antenna-theory.com

[rons]

I am finalizing my configuration for an RFI tracker as I have a growing number of noise signals visible on HF. I plan to use an SDRPlay connected to a laptop or tablet (the SDRPlay is a better version of the $20 SDR dongle and includes an up-converter). This will allow triangulating specific HF noise signals.

I am considering a handheld receive-only yagi antenna to help triangulate the noise. The antenna will necessarily be non-resonant since I am looking for noise on multiple bands. Will a non-resonant yagi still maintain useful directional characteristics but with lower gain?

Thanks, Ron
K2RAS

[admin]

OK, some things:

" The antenna will necessarily be non-resonant since I am looking for noise on multiple bands"

-- there's nothing that says an antenna cannot cover multiple bands. This could be any number of wideband antennas. Also, what does non-resonant even mean? Nothing.

Directionality necessarily requires an antenna that is at least a couple wavelengths in size. If you're at HF, I'm not sure you're going to have a handheld device that is at all direcitonal, particularly at the low end of HF (3 MHz, where a wavelength is 100 meters)

[helix]

admin -- you've noted the wavelength is long. from a practical (limited physical size) standpoint, then, there IS something that prohibits the antenna from covering multiple bands -- Chu's limit. of course you must define what you mean by "band", but certainly the matched impedance BW is governed by Chu's limit.

i don't imagine you'd like to carry around a HF log-periodic on your car.

and i think the term "non-resonant" is far from meaningless. but a more meaningful term might be "non-self-resonant." this could be taken to mean a non-matched, receive only antenna such as an electrically small dipole or loop. if you're not concerned with impedance match, then you're not constrained by Chu's limit. it turns out that you can build a decently sensitive and broadband receiver with such an antenna if you do the LNA correctly.


rons -- at HF, amplitude finding may not be your best approach. null finding (e.g., with a loop) might be more profitable. there are many other well-known RDF techniques that are likely more suitable at low frequencies.