Making 5.8 GHz. Antenna

[bob195558]

Hi
Repairing broken antenna on a small camera with built in 5.8 GHz transmitter.

Camera

I solder a CONN UMC RCPT STR 50 OHM SMD antenna connector to the camera board.

SMD antenna connector

I have a FrSky receiver Whisker Antenna that is tuned to 2.4 GHz frequency and I want to change it to a 5.8 GHz frequency.

whisker antenna tuned to 2.4 GHz frequency

What do I need to do to change a FrSky Whisker Antenna from 2.4 GHz frequency to the 5.8 GHz frequency tuning ?

Bob B.

[KAL]

Hi Bob,

I'm not an expert but can it be you mixed some digits?

With 2,40GHz (start of band) I would expect l = λ/4 = 31,2 mm and
with 2,48GHz (end of band) I would expect l = λ/4 = 30,2 mm.
So the best length should be somewhere in-between (30,7 mm).

So for 5,8 GHz (which is mid of the frequency band) I would expect l = λ/4 = 12,9 mm.

( λ = c / f where c = 299 792 458 m/s (speed of light))

Klaus

[Daedalus66]

In fact, different 2.4 receivers use slightly different lengths between 31 and 33 mm. And if you measure various examples of a given receiver type you may find differences of 1mm or so.

Since it's better to be very slightly too long than too short, I should think 13mm would be good for 5.8 GHz.

[bob195558]

Hi Klaus,
Thank you for your reply.
The about 33.13 mm length is an eyeball measurement from the replacement FrSky Receiver Whisker Antenna tuned to the 2.4 GHz frequency.

Replacement FrSky Receiver Whisker Antenna

I am finding it difficult to find information about building this type of antenna.
This is like a whole new science to me and it has been very difficult acquiring a good understanding about this subject.

Bob B.

[bob195558]

Hi Daedalus66,
Thank you for your reply.
So maybe trim a little off the end or use it (FrSky Whisker Antenna) as is ?

Bob B.

[Kilrah]

Trim to the length he mentioned.

[KAL]

Hi bob,
it has be found that the best length for a rod antenna (mono pole) is 1/4 of the wave length called lambda (λ).
This wave length can be calculated as I wrote in my last post or e.g. here.

For 5,8 Ghz you should trim the end to a length of 13mm.
Using the whole length of 31mm is not "slightly too long" (as daedalus66 wrote) but faaaaaar too long.

Klaus

[bob195558]

OK, so I will trim the end of the antenna to 12.9 for 5.8 GHz.
I am weak in understanding the math, I will try to make better understanding.

Added note to how the math works-out: 300 divided the 5.8 GHz frequency = 51.7241
Then because the frequency it is a quarter wave length, this results is then divided by 4.
51.7241 divided by 4 = 12.9 mm.
The frequency of this TX5804 Camera is 5.865 GHz. (viewtopic.php?f=95&t=8580&p=112407#p112494).
300 / 5.865 = 51.1508 / 4 = 12.7877 mm long.
Which causes the antenna length to be worked-out to: 12.8 mm. long.

Bob B.

[Daedalus66]

For 5,8 Ghz you should trim the end to a length of 13mm.
Using the whole length of 31mm is not "slightly too long" (as daedalus66 wrote) but faaaaaar too long.

Klaus

If you re-read what I said you will see that I recommended 13mm for 5.8 GHz, which is indeed "slightly too long" compared to 12.9.

[bob195558]

Hi,
Photo showing where I trimmed the end of the FrSky Whisker Antenna changing it to a 5.8 GHz frequency antenna.

5.8 GHz Whisker Antenna

I am now looking for a way to test this new 5.8 GHz antenna.
I need to come up with a way connect it to the ImmersionRC RF Meter.

5.8 GHz Whisker Antenna with the CONN UMC RCPT STR 50 OHM SMD antenna connector

Bob B.

[bob195558]

I did some testing using this TX5805 camera with the Spectrum Analyzer: RF Explorer 6G combo.

Spectrum Analyzer: RF Explorer 6G combo

RF Explorer 6G combo

I soldered two CONN UMC RCPT STR 50 OHM SMD antenna connector together and was able to connect to the ImmersionRC RF Meter.

Using the new 5.8 GHz whisker antenna with this TX5805 Camera, the video is better compared to when using the 2.4 GHz FrSky whisker antenna.

TX5805 camera new 5.8 antenna.

Bob B.

[bob195558]

5.8 GHz Rubber-Ducky antenna

The normal 5.8 GHz antenna length is 12.9 mm.
Photo of this 5.8 GHz Rubber-Ducky antenna is shorter in length of about 11.03 mm, is this shorter length OK ?

Also there is metal tube soldered to the ground, what is this for or do ?

Bob B.

[KAL]

Slightly longer than 12.9mm should be better as daedalus66 wrote.
But Imho 2 mm difference are too much away from the aimed value (17%).
This may work, but I think the signal would be much better with correct length.

The piece of tube you can see as a kind of counterbalance for the antenna rod.

Klaus

[jhsa]

That piece of tube soldered to ground makes it a dipole antenna..

João

[bob195558]

Thank you Klaus and João for your replies.
The tube soldered to ground making it a dipole antenna is what I was supposing it was for.
But a kind of counterbalance for the antenna rod, I have a hard time understanding this ?
It is a lot more difficult to add more length to this type of antenna to make it 12.9 mm long.

I have two Rubber-Ducky 5.8 GHz antennas and the bottom one is a little longer.
This maybe bad manufacturing quality.

Two Rubber-Ducky 5.8 GHz antennas.

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Also I pulled apart a FrSky Rubber-Ducky 2dB Module Antenna (2.4 GHz), but it was very hard to pull the Rubber-Ducky part off
and did not realize was squeezing on the tube soldered to ground at the same time and pulled the antenna apart.
I then took more of it apart hoping to be able to repair it, but it looks to be more difficult then I think I can do.

2.4 GHz FrSky Rubber-Ducky 2dB Module Antenna.

They do not cost a lot, so I am ordering a new one as this is also a lot easier to do.

2.4 GHz antenna 25mm both ways.

Rubber Ducky FrSky 2.4 GHz 2dB Module Antenna

The math for 2.4 GHz: 300 / 2.4 = 125.0 / 4 = 31.25 mm. long.

Bob B.

[bob195558]

Here is another 5.8 GHz antenna.

5.8 GHz antenna that came with the RF Explorer 6G Combo handheld digital spectrum analyzer.

This has a metal tube on top and on the bottom.

Bob B.

[bob195558]

Here is a video about FPV / Antennas / Frequency and Frequency Signals: (https://www.youtube.com/watch?v=wUDZpSSRQ1E)
and (http://flitetest.com/articles/fpv-basics).
Cloverleaf Antenna: (https://www.youtube.com/watch?v=D3HW8n89rQQ).

Bob B.