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Re: [TowerTalk] 43ft Vertical Feeding Question and Balun type

Subject: Re: [TowerTalk] 43ft Vertical Feeding Question and Balun type
From: "Dan Zimmerman N3OX" <>
Date: Fri, 21 Nov 2008 00:42:17 -0500
List-post: <">>
AB7R writes:

His tuner allowed him to tune on all bands...except maybe 160.

A lot of tuners allow you to tune *the lack of antenna* or a *short circuit*
up on many bands, too.  Doesn't mean a tuner with no antenna radiates much
power ;-)

> I know many people say it would be no different than just running a 43ft
> vertical
> wire and employ it in the same fashion....which I suspect is true.  But not
> everyone has supports available to install a 43ft vertical wire.  This is
> where
> this stout vertical really comes into play I think.

But why not *ANY* self-supporting vertical?  Plenty of antennas fit that

 Some will be better and some will be worse than an unloaded 43 foot
vertical with even a good balun.  I've heard Tom from Zero-Five say that
they've put the Zero-Five + balun+good coax up head to head in field
strength tests against some other antennas and the ZF won.  I don't doubt
that either, but I do the overall efficiency of any vertical antenna system,
especially one that has no loading or matching devices on its own, is
determined largely by the installation and the way you interface it with the
coax, and if you don't understand the details of the antenna, there's a good
healthy dose of dumb luck.

You decide to scrimp and save for the impressive stick of aluminum that is a
Zero-Five, for example, but then you pick a cheapo $12.95 4:1 voltage balun
from N3OX's Balum Balporium and Wheel Balancing SuperBal Shop, wound on a
Genuine Rusty Nail with patented Some Ol' Wire I Found,  and you use that
same old ratty RG-58 that you bought on the day your college age kid was
born, and your results might be a bit different.  And even if you go for the
"tuner balun" and expensive coax, there are some serious installation issues
that can crop up (see much further below).

Everyone gets to make their own choice on what does the radiating at their
station.  If you like a particular stick of aluminum a whole lot, by all
means, buy that thing and use it with pride.  But don't attribute too much
radiating efficiency to the stick itself.  It's a single element vertical
antenna.  At absolute best it can hope to be a dB or two louder than a
decent trap vertical or quarter wave, all other things being equal.

K2XT writes:

I know there is a guy in Chicago on 20 meters running one of them with no
> radials
> who comes into NJ 20 over 9 at times and claims no knowledge as to how he
> does it.

I know there's a guy on 20m running 100W into a dipole out on Hawaii who
comes in audibly but doesn't move my meter.

I know there's a dozen guys in Texas who come in about 35dB over S9 on my
meter in the afternoons on 20m.    If I remember my S-meter calibration
right ,it's something like 1dB for S0 to S1 and S1 to S2, climbing up toward
the oft-quoted but usually wrong 6dB per S-unit around 7,8 and 9, and pretty
dead on 10dB per 10dB above that.

So that guy who's 35dB over 9 is coming in hear about 70dB stronger than the
suffering KH6.

Well, OK, he's super loud, maybe he's got a huge huge monobander on a giant
tower.  Let's be generous and give him 20dBd antenna gain.  He's still got
to pick up 50dB somewhere.  So he's just got to run an amplifier to the tune
of... uh... lessee... what's 50dB over 100W?

Just a mere QRPer at 10 million watts output.  Uhoh, did he just say he was
running a DIPOLE?  Well... I... uh.

Guess he's pushing a gigawatt!  ;-)  Everyone gets 59+20dB reports
sometimes.  I called D4C in a SSB contest running 100W to my Moxon at 30
feet and got an unsolicited comment, from a real contester in a real DX
country in the middle of a real DX contest, on how loud I was.   These
things happen when you run a halfway decent antenna on a day with good

>Wouldn't it be
>interesting to compare his signal in real time with his neighbor running a
beam, or
>a quarter wave vertical.

That's the only reasonable test.  I get stations in here from Colorado
nearly pinning my S-meter at 59+40dB by running 1500W to a decent beam,
maybe 12dBi at the right time of day.   The guy coming in 59+20dB from the
same town running 1500W into his vertical is likely to be using a NEGATIVE
8dBi antenna ;-)

A 43 foot vertical fed against a ground rod   and using an ideal 4:1 unun
transformer and tuner in the shack on 20m is going to be better than that by
a good margin.  Maybe -3dBi  with good coax?, and much of that is loss
attributable to the lack of radials.  Look, the 43 foot vertical holds up
pretty well on the higher bands (40 and up) if you use low loss coax and the
right transformer type stoutly built.  It does so despite all the
hand-wringing and gnashing of teeth by those of us who hate to see even a
single dB of extra mismatched line loss.  You see 1dB or 2dB or 3dB loss in
the feedline,and 3dB never even put a little tiny dent in the 59+20dB report
of a W9 booming into W2 land.  It honestly in almost all situations will
turn into a really terrible antenna on 80m and 160m if you don't take some
drastic action though.

Sometimes the loss is really,  totally negligible.  The guy who was having
such an apparent problem with his 43 footer in that eHam thread that's been
mentioned *should have had* an antenna almost identical or slightly better
in performance to a full size quarter wave 40m vertical.... he had a 60 foot
run of decent coax, and as long as there wasn't much balun loss and as long
as it did a nearly 4:1 impedance transformation, he would have been just
fine with the tuner in the shack.  0.5dB extra loss or something.

But there was a particular nasty trick that a 4:1 voltage balun (what he
had) plays when feeding a heavily unbalanced antenna.  If you apply a
voltage balun such that it tries to drive an equal voltage on the ground
radial system and on the radiating element with respect to the coax
connection, what happens?

Let's say the feedpoint voltage will go up to 360V (about what you get on
40m with this antenna, 364V @ 59 degrees according to eznec) Let's take a
snapshot right when the feedpoint voltage is at a maximum, and the radiator
is more positive than the radials.  The earth goes down  to -180V, the
radiating element goes up to 180V, and the coax shield stays right there at
zero.  Wait, did I say the earth goes DOWN  to a voltage -180?  Well, yeah,
you can pick your reference whereever you want with voltages, but let's be
more conventional and call the earth 0V.

Now the radiating element is at 360V and the end of the coax shield is at...
huh... that's funny, 180V above ground potential.

You have 180V of RF trying to drive current on the coax shield.

Oops.  The problem this causes is ENTIRELY dependent on the common mode
impedance of the rest of the coax  shield circuit to earth.  I think in the
particular case we were looking at on eHam, on the 40m band with the
particular setup this ham had, the common mode circuit was nearly as bad as
it could possibly be for the transformer he had installed.

I learned a lot from the eHam thread.  I'll post it again.  There's a quick
potential improvement for many users of a popular combination there:

But in the end, if you buy a stick of aluminum from ANY company, you have to
remember it's NOT the stick that's doing the hard job. It's made of
aluminum, it knows how to radiate.  The hard job is how you feed it power
efficiently.  43 feet is really a fine choice for an 80m up to perhaps 17m
vertical if you feed power to it right, and on 15m and up if you feed power
to it efficiently, you probably won't mind the high angle issue because
those bands are so quiet you only need flea power to work the world.

But if you *don't* feed power to it efficiently, it can be a real dog, and
even springing for expensive coax and an expensive transformer won't
necessarily feed power to it efficiently, especially if the wrong type of
4:1 transformer is used and the installation becomes dependent on all kinds
of weird external factors you didn't anticipate, like how you did up your
lightning grounds and what the impedance of your house wiring is with
respect to earth on 7MHz.


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