magnetic loop antenna build

S

st25r

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Hello, I have a Sony ICF-SW7600GR and want to build a magnetic loop or square copper tubing antenna for it. It has a 1/4" jack for an external antenna. The frequency range on the radio is 150-29999 KHz, and where I live the reception is weak, but man that FM tuner is strong! I have looked around at various ham websites from the late 90's which used to have good links, but many appear to be broken. One of my goals is acquiring my tech license and am looking further down the line to make an antenna which will transmit and receive with capable equipment. Definitely a novice here, but would love to be able to hear stations and other oddities from around the world for now.
I found a calculator here: Small Transmitting Loop Antenna Calculator • 66pacific.com and was wondering if I could use it for a square version, or does someone have a google spreadsheet or a better online version I could use?

I would also like to see some detailed pictures of how it is constructed and electrical connections, if possible. Heck, I don't even know what frequency it should be tuned to. Please help!
 
prcguy

prcguy

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I don't think you want a tunable transmitting type loop for receive only, they are very narrow band and otherwise have no amplifier. A simple loop about 3ft diameter has an impedance around 140ohms over a very wide frequency range and using a 4:1 balun will match it just fine. That will make a simple untuned loop that will receive stuff and null very well.

To make it really play nice you need about 20-25dB of amplification. I tried one of these which is a preamp that matched directly to an untuned loop and competes somewhat with the expensive loops. You would need the preamp and a power inserter board offered by the same seller and if you get the preamp board you don't need the 4:1 balun. HF Receiving Loop Antenna Amplifier - Amateur or Shortwave SWL - Updated! | eBay
 
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st25r

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jland138 said:
The "loopantennas" group on https://groups.io/groups is very active and has lots of information including pictures and various designs in their photo and files section.
Click to expand...
Thanks, jland138!
prcguy said:
I don't think you want a tunable transmitting type loop for receive only, they are very narrow band and otherwise have no amplifier. A simple loop about 3ft diameter has an impedance around 140ohms over a very wide frequency range and using a 4:1 balun will match it just fine. That will make a simple untuned loop that will receive stuff and null very well.

To make it really play nice you need about 20-25dB of amplification. I tried one of these which is a preamp that matched directly to an untuned loop and competes somewhat with the expensive loops. You would need the preamp and a power inserter board offered by the same seller and if you get the preamp board you don't need the 4:1 balun. HF Receiving Loop Antenna Amplifier - Amateur or Shortwave SWL - Updated! | eBay
Click to expand...
I don't know if what I had in mind is considered a magnetic loop antenna or not. Maybe it is just called a loop antenna, I don't know. The one I had in mind has several winds of wire around a square with a variable tuning air capacitor to bring in the signal. Thanks, too prcguy, for pointing out the different types of calculators. A receive only would be best like you said. Thank goodness I didn't buy any materials or make any cuts yet!
 
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ka3jjz

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st25r

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I love the idea of the SULA! I don't think though that I'm ready to attempt this design though since I know nothing about galvanic transformers and constructing a balun. Still learning about the how to assemble the more primitive loop antennas. I will bookmark the links and come back to them to study the plans once I got a hang of the simple stuff.
 
in6236swl

in6236swl

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As for the SULA, further build infos can be found here


and here


regarding the Balun/Transformer, if one doesn't want to build his own (e.g. using a binocular ferrite core), the NooElec v2 BalUn will just fit (the V1 will fit too, but you'll need to cut the "R1" trace on the back of the PCB to obtain galvanic isolation); the same goes for the preamplifier, any preamp offering about 20dB gain and covering the desired range (the SULA works ok from MW up to around 500MHz) will work, be it a homebuilt one or a commercial one, a couple preamps which may fit are the NooElec LANA HF and the SV1AFN but by the way others preamps will work too, notice that the SULA offers an impedance near 50 Ohms over the whole working range, so any preamp accepting such an impedance will fit (no need for dedicated loop preamps)

HTH

Andrew (grayhat)
 
mbott

mbott

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Hi Andrew!

Ollie did a bang up job presenting the SULA. I'm looking forward to putting one together.

--
Mike
 
in6236swl

in6236swl

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mbott said:
Hi Andrew!

Ollie did a bang up job presenting the SULA. I'm looking forward to putting one together.

--
Mike
Click to expand...

Hi Mike, it has been quite some time since I used this account, I almost forgot about it, but since I found this reference to the "SULA" antenna, I thought to chime in; and... yes, Ollie did a very good job, NOT ONLY writing down the posts (I'm not good at that) but also buiilding and testing the SULA; to tell the whole story... I had some issues with my wrist (still here, but I'm getting better) so I was unable to "fiddle and ferret around" as I'd like, so... I decided to play with NEC (the free 4NEC2 in my case), now, since I had it sitting on my disk for a while, and since I already got some grip on it, I decided to try finding an antenna design which could help SWLers, not a "miracle antenna" (those are made out from unobtainium), just something with a size allowing even an "apartment dweller" to use it and at the same time easy to carry around for people going to some "remote listening post", the other requisites were that such antenna should be simple to build, by sourcing cheap and easily available parts (either online or at some local shop) and that it should show some good properties... anyhow, making a long story short, I started from the KK5JY SRL design which I already tried and for which I already had a NEC model, starting from such a model I begun adding a resistor to flatten the "curve" and then moving both the resistor and the feedpoint around as you can see reading the SWLing forum thread, and after some more fiddling, thanks to the GREAT contribution from Ollie, the "SULA" (as a note, check the discussion about the antenna name on the forum :D !) was born, and luckily it's showing quite some promise, what we need now are more builders/testers willing to try the SULA and report back (possibly on the SWLing forum), since I believe that it may be possible to further improve such a simple antenna
 
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