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Looking for suggestions for a portable antenna for use with a SDRPlay RSP1A. I notice that most other SDRs come with a few antennas, but not the RSP1A. I have a 2m/70cm HT, so I own a Nagoya NA-771R whip and a mobile-mount 2m antenna. I also have a J-pole, but that’s not traveling with me. So, I’m looking for a portable antenna that I can take to the cabin this summer.

I’m interested in the lower frequencies, so I was thinking about a loop, dipole, or long wire. I’ll have no mast, but lots of nearby trees. Does anyone make a dipole that can be hoisted over a branch — but collapsible for travel?

What are others using with their SDRPlay?

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Most users of SDR receivers use active antenna for the frequency range up to 50 MHz.

The choice for a loop antenna (magnetic field sensor) or a small telescope antenna (E-field sensor) depends mainly on the environment. Since you have plenty of room both options are good choice.

When the tree density is high may be the loop is a better choice. When there is interference generated by local electronics, also the loop is a better choice. The disadvantage of the loop is the directivity, specially for ground wave signals: there is a null in the directional sensitivity. This can also be an advantage.

Loop antennas for reception: tuned loop with high sensitivity can be small, circumference 1 meter is sufficient. Amplification is not necessary. Wideband loop needs no tuning but for good sensitivity the circumference must be 2 or 3 meters and a special amplifier is a must.

Do not forget that the coaxial cable between the antenna and the SDR is a conductor that brings, via the screen, interference from computer and power supply to the base of the antenna and that interference will influence the lowest level signals: the noise floor. Use common-mode means in the coax and ground the coax were it is connected to the antenna. Also a loop antenna will benefit from this interference-to-grond path (poor description, yes).

See also: Using an SDR on a Laptop with Noisy Power Supply

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  • $\begingroup$ How is the directivity of a small loop different from that of a short dipole or monopole? $\endgroup$
    – Phil Frost - W8II
    Commented Apr 30, 2021 at 19:03
  • $\begingroup$ (You shouldn't ask things you know better than I know). Vertical monopole to ground is omnidirectional. Horizontal dipole above ground is mainly sensitive for skywave reflected signals; directivity is better for higher frequencies since the arriving angle (signal above the horizon) is lower. Loop antenna has "figure-8" directivity. mwcircle.org/mw_antenna.htm The combination of E and H field gives cardioid pattern. $\endgroup$
    – user16925
    Commented Apr 30, 2021 at 21:33
  • $\begingroup$ I'd put it this way: a small dipole and a small loop have identical radiation patterns in free space (and thus, identical directivity), but complementary polarizations. Either can be omnidirectional or figure-8, depending on orientation. $\endgroup$
    – Phil Frost - W8II
    Commented May 3, 2021 at 14:34
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I have an RSP1a and an RSP2. For HF, I've used them with a long wire in a tree, and an isolated LOG (loop on ground).

The LOG works better for me, because for some reason it picks up less RF noise from the local environment and thus provides me with a slightly better S/N signal. The LOG is made from 40M of random scrap wire and a small ferrite toroid transformer.

The long wire in a tree works for VHF receive as well.

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