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Objective

Our gate opener remote receiver works much better with the antenna horizontal than vertical? By much better, I mean 300' vs 100'. Why?

Background

The distance the remote will operate the gate appears to be independent of time of day, and/or weather conditions.

The antenna is directly connected to the receiver which connects to the gate controller with a 3-wire cable. As best as I can determine the receiver sends remote codes to the controller on one of the 3-wire cable conductors, the other two are for power and common.

Frequency is ~320MHz, and the antenna is ~9” long.

The antenna originally was near vertical, but it sagged under gravity to a more horizontal orientation. I know the antenna will continue to sag and I'm thinking distance will suffer as it becomes more vertical.

I could straighten the antenna to vertical and the range would suffer, I 'know' it is antenna orientation but can't explain it to myself.

Imagery

receiver with antenna horizontal

~8' pipe showing receiver at top

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  • \$\begingroup\$ Normaly a quarter lambda is positioned in vertical position and grounded. If you have a balanced dipole antenna then IMO polarization has no such importance (best if remote and antenna have the same). More likely it has some cable issue, when you move it touches ground. \$\endgroup\$ – Marko Buršič Dec 7 '15 at 20:59
  • \$\begingroup\$ This looks like a simple case of vertical vs horizontal polarisation. Or am I missing something? \$\endgroup\$ – Chu Dec 8 '15 at 0:06
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I'm not an antenna design expert, or an RF guru, but I did quite a bit of work with RF telemetry installations in hospitals using a similar RF band. I also worked with MRI RF systems, head/body coils, etc. Many factors can effect the loading of your antenna system, other conductors, metal fencing, etc. and something like that is probably happening here. If you have a spectrum analyzer you can tune your circuit to optimize the impedance, but I'm guessing that this type of equipment is way overkill for your application. Did you run A/B repeatibility tests to verify something else didn't change? You could probably have one person got to the edge of the remote range, and another person at the antenna, then communicating on your cell phone tune the antenna position for the best possible range. Then definitely fix it so that gravity, wind, etc is not changing the position of your antenna. Good luck.

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Not enough information/measurements (obviously), but here's a shot at it...

Loading & Reference Plane(s)

In your photo is seems that there is nothing below the aerial (antenna wire) at the top of the mast. In the vertical position the field lines must terminate on the surface of the Earth below or (more likely) on the grounded metal nearby.

The greater-than-expected distance makes the antenna have (in general) lower radiation resistance and appear electrically shorter than designed. This would result in a worse "match" to the transmission system, lower radiation efficiency, and shorter range. This "detuning" has a very non-linear effect so could explain the observed behavior.

In the horizontal orientation the antenna is right angle to the grounded metal frame of the solar panel and riser pole, which might provide a closer proximity reference better in line with the design equations' assumptions of an aerial orthogonal to a reference plane.

You could fix it

This is what a pole-topping 1/4 wavelength monopole antenna should look like. Note the three lower extensions that are connected to ground to provide the reference plane.

enter image description here

Also consider transmitter orientation

You should also check that your transmitter is aligned to the orientation of your gate's receiving antenna. If, for example, the transmitter is clipped to the visor in your car, you may not realize that you have horizontally polarized your transmission. Just something else to check.

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Here's how I see it: -

enter image description here

320 MHz has a wavelength of 93.75 cm and a quarter wavelength of 23.4 cm (9.22 inches in old money). This makes it a quarter wave monopole and these sorts of antennas like to see a ground plane at their base.

As far as I can tell there's another 9 inches to the large metal tube and this length of cable is also resonant at 320 MHz. This means all sensible bets are off but here's some speculation: -

Basically it's a bad implementation. If you lowered to box that the antenna connects to to the top of the large metal tube and poked the antenna back up to the sky it would probably work better than ever.

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  • \$\begingroup\$ IF that is a steel pipe, and quarter lambda antenna it is good thing to have near such big mass, it makes a good virtual ground. \$\endgroup\$ – Marko Buršič Dec 7 '15 at 21:04
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    \$\begingroup\$ @MarkoBuršič Not when there is a gap of another quarter of a wavelength - didn't you understand what I wrote? \$\endgroup\$ – Andy aka Dec 7 '15 at 21:07

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