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Since my this particular question didn't get any answer, I thought of asking a more focused question, along a path which seems a bit more feasible after few tests.

Is it possible to install the antenna of the 433MHz ASK/OOK TX module, some distance away from the module itself ? All my present tests use the antenna wire directly attached to the module, and of course, they work fine. However, if I add a length of wire to increase the distance of antenna, the whole wire, I believe, would behave like an antenna - right ? And that would detune the antenna ? Any solutions to the problem where TX module and antenna need to be spaced out ?

Edit

Based on the comment (PeterJ's) and answer (pjc50's) so far, here's what I understood as the possible solution.

enter image description here

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  • \$\begingroup\$ What kind of antenna are you using? If it has a 50 ohm impedance the usual way would be to use coax. \$\endgroup\$ – PeterJ May 4 '13 at 8:04
  • \$\begingroup\$ @PeterJ, thanks for taking time to look at the question. The antenna, in my experiment has the absolute poor-man's solution, i.e. a quarter-wave monopole, i.e. about 16cm length of AWG26 straight wire. \$\endgroup\$ – bdutta74 May 4 '13 at 9:14
  • \$\begingroup\$ As per pjc50's answer and comment below 50 ohms is the impedance of the cable so you won't want the series resistor, but at the transmitter end you'll want to tie the shield of the coax to ground. \$\endgroup\$ – PeterJ May 4 '13 at 11:14
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As PeterJ says, the usual solution is coaxial cable. Because the wire down the centre is shielded by the outer braid (which should be connected to ground), it's not "visible" as an antenna and doesn't affect its effective length.

The 50 ohm controlled impedance avoids distortion of the signal down the length of the coax.

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  • \$\begingroup\$ Thanks @pjc50. I've updated the question, because I didn't know how to add an image/graphic to the comment. Could you please confirm (or correct) my understanding of the proposed solution ? As mentioned in the diagram and comment to PeterJ, it is a quarter-wave monopole antenna in question. \$\endgroup\$ – bdutta74 May 4 '13 at 9:26
  • \$\begingroup\$ 50 ohms in this case isn't a resistor, it's a measure of the cable at high frequency. \$\endgroup\$ – pjc50 May 4 '13 at 10:23
  • \$\begingroup\$ How does one ensure the cable has "controlled impedance" of 50 ohm at high frequency ? I have some spare coax cable used for video transmission. Can I use those ? In the diagram, if I just remove the explicit resistor (50Ohm), can I make the connections, the way shown ? \$\endgroup\$ – bdutta74 May 4 '13 at 13:23
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    \$\begingroup\$ @icarus74 the characteristic impedance of the coax will be in the datasheet. Usually there's something printed on the cable that you can put into Google. It likely starts with "RG-". Most video cable is \$75\Omega\$, which may be "close enough". You will get a higher SWR, which may or may not be acceptable to your TX module. \$\endgroup\$ – Phil Frost May 4 '13 at 13:49
  • \$\begingroup\$ Thanks @PhilFrost. Ordering (weightwise) heavy items from web-based international distributors is prohibitively expensive for me... more so for my project. To scrounge the local-market for something acceptable, what should I watchout for, say in terms of the cable-markings, that might suit my purpose better ? Is there something you could suggest ? \$\endgroup\$ – bdutta74 May 4 '13 at 14:23

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