HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on November 24, 2015, 1321 UTC
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An interesting paper I found: http://www.brisdance.com/vk4amz/files/Download/UnderMagLoop.pdf
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Very nice overview. As the author ments, there is a TON of info on the tubes, and this article condenses a lot of what's around concisely.
Thanks for posting!
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Thank You!
+-RH
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Given my failed attempts thus far at getting out on a 40 M dipole and a vertical, I've decided to go down the path of building a magnetic loop antenna. The vacuum tube is on order from Ukraine and will probably be here after the first of the year. Also ordered a 50' roll of 3/4" soft copper tubing. I'll get to building it next month and will report back on the progress.
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Yep, I got one of the 'Ukrainian' caps too (100pF).
around 20' and the cap will get me where I want to be.
Surprised your having a problem getting out on a vertical or dipole.
Are you using 'online' SDR's are just relying on reports?
Str.
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Well, it's just crappy antenna choices at the moment until I can build a MLA. Right now all I have to work with is a 40 meter dipole mounted on a fence 6' off the ground, or a 12' vertical, also mounted 6' off the ground.
Until now, I've just been relying on reports (or the lack thereof). I'll give online SDRs another look as well. The last time I checked there were very few that monitored the band I'd be on anywhere close to me, but it's definitely worth a more detailed search.
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Sorry if this is a stupid question, but I just want to be sure. Are these resonant verticals/dipoles you're using? Reason I ask is I've used both with great success though a 40m dipole seems to operate best when at least 30' or better off the ground (at least a 1/4 wavelength).
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Sorry if this is a stupid question, but I just want to be sure. Are these resonant verticals/dipoles you're using? Reason I ask is I've used both with great success though a 40m dipole seems to operate best when at least 30' or better off the ground (at least a 1/4 wavelength).
By resonant, do you mean to ask if they're designed for use on the frequencies I'm broadcasting on? If so, "yes." The vertical is a 40M - 2M with an adjustable loading coil. Both antennas show an SWR of around 1.1/1.2:1 with barely any manual tuning needed. I've pretty much ruled out using the dipole as I recognize it's just not going to work as it's presently mounted. With HOA rules, I'm pretty well restricted to nothing taller than 6' (so it hides behind my privacy fence. I only put up the 12 vertical at night when it can't be seen (and it's also painted black for good measure).
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The dipole is acting as a Near Vertical Incidence Skywave (NVIS) antenna at that height. You should be putting out a decent signal from say 40 to 400 miles from your tx site with it running 100 watts. It could be there aren't a lot of pirate listeners in your area.
Is the dipole flat for it's length? If so there are a couple of quick and dirty tricks to boost the signal from that cloud warmer. The first is to cut a halfwave wire and mount it as counterpoise about a foot off the ground directly below the dipole, don't cut it in the middle, it's not necessary. It will act as a director to enchance the NVIS effect.
You can also cut the halfwave counterpoise, mount it it at the one foot level about a 10th of a wavelength to one side, opposite of where you want the signal to go.
Finally if you want the signal to go both ways re; the dipole, set another counterpoise a 10th of a wavelength to the other side of the low dipole.
Essentially what you're building are NVIS beams. They're cheap as dirt, easy to build and work well in a compromise situation.
Transmitting loops have tendency to cause high voltage fields even at low power. Screwing up TV reception is the least of your worries with them. Hook up that amp to one of the things and you'll be shocking everyone who touches ground or metal within a hundred feet or more of the thing.
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Gotchya'. Ok well, I understand now.
Sorry if this is a stupid question, but I just want to be sure. Are these resonant verticals/dipoles you're using? Reason I ask is I've used both with great success though a 40m dipole seems to operate best when at least 30' or better off the ground (at least a 1/4 wavelength).
By resonant, do you mean to ask if they're designed for use on the frequencies I'm broadcasting on? If so, "yes." The vertical is a 40M - 2M with an adjustable loading coil. Both antennas show an SWR of around 1.1/1.2:1 with barely any manual tuning needed. I've pretty much ruled out using the dipole as I recognize it's just not going to work as it's presently mounted. With HOA rules, I'm pretty well restricted to nothing taller than 6' (so it hides behind my privacy fence. I only put up the 12 vertical at night when it can't be seen (and it's also painted black for good measure).
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Hey, I just found this web page this week. It has a wonderfully simple capacitor.
It uses pex pipe with aluminum sandwiched inside for the radiator. And for the capacitor a bit of coax cable stuffed inside. You slide it in and out to adjust the capacitance.
http://draaggolf.blogspot.com/2014/04/finally-pexalpex-loop.html