Original antenna of RFXtrx433 actually quite small

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Bernd
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Original antenna of RFXtrx433 actually quite small

Post by Bernd » Thursday 04 June 2015 8:48

I opened the antenna which come with the RFXtrx433: HAVE A LAUGH, THEN CRY :(
http://i.imgur.com/3wlgTQy.jpg

This is really a cheap China antenna, fooling the users.

Most of the antenna is empty!
A very short coil only.

Using such a coil is only necessary when there is no space, but in the case of the RFXtrx433 there is enough space around. So why spending money on empty plastic?

For good coverage you need a 1/4 lambda antenna, or a 5/8 lambda. To keep the length reasonable a coil is used to shorten the length, but the coil is just a small part of the total antenna.
This China-antenna does not fulfil the performance criteria we as users can expect.

Just using a copper wire of 16.8 cm works much better than this China crap!

PE1AYV
Last edited by Bernd on Thursday 04 June 2015 14:30, edited 1 time in total.
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Re: Original Antenna of RFXtrx433

Post by ThinkPad » Thursday 04 June 2015 8:55

Interesting, but i never had any issues regarding the range. So i wouldn't judge RFXCOM too quickly. Maybe there is a good reason behind this choice.
Did you ever open a 2,4Ghz WiFi antenna? They are also a lot smaller than the plastic tube around them lets you think. But ofcourse 2,4Ghz is a higher frequency which automatically means a smaller antenna can be used. For 433Mhz you often see a coil type antenna is used instead of a straight wire, so i guess there has to be a reason for it.

What lambda would this one correspond to? I think if you would stretch the coil, the wire will also be around 16,8cm?
That would also be an easy fix then. Just remove the plastic antenna shell and straigthen out the wire and cut off a piece when it is longer than 16,8cm.

Did you replace it for an other one?
I think i will order a RP-SMA connector from eBay and solder a 16,8cm wire to it. Is that easy to do? Not familiar with those connectors.

I also posted a link to this topic here: http://domoticz.com/forum/viewtopic.php?f=44&t=3542
The guy behind the RFXCOM ('b_weijenberg') is also active there, so maybe he responds. I am interested in his reaction. Maybe even he didn't know this :lol:

P.S. For future reference i uploaded a copy of your image here: http://i.imgur.com/3wlgTQy.jpg
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Re: Original antenna of RFXtrx433 actually quite small

Post by b_weijenberg » Thursday 04 June 2015 13:12

This antenna is tuned to 433.92MHz and the coil is wounded a special way for this.
The choice for this antenna is based is also based on a mix of aesthetic and performance.

Note that the RFXtrx433 is CE certified with the supplied antenna.
An alternative is:
http://www.ebay.com/itm/433Mhz-5DBI-GSM ... 2eccdec506
Also available in NL:
http://www.onlinekabelshop.nl/DLCK-8887 ... DLCK-88877

PA3DEG
RFXtrx433, RFXtrx433E

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Re: Original antenna of RFXtrx433 actually quite small

Post by Bernd » Thursday 04 June 2015 14:29

Hi,

I am not judging RFCOM, I am pointing a finger to the designer of this antenna. I assume RFCOM just bought it from a supplier and is most likely manufactured in China.
As a certified radio amateur I know about antennas a lot, especially for 2 meter (144 MHz) and 70 cm (433 MHz) band.
This plastic device is full with ...... air. For aesthetic reasons??? Just some cm longer and you could have a proper working 1/4 lambda antenna. Also very nice to look at ;)
>>> Always have performance above aesthetic ! <<<

The RFCOM product (without the antenna) is working great: nothing than a big hand to Mr Weijenberg. It is the range of the product as a whole which does not suit my home/garden: but with a simple wire it does.

Fulfilling the official requirements regarding output power is of no concern to me: it is the reception sensitivity which laks and for that no requirements do exist: you are allowed to make the most sensitive receiver ever without violating the law. With a better antenna for reception I automatically have a better range for the transmitted commands, but that wasn't the reason to look for a better antenna.

Thanks for replying!
Bernd
PS: The picture size was too big to upload and I don't know how to decrease the file size....
Last edited by Bernd on Thursday 04 June 2015 14:34, edited 2 times in total.
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Re: Original antenna of RFXtrx433 actually quite small

Post by Bernd » Thursday 04 June 2015 14:32

I tried that one already, but no improvements (too long cable with too much loss??).
73
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Re: Original Antenna of RFXtrx433

Post by Bernd » Thursday 04 June 2015 14:40

ThinkPad wrote:What lambda would this one correspond to? I think if you would stretch the coil, the wire will also be around 16,8cm?
That would also be an easy fix then. Just remove the plastic antenna shell and straigthen out the wire and cut off a piece when it is longer than 16,8cm.
I stretched the wire and came to 30 cm. Unfortunately it broke close to the SMA-connector. I now soldered a copper wire of about 16.8 cm and wow, what a step in performance :) .

ThinkPad wrote: I think i will order a RP-SMA connector from eBay and solder a 16,8cm wire to it. Is that easy to do? Not familiar with those connectors.
Soldering a wire on the SMA-connector from the original antenna is easy.
When buying a spare SMA connector it is more complex as the center pin is not fixed inside the connector. You have to glue it in a way.
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Re: Original antenna of RFXtrx433 actually quite small

Post by Ron » Wednesday 10 June 2015 22:23

Interesting.
At what point from the sma connector does the16,8 cm length begin?
As i have a few wifi router aerials i will spoil some of them to make a version like yours.

