[TenTec] Trading radios

[Rick - DJ0IP / NJ0IP]

Response to Mike:  Yes, I did misunderstand you.  Sorry, we were referring
to two different things.  I agree with you.

Response to Jim:  Having a balun at the feed point is never a bad thing from
an "electrical aspect".  There are other reasons.

If you are running low power and especially QRP, and especially on portable
operations where weight at the feedpoint of an ultra-light pole is a bad
thing, then the balun is an unnecessary thing and has been the cause of many
people breaking their fiberglass poles.  Again this assumes your coax is run
"equal distance from both legs of the antenna".
With QRP, it is hard to induce enough common mode current onto the coax to
even measure it.  I have tried and could not do it.  I was measuring with a
very sensitive RF-Ammeter.

If you are running very high power, then you absolutely should always use a
balun.  No question there.

BTW, others such as W7EL in his paper on "Baluns, what they do and how they
do it", agree with me on this point.

Response to Bob:  Note: This time (above) I said "equal distance", not right
angle.  Equal distance is the more correct term.  For a dipole, right angle
is equal distance.  For an inverted-v, running equal distance (for instance
straight down the pole) is still keeping the coax in balance in relation to
the two legs.  If the coax is hit stronger by the RF field from one leg than
from the other, then you get problems.  Therefore I don't see why an
inverted-V would be any different from a dipole - but I DO NOT KNOW.  One
way to find out.

I have never noticed that an inverted V has more common mode current
problems than a flat top dipole.  
This will be easy to check.  I have already measured the CMC on an inverted
V.  I'll put the same antenna back up, measure again, and then raise the
legs such that they are horizontal.  Will be interesting to see if there is
a measurable difference.  However it will be later this summer before I find
time to do so.  Other projects have priority.

The BIGGEST difference in CMC is caused when you begin to run the coax
diagonally - which in many cases is unavoidable.

For home use where I have stronger poles, I always use a balun with dipoles
or inverted V's.  
But for portable use at 100w or less, I have never used a balun.  Of course
when there are no consumer devices around, you might not notice anyway, even
if you did have a little CMC on the line.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Monday, June 02, 2014 4:08 AM
To: tentec at contesting.com
Subject: Re: [TenTec] Trading radios

On 6/1/2014 1:04 PM, Rick - DJ0IP / NJ0IP wrote:
> With a picture perfect antenna, dipole with coax running 90 degrees 
> from the radiator, placing a balun or choke (basically same - same) at 
> the feedpoint is a WASTE OF MONEY.

WRONG. A good choke at the feedpoint of a balanced, reasonably well matched
antenna is ALWAYS a good thing.

73, Jim K9YC


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