Ham Radio - Is the Airspy Discovery HF+ sensitive on VLF? Testing with a Garrett metal detector.

[@robertvandersanden]

Before ordering loads of magnet wire - how about winding something on a ferrite rod like in the AM radios in the old days and put a transistor gain stage behind it? And a ferrite rod is light weight enough that you could raise it up into a telescopic mast, out of the way of noise sources in the RV. If you think about something resonant with a tuning cap then you need quite a wide capacitor range. 3 - 30kHz is a decade and requires 2 decades of C variation (because the frequency goes with the square root of the LC product).

[@Trainwreck144]

Yep. The classic WWVB receiver in millions of clocks have a small ferrite rod antenna.

[@stevec5000]

I was also going to suggest a ferrite antenna and if you get some Litz wire and large ferrite bars from Russia to use like DXerGary has in his video that will make it a lot more sensitive. kzbin.info/www/bejne/jYrYmp6Hn5yshqM

[@Trainwreck144]

Litz wire is effective between 300 khz to 3 mhz according to RCA Radiotron Handbook, 3rd ed.

[@USXPOP]

Learn something new almost every time I see one of your videos. Good work.

[@56932982]

The classic VLF exercise is to receive SAQ at 17.2 kHz. (UNESCO World Heritage Site Grimeton Radio Station)

[@Mach7RadioIntercepts]

There are some nice voltage probe (amplified whip) antenna designs posted on the internet. Interestingly, I've noticed a few KiwiSDRs on the net receiving very nicely on what are essentially 1m or 2m diameter amplified loops.

[@skinnyflea2628]

I’m exited! I love receiving ndbs and I haven’t been able to come up with a low noise antenna except a loop. I am having trouble finding documentation on how to build a loop for those frequency’s so hopefully your future videos can help me learn. :)

[@Steve-GM0HUU]

👍Interesting experiment Kevin, thank you. SDRs are just amazing for this kind of thing. The only antenna suggestion I can think of not already mentioned (for reception) is a ground loop. Not a loop on ground but something like a variable capacitor with as much wire as you have running off in each direction to electrodes in the ground. No idea what the geology is were you are. It makes use of Skin Depth and the theory is that less conductive bedrock gives best results.

[@JELmusic]

Speaking from experience; a small loop (Less than a foot in diameter) with many loops (Several hundred) is no good down there (I'm not talking about ferrite-rod loops, but 'normal' loops (Donuts, if you will, with nothing in the center of the loop)) Big is not necessarily the way to go, but I tried a few different sizes and layouts and found that a single-loop triangle (15 feet on the long ends, 10 feet on the short) worked really well on around 200-300 kHz. I currently use 2 rectangular loops in parallel (Positioned perpendicular to each other). Each is 15 feet on the long ends and 5 feet on the short ends. They are standing like fences on the ground (For practical reasons and because I live in a place where I can't raise their height) They work very well at VLF (And all the way up to about 18 MHz, above which they begin to only pick up local OTH transmissions) Good luck and please share experiences :) jacob.

[@tombaffa9374]

So many amazing things we have to experiment with. Have fun and thanks

[@denniswilliams8747]

Back in the '70s the price of copper sky rocketed. I believe the rise was caused by the big VLF antennas being installed. Thanks

[@Nicktgrief]

I used to use a box loop ( like your 630m one) for MW dxing. That was 7 turns of wire on a 40” frame. With a single turn wrapped round the centre turn for pick up and a 360pf cap for tuning. That would be a place to start. I can e:ail you the details if you’re interested

[@BarefootBeekeeper]

Also interested in VLF, if you were thinking of doing more...

[@albing1397]

Look up the papers or Dr. Heinz Schlicke. He was a German U-Boat Commander (Scientific - U234). When he was at Allen Bradley in the early 70's, we experimented with brain wave feedback using active filters in the 7 Hz range. Basically, you attached head probes, through a 7 hz passband filter to a headset. If you thought good, relaxing thoughts, you could relax (signified by a tone). However, brainwaves could be generated near 7 Hz that would make you psychotic. We had to carefully tune the twin tee active filters to get a good result. Will the Airspy work that low? (PS, Dr Schlicke was a founding member of the IEEE Electromagnetic Compatibility group). His work for the Germans was on proximity fuses (using RF). Came to America as part of Operation Paperclip. (Worked for him as a young MSOE graduate) - WA9RYO

[@dandruff7807]

You could possibly use an old degaussing coil as a receive antenna. Though very difficult to acquire.

[@electronica56]

Kevin, how about hooking up a keyer to the Garrett and try modulating the signal. ;)

[@milesprower6641]

I imagine a nice sound card plus isolation and a preamp would be very sensitive down there. An audio transformer or even one from a big power supply would work

[@loughkb]

There's a few vids out there on using the sound card as a receiver down at VLF freqs.

[@glenmartin2437]

Interesting. Thanks.

[@W8QH]

Submarines, drag a long wire for the reception. The transmission is low-speed data, one way from the base.

[@Mach7RadioIntercepts]

Over here, my RTLSDR can pick up weak FSK sigs around 23 kHz, using several yards of wire, end fed.

[@dandruff7807]

Hi Kevin..........Use your metal detector coil as a receive antenna?

[@gfl1957]

Interesting that your SDR works that low. Would be great to get an antenna and listen that low. The Air Force E-4B "Doomsday plane" has a wire antenna that spools out 3 miles behind the aircraft for VLF.

[@hamandshortwaveradioirelan4773]

Another interesting video - great stuff - keep’em coming 👍

[@o2bnov0307]

Are you still in the RV? Cool video.

[@Barracuda48082]

bell 28 to 32 ga ?..the same on older phone systems?..near a full spool sitting here, white, blue id spots

[@freedomvigilant1234]

I wonder what signals one could pick up on VLF if a Beveridge Antenna was utilised?

[@robertvandersanden]

A decent beverage antenna is at least a wavelength long. At 10kHz VLF you are talking about at least 20 miles of wire. That's an aweful lot of fence posts to hammer into the ground.

[@freedomvigilant1234]

@@robertvandersanden Good point. It would make Fence Post and Antenna wire suppliers happy with the amount one would have to purchase. :D

[@dannythomas6194]

In the words of Martie Johnson "Very Interesting."

[@stridermt2k]

Artie

[@jacobboth1914]

Hi Kevin. I remember you own a MiniWhip. It seems to do well on VLF, HF and MW. Google on MiniWhip VLF and see what you get. Jaap PE1LLA

[@stridermt2k]

This was fun

[@zman4150]

Although not exactly where you want to receive, WWVB has a transmitter at 60khz...

[@jbammi]

Hi Kevin, you may be interested in W1VLF channel here on youTube. Just going by his call Paul is a VLF guy and has interesting videos of Discovery and airspy HF (regular and modified) and also ferrite based antennas for VLF

[@muddyexport5639]

GL - 73 de N5XS

[@CarmineIannace]

Interesting video! I would suggest that before you invest time and money in a traditional large loop or ferrite rod type of antenna you explore a small active vertical or loop antenna. Didn't you previously test a mini whip? The updated mini whip should give you reception down to at least 10 kHz. You are in a relatively low noise environment and should be able to get an active antenna away from nearby noise sources (like your RV) with the help of a common mode choke on the coax. Check out this video from W1VLF - kzbin.info/www/bejne/mGGtqWClg5iMoqM

[@charlesschindler1971]

Yo!+Meow! 👋