OK, this sounds quite rationale and compelling. Will scrap the full size loop
antenna.
Any other creative suggestions on how to make the most of the tower for the
lower bands? I don't plan on using it on 160m as the idea is to build 4SQ for
160 as well.
I do believe that having antenna diversity is helpful and don't want to have
just the 4SQs.
Rudy N2WQ
From: David Gilbert <xdavid@cis-broadband.com>
To: Rudy Bakalov <r_bakalov@yahoo.com>
Cc: Tower Talk <towertalk@contesting.com>
Sent: Sunday, December 28, 2014 4:05 PM
Subject: Re: [TowerTalk] Low loop in a sloping configuration
Received signals don't just magically find their way to the feedline ... they
induce a current in the antenna that behaves virtually the same as transmitted
signals. Incremental field radiation and incremental field reception both
follow current distribution. Your proposed loop puts a greater percentage of
the current close to the ground ... thereby raising your takeoff and receive
angle because of ground reflectivity. It's not quite a cloud warmer, but it's
heading in that direction.
Think of it this way ... would you intentionally drop your Inverted-V from 90
feet to 45 feet? No, and the reason you don't is the same reason you don't
want to shift your current distribution closer to the ground.
With regards to your other comment, size generally doesn't increase
signal-to-noise ratio. It increases the strength of the captured signal
(usually), but it also increases the strength of the noise unless you get
significant directionality improvement out of the larger loop. Small loops can
be effective RX antennas mostly because they can have sharp directionality for
nulling unwanted noise/QRM.
But yes, large loops can be effective RX antennas if they point in the desired
direction. You proposed loop won't (in terms of takeoff angle), though, at
least not compared with your Inverted-V. At least half of the effective field
radiation/reception in your proposed loop is going to be at a lower height
above ground than the current in your Inverted-V ... probably more than half
since you're going to have to decrease the apex angle for your loop.
73,
Dave AB7E
On 12/28/2014 1:06 PM, Rudy Bakalov wrote:
So here's a bit more of my thinking: my main goal is improved RX performance
so does current distribution, presumably a TX consideration, really matter?
The loop is recognized as a low noise antenna so increasing its size should
only improve SNR. No?
Then the other comparison I draw is to small RX loops, which also are widely
acknowledged as effective RX antennas. So what if we make the small loop big.
Really big. Full wavelength big. Is it still effective as a RX antenna?
Rudy N2WQ
Sent using a tiny keyboard. Please excuse brevity, typos, or inappropriate
autocorrect.
On Dec 28, 2014, at 1:21 PM, David Gilbert <xdavid@cis-broadband.com> wrote:
In general, there is nothing beneficial about simply having more wire as long
as what you already have is electrically efficient. Yes, there are some
configurations where "more wire" can help ... a loop high enough off the ground
has a db or so gain over a dipole at the same average height, a curtain array
has gain, a dipole extended in length with capacitance has a bit of gain, etc
... but in your case your additional wire simply moves more of the current
distribution closer to ground, thereby raising your takeoff/receive angle. It
might be a bit quieter, but not necessarily in a good way ... in my opinion.
If you want to hear better toward Europe, maybe you could try running a rope
westward off your tower to an anchor point as far from the tower as you can get
it, and then hang a reflector wire off that rope about 100 feet away from the
tower. The reflector would be pretty close to the ground, but might ... might
... offer some benefit. Slight improvement in forward gain, modest
improvement in rearward rejection, possibly decent sideward rejection, very
slight lowering of takeoff angle. If probably would alter your current tuning,
but might be worth a try.
73,
Dave AB7E
On 12/28/2014 7:35 AM, Rudy Bakalov wrote:
I actually do have the exact same setup- an inv-V at roughly 90' with both
ends sloping a couple of hundred feet away from the tower. The apex is more
likely ~120 degrees than 90. It works really well (skimmer data shows actual
performance much better than theoretical), but I was wondering if I can improve
on it, particularly on receive where I feel I don't hear well enough. I guess
my question is "if a piece of wire of certain length works really well, what
happens if I double the length of the wire".
Rudy N2WQ
I'm curious what you desire to achieve from such an antenna. It's not
likely to be an improvement over what you already have.
A few years ago, before I was able to put up my current tower and yagis,
I suspended a 40m diamond-shaped loop from a 55 foot tall pole ...
sloped toward Europe from here in Arizona and fed at the bottom apex.
It worked OK, mostly because I live on a steep hillside facing Europe,
but in my opinion it didn't offer anything special other than it was
also possible to use it on other bands with a decent tuner. Keep in
mind that unless you feed it at one side for vertical polarization that
half your current distribution is going to be pretty close to the ground.
In my opinion, you'd be better off stringing an Inverted-V from the top
of your tower if you want something horizontally polarized to complement
your existing verticals.
73,
Dave AB7E
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