a single
Hi Guy,
OK I'll own up. I have used isolation transformers as recently as this
year before leaving Scotland, in the feed system of a Laport Rhombic (dual
rhomboid). I used this antenna, aimed towards your side of the pond, to
listen for VHF signals between 88 MHz and 148 MHz in the pious
On 12/31/2011 9:42 AM, Don Wilhelm wrote:
My first rule is to use balanced antennas - off center fed antennas are
famous for feedline radiation and RF in the shack.
RIGHT! Some important fundamental principles here.
1) A two wire line will be balanced ONLY if what is connected at each
end is
Message-
From: Robert G. Strickland
Sent: Saturday, December 31, 2011 12:40 PM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] open wire feeders
Don...
Many hams - as I have done/do - use coax to get out of the house,
connect it to a balun, and then connect twinlead from the balun
(:-)) I actually have a few Twinax connectors, both male and female.
Same as PL-259 / SO-239's, except two pins.
HAPPY NEW YEAR, and ...
73!
Ken
On Sun, Jan 1, 2012 at 12:41 AM, Phil Kane k2...@kanafi.org wrote:
On 12/31/2011 11:34 AM, Don Wilhelm wrote:
It is just as easy to use two
Sandy,
Take the information on K9YC's balun comments to heart. Jim has done a
wonderful job of measuring the isolation effect of baluns (more
specifically common mode chokes).
Yes, the reactive and resistive components of the feedpoint impedance
play a large part in how the whole system
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