A discussion on the towers reflector mentioned, in passing, that a current
balun helped lower received noise. The discussion was about something else
and this aspect was not explored.

Is this common? I had never heard of it before, but I many holes in my
understanding of antennas. Under what circumstances would this apply? Where
would the balun (toroids) be placed? Feed point or at bottom of tower? (My
particular interest is for use with a half sloper and for 160/80/40 meters.)

Bill
W2WO

Without a balun, your feedline could become part of the antenna. If
noise is being radiated by such things as house wiring, the feedline
part of the antenna is likely to pick up more noise because it goes near
and into the house. A current balun prevents the feedline from becoming
part of the antenna and so it can reduce the noise.

A lot of local noise is predominantly vertically polarized. So if you
have a horizontal antenna without a balun, the feedline, which often is
vertical, can pick up a lot more noise than the antenna. Again, a balun
prevents feedline pickup and can make things quieter.

If you're feeding the antenna with coaxial cable, put the balun at the
feedpoint. If feeding with twinlead, put it where the feedline connects
to the tuner or receiver.

To learn more about baluns, see
http://eznec.com/Amateur/Articles/Baluns.htm.

Roy Lewallen, W7EL

Bill Ogden wrote:
A discussion on the towers reflector mentioned, in passing, that a current
balun helped lower received noise. The discussion was about something else
and this aspect was not explored.

Is this common? I had never heard of it before, but I many holes in my
understanding of antennas. Under what circumstances would this apply? Where
would the balun (toroids) be placed? Feed point or at bottom of tower? (My
particular interest is for use with a half sloper and for 160/80/40 meters.)

Bill
W2WO

Just today, I happened to revisit a voltage balun I wound years ago for my
FD 80/40m inverted vees. It started out as an Amidon AB240 kit (Amidon
#FT-240-61 or Fair-Rite #5961003801 ferrite core). On the network analyzer,
it looked kinda cruddy... the ratio wasn't quite 1:1, and there was a bit
too much reactance in the measurement. I rewound it as a
super-inductor/choke balun with RG-58 like this:
http://www.iol.ie/~bravo/low_band_antennae.htm

Now, it IS 1:1 (by nature of the RG-58), and there is hardly any rectance
(less than an ohm up to about 20MHz). Common-mode reactance is about 200
ohms at 1.8 MHz, and 400 ohms at 3.5 MHz. I didn't bother checking above
80m.

Vy 73,
Bryan WA7PRC
PS: The correct link to Roy's info is a PDF file:
http://www.eznec.com/Amateur/Articles/Baluns.pdf

Roy Lewallen wrote:
Without a balun, your feedline could become part of the antenna. If
noise is being radiated by such things as house wiring, the feedline
part of the antenna is likely to pick up more noise because it goes near
and into the house. A current balun prevents the feedline from becoming
part of the antenna and so it can reduce the noise.

A lot of local noise is predominantly vertically polarized. So if you
have a horizontal antenna without a balun, the feedline, which often is
vertical, can pick up a lot more noise than the antenna. Again, a balun
prevents feedline pickup and can make things quieter.

If you're feeding the antenna with coaxial cable, put the balun at the
feedpoint. If feeding with twinlead, put it where the feedline connects
to the tuner or receiver.

To learn more about baluns, see
http://eznec.com/Amateur/Articles/Baluns.htm.

Roy Lewallen, W7EL

Bill Ogden wrote:
A discussion on the towers reflector mentioned, in passing, that a
current
balun helped lower received noise. The discussion was about something
else
and this aspect was not explored.

Is this common? I had never heard of it before, but I many holes in my
understanding of antennas. Under what circumstances would this apply?
Where
would the balun (toroids) be placed? Feed point or at bottom of tower?
(My
particular interest is for use with a half sloper and for 160/80/40
meters.)

Bill
W2WO

Roy Lewallen wrote:
. . .
To learn more about baluns, see
http://eznec.com/Amateur/Articles/Baluns.htm.

Correction -- that should be

http://eznec.com/Amateur/Articles/Baluns.pdf.

I apologize for the error.

Roy Lewallen, W7EL

In addition to Roy's article,
http://eznec.com/Amateur/Articles/Baluns.pdf

you should probably read:
http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf
= http://tinyurl.com/qnzs3

and also an excellent paper by K9YC:
http://audiosystemsgroup.com/RFI-Ham.pdf

The W1HIS article is written from your viewpoint, as it begins: "Your
ability to hear weak MF and HF signals is limited by noise, generated
mostly by solid-state electronic switches within your own house,
conducted via the 60-Hz power line to your shack, and from there to your
antenna by common-mode current on the feedline. Putting common-mode
chokes on your feedline, power, and other cables will substantially
reduce your received noise level."

However, W1HIS did get rather carried away with the project, and ended
up with ferrite everywhere! For the rest of us, the best advice is:
"When the problem goes away, then stop buying ferrite."



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote in
:

....
you should probably read:
http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf
= http://tinyurl.com/qnzs3
....
However, W1HIS did get rather carried away with the project, and ended
up with ferrite everywhere! For the rest of us, the best advice is:
"When the problem goes away, then stop buying ferrite."

I saw that some time ago and did wonder if he held shares in one or more
magnetics companies!

Perhaps the need for gross suppression points to a fundamental design
issue, perhaps even an OHS issue.

But, it is a good article, it shows a range of techniques for applying
ferrites for suppression.

On a lighter note, I had a job with a telecommunications carrier some
years ago, their scope included operating a national GSM mobile network.
On my first day on the job, I received an email from one of the phone
reps offering a fold up lead and aluminium radiation shield with a
central hole about the size on an ear, which one unfolded and placed
against the head over the ear before applying the mobile phone to the
ear. I said to the guy alongside "have you checked this email, it is
pretty liberal of the company to allow customer reps to be creating FUD
(fear, uncertainty and doubt) about the safety of mobile phones". He got
on the phone and advised that they guy had already been sacked, he had
violated a condition of his employment that he not represent competitive
products, mustn't have taken 10 minutes. What do they teach business
graduates at university these days?

Owen

Thank you, Roy and others.

My background noise on 80 and 160 seems high, but it does not sound like
man-made noise (as best I can judge by ear). The antenna in question is a
half sloper. I will try some clamp-on cores the next time I crank it down.
(I just cranked it up yesterday, so my timing is bad.) The coax runs down
outside of the tower (with the standard UST standoff cable guides). Using
the half sloper, the tower itself (and the outside of the coax, and all the
other cables coming down from the tower) are part of the antenna, of course.
Perhaps the ferrite cores will reduce some of the noise pickup.)

I realize that not everyone likes half slopers. I do not have any other tall
supports other than my 55-foot tower. I have a terminated inverted V near
the top (and a Steppir on top). The half sloper is attached at about 40'
(top of second section of the crankup). I have a good number of radials.
The SWR wanders around across 80 meters, but is below 3:1 everywhere. It
seems to transmit well, but seems too noisy on reception.

The "terminated dipole" has a resistor to ground at each end. (It is from
TenTec. Moderately low SWR from 160 to 20 meters; not great; probably not
worth the cost.)

Bill
W2WO