2.4GHz RF - Unexpected result!

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These little modules, with antenna etched onto the board

get nearly twice the range of these modules with the short rubber type antenna!

When used with the same, crude, hardware.

Perhaps the black antennae are expecting to be mounted in a metal box with a ground plane?

What do you experts think?

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Are you sure those antennas are 2.4 GHz? They look like 900 MHz band antennas.

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Twice poor is technically semipoor :)
What is the actual range?

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They're the ones that came with the modules. That would explain the discrepancy!

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A loop antenna is not (very) dependent on having a good ground plane. A 1/4 wave 'stub' stub, on the other hand, is very dependent on having a proper ground plane.

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I see. As I thought.

Outdoors:
The stub antenna goes almost 100 ft at 0db and 2Mb/s. The PC board antenna goes almost 200ft with the same parameters.

Indoors:
With the other on the work bench, the sub antenna works a little ways outside my apartment door. The pc antenna works outside the apartment, down the stairs, outside the building and quite a ways down the drive.

Perhaps then, if I wish to use the stub antenna, I should figure on a metal hand held box, not a plastic one. I planned to have the stub poking out the end of a serpac 1500 plastic box with my tft display looking out a hole and the works inside.

If I switched to 1Mb/s, I understand the range would be farther. Given the application, half fast would be more than fast enough.

So the square base on the gold connector should seat against the inside of the grounded conductor?

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Bet the "rubber duckies" (the official technical name for those things) are less directional. That is, you could have the far one 100' away, and rotate the near one with very little change in sensitivity.

The PCB antennas are probably more directional, though odds are pretty good that they have made some effort to reduce that. Put the transmitter 100' away, and rotate the receiver, and see how the sensitivity changes.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Interesting info - I just got a couple of those PCB-antenna boards, and a couple of another design of PCB-antenna (ebay is so fun/dangerous). Looking forward to playing with them. Your range figures are pretty impressive.

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Although the rubber duckies have a certain length they probably are not 1/4th but shorter, with compensating caps/inductors inside.

What Happens if you mount 4 pieces of coper wire from the ground connections of the SMA connector outward at 90 degrees? does the performance increase? If yes then they do need a groundplane,

edit:

ow and where did you buy these? Want to do some playing with wireless connection and these seem nice and small modules that even have a nice range.

Last Edited: Fri. Apr 26, 2013 - 06:07 AM
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Those antennas usually have a real 1/4 wave piece of wire wound in a spring.

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At 2.4G, A quarter wave is just over 3cm.

What little I know about RF is beginning to sneak back into memory.

Perhaps putting a wire to ground would make it a dipole?

Where to get them? Goodness! Go to ebay.com and type NRF24L01!

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Tom ... and others. If I remember correctly, Nordic recommend the NRF24L01+ version instead. Yep. Just found this. http://www.hstnet.com.tw/new/200...

And here is an ebay pair.

http://www.ebay.com.au/itm/NRF24...

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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Yes. You won't find any that aren't the + version.

I find they cost twice as much if they're labeled "For Arduino."

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Torby wrote...

Quote:
Perhaps putting a wire to ground would make it a dipole?

Not unless it is a proper ground plane.

Recall that a 1/4 wave antenna is simply half of a dipole (1/2 wave). The 'stub' forms the 'real' part of the dipole, while the 'imaginary' part of the dipole is provided by the ground plane.

In theory, the ground plane should be perpendicular to the stub at the feed point, and extend 1/4 wave all around ( a 1/4 wave conductive disc ).

It is generally accepted though that this should really be 3/8 wave or larger, the larger the better.

The use of 'radials' was mentioned by @meslomp. This implements a 'virtual' ground plane, allowing the creation of the 'virtual' dipole. While not as effective as a 'solid' ground plane, electrically it is a very effective strategy, and is easy to implement, although the optimum angle of the radials is usually 45 degrees, which depends on the radial length.

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So here are internals of one of the antennas.

This one has central wire straight and shield (ground) is wound around it.

This is different from what I've seen before, where it was just a central wire wound and ground was not connected anywhere.

This one is 2.4 GHz for sure and size is very typical.

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I've disassembled another type of antenna and here is how it looks inside. I'd like to hear some theory on how they really supposed to work.

Attachment(s): 

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Well, Wiki Rubber Duckie Antenna is a good starting point.

JC

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Is that a tophat antenna... folded? Or some sort of cavity resonator? (I have been away from antenna theory too long)

Ross McKenzie ValuSoft Melbourne Australia

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Bet those rubber duckies are colinears. They are very easy to make for frequencies above 1GHz but not TOO high. Uses several sections of 1/4 wavelength coax. You find them on many WiFi routers,

If not colinear, then simply odd number of 1/4 wavelengths. Done right, they are also usable on 5.6GHz.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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I haven't taken one apart. It's about 5cm long, unless, of course, it's the little thing shown above and the rest if just plastic.

Since I'm considering a handheld remote, along these lines:

A 3/8 wave circle would be only a little less practical than a 4 wire virtual ground plane.

With the TFT display, the little PCB antenna would be right behind the metal back of the display. That probably wouldn't work very well, so I thought of using the external antenna to get it out from behind the display. Maybe I could get a long enough box that the RF module sits by itself "above" the display.

I was wondering if a wire to ground could provide the missing part of the dipole, perhaps like this, or perhaps on the PC board itself, which, unfortunately, would be behind the tft display.

Perhaps I should go to Mouser and look for a specific kind of antenna rather than the unknown thing the Chinese included? What are "Chip Antennas" and what are their characteristics?

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