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I am using two 443 MHz transceivers (FY-605 transceiver) with both having different antenna lengths. One antenna is around 12cm long and the other antenna is around 17cm long. Will this cause problems? And does it affect the range or doesn't it work at all? Also the ±12cm antenna is connected to the transceiver with a coax cable. As far as I know this doesn't cause harm. Can anyone confirm this for me?

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  • \$\begingroup\$ Have you tested this? You are going to get better answers doing tests. \$\endgroup\$ – Andy aka Oct 8 '14 at 14:04
  • \$\begingroup\$ Well I haven't tested it, it is a project someone else worked on. He said that it all worked but the range was very disappointing. after like 200m the signal was bad. The transceivers should easily handle 500m, and I read some reviews that they got a lot further then just 500m. Also i only have those two antenna's so i can test the difference between 2 antenna's of the same vs the current setup \$\endgroup\$ – T J Oct 8 '14 at 14:11
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    \$\begingroup\$ There are a whole bunch of things that could cause this lower range. One that springs out is the coax - type and length could be critical at 434MHz \$\endgroup\$ – Andy aka Oct 8 '14 at 14:25
  • \$\begingroup\$ Ok thanks, I will try to move the parts in the unit so I can remove the coax cable and move the transceiver closer to the side of the unit so the antenna can be connected with no cables needed \$\endgroup\$ – T J Oct 8 '14 at 16:59
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As Andvaka said, there are many things that could be affecting range. For this to be properly answered, more information should be given. Without this information, I am assuming you are using two quarter-wave monopole antennas. Any change in length from the ideal quarter-wavelength length will, most likely, degrade the performance of the antenna. In order to properly design these antennas, a network analyzer would be needed to tune the antenna for the given environment (most things within the near-field range of the antenna will affect its resonance frequency). Without this equipment, I would design their lengths to be a quarter-wavelength in length. Also, since this type of antenna works with a single-ended signal, you need to ensure that you are actually feeding the antenna with a single-ended signal and not a differential signal. In addition to all this, make sure that the antenna are oriented so that there is no cross-polarization mismatch. This essentially means that both antennas should be oriented in the same fashion, i.e., both vertical. I hope this helps...

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  • \$\begingroup\$ I will try to get some more information about the antenna's tomorrow. I didn't bought the antenna's myself, someone who was working on this project before bought them. Just one more question, the length of the antenna should be measured from the 'screw' till the end of the antenna or the point where you can orientate it horizontally or vertically? \$\endgroup\$ – T J Oct 8 '14 at 17:02
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    \$\begingroup\$ Ok, I just looked up the manual for the transceiver. I thought you were trying to built your own antennas. I understand now that this is not the case. Measure from the pivot point to the end, its not exact but you can determine from that whether it is roughly a quarter-wavelength. The antennas proposed in the user manual are called quarter-wavelength monopole antennas; this is most likely what you have. With that being said, some antennas have what are called loading coils built into them, if this is the case, the antenna will measure short of the quarter wavelength. \$\endgroup\$ – Awm0121 Oct 8 '14 at 17:33
  • \$\begingroup\$ Does a lading coil give the antenna more gain? The person who worked on this before said that one of the antenna's had more gain then the other but he didn't say which one it was. And what happens if one antenna is with a loading coil and one without? \$\endgroup\$ – T J Oct 8 '14 at 17:41
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    \$\begingroup\$ A loading coil would not necessary give an antenna more gain as compared to an isotropic antenna; it simply allows for a shorter antenna to still be efficient at radiating energy. \$\endgroup\$ – Awm0121 Oct 8 '14 at 19:21
  • \$\begingroup\$ is there a way to see if the antenna is a monopole antenna? I'm not that experienced with antenna's. \$\endgroup\$ – T J Oct 9 '14 at 7:14

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