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Comment by sidewndr46 | Hacker News Reader

not sure you what you're thinking of, but most amateur radio can be done with an omni antenna.

to be fair a lot of high frequency stuff has pointing :-) But certainly HF stuff, especially below 30MHz, is like any old wire will do. (or loop)

You still have to point it at things. I had the worst possible plot for my HF antenna which meant the lobes were in the wrong place for about 5 years :(

Be careful not to confuse antenna design with "needing to point". :-) There are antennas with pretty circular gain in azimuth but asymmetrical gain in altitude. I have a 08-ANT-0861 from MP Antenna that pretty much looks every which way. And I can recommend it for people who need "one" antenna for a bunch of different experiments.

Quick look of the datasheet suggests that's specified for three bands around UHF, VHF base stations. I mean I'm sure it'll sort of work outside those bands on receive to some varying degrees of success but on transmit, it's going to be a terrible terrible mismatch.

Would love to see an S11 sweep on a proper VNA for that antenna. I bet it looks like a polynomial with a googol order. On some bands the feed might be a better antenna.

My antenna comment was more about the launch angle. It was in inverted V which was steep aka a "cloud burner".

Fair enough, I've got an Agilent 8753A (3GHz version) that I can do an S11 sweep on. It that counts as a "proper" VNA :-) Drop me an email (contact is in my profile) if you would like me to send you a copy of it. (note it won't be right away as the bench is covered some different equipment at the moment)

That is about as proper as VNAs get :). Would be interested in that but will not share my email here as this is my trash account. If you can attach the sweep on imgur I can look at it there.

> But certainly HF stuff, especially below 30MHz, is like any old wire will do

I've got a couple mostly horizontal wires running along the length of my living room--the speaker wires from my A/V receiver to my rear surround speakers.

I've wondered if that could be used as an HF antenna while simultaneously still being used for the speakers?

The audio signals for the speakers are all below 20 kHz. The radio signals I'd want to receive (and maybe transmit) are all about 1 MHz.

The idea then would be to put low pass filters on the audio connections and high pass filters on the radio connections. The cut off for the filters could be somewhere in the middle between 20 kHz and 1 MHz, so that both the audio signals and radio signals are far enough way from the cut off that the filter is flat.

Could that actually work or is it likely to fry the A/V receiver and/or the speakers and/or the radio?

Heh, the answer is sort of. Your receiver likely already has a filter network to "ground out" any coupled electro magnetic interference (EMI) coming from those wires. All conductors "receive" to a greater or lesser degree and so people building things that connect to wires have to account for that and plan for it. So using your speaker wires directly would probably not work very well because of filter networks in the receiver.

For folks just playing around receiving HF I find the YouLoop[1] is a low cost and very effective magnetic loop antenna that you can set up on a wall in a dorm room (or living room :-) or pretty much anywhere. The Airspy HF+ discovery[2] is probably the best valued HF SDR you could use with that, but it works well with RTL-SDR V4 dongles[3] as well and the RT832 ones from NoElec[4] although NoElec and the V3 or earlier dongles don't go below about 55 MHz and need an upconverter like the HamItUp! [5] to move the bottom part of the HF spectrum up into a region the RTL832T receiver can tune them. (the V4 RTL-SDR dongle has an internal up converter for this purpose).

[1] Youloop magnetic loop antenna -- https://airspy.com/youloop/

[2] AirSpy HF Discovery + -- https://airspy.com/airspy-hf-discovery/

[3] RTL-SDR "dongle" V4 (low end ~1 Mhz) -- https://www.rtl-sdr.com/rtl-sdr-blog-v4-dongle-initial-relea...

[4] NoElec NESDR SMArT (low end 55 MHz) -- https://www.nooelec.com/store/sdr/sdr-receivers/nesdr-smart-...

[5] HamItUp! -- https://www.nooelec.com/store/sdr/sdr-addons/upconverters-do...

I haven’t done much radio aside from basic SDR stuff, but receiving imagery from for example a GOES satellite requires a parabolic antenna.

Sure you can do things with a close to isotropic antenna, but there's a lot of gain to be had if you make things worth pointing at things.

You can do more with 5 watts and a decent directional antenna than 100 watts with a turd on a stick.

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