Loop antenna for frequency range of 160 meters to 10 meters

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P-40 Warhawk
Posts: 92
Joined: Thu Jun 26, 2014 11:55 pm

Loop antenna for frequency range of 160 meters to 10 meters

Post by P-40 Warhawk » Mon Apr 24, 2017 2:54 pm

I will start with what I have now for a setup , then I will get into what I hope I can do . I have a V3 dongle and I have a MfJ - 1020C pre-selector in front of it . Now for a HF antenna I am using the aluminum flashing on the eves of my house . This gives me a 246 foot horizontal loop antenna that is about twelve feet above the ground . I also have a inverted ( W ) under the roof of my house , they are tided together through a terminal block with out any interface between them . My frequency range is from 500khz to 50mhz . The reception isn't to bad , last week I pickup a guy by the name of Paul in Valencia , Spain ( EA5JJ ) on twenty meters and he was doing about S 7.5 . I guess that isn't to bad for being in Pensacola Florida , I am sure that the gods of propagation were with me that day .

Now what I would like to do , I would like to get a smaller loop antenna up higher off the ground . To maybe twenty feet off the ground . Everybody that has put anything on the internet about loop antennas didn't understand the KISS principle "Keep it simple, stupid" . Somethings that I come to understand about loop antennas from surfing the internet . The fatter the loop the better it works . Thirty six inch's diameter single loop for a wide band loop antenna . Wide band loop antenna should be half wave of the lowest frequency you want to receive . Surfing the net I ran
across someone that wanted to pickup VLF . He used a twenty inch BMX plastic wheel winding up to three hundred turns of wire to give him a loop antenna . I like the idea of the BMX wheel with lot's of turns of wire on it . I would like to hear from people out their and what they think .
Last edited by P-40 Warhawk on Wed Apr 26, 2017 2:21 pm, edited 1 time in total.

Kenn
Posts: 51
Joined: Fri Apr 08, 2016 8:43 pm

Re: Loop Antennas ????????????

Post by Kenn » Mon Apr 24, 2017 8:55 pm

I too was looking at small physical size loop antennas when I was living in a restricted community. Basically a home-brew mag loop antenna along the lines of the MFJ for use on HF. The small size and wide frequency range sounded appealing, but to utilize all the bandwidth they must be retuned. Hence the variable capacitor and remote tuning circuitry. Sure, I could make that but the KISS principle is fading fast ...

My conclusion was that if I was doing just amateur radio and working say one band at a time, this would be great. Especially if the band was crowded, just tune the loop to the frequency I'm on. But since I'm more into general scanning and SWL, wanting to look a several megahertz worth of spectrum at a time, a small mag-loop might not be my best option.

Being a chronic tinkerer, I plan to give the loops a try for AM broadcast. I picked up some hula-hoops at a yard sale for use as a radome and do something like what these people did:

http://socalradiowaves.com/columns/am_antenna.html

Or especially this one, snaking a multi-conductor cable through one of those hoops:

http://www.mile204.us/PotsdamDan/RubeGo ... te_AM.html


Your current setup of using the flashing around your house seems like a large skywave loop and a good arrangement. Perhaps you can improve on that by making sure each section of flashing is electrically well connected to the next ... like stainless steel sheet metal screws.

-Kenn

KA0SBL - https://ranous.wordpress.com

snn47
Posts: 223
Joined: Tue Dec 27, 2016 11:00 pm

Re: Loop Antennas ????????????

Post by snn47 » Mon Apr 24, 2017 9:31 pm

Somethings that I come to understand about loop antennas from surfing the internet. The fatter the loop the better it works. Thirty six inch's diameter single loop for a wide band loop antenna . Wide band loop antenna should be half wave of the lowest frequency you want to receive . Surfing the net I ran across someone that wanted to pickup VLF . He used a twenty inch BMX plastic wheel winding up to three hundred turns of wire to give him a loop antenna . I like the idea of the BMX wheel with lot's of turns of wire on it . I would like to hear from people out their and what they think .
There are many different designs/principles for loop antennas, some only for receive, some for transmitt and receive, which adds some more details to take into account to alllow for an efficient transmission. So it is hard to answer if you are not specific about the design/type you want to know about, and which frequency range do you understand under VLF (3 bis 30 kHz)?

The form of most are round, but also forms using multiple bends, down to 4 (quad or square loops), 3 (triangle loop) or 2 (a folded dipole is a special form of a loop) exist.

Full wavelength loops have a limited bandwidth (at best several hundred kHz at SW), but are usefull as easy to built TRx antennas and beams well into the GHz range.

