Dissecting a WIFI rubber ducky antenna - Page 1
Forum section: electronics / general

author: soldar
author_rank: Super Contributor
timestamp: October 14, 2019, 03:40:33 pm
content: I have a WIFI antenna which has a longish cable with no connector at the end. I was looking for a standard antenna connector, of the screw in type, whatever they are called, but could not find one so I decided to take the connector from an antenna. I opened the antenna to see how it was built and it is just a tiny dipole fed at the center. From tip to tip of the dipole is about 51 mm which is a bit shorter than a direct calculation from the speed of light would suggest. Probably the speed of the signal in the antenna is about 15% slower than in vacuum.I was surprised to see how extremely simple and inexpensive it is.Now I will cut the cable and splice it to the other antenna.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 14, 2019, 05:10:21 pm
content: Interesting, I never guessed that is was constructed that way. I dissected a few rubber ducky scanner antenna's and they are mostly constructed as a spiral. Also very convenient that the plug comes with the coax already connected

author: soldar
author_rank: Super Contributor
timestamp: October 14, 2019, 07:30:53 pm
content: I think it has to do with wavelength/frequency and the spiral ones are for lower frequencies which would be too long if straight.I remember in my CB days building whip antennas with a coil in the center to make it electrically longer.I did put the connector on the other antenna with a longer cable but tests have been disappointing and the short antenna plugged directly into the device gives much better reception than the bigger antenna with cable. I guess there is too much loss in the cable or the splice I did presents some impedance mismatch. Oh well.

author: ajb
author_rank: Super Contributor
timestamp: October 14, 2019, 07:39:52 pm
content: I'm profoundly disappointed by the lack of actual yellow rubber ducks with antennas in this thread.

author: soldar
author_rank: Super Contributor
timestamp: October 14, 2019, 08:01:39 pm
content: Quote from: ajb on October 14, 2019, 07:39:52 pmAfter what happened to the NBA we don't want to get on the bad side of uncle Xi.

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 14, 2019, 10:01:35 pm
content: Quote from: ajb on October 14, 2019, 07:39:52 pmI'm dissapointed by the lack of phishing and malicious access devices.

author: ajb
author_rank: Super Contributor
timestamp: October 15, 2019, 05:17:07 am
content: I guess if you want something done.... I was fresh out of regular yellow ducks, so this green dragon one will have to suffice for now.

author: Berni
author_rank: Super Contributor
timestamp: October 15, 2019, 05:36:52 am
content: Splicing coax cable with good return loss is pretty difficult.As for the antenna not quite being the textbook calculation length, that's quite common in real antenna designs. The metal ground cylinder serving as the other pole has some effect on it all. But also just putting the antenna into its plastic case (non air dielectric) has the effect of detuning it. They also might want to tune it slightly high so that when people put objects close to the antenna it tunes it down towards where it should be rather than away.You can just strip the end of any coax with the right length and makes a decent omnidirectional antenna. It's a lot easier to do if you have a way of measuring the antennas return loss at the designed frequency like s SwR meter, antenna tuner, network analyzer etc... so that you can take some wirecutters and trimm the end to be perfectly tuned. But that's quite difficult at 2.4GHz since the gear for that tends to be rather pricy. Guessing it trough calculation gets pretty close tho

author: OwO
author_rank: Super Contributor
timestamp: October 15, 2019, 06:17:31 am
content: That plastic outer jacket is very lossy. It only took about 20W @ 2.4GHz to burn a hole in it.

author: tautech
author_rank: Super Contributor
timestamp: October 15, 2019, 07:58:27 am
content: I much prefer this type of dissection

author: Whales
author_rank: Super Contributor
timestamp: October 15, 2019, 08:31:00 am
content: 2.4GHz (and above) do not need very long antennas, so they have no need to spiral them to fit in a small space.I am not even sure if you can call these rubber duckies - Ithink"rubber duckies" refers specifically to the spiralled and flexible (springy) variety, but I might be wrong. I would just calls these whips.Soldar: I had a hard time stripping the coax from one of these and connecting it to things, make sure to be gentle and have some spares.EDIT:QuoteActually I might argue this is a monopole (whip) and not a dipole, as it's unbalanced fed. Ie little/no current should be in the shield. The folded metal sheath is more of a not-enough-space-so-lets-just-fold-it groundplane design. It's pretending to be flat