A loop antenna can be used either for connection to a receiver or a field strength meter. A large loop is reasonably sensitive and directional and the loop described here can be used for either purpose.
The loop frame was constructed from 3/8" dowel rod and scraps of wood. Eight turns of number 28 wire (not critical on size) were wound on the frame with 36" diagonal measurement (27" on each side). The wire was routed through slotted wood guides attached to the ends of the dowels.
A meter and circuitry were mounted on the frame to perform the field strength indication function.
The device is sensitive enough to detect the field from a part 15 AM transmitter antenna. Positioned about 6 feet from an outdoor base coil loaded antenna and rotated for maximum reading the meter indicates 50 uA. At 20 foot distance the meter indicates 8 uA.
This loop and meter are useful for fine tuning and checking operation of tuned antenna systems.
The loop was connected to the antenna terminals of a BC-1004-C receiver and Radio Chechnya was heard 5X9 (loud and clear) on 9409 kHz. Rotating the loop allowed for maximizing the received signal as well as nulling out electrical noise.
Neil
That would be very interesting
to look at.
I love loops.
Bruce, GNAT 90.9 "If you can hear us,
then you must be eating in our kitchen."
Click on the bold lettered words. They are links.
Neil
An interesting thing about loop antennas as described is you can place a portable radio next to it with no physical connection and enjoy increased signal and directivity.
Man, Neil, they really look good!
Very impressive.
Bruce "Weaker than a local oscillator,
it's, GNAT 90.9"
Guess I was being too slick with the links. Just thought it would be a little cleaner to do it this way and didn't realize some may not know that they were links. Anyway, problem solved. It was a nice little project done on a whim.
A historical note: The wire used is from a focus coil salvaged from the first RCA TV my parents owned back in the '50s. I've had it in my junk box since then but can't use it for much since the enamel insulation is rotting away but it worked for this because of the turns separation. I never throw any electronic stuff away!
MRAM,
I didn't try using it with inductive coupling to a portable but have read where it works well if a tuning capacitor is used to peak it. Another project for winter here perhaps.
Neil
That's a really nice creation. Thanks for sharing it.
Is the frame required to be that size? Or could it be smaller?
Neil, Yes my 15 turn loop has a tuning cap for peaking. A coupling loop of one or two turns on the same form is used to directly connect to a radio. The thought is this leaves the main loop lightly loaded for improved selectivity.
Then I found that placing a portable radio next to the loop with no direct connection also improved reception.
Neil is a genius. i save all his designs he posts here in my archives for future reference for someday tinkering projects.
Rich,
The sensitivity of a loop antenna is proportional to the loop area and the number of turns so for this application where a rather large current is needed to drive an analog meter but adding turns adds inductance and raises the loop impedance I chose to use a big area rather than more turns. The diagonal length was set by using standard length dowel rod from the lumber yard which was 36" and was cut in half giving 18" from the hub to the wire guide. There was no other "magic" in setting this dimension. The number of turns (8) was copied from an article I read about loop antennas. I don't think the number of turns or size is critical unless a tuning capacitor is going to be used in which case this might matter.
Neil
Neil, it's a beautiful loop.
You have so many treasures that
you have shown us. I sure enjoy it.
As a member of the "crystal set crowd"
in past years, I have seen crystal sets
that used very big loops so that no
outside antenna would be needed. I don't
know if your loop is compatible with that
kind of application, but I wondered about
it anyway.
Bruce, Chief Engineer, Chief Operator,
Chief Cook and Bottle Washer, Chief Program
Director, Chief Traffic Director, And Chief Janitor,
at GNAT 90.9.
"Where you need a big fan to blow the radio
waves next door."
And still, they only get half way there.