Tagged: magnetic loop

The K9AY Loop Antenna: A Directional E-H Antenna for HF

Thank you to Frank Sessink (PA0FSB) for submitting to us his document describing the K9AY loop antenna (pdf), which is the antenna that he successfully uses with his RTL-SDR for HF reception. The antenna combines magnetic (H) and electric (E) field reception in order to create a directive radiation pattern. Frank extends the idea by showing a method that can adjust the directivity electrically with some simple resistor switching.

The antenna that I use is for medium wave DX, specially to receive MW from USA here in Europe/The Netherlands. The antenna is a combination of a magnetic loop and a sense antenna for the E-field. The magnetic loop is directive, but has no front-rear ratio. The E-field antenna has omnidirectional sensitivity. The combination, in correct phase and amplitude, results in a front-rear ratio of more than 25 dB over the frequency range from 500 kHz to around 3 MHz. Higher frequency makes no sense, since skywave signals distort the ground wave directivity pattern.

A simple modification is used as directional antenna with remote control: two orthogonal loops that combine E and H-field in a simple way. I can make 8 selectable directions.

The full document is available here in PDF format.

The K9AY E-H HF Antenna
The K9AY E-H HF Antenna

A Homemade Magnetic Loop Antenna used with RTL-SDR Direct Sampling

Over on our forums user "SandB"  has submitted his designs for a homemade magnetic loop antenna with preamp that he uses together with his RTL-SDR in direct sampling mode. The antenna looks like an interesting build so we are resharing it here. He writes:

So, antenna itself represents as handmade on-PCB winding made of two-side-foiled fiberglass size of 30x40 cm. Both 'windings' connected in the middle and thus winded to 'continue' each other.

Preamp located in metal box attached to antenna and connected via 1.5m S/FTP cable to another box with RTL stick. Note that some transistors soldered on PCB in upside-down - dot on layout means base.

Electrically preamp made as 3-stages balanced signal amplifier with low-input impedance and low-pass filter before input with cut-off at 15MHz. Such complications were required to reduce interferences and intermodulations. Antenna itself is more effective on long-medium waves, so preamp has higher gain on short waves (gain varies from 45db at 200KHz to 68 db at 10MHz - see attached freq responce pic). Getting more flat responce at lower frequencies is possible by increasing C10/C11/C12 to 22nF.

My implementation has some additional elements to make possible to adjust preamp's gain in few db's. But seems its quite useless so that details not included in this post. Anyway, its possible to reduce gain by increasing R6 to 500K.

Box with RTL SDR: I put both signal wires as 3 windings via ferrite ring with high permeability just before RTL chip. This noticeable reduced stray interference, that induced in that cable but doesn't affect differential signal.

ant_preparing
rtl-box
on-the-wall
preamp_n_antenna
ant_preparing2
board-front
board-back
principal
freq_responce_modeled

The K9AY Loop Antenna: A Directional E-H Antenna for HF

Thank you to Frank Sessink (PA0FSB) for submitting to us his document describing the K9AY loop antenna (pdf), which is the antenna that he successfully uses with his RTL-SDR for HF reception. The antenna combines magnetic (H) and electric (E) field reception in order to create a directive radiation pattern. Frank extends the idea by showing a method that can adjust the directivity electrically with some simple resistor switching.

The antenna that I use is for medium wave DX, specially to receive MW from USA here in Europe/The Netherlands. The antenna is a combination of a magnetic loop and a sense antenna for the E-field. The magnetic loop is directive, but has no front-rear ratio. The E-field antenna has omnidirectional sensitivity. The combination, in correct phase and amplitude, results in a front-rear ratio of more than 25 dB over the frequency range from 500 kHz to around 3 MHz. Higher frequency makes no sense, since skywave signals distort the ground wave directivity pattern.

A simple modification is used as directional antenna with remote control: two orthogonal loops that combine E and H-field in a simple way. I can make 8 selectable directions.

The full document is available here in PDF format.

The K9AY E-H HF Antenna
The K9AY E-H HF Antenna

A Homemade Magnetic Loop Antenna used with RTL-SDR Direct Sampling

Over on our forums user "SandB"  has submitted his designs for a homemade magnetic loop antenna with preamp that he uses together with his RTL-SDR in direct sampling mode. The antenna looks like an interesting build so we are resharing it here. He writes:

So, antenna itself represents as handmade on-PCB winding made of two-side-foiled fiberglass size of 30x40 cm. Both 'windings' connected in the middle and thus winded to 'continue' each other.

Preamp located in metal box attached to antenna and connected via 1.5m S/FTP cable to another box with RTL stick. Note that some transistors soldered on PCB in upside-down - dot on layout means base.

Electrically preamp made as 3-stages balanced signal amplifier with low-input impedance and low-pass filter before input with cut-off at 15MHz. Such complications were required to reduce interferences and intermodulations. Antenna itself is more effective on long-medium waves, so preamp has higher gain on short waves (gain varies from 45db at 200KHz to 68 db at 10MHz - see attached freq responce pic). Getting more flat responce at lower frequencies is possible by increasing C10/C11/C12 to 22nF.

My implementation has some additional elements to make possible to adjust preamp's gain in few db's. But seems its quite useless so that details not included in this post. Anyway, its possible to reduce gain by increasing R6 to 500K.

Box with RTL SDR: I put both signal wires as 3 windings via ferrite ring with high permeability just before RTL chip. This noticeable reduced stray interference, that induced in that cable but doesn't affect differential signal.

ant_preparing
rtl-box
on-the-wall
preamp_n_antenna
ant_preparing2
board-front
board-back
principal
freq_responce_modeled

Using the SDRplay with a W4OP Loop

Over on YouTube user SignalSearch has uploaded a video showing and explaining the use of a W4OP magnetic loop antenna on a SDRplay SDR. On the video he explains what the W4OP loop is, and demonstrates it’s operation in SDR-Console with his SDRplay. The video description reads:

Experiment: Hookup the SDRPlay RSP 1 (SDR receiver) to the W4OP (Small Transmitting Loop). I’ve always wanted to try hooking up a loop to my SDRPlay. Though different from an active receive loop (one that has a Low Noise Amplifier), this loop can be used for transmitting @ QRP levels – but works great for shortwave listening too! For more info. please visit my website @ www.k5acl.net!