09-03-2015, 23:51
(This post was last modified: 09-03-2015, 23:53 by meteoestarreja.)
Hello uncle_bob,
First of all, never trust a multimeter for test an antenna.
Not for looking for a short at least ... The thing is, even if you encounter a short-circuit between the inner conductor and the shield, that does not mean that the antenna is rubbish ... in some cases, it could mean the opposite.
I have several antennas that have that behaviour and electrically speaking, in fact they are in short using a coil (the coil is not in plain sight) ... RF speaking, that coil isn't a short and do his job perfectly. I'm remembering one example and the antenna could work with hundreds more power that those tx module that we use in our weather station.
Now, looking at your problem, it looks like the same problem that I spoke today in another topic.
It seems that you have an antenna for working somewhere else than 433Mhz ... Chinese people sometimes does not put the right description in the right article.
The receiver that we use, do have a good sensitivity with good noise rejection and even with a poor antenna, they do a pretty nice job. I was able to run several tests and the receiver performed very well - thanks for the previous research Werk_AG, you saved me a few bucks in orders for testing RX modules
For TX modules in another hand, the thing is completly diferent, you need a good antenna or at least, an antenna calculated well for the frequency you want. If you use no antenna or an antenna that is not resonant for the frequency that you will broadcast, the result is poor or no signal at all.
So, in this case I belive that's precisely the problem, I think that the description is wrong because that don't seem to be an 433 antenna, or at least, it's behaviour it's not suggesting that.
Did you tested to take the antenna apart? Sometimes in that kind of antennas, it's relatively simple to take the black plastic and watch inside without break anything.
I have plans for building an antenna analyser using an arduino (not a nano, but a more musculated "cousin"), maybe then I will accept all those antennas from ebay for testing and tell you for which frequency are they designed to
First of all, never trust a multimeter for test an antenna.
Not for looking for a short at least ... The thing is, even if you encounter a short-circuit between the inner conductor and the shield, that does not mean that the antenna is rubbish ... in some cases, it could mean the opposite.
I have several antennas that have that behaviour and electrically speaking, in fact they are in short using a coil (the coil is not in plain sight) ... RF speaking, that coil isn't a short and do his job perfectly. I'm remembering one example and the antenna could work with hundreds more power that those tx module that we use in our weather station.
Now, looking at your problem, it looks like the same problem that I spoke today in another topic.
It seems that you have an antenna for working somewhere else than 433Mhz ... Chinese people sometimes does not put the right description in the right article.
The receiver that we use, do have a good sensitivity with good noise rejection and even with a poor antenna, they do a pretty nice job. I was able to run several tests and the receiver performed very well - thanks for the previous research Werk_AG, you saved me a few bucks in orders for testing RX modules
For TX modules in another hand, the thing is completly diferent, you need a good antenna or at least, an antenna calculated well for the frequency you want. If you use no antenna or an antenna that is not resonant for the frequency that you will broadcast, the result is poor or no signal at all.
So, in this case I belive that's precisely the problem, I think that the description is wrong because that don't seem to be an 433 antenna, or at least, it's behaviour it's not suggesting that.
Did you tested to take the antenna apart? Sometimes in that kind of antennas, it's relatively simple to take the black plastic and watch inside without break anything.
I have plans for building an antenna analyser using an arduino (not a nano, but a more musculated "cousin"), maybe then I will accept all those antennas from ebay for testing and tell you for which frequency are they designed to
(09-03-2015, 22:29)uncle_bob Wrote:(20-02-2015, 11:33)meteoestarreja Wrote: If you want to do that and need some help, just talk to me. I can help you and/or give you an emulator for analysis
Hi meteoestarreja,
Interestingly on a new TX unit I've just built, if I attach a "rubber ducky" type antenna the signal stops being received (at a distance off less than a metre). Here's the actual ebay item http://www.ebay.com.au/itm/281126334076
Its like if there's a dead short across it, yet a test with a multimeter shows it's an open circuit between the antennas' nut and conductor.
It seems to work ok on a receiver though.
Any ideas?