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Re: Original antenna of RFXtrx433 actually quite small

Post by EA1UR » Wednesday 10 June 2015 22:49

Thanks. I never think you can find something like that ¡¡¡¡ EA1UR
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Re: Original antenna of RFXtrx433 actually quite small

Post by ThinkPad » Thursday 11 June 2015 10:21

Ron wrote:Interesting.
At what point from the sma connector does the16,8 cm length begin?
As i have a few wifi router aerials i will spoil some of them to make a version like yours.
That won't work i think.

First, the connector has probably the wrong polarity
Second, a wifi antenna has a quite short wire inside
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Re: Original antenna of RFXtrx433 actually quite small

Post by Ron » Thursday 11 June 2015 12:44

I wil only use the connector of the wifi antenna, en not the antenna itself.
It doesn't matter if the wire inside is very short, i am an expert in soldering and this should not be a problem for me.

The connector ofcourse has to be the same, i assumed this is the case.

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Re: Original antenna of RFXtrx433 actually quite small

Post by ThinkPad » Thursday 11 June 2015 13:24

Ah ok.

I'm not sure, but i thought the polarity of the RFXCOM antenna is the opposite (male/female) of the antenna from a wifi device.

RP-SMA vs SMA connector.
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Re: Original antenna of RFXtrx433 actually quite small

Post by Ron » Friday 12 June 2015 23:15

You're right, there is a male/female issue with these two antennas :-)
I didn't notice it before

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Re: Original antenna of RFXtrx433 actually quite small

Post by ThinkPad » Sunday 28 June 2015 11:12

Does anyone have a eBay link or so where i can order the correct antenna connector? Want to make a new antenna myself, by using the right connector + 17cm of 'VD-draad / installatiedraad'
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Re: Original antenna of RFXtrx433 actually quite small

Post by rtna » Sunday 28 June 2015 11:54

Search on E-Bay or AliExpress for SMA male connector.

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Re: Original antenna of RFXtrx433 actually quite small

Post by ThinkPad » Sunday 28 June 2015 18:26

Bernd mentioned:
When buying a spare SMA connector it is more complex as the center pin is not fixed inside the connector. You have to glue it in a way.
So i looked for a male SMA connector with a wire already attached, and found this: http://www.ebay.com/itm/FOR-PCI-ROUTER- ... 27f20fe79d

Could that work? I plan on carefully stripping it and soldering a 17cm piece of copper wire to the wire/pin that becomes visible after cutting the heatshrink.

Or what about buying this one: http://www.ebay.com/itm/NEW-Extension-c ... 20f381ec4e cutting it to 17cm wirelength and then removing the outer mesh? (so only the inner wire is left)


Edit: Ordered them both, for those cheap prices it is worth trying :)
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Re: Original antenna of RFXtrx433 actually quite small

Post by Raspberry Piet » Sunday 28 June 2015 21:03

@Thinkpad:
Better buy a complete antenna, just pull the plastic off, desolder the coil and solder your VD-draad to the SMA connector.
I just did this yesterday. The SMA connector of the antenna has a little "window" where the tip of your soldering iron can desolder/solder a wire easily.

Result:
Image

I think it is this antenna:
http://www.aliexpress.com/item/Momentee ... 27737.html

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Re: Original antenna of RFXtrx433 actually quite small

Post by ThinkPad » Sunday 28 June 2015 21:05

Damnit, your message came just 1 minute too late. I just edited my previous post because i bought those two cables.
Well, will buy that antenna also then :D

Edit: Bought this one: http://www.ebay.com/itm/281126334307 as i still had my eBay logged in. Will report my findings when the stuff has arrived.
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Re: Original antenna of RFXtrx433 actually quite small

Post by ThinkPad » Sunday 12 July 2015 0:40

Received the antenna i mentioned a few days ago. I could easy pull the plastic off. Inside was a almost equal coil to the one in the picture of your original RFXCOM antenna.

I tried to stretch the coil (so i could cut it at 17cm), but it snapped :? So like you said, i unsoldered it and grabbed a single wire from a networkcable. Cut it to 17cm and soldered it to the connector. RFXCOM still works fine. I don't see any signal improvement, but my house is quite small (56m2) so i didn't have any problems earlier on with the original antenna.

But it is good to know, easy fix if you do encounter problems with reception/transmission. For sensors it is also a easy mod: https://www.brunier.nl/?p=622 (not my website).
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Re: Original antenna of RFXtrx433 actually quite small

Post by ed0 » Monday 20 July 2015 23:40

I had low signal from my DS90 sensors, thus missing most of the events. I bought this antenna a few days ago and it's working quite good:

http://www.ebay.com/itm/433Mhz-High-Gai ... 20fcbf226f

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Re: Original antenna of RFXtrx433 actually quite small

Post by Derik » Tuesday 21 July 2015 8:14

Xu4: Beta Extreme antenna RFXcomE,WU Fi Ping ip P1 Gen5 PVOutput Harmony HUE SolarmanPv OTG Winddelen Alive ESP Buienradar MySensors WOL Winddelen counting RPi: Beta SMAspot RFlinkTest Domoticz ...Different backups

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