The mostly in the SW range (3,5 -30 MHz) by HAM OP for transmitt and receive used "magnectic" loop are basically a LC circuit with one loop and a variable capacitor for tuning. The circumference is>1/4 of a wavelength and has to be tuned via a variable condensator/capacity diode.
For receive use only, losses are low and therefore very thin wires can be used, but thin wires require mechanical support to stay in shape, while solid grounding wires (>3 mm) or tubing can be self supporting. The tuning range is limited to about one octave (e.g. 28 to 14 MHz) due to the limited capacity variation available. One soultion to extend is to switch between two variable capaciter, one for the first tuning range with as low starting capacitor as possible, the second one starting at the max. capcitance of the first you can get about two octaves of tuning range down to about 7 MHz. However the shorter the loop circumference is the lower the gain.

The circumference can be reduced by multiloop = winding a coil. For transmitt at max. a few turns can be used, for receive the extreme is a multi hundred turn winding loop you mententioned. At lower frequencies solid wire should be replaced by multithreaded each wire insulated "Litz" wire.

An alternative to building you own antenna and reduce dimensions, is to use a smaller coil fixed on a ferrite core, which you can salvage from an old AM radio. The frequency range depends on the properties of the ferrite type used, you can expect them work well below 500 kHz, 100 kHz if the receiver covered these range as well.

If you have enough space, you may try unwinding the cooper wire from an discarded transformer, stick one end through a large potatoe and through it into trees, a potatoe is soft enough not to do to much damage and bio degradable :). Unless you live within range of transmitter you may not need preselector/filter to avoid overloading your receiver.
Last edited by snn47 on Tue Apr 25, 2017 10:49 am, edited 1 time in total.

rtlsdrblog
Site Admin
Posts: 2784
Joined: Mon Nov 19, 2012 11:54 pm

Re: Loop Antennas ????????????

Post by rtlsdrblog » Tue Apr 25, 2017 9:26 am

Experiment the height of your loop. Sometimes higher is not always better when it comes to small loop antennas. Many actually work better when on the ground.

snn47
Posts: 223
Joined: Tue Dec 27, 2016 11:00 pm

Loop Antennas !!!!!!!!!!!!!!! if you do it right

Post by snn47 » Tue Apr 25, 2017 11:12 am

A tuned magnetic antenna works also well inside a building, unless you have steel increased concrete.
A short overview is also on https://en.wikipedia.org/wiki/Loop_antenna

The word I couldn't remember and added to my above post was High Frequency Litz wire, which is a multi-stranded wire each isolated more information on the benefits consult https://en.wikipedia.org/wiki/Litz_wire. I would thereofre advise against the use of solid wired as described in http://socalradiowaves.com/columns/am_antenna.html

The patent https://www.google.com/patents/US6529169 give a short sumary of Litz wire ferrite antenna use and may an idea for your own experiments.

I never had any interest in such low frequencies, but I doubt if going to extremes like described at http://www.mediafire.com/?dshnqlbydf6qu25 will rellay bring benefits. The OP seems convinced but for the lack of objective comparisson I doubt it.

Using HF-Litz and antenna you can find more (DIY) information with and without use of ferrites.

vy 73

PS.: another design antenna coil design is here http://pe2bz.philpem.me.uk/Comm/-%20Rec ... spider.htm

P-40 Warhawk
Posts: 92
Joined: Thu Jun 26, 2014 11:55 pm

Re: Loop Antennas ????????????

Post by P-40 Warhawk » Tue Apr 25, 2017 2:19 pm

I thank you .

Kenn , snn47 , Administration .

I had to smile when I readed about the stainless steel sheet metal screws , that was the first that I did . The DC resistance of the loop was only was four ohms . Also for those who would like to know the aluminum flashing on my house is four inch's wide . Also 246 foot circumference is about half wave of 160 meters . I also have a disk cone antenna , the frequency cross over point
of the two antennas is 50 MHZ . This is information that I thought people would like to know .

I am not sure that their is going to be anyway to do what I would to do , the antenna is going to be 10 feet horizontally away and 20 feet up under the roof , not easily gotten to , to make adjustments to . The Ferrite loop stick antenna is a thought as long as I won't have make adjustments at the antenna but it doesn't look that way . It looks like the plastic with lots turns of wire on it is the thing to try first .

snn47
Posts: 223
Joined: Tue Dec 27, 2016 11:00 pm

Re: Loop Antennas ????????????

Post by snn47 » Wed Apr 26, 2017 12:31 am

Youre welcome. As a suggestion you may consider modifying your title to reflect what you want to use the Loop antenna for to allow others to identify if the information contained in this thread might be interesting to them or if they can contribute something as well e.g. Loop antenna for and then the frequency range you like SW and below
Have fun

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