HF Active Loop Antenna v4 released


Chris Moulding
 

One point I forgot to mention. If it's mounted horizontally it has to be in a RF quiet location as you cannot null the noise out like you can with vertical mounting.

Regards,

Chris


Chris Moulding
 

Mounting the loop horizontally gives an omni-directional pattern.

The nulls are vertically up and down so it's not ideal for NVIS operation.

Mounting at a low height say 8 to 10 feet above ground gives a fairly high angle doughnut shaped pattern. I confirmed this in testing this morning. Strong signals heard from around Europe on 10 MHz and above.

Mounting at height say on a tower or high building will give a very low angle especially if it's several wavelengths high at the frequency of operation. A steel framed building will tend to act as a reflector behind the antenna and affect the antenna pattern.

Regards,

Chris


martinbradford2001
 

Sounds good, Chris. 

I really don't want to get involved in rotators at the moment, so I would be interested in mounting it horizontal for an omnidirectional pattern. As you know already, I'm using your LAA++ amplifier with a 1m loop vertically oriented and another passive 1m vertical loop at right angles. That works remarkably well, but I'm always looking for improvements - would be interested in how this new loop is likely to perform oriented horizontally and something like eight or ten feet above the ground...

Martin (G8FXC)


Chris Moulding
 

Comparison tests with my 1 m diameter test loop using  LDF-4-50 show that signal levels are a few dB down but the signal to noise ratio is significantly improved.

The nulls on the double loop are remarkable around 50 to 60 dB down. Most other loops fill the nulls with noise picked up by the loop acting as an electric field antenna.

i usually use a 5m vertical with a High Z Antenna Amplifier as a reference "sanity check" at the workshop. The double loop is the only loop design to beat it so far.

I'll see if I can run a comparison test on the video.

Regards,

Chris


martinbradford2001
 

Very interesting! Any idea how to expect it to compare with the LAA++ on a 1m loop as a low noise RX antenna?

Martin (G8FXC)


Chris Moulding
 

We have just started building the first production batch of the HF Active Loop Antenna v4. They will be ready for shipping in about a week.

The antenna uses a small double loop 350 mm or 14" in diameter.

it uses a variant of our Loop Antenna Amplifier ++ with sharp RF filtering to limit the frequency response to 500 kHz to 55 MHz.

The small size of the loop and the input transformer design are designed to prevent the loop element acting as an electric field antenna. This antenna acts as a true magnetic loop with very deep nulls for direction finding or noise rejection.

Due to the small size it's ideal for use as a portable antenna and will easily store away in a car. From the size you can see why during development it was called the "Pizza box loop"!

Later this week I'll make a video in the workshop to demonstrate the loop. If we get a dry day I'll take one out to make a video of some testing in the field.

I've got to thank the members of the forum for inspiring the development of this loop antenna. When we released the Loop Antenna Amplifier we had so many questions about loop types that I ran a project to try as wide a range of loop designs as possible, This small double loop design with a very low self-inductance was comparable to much bigger loops at medium wave and HF.

The web page for the new antenna is https://www.crosscountrywireless.net/active_loop_antenna.htm

Regards,

Chris