2.4GHz antenna placement on a metal case

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MaxZ
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Location: Boskoop, Netherlands

2.4GHz antenna placement on a metal case

Post by MaxZ »

As I reported in this topic viewtopic.php?f=25&t=1168&start=10 , I am in the proces of converting a WebraPicco to 2.4GHz. The case is entirely metal, an aluminium casting and aluminium sheet backplate.
The antenna of the internal Frsky DHT module could be placed in the same position as the original 27MHz antenna, as Frank (tiptipflyer) has done, properly insulated, but the owner has expressed a wish to keep the original antenna as a dummy, and place the 2.4 antenna somewhere on the backplate.
I did warn him that the antenna should be kept as far as possible from the case to avoid any interference or shielding of the signal.

However, on reflection I wonder if it makes much difference if I did mount it on the backplate. In that case I would choose the left-upper most corner, as seen from the front. I usually swing my antennae on my own transmitters to the left, to an almost horizontal position, as I learnt that this is the most effective attitude to ensure the donut-shaped signal strength shape is strongest in the direction of your (flying) model.
I cannot see any shielding happening this way, but I am not sure about the proximity of the metal case.

Does anyone have any experience with this?

Cheers,
Max.
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PaulJ
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Re: 2.4GHz antenna placement on a metal case

Post by PaulJ »

Max, this would be an ideal candidate for hiding the 2.4GHz antenna in a dummy frequency pennant.......

You either find a natural way through or drill a small hole for the antenna co-ax and make your own dipole antenna, which is a bit of a fiddle but not difficult......
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The antenna itself is made from the co-ax connector cable. The actual lengths of the "whisker" and the tube are fairly critical to get it to resonate at exactly 2.4GHz. Following help and advice from Martin, I invested in a Vector Impedance Analyser which enables you to "tune" an antenna to some extent but using it, I have found that very few of the commercially supplied antennas are well matched anyway! You don't really need the VIA, if you make both whisker and tube 28mm long you shouldn't be too far out. though before using any homemade antenna you should extensively range check it just to make sure it is up to the job.

Paul
MaxZ
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Re: 2.4GHz antenna placement on a metal case

Post by MaxZ »

Thanks Paul. I see that Phil has also reposted an old post on the same subject, coincidence or he has read this topic as well :) But the dimensions in that post are different from yours. Besides, the coax on the DHT is only 1 mm total diameter, inner and outer conductors/insulation. Much too small for my skills I am afraid, and not stiff enough to prevent flapping in the breeze. I have not peeled the wrap from the DHT, so I don't know what connects the antenna wire to it, but if it is a standard connector maybe I could buy a thicker coax antenna wire/connector?

Cheers,
Max.

Edit: assuming the module has an ipex connector, would something like this do for a Tx as well?
Edit2: it helps to include the link.........https://www.aliexpress.com/item/2014011 ... lsrc=aw.ds
Last edited by MaxZ on 09 Jan 2021, 17:45, edited 3 times in total.
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tiptipflyer
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Re: 2.4GHz antenna placement on a metal case

Post by tiptipflyer »

Hi Max,
I am using similar antennas to those in your request, intended for Rx in some of my converted transmitters (Metz 3channel, Engel Handy).
The Metz antenna is located within the plastic case, the Engel Handy antenna is sticking out.
They do quite well both. I did not have any issues until now.
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Frank
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Wayne_H
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Re: 2.4GHz antenna placement on a metal case

Post by Wayne_H »

Max, I have also done the "hidden in the flag" & internal versions as the other guys have suggested. I have used both commercial antenna - Banggood link - & homemade versions.

After range checking, all have performed well. The previous FrSky modules, including DHT, use an ipex connector, but I've not used or seen the XHT "in the flesh" so can't comment on it.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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PaulJ
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Re: 2.4GHz antenna placement on a metal case

Post by PaulJ »

Phil_G wrote: 09 Jan 2021, 17:07 Hi Max, I saw your query so I found the old thread from reunited and bumped it in case it helped.
Re the measurements, if you have a vswr device like Pauls you can optimise it but its really not that critical, Paul starts long and trims them down, so maybe we end up with similar results anyway :D Paul is your man though, he's done more of these than anybody ;)
I haven't tried it but I suspect that the "internal antenna" wouldn't work inside the Pico's metal casing.

Max, I am not familiar with the Frsky module but I have made antennas from both the thin RG178 and the thicker coax connecter that is sometimes supplied with Orange modules and both thicknesses have performed well. When I started making these things I used the lengths suggested by Phil but since I aquired the VIA and was able to measure the performance I have fiddled with the length and ended up with 28mm. Start with it a bit longer and trim it down if the range isn't good enough.

I think the antennas in the link you supplied would work very well.

Paul
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ozrs
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Re: 2.4GHz antenna placement on a metal case

Post by ozrs »

You could also just cut the plastic off the antenna provided with the DIY module, leaving you with an antenna with the SMA connector, to save any soldering.
Richard
MaxZ
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Re: 2.4GHz antenna placement on a metal case

Post by MaxZ »

Thanks for the comments guys.
Wayne_H wrote: 09 Jan 2021, 23:50 The previous FrSky modules, including DHT, use an ipex connector......
That's good to know Wayne, I will be using the DHT and I was just about to cut the wrap open to see how the antenna connects. I will order the antenna I did link to right away.
ozrs wrote: 10 Jan 2021, 10:18You could also just cut the plastic off the antenna provided with the DIY module, leaving you with an antenna with the SMA connector, to save any soldering.
Yeah, I thought about that but the antenna will still be in close proximity to the metal box. Besides, the idea is to make it as inauspicious as possible, and the SMA connector would be very visible....

Cheers,
Max.
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