[hvalentim]

Still progressing on my Lego for the parts I am now looking at the antenna portion.

I read somewhere that straight whip type designs are the best but I also came across other less conventional models. Particularly the three types below.

Does anyone have experience with them? Any thoughts as to which might be the most efficient?

433MHZ High Gain Antenna SMA Within Needle Rubber Glue Stick 6DBI

In favour: Claims a 6DBI gain. Affords some flexibility in orientation.
Doubts: it's not gold plated. 6BDI claim is perhaps mambo jambo.


SMA Male Plug Head Crimp 3DbI GSM GPRS 433MHz Antenna Cable 1.5M Magnetic Base


Since the signal will come mostly from above it's perhaps a good compromise between a whip type and a rolled wire model?
Doubts: comes with a 1,5 meter cable. Can the receiver handle this? The magnetic base is perhaps not a good idea for home use.


433Mhz 2dbi SMA male plug connector with horn patch antenna


Again, since the signal will come from the roof, this could make sense for the RX part?

[meteoestarreja]

Hi there,
to be honest, I believe none of them had the gain they claim.
The first one that claim to have 6 dbi, looks like an ordinary wifi antenna (in wifi that really should be an 6 dbi antenna) ... and for 6 dbi for 433 Mhz, it just seems too shortest.
Anyway, unless you have a big distance between both equipments, probably any of them will work, although the first one seems nicer to be seen (I think).
From those, the only one that should be more precise on gain description probably it's the latest one. 2 dbi should be more or less 0 db (dipole) and that's what that antenna looks like, a dipole ...

[meteoestarreja]

Hello again,
I think that I could give a better answer, so, I will try to add some info based on what I already experienced.

The first antenna in my opinion will do the job if the TX is not that far away form the RX and at the same time, probably will fit better side by side with some kind of "box" that you my have with your station.

I have one antenna (and the magnetic base also) like the second one but I use it for another purpose.
That antenna although have a little (if any at all) gain, do have enough bandwidth for getting 433Mhz acceptably. The cable length, won't be such a problem unless you have severe radio interference around.

The latest one, I never tested that model although already tested the "model". It will perform better - in my opinion - when mounted in vertical position, not on horizontal like the photo may suggest.

Anyway, the actual results, it will depend every time by your own conditions, like interference that you may have, location, distance, etc etc ...
The ideal would be test it all, but obviously, you won't be interested on that
Hope that this post will help you somehow ...

[werk_ag]

MeteoEstarreja is our expert in radio matters, so the only thing I can add is my practical experience with some type of antennas.



I never tested it. I have similar models, with metal SMA connector, and it's my prefered antenna for TX units. Also works very well for RX



I don't know why, but this kind of antenna seems to not perform well for transmitter. Works fairly well for receiving.
There are other type, without the coil in the middle, that its very good for receiving (even with a 3m cable), but also not perform well for TX.


I never tested one of those.

There are also this type:



I'm using a lot of them on my WD units, and one in my second TX unit. They perform well for TX and RX. Inside, they just have a small coil.

and these... they are cheap, and perhaps they work well, but I don't know. Someday I will order some units for test.

[meteoestarreja]

I'm sorry if what I'm gonna write will be boring, I'll just try to explain the bigger picture behind antennas:

No matter of what kind is the antenna, the coil it's there basically to increase inductance.
One of the "effects" is getting lower ressonant frequency. As in this case, size matters (the right size), as lower the frequency is, the bigger must be the antenna.
So if we want a smaller antenna, we know that the frequency that it will produces best results will be higher (the smaller the antenna, the bigger "it's frequency") and that's where inductance enters, by adding a coil increasing the inductance, the ressonant frequency will be lower, so, arranging the right inductance with the right size, it will be possible to have a smaller antenna for a lower frequency.
Without the coil and with the same antenna length, the frequency would be bigger.
That's why, those "coil antennas" like Werk_AG posted, will be smaller than others and at the same time, will work "well" on desired frequency (antenna's gain it's another question).
I guess I could roughly say something like, the bigger the coil, the smaller the antenna would be.
If you ever picked inside a regular radio receiver with AM, probably you noticed a big coil with hundred of turns ... that's precisely the AM antenna, it would be impossible to have an antenna with the needed lenght, not inside your home at least.

Werk_AG said that he tested some antennas that performed well in RX but not in TX, that could happen for many reasons like harmonics, bandwidth, etc
Imagine an antenna with large bandwidth (enough for receiving 433 signals), with no gain - that probably would not matter because the TX almost for sure is near. That would work for RX but when you try to TX, the result it's not the same. Probably the antenna will not resonate as it should on 433 or can even not resonate at all, that would be catastrophic and that's why it won't be good for TX and also because in the other side (on RX) you probably won't have a "super" antenna to compensate the problem you have on TX side.

