Home Brew Magnetic Loop for the Lower Bands

[RadioRay]

After getting to know about magloops by purchasing an AlexLoop (works WELL, BTW) , I have sold it and made a larger loop for the bands from 20 meters down to 60 meters.  Unfortunately, the Soviet surplus high voltage capacitor I ordered was damaged, however, the vendor took care of the situation admirably.  I'd happily shop with him again.

Attached is a picture of the loop at present, while I get the primary loop (feed point) dialed-in  - duck tape and all . . .

The outer loop is 5'3" diameter, made from 7/8" copper Heliax "hardline" that I got as a reel end on E-Bay for far less money than I could buy 1" copper pipe, and it's easy to shape by hand.

The original capacitor arrived damaged, so I used a WW II 'junk' double stator capacitor as a 'butterfly' capacitor so that the lossy rotor contacts are not part of the circuit.  This keeps resistance low and Q/efficiency high.

The tuning capacitor is turned using an old 3:1 reduction drive, Velvet Vernier dial - likely made in 1940-50. This makes finding the SWR dip relatively easy. 

Tune-up is simple:

1.  Peak the RF noise at the desired freq.

2.  Transmit a carried and re-turn the loop capacitor for lowest dip in SWR.

3.  Have fun on the air.

I've been running 5 Watts from the LNR Precision LD5 (which I like a LOT!) with the loop inside of my front room, due to stupid HOA restrictions.  I have been able to participate in my CW nets and people were shocked when they learned that I was running 5 Watts into a home brew loop.

The loop is capable of moderate power levels with the WW II capacitor in there.  There is a limit, because mag loops develop VERY high voltages and voltage can jump across the capacitor plates. My barn-yard math, based on plate spacing, says that I'm good to almost 4 KV, which is right at 100 Watts on most frequencies.  However, 20 - 50 makes more sense.  I hope to try it using my home brew amplifier.

So, that's what I've been doing on this end.  I hope to paint it, cover it with plastic flowers , string it up and hang glass wind chimes and feathers in it, put it in our little garden and declare it a 'Dream Catcher(which , in a way - it IS!)


de RadioRay ..._  ._

[gil]

Looks great Ray! It does seem a bit small for 60m though..?

Gil.

[RadioRay]

The calculator says that it's only 23% efficient at 5.3 MHz.  However that's just barely one S-unit down from their reference. Not bad -eh!  :-) Made some CW contacts on 60m using the FT817.

Ray

[RadioRay]

Today I greatly improved the feed loop matching and WOW! Even SSB on forty meters got me checked-in with a NCS on a mid-day net with marginal condx. I am able to use my old sailboat SSB transceiver , an M700 at 150 Watts voice with no arcs or smoke. Signal reports are VERY good at that power level!!! QRP CW has been super on 20 meters with LOUD signals reported from my station.

Time to build a very portable one , or buy a truck... Haha!

De RadioRay. ..._  ._

[Lamewolf]

Today I greatly improved the feed loop matching and WOW! Even SSB on forty meters got me checked-in with a NCS on a mid-day net with marginal condx. I am able to use my old sailboat SSB transceiver , an M700 at 150 Watts voice with no arcs or smoke. Signal reports are VERY good at that power level!!! QRP CW has been super on 20 meters with LOUD signals reported from my station.

Time to build a very portable one , or buy a truck... Haha!

De RadioRay. ..._  ._

Portable you say ?  Give the Army Loop Tuner" a try - can be built in a small box with terminals for various size loops that can be changed out.  Here's a skizmotic for it.