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Author Topic: Groundplane - does size matter  (Read 11127 times)

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tarbat

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Groundplane - does size matter
« on: February 28, 2008, 11:58:25 AM »
Since getting my ANRB, I've been using the same groundplane as I used for my SBS-1, an old metal side panel from a PC, which measures approx. 40cm square.

Now the Radarbox comes with it's own groundplace, which is circular and 12cm diameter.

My question is, will the 12cm disc give better results than my 40cm square groundplane?

Allocator

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Re: Groundplane - does size matter
« Reply #1 on: February 28, 2008, 12:14:36 PM »
Since getting my ANRB, I've been using the same groundplane as I used for my SBS-1, an old metal side panel from a PC, which measures approx. 40cm square.

Now the Radarbox comes with it's own groundplace, which is circular and 12cm diameter.

My question is, will the 12cm disc give better results than my 40cm square groundplane?

If I remember correctly, the size of the groundplane required is proportional to the frequency being used.  ADS-B is UHF, so only a small ground is plane required.

I think that if the groundplane is too small, performance suffers, but if it's bigger than needed then there is no advantage.

tarbat

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Re: Groundplane - does size matter
« Reply #2 on: February 28, 2008, 10:25:34 PM »
Thanks Allocator.  I was just wondering whether the 12cm disc might be better "tuned" to 1090MHz, so might actually give better reception than a 40cm square one.  If I've done my sums correctly, 1090MHz has a wavelength of 27.5 cm, so I guess ideally the groundplane should be a multiple of that.

Anyway, I've got up in the loft today and switched over to the 12cm disc, reset my polar diagram, and I'll compare the results after a few days.  It' probably not important anyway.
« Last Edit: February 28, 2008, 10:34:00 PM by tarbat »

Dan

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Re: Groundplane - does size matter
« Reply #3 on: March 01, 2008, 07:16:15 PM »
Hi ,

I noticed a gain in distance of abt 20 to 30nm  when using a groundplane with a diameter of about 30 cm .
Regards .
Dan.





tarbat

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Re: Groundplane - does size matter
« Reply #4 on: March 02, 2008, 08:45:19 AM »
Thanks Dan.  Confirms my testing this week.  Reduced distance with the 12cm disc, which may or may not be caused by it, or by different reception conditions.

Anyway, think I'll take my 40cm square groundplane and cut it down to 30cm diameter and test that.

Found this on "another" forum:
Size - The diameter of the ground plane should be at least as large as the antenna height. More does not harm at all, but the increase in performance is hardly discernible.

Thickness - Thickness does not matter much. A tin foil would be sufficient, were it not for mechanical reasons better to use something from 0.5mm or thicker.

Conductivity - Conductivity does matter. Wood is useless, any metal will do. Differences in conductivity like between steel and copper are only discernible with very sensitive equipment. Go for steel, whether stainless or not.

Magnetic metal or not? - Since the base of the antenna is a magnet to be used on a steel car some people think that the magnetivity (sp?) of the metal does matter - it does not. So aluminium will do fine, as will brass or any other non magnetic metal.

Shape - Shape of the base plate does not matter, as long as it is at least one antenna height wide in any direction. A baking tray will do fine and is probably a very economic solution.
Even some horizontal wires or metallic tubes will do fine, it does not have to be solid. Install at least four, better six or more straight tubes, rods, threaded bolts or whatever at the base of the antenna. Distribute evenly.   A narrow grid mesh is also a viable solution.

Angle of ground plane vs. antenna - The angle between the groundplane and the antenna affects the impedance (simplified: HF resistance, matching) of the antenna. This antenna is designed for a 90° angle, so go for that.
« Last Edit: March 02, 2008, 08:57:06 AM by tarbat »

Dan

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Re: Groundplane - does size matter
« Reply #5 on: March 02, 2008, 05:30:46 PM »
I am glad you confirmed my findings . I am a retired communications engineer and have been dealing with different antenna configurations and installations  a lot . In fact the small antenna which came  with RadarBox is a vertical antenna feeded at his base .  Any vertical antenna needs a good "counterpoise" , in other words a good ground. In our case this is the small disk . By experience I know the better the " ground " the better the performance . So the groundplane can be too small in diameter but never too big . From a certain diameter there will be no more improvement. I am working from my appartment at the sixth floor and simply put the antenna on the backside of a cast iron cookpan with a dia of 30cm... I can track planes upto a range of 230 nm   If  I compare with the delivered disk I am noticing not only a gain of at least 30nm but also the number of targets  nearer from which the signal could be weaker due to obstructions improve. As you mentionned also wires or metallic tubes can be used . Many " groundplane " hamradio antennas use 3 wires 120 dgs apart under an angle of abt 30/45 dgs  to  match the 50 ohms impedance of the coaxial cable used and to improve the reception angle.
If you compare antennas its better to do it always under the same circumstances and time . Therefore , I think using the polar diagram over a longer period to compare two different antennas is tricky , especially when the difference is not so big . It is always possible that the less good antenna could have be tested during a period of time when the propagation conditions were better...Nevertheless the delivered antenna with his disk is doing a very good job and can be improved a  little by using a bigger groundplane ( disk ) .
Regards.
Dan.