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There is an iron chimney near my house that is not used anymore. It is ~15 meters in length and ~0.5 meter in diameter. How good will it be as an antenna for rtl-sdr?

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  • $\begingroup$ It doesn't matter what kind of receiver you have, and therefore I've edited your question. What range of frequencies does your RTL-SDR cover? $\endgroup$ – Mike Waters Mar 17 '18 at 19:34
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    $\begingroup$ Iron is a very bad conductor at any high frequency due to skin effect. This is why copper or aluminium are used. $\endgroup$ – Juancho Mar 17 '18 at 19:42
  • $\begingroup$ If it's safe to climb to the top, consider mounting an antenna there. $\endgroup$ – Mike Waters Mar 17 '18 at 20:27
  • $\begingroup$ @Juancho Yes, especially because of its paramagnetic losses. But it's likely better than a thin wire at HF. My guess is that it's VHF and above; and if that's the case, it will be worthless as an antenna. $\endgroup$ – Mike Waters Mar 17 '18 at 20:32
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Assuming that your RTL-SDR covers VHF and up, 15 meters is too tall. You would be better off using it as a support for a suitable antenna.

Iron has far more losses than copper, aluminum, or other non-magnetic materials. Having said that, on HF a 15 x .5 meter pipe should have considerably less loss than a thin 15 meter iron wire and could be used for receiving with just a ground rod at the base. However, for transmitting you will need to minimize the losses with a good RF ground at the base, the feedpoint (and not just a ground rod!) consisting of suitable radial wires, either elevated or laid on the surface of the ground.

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    $\begingroup$ for an HF receive-only application I doubt the radials are so critical or the iron losses especially consequential. $\endgroup$ – Phil Frost - W8II Mar 18 '18 at 12:46
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    $\begingroup$ @PhilFrost-W8II Thanks, answer edited. $\endgroup$ – Mike Waters Mar 18 '18 at 20:48
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It is a quarter-wave at 60 meters, 5 MHz. With the large diameter, losses would be negligible despite the poor conductivity and magnetic losses in iron. This would be a good transmit antenna if you can find a way to feed current into it with low losses. I think that would be possible with an appropriate set of ground plane wires and maybe a better metal (aluminium foil) on the lowest couple of meters so you could couple by use of fairly short high Q couplers.

For receive with an rtl-sdr, just use it to support something for the frequency of interest. For HF, a thin wire from the top, for vhf a 15 m high tower to mount antennas on is excellent:-)

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Not so much! Iron is a poor conductor of RF and will likely result in spurious transmissions.

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  • $\begingroup$ You are correct that iron is a poor conductor. But how can a poor conductor (compared to copper) cause spurious emissions? $\endgroup$ – Mike Waters Sep 3 '18 at 19:21

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