anyone here have antennas for VLF and below? experiances - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: March 11, 2018, 03:44:43 am
content: so I was readingwww.vlf.itrecently and it has quite a bit of content about VLF/ELF antennas, studying earth resonances, etc, but there does not appear to be much discussion about this on forums etc.Does anyone have any experiences, specialized equipment, etc for this frequency range?

author: mark03
author_rank: Frequent Contributor
timestamp: March 11, 2018, 07:30:37 am
content: If you can find it, "The Design of Broad-Band VLF Receivers with Air-Core Loop Antennas" by Evans Paschal is a good reference, if slightly dated. It describes in detail the design of the Stanford VLF group's research receiver.Basically, if you have the space and $$ for copper, you want a B-field (loop) receiver. Paschal shows that the overall receive sensitivity is proportional to the mass of copper in the loop.High impedance E-field receivers are useful mainly for portable work. Paul Nicholson (http://abelian.org/) wrote some antenna modeling software for VLF that you can use to find an equivalent circuit, basically a pure capacitance for an E-field probe. He was involved in the first transatlantic amateur communication at 9 kHz.Propagation at VLF maintains phase coherence over long integration times, so you really can trade off TX power and communication rate to a fairly astonishing degree, given GPS-locked frequency standards at both ends. This is fortunate, as it's difficult to get more than microwatts ERP at VLF, unless you're the military

author: awallin
author_rank: Frequent Contributor
timestamp: March 28, 2018, 06:06:12 pm
content: Quote from: CopperCone on March 11, 2018, 03:44:43 amFor VLF (down to 3 kHz) reception I think a Mini-Whip antenna works quite well.I have a toy SDR (USRP N210) with a Mini-Whip antenna over here:http://194.100.49.156:8073/Usually the signals are far above thermal noise but buried in interference/noise from other sources (powersupplies etc) - so the small mini-whip works quite well (and a larger antenna would not help SNR since you get more signal AND noise).For ELF and other exotic things big magnetic loops might be the way to go - no experience on those...

author: gregariz
author_rank: Frequent Contributor
timestamp: April 09, 2018, 06:55:05 pm
content: In Geophysics - ie mapping the subsurface (finding minerals etc) the antenna is buried in the ground ie a hole is bored and a dipole (many turns on a former) is buried at appropriate places. Remember wavelength has been reduced so you are not sinking it miles. By making these field measurements at known positions, one can then use electromagnetic solvers to roughly predict the ground composition. There are a number of techniques that are similar in what they are looking to measure.https://en.wikipedia.org/wiki/Magnetotellurics

author: CopperCone
author_rank: Super Contributor
timestamp: April 10, 2018, 04:12:11 pm
content: I made a large ferrite rod out of a bunch of inductors. It is about 1 foor long and an inch and a half wide.I thought something for recieving vlf can be made.Any good ideas? I think its manganese zinc type

author: GerryBags
author_rank: Frequent Contributor
timestamp: April 26, 2018, 09:54:45 pm
content: I found these guys a while back(http://www.stormwise.com/page28-ELF.htm)but I have sooooo much else to buy before I'm ready to start seriously mucking with LF, but it's on my list. The study of the upper reaches of the frequency domain has been more favored by technological advances than the lower end. Both were originally miltary-led, but miniaturization and process control advances have put ridiculously high freq. devices in the hands of hobbyists, but the low end still calls for big caps, big coils, everything is either big or long.I came across a couple of posts (literally: two) last year about using an active antenna for very low freqs, but the details were sketchy and it was trying to fillin the gaps in my knowledge so that I could fill in the gaps in this idea that l have lead to me buying old 'scopes, blowing up capacitors and selling off a very decent sword collection to buy TE, and hanging out here. It's very entertaining now I have a sort of clue what you guys are all gassing about.

author: CopperCone
author_rank: Super Contributor
timestamp: April 27, 2018, 12:29:13 am
content: yea, thats the website I got the idea for making my ferrite.I had a lot of large cylinderical inductor cores, which I ground flat on the sides to remove the coating and used super glue to make a long one, then I reinforced it with a steel threaded rod with some nuts/washers down the middle.Stormwise sells cores like that for 90-150$, I made it now I wanna make an antenna out of it but I am not sure how to make it.Also the interesting thing about LF reception is that you can use gyrators to replace big inductors and stuff or do other interesting things. I heard the gyrator was useful for military submarine communications from someone I know but he did not offer any real details as to why the navy liked them so much (apparently top secret)