If you are gonna have long distance from TX and RX, you can also think about a directional antenna, that would extend the range.


A good calculated antenna no matter its "style", will do a great job even with longer cable attached to it - the cable it's also important, but I guess it's better to stop with this because in a while, no one will be reading this post this far

ps. Sorry for the "off-topic lecture", I hope that no one has fallen asleep reading this ...

[werk_ag]

You are not "off-topic", and to me, you can go on!
As you know, having a good and strong radio link is one of my main requirements for the WeatherDuino Pro2 system, but using simple and cheap radio modules as the ones we use. I believe that the antennas play an important role to get this goal.

[hvalentim]

Thanks a lot for your comments as they did draw my attention to a number of things. Getting to have a notion of the different matters at stake such as in meteoestarreja's "lecture" is part of the fun.

Actually I am pretty sure any of the models will work. Because I will have the receiver perhaps 5 meters underneath the transmitter, close to a window. But of course the big advantaged of doing things by yourself is that you can always try to insure it will be done right and you will get the best possible results out of every penny spent. Who knows, perhaps tomorrow I decide I want to place a second TX 20 meters away with a bunch of walls in between.

All considered, right now, performance wise, I am inclined to think that the most secure value may very well come from picking a portable hamradio antenna.

Something like this:


RH701 SMA-M SMA-F BNC VHF/UHF Dual Band Radio Antenna 144MHz/430MHz

Perhaps a clone of the Diamond original?
"RH701: 144/430MHz(2m/70cm)
Length:21cm / Weight:30g
Max.power rating:10W FM / Impedance:50ohms
Type:1/4wave(144/430MHz),120/150/300/450/800/900MHz for receiving only"

I am just wondering if it will perform well with the comparatively low transmission power of the Superheterodyne 3400 RF Transmitter - 25mW (315MHz at 12V).

Also assuming that it can easily get to work 3MHZ above (RX/TX), with the 433Mhz.

Do you see any caveats?

[meteoestarreja]

Well, at 5 meters you almost don't need an antenna (just kidding)
If you are going to choose an ham antenna, you could try to find a mono band antenna just for uhf, you will get a shorter antenna (since vhf being a lower frequency, needs a bigger antenna - like I said in last post). It's only about the size of it, being a dual band there is no problem.
What you said about working 3Mhz above, that's not a problem, the referenced frequency it's just a reference of the band, in amateur bands, you don't "work" on a single frequency, when 430Mhz it's referenced, it means that the antenna will work at least from 430 to 440 Mhz, having the best results somewhere around the middle and getting increasingly worse as you getting out from that "point".
That antenna looks like a clone of Diamond and I guess that it won't have any gain, but yes, it should perform ok.
You should also pay attention to antenna's connector, avoid different connector because as more adapters you use, the higher is gonna be the loss, and like you said, with 25 mw, you don't want to lose that much.

Also in the pcb, Werk_AG didn't have a long path between TX module and antenna's connector and that's good, the pcb "route" being an ordinary electrical conductor and not being shielded, the pcb itself in that small path became an antenna, the shortest, the better

[hvalentim]

(...) you could try to find a mono band antenna just for uhf, you will get a shorter antenna
(...) in amateur bands when 430Mhz it's referenced, it means that the antenna will work at least from 430 to 440 Mhz
(...) pay attention to antenna's connector, avoid different connector because as more adapters you use, the higher is gonna be the loss...

Thanks for the tips. I am now trying to figure in more detail how "gain" works with antennas.

[meteoestarreja]

Basically, gain is how much an antenna can transform RF into electrical signal.
The higher the value, the best.
Imagine that a receiver is only capable of receiving signals better than -50 dBm and the signal to receive isn't that "good", putting an antenna with a better gain, could make the difference and kind of "amplifying the signal" making it enable to be heard.

The receivers that we use in the weather station (superheterodyne), claims to have a sensitivity of -105 dBm, if this value is accurate, you won't need a very complicated antenna in the major of installations because the distance/obstacles probably won't be that much, although, UHF communications (433Mhz belongs to UHF), is made in line of sight basis.

(...) you could try to find a mono band antenna just for uhf, you will get a shorter antenna
(...) in amateur bands when 430Mhz it's referenced, it means that the antenna will work at least from 430 to 440 Mhz
(...) pay attention to antenna's connector, avoid different connector because as more adapters you use, the higher is gonna be the loss...

Thanks for the tips. I am now trying to figure in more detail how "gain" works with antennas.