[Lowfer] Active Whips

[Douglas D. Williams]

Tom and John make very good points. Battery power is an excellent method of
eliminating common mode currents.

There are a few reasons I have not implemented it here at my receive
station.

(1) I build my own desktop computers and build them with gaming in mind.
They tend to draw a good bit of current, making battery powered LF
receiving (i.e. any receiving that requires computers, which means
almost everything I do) problematic. My wife uses our only laptop.

(2) My receive equipment requires various voltages, including 13.8 volts
DC, 24 volts DC, and 24 volts AC. Again, problematic using battery power.

(3) With the above in mind, I have spent a significant (to me) amount of
money installing common mode chokes. All those $$ would be wasted if I
switched to DC power.

(4) I do most of my LF receiving "in absentia". If I had to actually be
present at the controls of my station during "prime time" I would find
another hobby. Up at 5 AM, in bed at 9 PM. Strange brew for one with my
schedule.

So, for me, DC power is not an attractive option.

As for JD's situation, he makes a good point. JD is actually using
a 40 foot long "active whip" to receive. I am using an 8 foot long "active
whip". When you get down to wavelengths that span 2000 meters, what's the
difference? Answer: pretty much no difference. They are both "e-probe" (I
know JD hates that term) antennas.

So, why are "active whips" good VLF/LF receive antennas, as opposed to
hundreds, or thousands of feet of wire?

In a very QRM quiet environment, the "tuned long wire" has the advantage,
IMO. In other than "QRM free" environments, your hundreds of feet of wire
are just going to pick up a lot of noise. A small "active whip" antenna,
well placed away from local QRM, will pick up much less noise. How many of
us have that "QRM quiet" environment"? Not many, is my guess.

So, you have to ask yourself, how much time, effort, and money are you
going to put into VLF/LF? According to Mike Mideke, it's the "world's
dumbest hobby", and he is probably correct.

73, Doug KB4OER





























On Wed, Jan 23, 2013 at 3:30 PM, JD <listread at lwca.org> wrote:

> I'm glad you mentioned the separate battery power approach, Tom.  I thought
> I might be something of a wacko loner in using that method myself, since
> one
> never seems to see mention of it anywhere...but it is definitely the more
> effective way at the lowest frequencies of keeping out noise and reducing
> signal loss.
>
> Someone taking a casual look at my antenna setup (a 40 ft vertical mast
> feeding a buffer amp at ground level) might not think of it as an active
> whip, but electrically it's no different from an active whip atop a pole
> reaching the same height.  The main differences are logistical: I don't
> have
> to lower it if I want to replace something or recharge the battery, and I
> have 30-some fewer feet of coax to worry about.
>
> With no coupler network at the amplifier end, the only potentially lossy
> element would be a ground isolation transformer at the receiver end.  But
> since I've gone mostly battery powered and almost never operate the radio
> from AC mains these days, I let the antenna ground be the radio's RF ground
> as well and don't bother with any isolation.  Despite the antenna sitting
> in
> a 60 Hz electric field that reaches 5 V/m on a bad day, there's no sign of
> common mode conduction from anything except sometimes the computer, which
> is
> also battery powered and usually easy enough to fix.
>
> John
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