Magnetic loop transmitting antenna

A look at a compact magnetic loop antenna capable of operation on all amateur bands between 160 and 10 metres.

The loop is made from 19mm annealed copper tubing mounted on a timber frame.

It accepts RF input powers of up to 50 watts or so.

Parallel capacitors are added for 160 & 80 metres. 10 metres is provided by a smaller loop made of wire that is clipped on to the main loop when required.

The antenna is suitable for indoor apartment use and has provided interstate contacts on bands down to 1.8 MHz.

Apologies for the terrible video quality - camera has now been replaced!

Category:

Science & Technology

Tags:

• magnetic
• loop
• indoor
• antenna
• amateur
• radio

[gmcjetpilot]

"It accepts RF input powers of up to 50 watts or so."

Do you mean transmitting. HOW is this a Transmitting LOOP? How does it connect to the radio for transmitting?

Also you have the radio in line with the plane of the loop, makes sense to me. However many youtube Videos show the radio at RIGHT ANGLES to the loop? Any comment on that. I assume it can work both ways. I have some small 9" loops and a Degen DE31MS mag loop and find in-line works best, but any comment appreciated.

[vk3ye]

Yes it's a transmitting loop. It's wired to the equipment, in this case an FT-817 transceiver. It isn't like a broadcast radio with an internal ferrite rod.

The feedline connects directly to the copper tubing which has a tapping point for the coax inner. Other builders use a second smaller loop instead.

[vk3ye]

Yep, I'm lucky I can now do that (moved to better QTH). For 160m I'll probably make a top-loaded vertical about 8m tall with a few radials. A loaded dipole for 80m & full-sized dipoles for 40 & 20.

But the previous QTH was a 1br flat with no private yard, no balcony, no courtyard. Either you used the magnetic loop indoors or you were QRT.

[vk3ye]

Greg - quite true - efficiency would be a few percent on 80m and well under 1% on 160m.

However I have worked VK6 & ZL on it on 80m and VK7 on 160m. Locally it does suprisingly well with 10 watts AM on 160m with good readable signals out to about 15km.

For transmitting it will never do as well as a full-sized antenna. But on a performance for size basis the magnetic loop comes out very well and the results are repeatable.

[29pu04]

if you build one for 11 meters please let me know

[jonnyasprin]

Are the magnets an amplifier or more so an antenna?

[OH2FFY]

Oh I agree 100%.

Small mag loops are one of ham radios best kept secrets.

I am building my third loop now. (video coming soon)

My recommendation though is not to put up with the 1% efficiency on 160 - thats hopeless.

I would run a small helical stick for TX and RX with the loop with auto change-over.

That way you can have the low noise RX characteristic of the loop and radiate a little bit more than 1 watt that you would be getting now with the loop and a TX power of 100W.

gW:-) OH2FFY

[OH2FFY]

Hi vk3ye , thanks for the video.

While the loop can tune across all HF bands , its efficiency below 7 MHz will be severely compromised.

Just by guesstimating it as 1.5 meters diameter its circumference is 4.7 meters.

Small loops are usually 1/10 wavelength in circumference.

Efficiency drops rapidly when you go smaller.

So this loops lowest recommended freq is the 47 meters.

40 meters being the closest band of operation.

Regards.

gregW:-) OH2FFY (ex VK6)