wb2vvv antenna blog: Recent Comments

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Comment on This is the REAL wb2vvv web site!

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Chris — Mon, 10 Aug 2009 02:25:55 GMT

Scott,

The two diamond loops on the corner exterior walls could be fed as a fat dipole (e.g., Bowtie Dipole) with both loops closed and your SGC tuner at the junction, or alternatively as a double loop which is in effect a Folded Dipole - by using the tuner and a short jumper wire between the two loops. In either case the antenna will be non-resonant at your desired frequency of operation and will not have a predictable radiation pattern. It could well be modeled with software at various frequencies to determine the specific radiation pattern at each frequency of operation. The pattern will actually differ at different frequencies.

I have a fair amount of experience with horizontal dipoles bent from 180 degrees to 90 degrees in the horizontal plane. I call these "Vee Dipoles" and they are roughly omni-directional. There are relatively small gain peaks and nulls in different azimuthal directions, and again this changes based on the frequency of operation.

When a Vee Dipole is operated at its resonant frequency there is approximately a 3 dB gain peak along the axis bisecting the two legs, but this is a relatively small perturbation to the azimuthal pattern which remains quite omni-directional overall. This is what I believe you are referring to as "inside the 90 degree angle", though most ham antenna articles will refer to utilizing a termination resistor with this configuration which converts the standing wave antenna I am referring to, to a traveling wave antenna and thus both very different, and have a different radiation pattern.

By proximity to the physical location of the wires/elements, the field strength of the radiated signal will be strongest outside the apartment building with the antenna wire(s) on the exterior walls. Conversely, the field strength inside will be weakest inside with this configuration. The proximity effect is inverse square law, and will typically overwhelm the antenna "pattern" as respects induced EMI, etc.

Unfortunately, I don't believe the radiation pattern of your current non-resonant multi-band antenna is predictable by any generalization. This again is something that computer modeling will help you understand.

73, Chris

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Scott — Fri, 07 Aug 2009 00:54:36 GMT

I am interested in your opposing diamond/loop idea and yes I am in the corner apt. In which direction would be the maximum radiation? If it were inside the 90 degree angle that would concentrate the rf towards myself and my equipment.

I am currently running it more as an inverted L with an inverted L as the counterpoise at 90 degrees. I was always under the impression that inverted L antennas were vertically polarized with the RF Maximum off out the end, is that true?

It's kind of nice having the antenna indoors, I can tinker as I like when ever I want. During the 2008 CQWW 160 CW contest I rearranged the whole thing at 11:00 at night, try doing that on a tower in the dark hi hi.

73's
Scott, K2ZS

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Chris — Thu, 06 Aug 2009 14:55:01 GMT

Scott,

I took a look at your current configuration and congratulate you on finding a way to get QRV in a tough situation. You also did a really nice job with the on-line drawings.

On to some antenna thoughts:

I have used horizontal quad loop antennas before and they work pretty well out in the open, even at low heights, for multiple bands. Yes, for lower frequencies than the loop will naturally resonate it is helpful to short both ends of the loop together and feed it as an electrically short top loaded (Capacitive hat) vertical against a counterpoise. But, this is all in my outdoor experience. As respects indoors, your apartment is connected to the other unit(s) alongside it, and is therfore reliant upon their space for RF propagation - which is two ways and can give you and them both some undesired noise/RFI. This is because in the horizontal plane your wire is essentially as much in their space as yours (the other side of their wall).

I think you might be better served trying a loop in the vertical plane on one exterior wall only - possiby 2 or 3 turns on that wall. This way a least half your RF reception is directly out of the apartment (and directed as far as practical from your neighbor).

If your apartment is on a corner, with two exterior walls, you might consider installing a shorted/closed diamond loop on each of the two exterior walls (point of each diamond in the middle of each wall, ceiling and floor boundary). Then put your SGC coupler between the two diamond points at the corner where the two closed diamond loops come together, and feed them as a fat broadband dipole.
As an alterrnative you could try feeding this as a double loop of sorts from this same spot, by breaking and joining the two loops together with a short jumper and the tuner.

My thoughts here are about refining your current success by trying to get even more RF out/in...

73, Chris

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Scott — Thu, 06 Aug 2009 03:30:08 GMT

I have details of my existing indoor antenna at my website. I have a visio floor plan showing how it's installed and slides to detail the installation. I find that now with the elevating A index I am having less success. It seems last year the A was hovering between 1 and 2. Now with it going up I can't hear as well.

I am considering dropping the counterpoise to floor level and running it more as an inverted L. My URL is:

http://www.k2zs.com